xref: /linux/fs/namespace.c (revision d27656d02d85078c63f060fca9c5d99794791a75)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  *  linux/fs/namespace.c
4  *
5  * (C) Copyright Al Viro 2000, 2001
6  *
7  * Based on code from fs/super.c, copyright Linus Torvalds and others.
8  * Heavily rewritten.
9  */
10 
11 #include <linux/syscalls.h>
12 #include <linux/export.h>
13 #include <linux/capability.h>
14 #include <linux/mnt_namespace.h>
15 #include <linux/user_namespace.h>
16 #include <linux/namei.h>
17 #include <linux/security.h>
18 #include <linux/cred.h>
19 #include <linux/idr.h>
20 #include <linux/init.h>		/* init_rootfs */
21 #include <linux/fs_struct.h>	/* get_fs_root et.al. */
22 #include <linux/fsnotify.h>	/* fsnotify_vfsmount_delete */
23 #include <linux/file.h>
24 #include <linux/uaccess.h>
25 #include <linux/proc_ns.h>
26 #include <linux/magic.h>
27 #include <linux/memblock.h>
28 #include <linux/proc_fs.h>
29 #include <linux/task_work.h>
30 #include <linux/sched/task.h>
31 #include <uapi/linux/mount.h>
32 #include <linux/fs_context.h>
33 #include <linux/shmem_fs.h>
34 #include <linux/mnt_idmapping.h>
35 
36 #include "pnode.h"
37 #include "internal.h"
38 
39 /* Maximum number of mounts in a mount namespace */
40 static unsigned int sysctl_mount_max __read_mostly = 100000;
41 
42 static unsigned int m_hash_mask __read_mostly;
43 static unsigned int m_hash_shift __read_mostly;
44 static unsigned int mp_hash_mask __read_mostly;
45 static unsigned int mp_hash_shift __read_mostly;
46 
47 static __initdata unsigned long mhash_entries;
48 static int __init set_mhash_entries(char *str)
49 {
50 	if (!str)
51 		return 0;
52 	mhash_entries = simple_strtoul(str, &str, 0);
53 	return 1;
54 }
55 __setup("mhash_entries=", set_mhash_entries);
56 
57 static __initdata unsigned long mphash_entries;
58 static int __init set_mphash_entries(char *str)
59 {
60 	if (!str)
61 		return 0;
62 	mphash_entries = simple_strtoul(str, &str, 0);
63 	return 1;
64 }
65 __setup("mphash_entries=", set_mphash_entries);
66 
67 static u64 event;
68 static DEFINE_IDA(mnt_id_ida);
69 static DEFINE_IDA(mnt_group_ida);
70 
71 static struct hlist_head *mount_hashtable __read_mostly;
72 static struct hlist_head *mountpoint_hashtable __read_mostly;
73 static struct kmem_cache *mnt_cache __read_mostly;
74 static DECLARE_RWSEM(namespace_sem);
75 static HLIST_HEAD(unmounted);	/* protected by namespace_sem */
76 static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */
77 
78 struct mount_kattr {
79 	unsigned int attr_set;
80 	unsigned int attr_clr;
81 	unsigned int propagation;
82 	unsigned int lookup_flags;
83 	bool recurse;
84 	struct user_namespace *mnt_userns;
85 };
86 
87 /* /sys/fs */
88 struct kobject *fs_kobj;
89 EXPORT_SYMBOL_GPL(fs_kobj);
90 
91 /*
92  * vfsmount lock may be taken for read to prevent changes to the
93  * vfsmount hash, ie. during mountpoint lookups or walking back
94  * up the tree.
95  *
96  * It should be taken for write in all cases where the vfsmount
97  * tree or hash is modified or when a vfsmount structure is modified.
98  */
99 __cacheline_aligned_in_smp DEFINE_SEQLOCK(mount_lock);
100 
101 static inline void lock_mount_hash(void)
102 {
103 	write_seqlock(&mount_lock);
104 }
105 
106 static inline void unlock_mount_hash(void)
107 {
108 	write_sequnlock(&mount_lock);
109 }
110 
111 static inline struct hlist_head *m_hash(struct vfsmount *mnt, struct dentry *dentry)
112 {
113 	unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
114 	tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
115 	tmp = tmp + (tmp >> m_hash_shift);
116 	return &mount_hashtable[tmp & m_hash_mask];
117 }
118 
119 static inline struct hlist_head *mp_hash(struct dentry *dentry)
120 {
121 	unsigned long tmp = ((unsigned long)dentry / L1_CACHE_BYTES);
122 	tmp = tmp + (tmp >> mp_hash_shift);
123 	return &mountpoint_hashtable[tmp & mp_hash_mask];
124 }
125 
126 static int mnt_alloc_id(struct mount *mnt)
127 {
128 	int res = ida_alloc(&mnt_id_ida, GFP_KERNEL);
129 
130 	if (res < 0)
131 		return res;
132 	mnt->mnt_id = res;
133 	return 0;
134 }
135 
136 static void mnt_free_id(struct mount *mnt)
137 {
138 	ida_free(&mnt_id_ida, mnt->mnt_id);
139 }
140 
141 /*
142  * Allocate a new peer group ID
143  */
144 static int mnt_alloc_group_id(struct mount *mnt)
145 {
146 	int res = ida_alloc_min(&mnt_group_ida, 1, GFP_KERNEL);
147 
148 	if (res < 0)
149 		return res;
150 	mnt->mnt_group_id = res;
151 	return 0;
152 }
153 
154 /*
155  * Release a peer group ID
156  */
157 void mnt_release_group_id(struct mount *mnt)
158 {
159 	ida_free(&mnt_group_ida, mnt->mnt_group_id);
160 	mnt->mnt_group_id = 0;
161 }
162 
163 /*
164  * vfsmount lock must be held for read
165  */
166 static inline void mnt_add_count(struct mount *mnt, int n)
167 {
168 #ifdef CONFIG_SMP
169 	this_cpu_add(mnt->mnt_pcp->mnt_count, n);
170 #else
171 	preempt_disable();
172 	mnt->mnt_count += n;
173 	preempt_enable();
174 #endif
175 }
176 
177 /*
178  * vfsmount lock must be held for write
179  */
180 int mnt_get_count(struct mount *mnt)
181 {
182 #ifdef CONFIG_SMP
183 	int count = 0;
184 	int cpu;
185 
186 	for_each_possible_cpu(cpu) {
187 		count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_count;
188 	}
189 
190 	return count;
191 #else
192 	return mnt->mnt_count;
193 #endif
194 }
195 
196 static struct mount *alloc_vfsmnt(const char *name)
197 {
198 	struct mount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
199 	if (mnt) {
200 		int err;
201 
202 		err = mnt_alloc_id(mnt);
203 		if (err)
204 			goto out_free_cache;
205 
206 		if (name) {
207 			mnt->mnt_devname = kstrdup_const(name,
208 							 GFP_KERNEL_ACCOUNT);
209 			if (!mnt->mnt_devname)
210 				goto out_free_id;
211 		}
212 
213 #ifdef CONFIG_SMP
214 		mnt->mnt_pcp = alloc_percpu(struct mnt_pcp);
215 		if (!mnt->mnt_pcp)
216 			goto out_free_devname;
217 
218 		this_cpu_add(mnt->mnt_pcp->mnt_count, 1);
219 #else
220 		mnt->mnt_count = 1;
221 		mnt->mnt_writers = 0;
222 #endif
223 
224 		INIT_HLIST_NODE(&mnt->mnt_hash);
225 		INIT_LIST_HEAD(&mnt->mnt_child);
226 		INIT_LIST_HEAD(&mnt->mnt_mounts);
227 		INIT_LIST_HEAD(&mnt->mnt_list);
228 		INIT_LIST_HEAD(&mnt->mnt_expire);
229 		INIT_LIST_HEAD(&mnt->mnt_share);
230 		INIT_LIST_HEAD(&mnt->mnt_slave_list);
231 		INIT_LIST_HEAD(&mnt->mnt_slave);
232 		INIT_HLIST_NODE(&mnt->mnt_mp_list);
233 		INIT_LIST_HEAD(&mnt->mnt_umounting);
234 		INIT_HLIST_HEAD(&mnt->mnt_stuck_children);
235 		mnt->mnt.mnt_userns = &init_user_ns;
236 	}
237 	return mnt;
238 
239 #ifdef CONFIG_SMP
240 out_free_devname:
241 	kfree_const(mnt->mnt_devname);
242 #endif
243 out_free_id:
244 	mnt_free_id(mnt);
245 out_free_cache:
246 	kmem_cache_free(mnt_cache, mnt);
247 	return NULL;
248 }
249 
250 /*
251  * Most r/o checks on a fs are for operations that take
252  * discrete amounts of time, like a write() or unlink().
253  * We must keep track of when those operations start
254  * (for permission checks) and when they end, so that
255  * we can determine when writes are able to occur to
256  * a filesystem.
257  */
258 /*
259  * __mnt_is_readonly: check whether a mount is read-only
260  * @mnt: the mount to check for its write status
261  *
262  * This shouldn't be used directly ouside of the VFS.
263  * It does not guarantee that the filesystem will stay
264  * r/w, just that it is right *now*.  This can not and
265  * should not be used in place of IS_RDONLY(inode).
266  * mnt_want/drop_write() will _keep_ the filesystem
267  * r/w.
268  */
269 bool __mnt_is_readonly(struct vfsmount *mnt)
270 {
271 	return (mnt->mnt_flags & MNT_READONLY) || sb_rdonly(mnt->mnt_sb);
272 }
273 EXPORT_SYMBOL_GPL(__mnt_is_readonly);
274 
275 static inline void mnt_inc_writers(struct mount *mnt)
276 {
277 #ifdef CONFIG_SMP
278 	this_cpu_inc(mnt->mnt_pcp->mnt_writers);
279 #else
280 	mnt->mnt_writers++;
281 #endif
282 }
283 
284 static inline void mnt_dec_writers(struct mount *mnt)
285 {
286 #ifdef CONFIG_SMP
287 	this_cpu_dec(mnt->mnt_pcp->mnt_writers);
288 #else
289 	mnt->mnt_writers--;
290 #endif
291 }
292 
293 static unsigned int mnt_get_writers(struct mount *mnt)
294 {
295 #ifdef CONFIG_SMP
296 	unsigned int count = 0;
297 	int cpu;
298 
299 	for_each_possible_cpu(cpu) {
300 		count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_writers;
301 	}
302 
303 	return count;
304 #else
305 	return mnt->mnt_writers;
306 #endif
307 }
308 
309 static int mnt_is_readonly(struct vfsmount *mnt)
310 {
311 	if (mnt->mnt_sb->s_readonly_remount)
312 		return 1;
313 	/* Order wrt setting s_flags/s_readonly_remount in do_remount() */
314 	smp_rmb();
315 	return __mnt_is_readonly(mnt);
316 }
317 
318 /*
319  * Most r/o & frozen checks on a fs are for operations that take discrete
320  * amounts of time, like a write() or unlink().  We must keep track of when
321  * those operations start (for permission checks) and when they end, so that we
322  * can determine when writes are able to occur to a filesystem.
323  */
324 /**
325  * __mnt_want_write - get write access to a mount without freeze protection
326  * @m: the mount on which to take a write
327  *
328  * This tells the low-level filesystem that a write is about to be performed to
329  * it, and makes sure that writes are allowed (mnt it read-write) before
330  * returning success. This operation does not protect against filesystem being
331  * frozen. When the write operation is finished, __mnt_drop_write() must be
332  * called. This is effectively a refcount.
333  */
334 int __mnt_want_write(struct vfsmount *m)
335 {
336 	struct mount *mnt = real_mount(m);
337 	int ret = 0;
338 
339 	preempt_disable();
340 	mnt_inc_writers(mnt);
341 	/*
342 	 * The store to mnt_inc_writers must be visible before we pass
343 	 * MNT_WRITE_HOLD loop below, so that the slowpath can see our
344 	 * incremented count after it has set MNT_WRITE_HOLD.
345 	 */
346 	smp_mb();
347 	while (READ_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD)
348 		cpu_relax();
349 	/*
350 	 * After the slowpath clears MNT_WRITE_HOLD, mnt_is_readonly will
351 	 * be set to match its requirements. So we must not load that until
352 	 * MNT_WRITE_HOLD is cleared.
353 	 */
354 	smp_rmb();
355 	if (mnt_is_readonly(m)) {
356 		mnt_dec_writers(mnt);
357 		ret = -EROFS;
358 	}
359 	preempt_enable();
360 
361 	return ret;
362 }
363 
364 /**
365  * mnt_want_write - get write access to a mount
366  * @m: the mount on which to take a write
367  *
368  * This tells the low-level filesystem that a write is about to be performed to
369  * it, and makes sure that writes are allowed (mount is read-write, filesystem
370  * is not frozen) before returning success.  When the write operation is
371  * finished, mnt_drop_write() must be called.  This is effectively a refcount.
372  */
373 int mnt_want_write(struct vfsmount *m)
374 {
375 	int ret;
376 
377 	sb_start_write(m->mnt_sb);
378 	ret = __mnt_want_write(m);
379 	if (ret)
380 		sb_end_write(m->mnt_sb);
381 	return ret;
382 }
383 EXPORT_SYMBOL_GPL(mnt_want_write);
384 
385 /**
386  * __mnt_want_write_file - get write access to a file's mount
387  * @file: the file who's mount on which to take a write
388  *
389  * This is like __mnt_want_write, but if the file is already open for writing it
390  * skips incrementing mnt_writers (since the open file already has a reference)
391  * and instead only does the check for emergency r/o remounts.  This must be
392  * paired with __mnt_drop_write_file.
393  */
394 int __mnt_want_write_file(struct file *file)
395 {
396 	if (file->f_mode & FMODE_WRITER) {
397 		/*
398 		 * Superblock may have become readonly while there are still
399 		 * writable fd's, e.g. due to a fs error with errors=remount-ro
400 		 */
401 		if (__mnt_is_readonly(file->f_path.mnt))
402 			return -EROFS;
403 		return 0;
404 	}
405 	return __mnt_want_write(file->f_path.mnt);
406 }
407 
408 /**
409  * mnt_want_write_file - get write access to a file's mount
410  * @file: the file who's mount on which to take a write
411  *
412  * This is like mnt_want_write, but if the file is already open for writing it
413  * skips incrementing mnt_writers (since the open file already has a reference)
414  * and instead only does the freeze protection and the check for emergency r/o
415  * remounts.  This must be paired with mnt_drop_write_file.
416  */
417 int mnt_want_write_file(struct file *file)
418 {
419 	int ret;
420 
421 	sb_start_write(file_inode(file)->i_sb);
422 	ret = __mnt_want_write_file(file);
423 	if (ret)
424 		sb_end_write(file_inode(file)->i_sb);
425 	return ret;
426 }
427 EXPORT_SYMBOL_GPL(mnt_want_write_file);
428 
429 /**
430  * __mnt_drop_write - give up write access to a mount
431  * @mnt: the mount on which to give up write access
432  *
433  * Tells the low-level filesystem that we are done
434  * performing writes to it.  Must be matched with
435  * __mnt_want_write() call above.
436  */
437 void __mnt_drop_write(struct vfsmount *mnt)
438 {
439 	preempt_disable();
440 	mnt_dec_writers(real_mount(mnt));
441 	preempt_enable();
442 }
443 
444 /**
445  * mnt_drop_write - give up write access to a mount
446  * @mnt: the mount on which to give up write access
447  *
448  * Tells the low-level filesystem that we are done performing writes to it and
449  * also allows filesystem to be frozen again.  Must be matched with
450  * mnt_want_write() call above.
451  */
452 void mnt_drop_write(struct vfsmount *mnt)
453 {
454 	__mnt_drop_write(mnt);
455 	sb_end_write(mnt->mnt_sb);
456 }
457 EXPORT_SYMBOL_GPL(mnt_drop_write);
458 
459 void __mnt_drop_write_file(struct file *file)
460 {
461 	if (!(file->f_mode & FMODE_WRITER))
462 		__mnt_drop_write(file->f_path.mnt);
463 }
464 
465 void mnt_drop_write_file(struct file *file)
466 {
467 	__mnt_drop_write_file(file);
468 	sb_end_write(file_inode(file)->i_sb);
469 }
470 EXPORT_SYMBOL(mnt_drop_write_file);
471 
472 /**
473  * mnt_hold_writers - prevent write access to the given mount
474  * @mnt: mnt to prevent write access to
475  *
476  * Prevents write access to @mnt if there are no active writers for @mnt.
477  * This function needs to be called and return successfully before changing
478  * properties of @mnt that need to remain stable for callers with write access
479  * to @mnt.
480  *
481  * After this functions has been called successfully callers must pair it with
482  * a call to mnt_unhold_writers() in order to stop preventing write access to
483  * @mnt.
484  *
485  * Context: This function expects lock_mount_hash() to be held serializing
486  *          setting MNT_WRITE_HOLD.
487  * Return: On success 0 is returned.
488  *	   On error, -EBUSY is returned.
489  */
490 static inline int mnt_hold_writers(struct mount *mnt)
491 {
492 	mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
493 	/*
494 	 * After storing MNT_WRITE_HOLD, we'll read the counters. This store
495 	 * should be visible before we do.
496 	 */
497 	smp_mb();
498 
499 	/*
500 	 * With writers on hold, if this value is zero, then there are
501 	 * definitely no active writers (although held writers may subsequently
502 	 * increment the count, they'll have to wait, and decrement it after
503 	 * seeing MNT_READONLY).
504 	 *
505 	 * It is OK to have counter incremented on one CPU and decremented on
506 	 * another: the sum will add up correctly. The danger would be when we
507 	 * sum up each counter, if we read a counter before it is incremented,
508 	 * but then read another CPU's count which it has been subsequently
509 	 * decremented from -- we would see more decrements than we should.
510 	 * MNT_WRITE_HOLD protects against this scenario, because
511 	 * mnt_want_write first increments count, then smp_mb, then spins on
512 	 * MNT_WRITE_HOLD, so it can't be decremented by another CPU while
513 	 * we're counting up here.
514 	 */
515 	if (mnt_get_writers(mnt) > 0)
516 		return -EBUSY;
517 
518 	return 0;
519 }
520 
521 /**
522  * mnt_unhold_writers - stop preventing write access to the given mount
523  * @mnt: mnt to stop preventing write access to
524  *
525  * Stop preventing write access to @mnt allowing callers to gain write access
526  * to @mnt again.
527  *
528  * This function can only be called after a successful call to
529  * mnt_hold_writers().
530  *
531  * Context: This function expects lock_mount_hash() to be held.
532  */
533 static inline void mnt_unhold_writers(struct mount *mnt)
534 {
535 	/*
536 	 * MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
537 	 * that become unheld will see MNT_READONLY.
538 	 */
539 	smp_wmb();
540 	mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
541 }
542 
543 static int mnt_make_readonly(struct mount *mnt)
544 {
545 	int ret;
546 
547 	ret = mnt_hold_writers(mnt);
548 	if (!ret)
549 		mnt->mnt.mnt_flags |= MNT_READONLY;
550 	mnt_unhold_writers(mnt);
551 	return ret;
552 }
553 
554 int sb_prepare_remount_readonly(struct super_block *sb)
555 {
556 	struct mount *mnt;
557 	int err = 0;
558 
559 	/* Racy optimization.  Recheck the counter under MNT_WRITE_HOLD */
560 	if (atomic_long_read(&sb->s_remove_count))
561 		return -EBUSY;
562 
563 	lock_mount_hash();
564 	list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
565 		if (!(mnt->mnt.mnt_flags & MNT_READONLY)) {
566 			mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
567 			smp_mb();
568 			if (mnt_get_writers(mnt) > 0) {
569 				err = -EBUSY;
570 				break;
571 			}
572 		}
573 	}
574 	if (!err && atomic_long_read(&sb->s_remove_count))
575 		err = -EBUSY;
576 
577 	if (!err) {
578 		sb->s_readonly_remount = 1;
579 		smp_wmb();
580 	}
581 	list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
582 		if (mnt->mnt.mnt_flags & MNT_WRITE_HOLD)
583 			mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
584 	}
585 	unlock_mount_hash();
586 
587 	return err;
588 }
589 
590 static void free_vfsmnt(struct mount *mnt)
591 {
592 	struct user_namespace *mnt_userns;
593 
594 	mnt_userns = mnt_user_ns(&mnt->mnt);
595 	if (!initial_idmapping(mnt_userns))
596 		put_user_ns(mnt_userns);
597 	kfree_const(mnt->mnt_devname);
598 #ifdef CONFIG_SMP
599 	free_percpu(mnt->mnt_pcp);
600 #endif
601 	kmem_cache_free(mnt_cache, mnt);
602 }
603 
604 static void delayed_free_vfsmnt(struct rcu_head *head)
605 {
606 	free_vfsmnt(container_of(head, struct mount, mnt_rcu));
607 }
608 
609 /* call under rcu_read_lock */
610 int __legitimize_mnt(struct vfsmount *bastard, unsigned seq)
611 {
612 	struct mount *mnt;
613 	if (read_seqretry(&mount_lock, seq))
614 		return 1;
615 	if (bastard == NULL)
616 		return 0;
617 	mnt = real_mount(bastard);
618 	mnt_add_count(mnt, 1);
619 	smp_mb();			// see mntput_no_expire()
620 	if (likely(!read_seqretry(&mount_lock, seq)))
621 		return 0;
622 	if (bastard->mnt_flags & MNT_SYNC_UMOUNT) {
623 		mnt_add_count(mnt, -1);
624 		return 1;
625 	}
626 	lock_mount_hash();
627 	if (unlikely(bastard->mnt_flags & MNT_DOOMED)) {
628 		mnt_add_count(mnt, -1);
629 		unlock_mount_hash();
630 		return 1;
631 	}
632 	unlock_mount_hash();
633 	/* caller will mntput() */
634 	return -1;
635 }
636 
637 /* call under rcu_read_lock */
638 bool legitimize_mnt(struct vfsmount *bastard, unsigned seq)
639 {
640 	int res = __legitimize_mnt(bastard, seq);
641 	if (likely(!res))
642 		return true;
643 	if (unlikely(res < 0)) {
644 		rcu_read_unlock();
645 		mntput(bastard);
646 		rcu_read_lock();
647 	}
648 	return false;
649 }
650 
651 /*
652  * find the first mount at @dentry on vfsmount @mnt.
653  * call under rcu_read_lock()
654  */
655 struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
656 {
657 	struct hlist_head *head = m_hash(mnt, dentry);
658 	struct mount *p;
659 
660 	hlist_for_each_entry_rcu(p, head, mnt_hash)
661 		if (&p->mnt_parent->mnt == mnt && p->mnt_mountpoint == dentry)
662 			return p;
663 	return NULL;
664 }
665 
666 /*
667  * lookup_mnt - Return the first child mount mounted at path
668  *
669  * "First" means first mounted chronologically.  If you create the
670  * following mounts:
671  *
672  * mount /dev/sda1 /mnt
673  * mount /dev/sda2 /mnt
674  * mount /dev/sda3 /mnt
675  *
676  * Then lookup_mnt() on the base /mnt dentry in the root mount will
677  * return successively the root dentry and vfsmount of /dev/sda1, then
678  * /dev/sda2, then /dev/sda3, then NULL.
679  *
680  * lookup_mnt takes a reference to the found vfsmount.
681  */
682 struct vfsmount *lookup_mnt(const struct path *path)
683 {
684 	struct mount *child_mnt;
685 	struct vfsmount *m;
686 	unsigned seq;
687 
688 	rcu_read_lock();
689 	do {
690 		seq = read_seqbegin(&mount_lock);
691 		child_mnt = __lookup_mnt(path->mnt, path->dentry);
692 		m = child_mnt ? &child_mnt->mnt : NULL;
693 	} while (!legitimize_mnt(m, seq));
694 	rcu_read_unlock();
695 	return m;
696 }
697 
698 static inline void lock_ns_list(struct mnt_namespace *ns)
699 {
700 	spin_lock(&ns->ns_lock);
701 }
702 
703 static inline void unlock_ns_list(struct mnt_namespace *ns)
704 {
705 	spin_unlock(&ns->ns_lock);
706 }
707 
708 static inline bool mnt_is_cursor(struct mount *mnt)
709 {
710 	return mnt->mnt.mnt_flags & MNT_CURSOR;
711 }
712 
713 /*
714  * __is_local_mountpoint - Test to see if dentry is a mountpoint in the
715  *                         current mount namespace.
716  *
717  * The common case is dentries are not mountpoints at all and that
718  * test is handled inline.  For the slow case when we are actually
719  * dealing with a mountpoint of some kind, walk through all of the
720  * mounts in the current mount namespace and test to see if the dentry
721  * is a mountpoint.
722  *
723  * The mount_hashtable is not usable in the context because we
724  * need to identify all mounts that may be in the current mount
725  * namespace not just a mount that happens to have some specified
726  * parent mount.
727  */
728 bool __is_local_mountpoint(struct dentry *dentry)
729 {
730 	struct mnt_namespace *ns = current->nsproxy->mnt_ns;
731 	struct mount *mnt;
732 	bool is_covered = false;
733 
734 	down_read(&namespace_sem);
735 	lock_ns_list(ns);
736 	list_for_each_entry(mnt, &ns->list, mnt_list) {
737 		if (mnt_is_cursor(mnt))
738 			continue;
739 		is_covered = (mnt->mnt_mountpoint == dentry);
740 		if (is_covered)
741 			break;
742 	}
743 	unlock_ns_list(ns);
744 	up_read(&namespace_sem);
745 
746 	return is_covered;
747 }
748 
749 static struct mountpoint *lookup_mountpoint(struct dentry *dentry)
750 {
751 	struct hlist_head *chain = mp_hash(dentry);
752 	struct mountpoint *mp;
753 
754 	hlist_for_each_entry(mp, chain, m_hash) {
755 		if (mp->m_dentry == dentry) {
756 			mp->m_count++;
757 			return mp;
758 		}
759 	}
760 	return NULL;
761 }
762 
763 static struct mountpoint *get_mountpoint(struct dentry *dentry)
764 {
765 	struct mountpoint *mp, *new = NULL;
766 	int ret;
767 
768 	if (d_mountpoint(dentry)) {
769 		/* might be worth a WARN_ON() */
770 		if (d_unlinked(dentry))
771 			return ERR_PTR(-ENOENT);
772 mountpoint:
773 		read_seqlock_excl(&mount_lock);
774 		mp = lookup_mountpoint(dentry);
775 		read_sequnlock_excl(&mount_lock);
776 		if (mp)
777 			goto done;
778 	}
779 
780 	if (!new)
781 		new = kmalloc(sizeof(struct mountpoint), GFP_KERNEL);
782 	if (!new)
783 		return ERR_PTR(-ENOMEM);
784 
785 
786 	/* Exactly one processes may set d_mounted */
787 	ret = d_set_mounted(dentry);
788 
789 	/* Someone else set d_mounted? */
790 	if (ret == -EBUSY)
791 		goto mountpoint;
792 
793 	/* The dentry is not available as a mountpoint? */
794 	mp = ERR_PTR(ret);
795 	if (ret)
796 		goto done;
797 
798 	/* Add the new mountpoint to the hash table */
799 	read_seqlock_excl(&mount_lock);
800 	new->m_dentry = dget(dentry);
801 	new->m_count = 1;
802 	hlist_add_head(&new->m_hash, mp_hash(dentry));
803 	INIT_HLIST_HEAD(&new->m_list);
804 	read_sequnlock_excl(&mount_lock);
805 
806 	mp = new;
807 	new = NULL;
808 done:
809 	kfree(new);
810 	return mp;
811 }
812 
813 /*
814  * vfsmount lock must be held.  Additionally, the caller is responsible
815  * for serializing calls for given disposal list.
816  */
817 static void __put_mountpoint(struct mountpoint *mp, struct list_head *list)
818 {
819 	if (!--mp->m_count) {
820 		struct dentry *dentry = mp->m_dentry;
821 		BUG_ON(!hlist_empty(&mp->m_list));
822 		spin_lock(&dentry->d_lock);
823 		dentry->d_flags &= ~DCACHE_MOUNTED;
824 		spin_unlock(&dentry->d_lock);
825 		dput_to_list(dentry, list);
826 		hlist_del(&mp->m_hash);
827 		kfree(mp);
828 	}
829 }
830 
831 /* called with namespace_lock and vfsmount lock */
832 static void put_mountpoint(struct mountpoint *mp)
833 {
834 	__put_mountpoint(mp, &ex_mountpoints);
835 }
836 
837 static inline int check_mnt(struct mount *mnt)
838 {
839 	return mnt->mnt_ns == current->nsproxy->mnt_ns;
840 }
841 
842 /*
843  * vfsmount lock must be held for write
844  */
845 static void touch_mnt_namespace(struct mnt_namespace *ns)
846 {
847 	if (ns) {
848 		ns->event = ++event;
849 		wake_up_interruptible(&ns->poll);
850 	}
851 }
852 
853 /*
854  * vfsmount lock must be held for write
855  */
856 static void __touch_mnt_namespace(struct mnt_namespace *ns)
857 {
858 	if (ns && ns->event != event) {
859 		ns->event = event;
860 		wake_up_interruptible(&ns->poll);
861 	}
862 }
863 
864 /*
865  * vfsmount lock must be held for write
866  */
867 static struct mountpoint *unhash_mnt(struct mount *mnt)
868 {
869 	struct mountpoint *mp;
870 	mnt->mnt_parent = mnt;
871 	mnt->mnt_mountpoint = mnt->mnt.mnt_root;
872 	list_del_init(&mnt->mnt_child);
873 	hlist_del_init_rcu(&mnt->mnt_hash);
874 	hlist_del_init(&mnt->mnt_mp_list);
875 	mp = mnt->mnt_mp;
876 	mnt->mnt_mp = NULL;
877 	return mp;
878 }
879 
880 /*
881  * vfsmount lock must be held for write
882  */
883 static void umount_mnt(struct mount *mnt)
884 {
885 	put_mountpoint(unhash_mnt(mnt));
886 }
887 
888 /*
889  * vfsmount lock must be held for write
890  */
891 void mnt_set_mountpoint(struct mount *mnt,
892 			struct mountpoint *mp,
893 			struct mount *child_mnt)
894 {
895 	mp->m_count++;
896 	mnt_add_count(mnt, 1);	/* essentially, that's mntget */
897 	child_mnt->mnt_mountpoint = mp->m_dentry;
898 	child_mnt->mnt_parent = mnt;
899 	child_mnt->mnt_mp = mp;
900 	hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list);
901 }
902 
903 static void __attach_mnt(struct mount *mnt, struct mount *parent)
904 {
905 	hlist_add_head_rcu(&mnt->mnt_hash,
906 			   m_hash(&parent->mnt, mnt->mnt_mountpoint));
907 	list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
908 }
909 
910 /*
911  * vfsmount lock must be held for write
912  */
913 static void attach_mnt(struct mount *mnt,
914 			struct mount *parent,
915 			struct mountpoint *mp)
916 {
917 	mnt_set_mountpoint(parent, mp, mnt);
918 	__attach_mnt(mnt, parent);
919 }
920 
921 void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct mount *mnt)
922 {
923 	struct mountpoint *old_mp = mnt->mnt_mp;
924 	struct mount *old_parent = mnt->mnt_parent;
925 
926 	list_del_init(&mnt->mnt_child);
927 	hlist_del_init(&mnt->mnt_mp_list);
928 	hlist_del_init_rcu(&mnt->mnt_hash);
929 
930 	attach_mnt(mnt, parent, mp);
931 
932 	put_mountpoint(old_mp);
933 	mnt_add_count(old_parent, -1);
934 }
935 
936 /*
937  * vfsmount lock must be held for write
938  */
939 static void commit_tree(struct mount *mnt)
940 {
941 	struct mount *parent = mnt->mnt_parent;
942 	struct mount *m;
943 	LIST_HEAD(head);
944 	struct mnt_namespace *n = parent->mnt_ns;
945 
946 	BUG_ON(parent == mnt);
947 
948 	list_add_tail(&head, &mnt->mnt_list);
949 	list_for_each_entry(m, &head, mnt_list)
950 		m->mnt_ns = n;
951 
952 	list_splice(&head, n->list.prev);
953 
954 	n->mounts += n->pending_mounts;
955 	n->pending_mounts = 0;
956 
957 	__attach_mnt(mnt, parent);
958 	touch_mnt_namespace(n);
959 }
960 
961 static struct mount *next_mnt(struct mount *p, struct mount *root)
962 {
963 	struct list_head *next = p->mnt_mounts.next;
964 	if (next == &p->mnt_mounts) {
965 		while (1) {
966 			if (p == root)
967 				return NULL;
968 			next = p->mnt_child.next;
969 			if (next != &p->mnt_parent->mnt_mounts)
970 				break;
971 			p = p->mnt_parent;
972 		}
973 	}
974 	return list_entry(next, struct mount, mnt_child);
975 }
976 
977 static struct mount *skip_mnt_tree(struct mount *p)
978 {
979 	struct list_head *prev = p->mnt_mounts.prev;
980 	while (prev != &p->mnt_mounts) {
981 		p = list_entry(prev, struct mount, mnt_child);
982 		prev = p->mnt_mounts.prev;
983 	}
984 	return p;
985 }
986 
987 /**
988  * vfs_create_mount - Create a mount for a configured superblock
989  * @fc: The configuration context with the superblock attached
990  *
991  * Create a mount to an already configured superblock.  If necessary, the
992  * caller should invoke vfs_get_tree() before calling this.
993  *
994  * Note that this does not attach the mount to anything.
995  */
996 struct vfsmount *vfs_create_mount(struct fs_context *fc)
997 {
998 	struct mount *mnt;
999 	struct user_namespace *fs_userns;
1000 
1001 	if (!fc->root)
1002 		return ERR_PTR(-EINVAL);
1003 
1004 	mnt = alloc_vfsmnt(fc->source ?: "none");
1005 	if (!mnt)
1006 		return ERR_PTR(-ENOMEM);
1007 
1008 	if (fc->sb_flags & SB_KERNMOUNT)
1009 		mnt->mnt.mnt_flags = MNT_INTERNAL;
1010 
1011 	atomic_inc(&fc->root->d_sb->s_active);
1012 	mnt->mnt.mnt_sb		= fc->root->d_sb;
1013 	mnt->mnt.mnt_root	= dget(fc->root);
1014 	mnt->mnt_mountpoint	= mnt->mnt.mnt_root;
1015 	mnt->mnt_parent		= mnt;
1016 
1017 	fs_userns = mnt->mnt.mnt_sb->s_user_ns;
1018 	if (!initial_idmapping(fs_userns))
1019 		mnt->mnt.mnt_userns = get_user_ns(fs_userns);
1020 
1021 	lock_mount_hash();
1022 	list_add_tail(&mnt->mnt_instance, &mnt->mnt.mnt_sb->s_mounts);
1023 	unlock_mount_hash();
1024 	return &mnt->mnt;
1025 }
1026 EXPORT_SYMBOL(vfs_create_mount);
1027 
1028 struct vfsmount *fc_mount(struct fs_context *fc)
1029 {
1030 	int err = vfs_get_tree(fc);
1031 	if (!err) {
1032 		up_write(&fc->root->d_sb->s_umount);
1033 		return vfs_create_mount(fc);
1034 	}
1035 	return ERR_PTR(err);
1036 }
1037 EXPORT_SYMBOL(fc_mount);
1038 
1039 struct vfsmount *vfs_kern_mount(struct file_system_type *type,
1040 				int flags, const char *name,
1041 				void *data)
1042 {
1043 	struct fs_context *fc;
1044 	struct vfsmount *mnt;
1045 	int ret = 0;
1046 
1047 	if (!type)
1048 		return ERR_PTR(-EINVAL);
1049 
1050 	fc = fs_context_for_mount(type, flags);
1051 	if (IS_ERR(fc))
1052 		return ERR_CAST(fc);
1053 
1054 	if (name)
1055 		ret = vfs_parse_fs_string(fc, "source",
1056 					  name, strlen(name));
1057 	if (!ret)
1058 		ret = parse_monolithic_mount_data(fc, data);
1059 	if (!ret)
1060 		mnt = fc_mount(fc);
1061 	else
1062 		mnt = ERR_PTR(ret);
1063 
1064 	put_fs_context(fc);
1065 	return mnt;
1066 }
1067 EXPORT_SYMBOL_GPL(vfs_kern_mount);
1068 
1069 struct vfsmount *
1070 vfs_submount(const struct dentry *mountpoint, struct file_system_type *type,
1071 	     const char *name, void *data)
1072 {
1073 	/* Until it is worked out how to pass the user namespace
1074 	 * through from the parent mount to the submount don't support
1075 	 * unprivileged mounts with submounts.
1076 	 */
1077 	if (mountpoint->d_sb->s_user_ns != &init_user_ns)
1078 		return ERR_PTR(-EPERM);
1079 
1080 	return vfs_kern_mount(type, SB_SUBMOUNT, name, data);
1081 }
1082 EXPORT_SYMBOL_GPL(vfs_submount);
1083 
1084 static struct mount *clone_mnt(struct mount *old, struct dentry *root,
1085 					int flag)
1086 {
1087 	struct super_block *sb = old->mnt.mnt_sb;
1088 	struct mount *mnt;
1089 	int err;
1090 
1091 	mnt = alloc_vfsmnt(old->mnt_devname);
1092 	if (!mnt)
1093 		return ERR_PTR(-ENOMEM);
1094 
1095 	if (flag & (CL_SLAVE | CL_PRIVATE | CL_SHARED_TO_SLAVE))
1096 		mnt->mnt_group_id = 0; /* not a peer of original */
1097 	else
1098 		mnt->mnt_group_id = old->mnt_group_id;
1099 
1100 	if ((flag & CL_MAKE_SHARED) && !mnt->mnt_group_id) {
1101 		err = mnt_alloc_group_id(mnt);
1102 		if (err)
1103 			goto out_free;
1104 	}
1105 
1106 	mnt->mnt.mnt_flags = old->mnt.mnt_flags;
1107 	mnt->mnt.mnt_flags &= ~(MNT_WRITE_HOLD|MNT_MARKED|MNT_INTERNAL);
1108 
1109 	atomic_inc(&sb->s_active);
1110 	mnt->mnt.mnt_userns = mnt_user_ns(&old->mnt);
1111 	if (!initial_idmapping(mnt->mnt.mnt_userns))
1112 		mnt->mnt.mnt_userns = get_user_ns(mnt->mnt.mnt_userns);
1113 	mnt->mnt.mnt_sb = sb;
1114 	mnt->mnt.mnt_root = dget(root);
1115 	mnt->mnt_mountpoint = mnt->mnt.mnt_root;
1116 	mnt->mnt_parent = mnt;
1117 	lock_mount_hash();
1118 	list_add_tail(&mnt->mnt_instance, &sb->s_mounts);
1119 	unlock_mount_hash();
1120 
1121 	if ((flag & CL_SLAVE) ||
1122 	    ((flag & CL_SHARED_TO_SLAVE) && IS_MNT_SHARED(old))) {
1123 		list_add(&mnt->mnt_slave, &old->mnt_slave_list);
1124 		mnt->mnt_master = old;
1125 		CLEAR_MNT_SHARED(mnt);
1126 	} else if (!(flag & CL_PRIVATE)) {
1127 		if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
1128 			list_add(&mnt->mnt_share, &old->mnt_share);
1129 		if (IS_MNT_SLAVE(old))
1130 			list_add(&mnt->mnt_slave, &old->mnt_slave);
1131 		mnt->mnt_master = old->mnt_master;
1132 	} else {
1133 		CLEAR_MNT_SHARED(mnt);
1134 	}
1135 	if (flag & CL_MAKE_SHARED)
1136 		set_mnt_shared(mnt);
1137 
1138 	/* stick the duplicate mount on the same expiry list
1139 	 * as the original if that was on one */
1140 	if (flag & CL_EXPIRE) {
1141 		if (!list_empty(&old->mnt_expire))
1142 			list_add(&mnt->mnt_expire, &old->mnt_expire);
1143 	}
1144 
1145 	return mnt;
1146 
1147  out_free:
1148 	mnt_free_id(mnt);
1149 	free_vfsmnt(mnt);
1150 	return ERR_PTR(err);
1151 }
1152 
1153 static void cleanup_mnt(struct mount *mnt)
1154 {
1155 	struct hlist_node *p;
1156 	struct mount *m;
1157 	/*
1158 	 * The warning here probably indicates that somebody messed
1159 	 * up a mnt_want/drop_write() pair.  If this happens, the
1160 	 * filesystem was probably unable to make r/w->r/o transitions.
1161 	 * The locking used to deal with mnt_count decrement provides barriers,
1162 	 * so mnt_get_writers() below is safe.
1163 	 */
1164 	WARN_ON(mnt_get_writers(mnt));
1165 	if (unlikely(mnt->mnt_pins.first))
1166 		mnt_pin_kill(mnt);
1167 	hlist_for_each_entry_safe(m, p, &mnt->mnt_stuck_children, mnt_umount) {
1168 		hlist_del(&m->mnt_umount);
1169 		mntput(&m->mnt);
1170 	}
1171 	fsnotify_vfsmount_delete(&mnt->mnt);
1172 	dput(mnt->mnt.mnt_root);
1173 	deactivate_super(mnt->mnt.mnt_sb);
1174 	mnt_free_id(mnt);
1175 	call_rcu(&mnt->mnt_rcu, delayed_free_vfsmnt);
1176 }
1177 
1178 static void __cleanup_mnt(struct rcu_head *head)
1179 {
1180 	cleanup_mnt(container_of(head, struct mount, mnt_rcu));
1181 }
1182 
1183 static LLIST_HEAD(delayed_mntput_list);
1184 static void delayed_mntput(struct work_struct *unused)
1185 {
1186 	struct llist_node *node = llist_del_all(&delayed_mntput_list);
1187 	struct mount *m, *t;
1188 
1189 	llist_for_each_entry_safe(m, t, node, mnt_llist)
1190 		cleanup_mnt(m);
1191 }
1192 static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput);
1193 
1194 static void mntput_no_expire(struct mount *mnt)
1195 {
1196 	LIST_HEAD(list);
1197 	int count;
1198 
1199 	rcu_read_lock();
1200 	if (likely(READ_ONCE(mnt->mnt_ns))) {
1201 		/*
1202 		 * Since we don't do lock_mount_hash() here,
1203 		 * ->mnt_ns can change under us.  However, if it's
1204 		 * non-NULL, then there's a reference that won't
1205 		 * be dropped until after an RCU delay done after
1206 		 * turning ->mnt_ns NULL.  So if we observe it
1207 		 * non-NULL under rcu_read_lock(), the reference
1208 		 * we are dropping is not the final one.
1209 		 */
1210 		mnt_add_count(mnt, -1);
1211 		rcu_read_unlock();
1212 		return;
1213 	}
1214 	lock_mount_hash();
1215 	/*
1216 	 * make sure that if __legitimize_mnt() has not seen us grab
1217 	 * mount_lock, we'll see their refcount increment here.
1218 	 */
1219 	smp_mb();
1220 	mnt_add_count(mnt, -1);
1221 	count = mnt_get_count(mnt);
1222 	if (count != 0) {
1223 		WARN_ON(count < 0);
1224 		rcu_read_unlock();
1225 		unlock_mount_hash();
1226 		return;
1227 	}
1228 	if (unlikely(mnt->mnt.mnt_flags & MNT_DOOMED)) {
1229 		rcu_read_unlock();
1230 		unlock_mount_hash();
1231 		return;
1232 	}
1233 	mnt->mnt.mnt_flags |= MNT_DOOMED;
1234 	rcu_read_unlock();
1235 
1236 	list_del(&mnt->mnt_instance);
1237 
1238 	if (unlikely(!list_empty(&mnt->mnt_mounts))) {
1239 		struct mount *p, *tmp;
1240 		list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts,  mnt_child) {
1241 			__put_mountpoint(unhash_mnt(p), &list);
1242 			hlist_add_head(&p->mnt_umount, &mnt->mnt_stuck_children);
1243 		}
1244 	}
1245 	unlock_mount_hash();
1246 	shrink_dentry_list(&list);
1247 
1248 	if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) {
1249 		struct task_struct *task = current;
1250 		if (likely(!(task->flags & PF_KTHREAD))) {
1251 			init_task_work(&mnt->mnt_rcu, __cleanup_mnt);
1252 			if (!task_work_add(task, &mnt->mnt_rcu, TWA_RESUME))
1253 				return;
1254 		}
1255 		if (llist_add(&mnt->mnt_llist, &delayed_mntput_list))
1256 			schedule_delayed_work(&delayed_mntput_work, 1);
1257 		return;
1258 	}
1259 	cleanup_mnt(mnt);
1260 }
1261 
1262 void mntput(struct vfsmount *mnt)
1263 {
1264 	if (mnt) {
1265 		struct mount *m = real_mount(mnt);
1266 		/* avoid cacheline pingpong, hope gcc doesn't get "smart" */
1267 		if (unlikely(m->mnt_expiry_mark))
1268 			m->mnt_expiry_mark = 0;
1269 		mntput_no_expire(m);
1270 	}
1271 }
1272 EXPORT_SYMBOL(mntput);
1273 
1274 struct vfsmount *mntget(struct vfsmount *mnt)
1275 {
1276 	if (mnt)
1277 		mnt_add_count(real_mount(mnt), 1);
1278 	return mnt;
1279 }
1280 EXPORT_SYMBOL(mntget);
1281 
1282 /**
1283  * path_is_mountpoint() - Check if path is a mount in the current namespace.
1284  * @path: path to check
1285  *
1286  *  d_mountpoint() can only be used reliably to establish if a dentry is
1287  *  not mounted in any namespace and that common case is handled inline.
1288  *  d_mountpoint() isn't aware of the possibility there may be multiple
1289  *  mounts using a given dentry in a different namespace. This function
1290  *  checks if the passed in path is a mountpoint rather than the dentry
1291  *  alone.
1292  */
1293 bool path_is_mountpoint(const struct path *path)
1294 {
1295 	unsigned seq;
1296 	bool res;
1297 
1298 	if (!d_mountpoint(path->dentry))
1299 		return false;
1300 
1301 	rcu_read_lock();
1302 	do {
1303 		seq = read_seqbegin(&mount_lock);
1304 		res = __path_is_mountpoint(path);
1305 	} while (read_seqretry(&mount_lock, seq));
1306 	rcu_read_unlock();
1307 
1308 	return res;
1309 }
1310 EXPORT_SYMBOL(path_is_mountpoint);
1311 
1312 struct vfsmount *mnt_clone_internal(const struct path *path)
1313 {
1314 	struct mount *p;
1315 	p = clone_mnt(real_mount(path->mnt), path->dentry, CL_PRIVATE);
1316 	if (IS_ERR(p))
1317 		return ERR_CAST(p);
1318 	p->mnt.mnt_flags |= MNT_INTERNAL;
1319 	return &p->mnt;
1320 }
1321 
1322 #ifdef CONFIG_PROC_FS
1323 static struct mount *mnt_list_next(struct mnt_namespace *ns,
1324 				   struct list_head *p)
1325 {
1326 	struct mount *mnt, *ret = NULL;
1327 
1328 	lock_ns_list(ns);
1329 	list_for_each_continue(p, &ns->list) {
1330 		mnt = list_entry(p, typeof(*mnt), mnt_list);
1331 		if (!mnt_is_cursor(mnt)) {
1332 			ret = mnt;
1333 			break;
1334 		}
1335 	}
1336 	unlock_ns_list(ns);
1337 
1338 	return ret;
1339 }
1340 
1341 /* iterator; we want it to have access to namespace_sem, thus here... */
1342 static void *m_start(struct seq_file *m, loff_t *pos)
1343 {
1344 	struct proc_mounts *p = m->private;
1345 	struct list_head *prev;
1346 
1347 	down_read(&namespace_sem);
1348 	if (!*pos) {
1349 		prev = &p->ns->list;
1350 	} else {
1351 		prev = &p->cursor.mnt_list;
1352 
1353 		/* Read after we'd reached the end? */
1354 		if (list_empty(prev))
1355 			return NULL;
1356 	}
1357 
1358 	return mnt_list_next(p->ns, prev);
1359 }
1360 
1361 static void *m_next(struct seq_file *m, void *v, loff_t *pos)
1362 {
1363 	struct proc_mounts *p = m->private;
1364 	struct mount *mnt = v;
1365 
1366 	++*pos;
1367 	return mnt_list_next(p->ns, &mnt->mnt_list);
1368 }
1369 
1370 static void m_stop(struct seq_file *m, void *v)
1371 {
1372 	struct proc_mounts *p = m->private;
1373 	struct mount *mnt = v;
1374 
1375 	lock_ns_list(p->ns);
1376 	if (mnt)
1377 		list_move_tail(&p->cursor.mnt_list, &mnt->mnt_list);
1378 	else
1379 		list_del_init(&p->cursor.mnt_list);
1380 	unlock_ns_list(p->ns);
1381 	up_read(&namespace_sem);
1382 }
1383 
1384 static int m_show(struct seq_file *m, void *v)
1385 {
1386 	struct proc_mounts *p = m->private;
1387 	struct mount *r = v;
1388 	return p->show(m, &r->mnt);
1389 }
1390 
1391 const struct seq_operations mounts_op = {
1392 	.start	= m_start,
1393 	.next	= m_next,
1394 	.stop	= m_stop,
1395 	.show	= m_show,
1396 };
1397 
1398 void mnt_cursor_del(struct mnt_namespace *ns, struct mount *cursor)
1399 {
1400 	down_read(&namespace_sem);
1401 	lock_ns_list(ns);
1402 	list_del(&cursor->mnt_list);
1403 	unlock_ns_list(ns);
1404 	up_read(&namespace_sem);
1405 }
1406 #endif  /* CONFIG_PROC_FS */
1407 
1408 /**
1409  * may_umount_tree - check if a mount tree is busy
1410  * @m: root of mount tree
1411  *
1412  * This is called to check if a tree of mounts has any
1413  * open files, pwds, chroots or sub mounts that are
1414  * busy.
1415  */
1416 int may_umount_tree(struct vfsmount *m)
1417 {
1418 	struct mount *mnt = real_mount(m);
1419 	int actual_refs = 0;
1420 	int minimum_refs = 0;
1421 	struct mount *p;
1422 	BUG_ON(!m);
1423 
1424 	/* write lock needed for mnt_get_count */
1425 	lock_mount_hash();
1426 	for (p = mnt; p; p = next_mnt(p, mnt)) {
1427 		actual_refs += mnt_get_count(p);
1428 		minimum_refs += 2;
1429 	}
1430 	unlock_mount_hash();
1431 
1432 	if (actual_refs > minimum_refs)
1433 		return 0;
1434 
1435 	return 1;
1436 }
1437 
1438 EXPORT_SYMBOL(may_umount_tree);
1439 
1440 /**
1441  * may_umount - check if a mount point is busy
1442  * @mnt: root of mount
1443  *
1444  * This is called to check if a mount point has any
1445  * open files, pwds, chroots or sub mounts. If the
1446  * mount has sub mounts this will return busy
1447  * regardless of whether the sub mounts are busy.
1448  *
1449  * Doesn't take quota and stuff into account. IOW, in some cases it will
1450  * give false negatives. The main reason why it's here is that we need
1451  * a non-destructive way to look for easily umountable filesystems.
1452  */
1453 int may_umount(struct vfsmount *mnt)
1454 {
1455 	int ret = 1;
1456 	down_read(&namespace_sem);
1457 	lock_mount_hash();
1458 	if (propagate_mount_busy(real_mount(mnt), 2))
1459 		ret = 0;
1460 	unlock_mount_hash();
1461 	up_read(&namespace_sem);
1462 	return ret;
1463 }
1464 
1465 EXPORT_SYMBOL(may_umount);
1466 
1467 static void namespace_unlock(void)
1468 {
1469 	struct hlist_head head;
1470 	struct hlist_node *p;
1471 	struct mount *m;
1472 	LIST_HEAD(list);
1473 
1474 	hlist_move_list(&unmounted, &head);
1475 	list_splice_init(&ex_mountpoints, &list);
1476 
1477 	up_write(&namespace_sem);
1478 
1479 	shrink_dentry_list(&list);
1480 
1481 	if (likely(hlist_empty(&head)))
1482 		return;
1483 
1484 	synchronize_rcu_expedited();
1485 
1486 	hlist_for_each_entry_safe(m, p, &head, mnt_umount) {
1487 		hlist_del(&m->mnt_umount);
1488 		mntput(&m->mnt);
1489 	}
1490 }
1491 
1492 static inline void namespace_lock(void)
1493 {
1494 	down_write(&namespace_sem);
1495 }
1496 
1497 enum umount_tree_flags {
1498 	UMOUNT_SYNC = 1,
1499 	UMOUNT_PROPAGATE = 2,
1500 	UMOUNT_CONNECTED = 4,
1501 };
1502 
1503 static bool disconnect_mount(struct mount *mnt, enum umount_tree_flags how)
1504 {
1505 	/* Leaving mounts connected is only valid for lazy umounts */
1506 	if (how & UMOUNT_SYNC)
1507 		return true;
1508 
1509 	/* A mount without a parent has nothing to be connected to */
1510 	if (!mnt_has_parent(mnt))
1511 		return true;
1512 
1513 	/* Because the reference counting rules change when mounts are
1514 	 * unmounted and connected, umounted mounts may not be
1515 	 * connected to mounted mounts.
1516 	 */
1517 	if (!(mnt->mnt_parent->mnt.mnt_flags & MNT_UMOUNT))
1518 		return true;
1519 
1520 	/* Has it been requested that the mount remain connected? */
1521 	if (how & UMOUNT_CONNECTED)
1522 		return false;
1523 
1524 	/* Is the mount locked such that it needs to remain connected? */
1525 	if (IS_MNT_LOCKED(mnt))
1526 		return false;
1527 
1528 	/* By default disconnect the mount */
1529 	return true;
1530 }
1531 
1532 /*
1533  * mount_lock must be held
1534  * namespace_sem must be held for write
1535  */
1536 static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
1537 {
1538 	LIST_HEAD(tmp_list);
1539 	struct mount *p;
1540 
1541 	if (how & UMOUNT_PROPAGATE)
1542 		propagate_mount_unlock(mnt);
1543 
1544 	/* Gather the mounts to umount */
1545 	for (p = mnt; p; p = next_mnt(p, mnt)) {
1546 		p->mnt.mnt_flags |= MNT_UMOUNT;
1547 		list_move(&p->mnt_list, &tmp_list);
1548 	}
1549 
1550 	/* Hide the mounts from mnt_mounts */
1551 	list_for_each_entry(p, &tmp_list, mnt_list) {
1552 		list_del_init(&p->mnt_child);
1553 	}
1554 
1555 	/* Add propogated mounts to the tmp_list */
1556 	if (how & UMOUNT_PROPAGATE)
1557 		propagate_umount(&tmp_list);
1558 
1559 	while (!list_empty(&tmp_list)) {
1560 		struct mnt_namespace *ns;
1561 		bool disconnect;
1562 		p = list_first_entry(&tmp_list, struct mount, mnt_list);
1563 		list_del_init(&p->mnt_expire);
1564 		list_del_init(&p->mnt_list);
1565 		ns = p->mnt_ns;
1566 		if (ns) {
1567 			ns->mounts--;
1568 			__touch_mnt_namespace(ns);
1569 		}
1570 		p->mnt_ns = NULL;
1571 		if (how & UMOUNT_SYNC)
1572 			p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
1573 
1574 		disconnect = disconnect_mount(p, how);
1575 		if (mnt_has_parent(p)) {
1576 			mnt_add_count(p->mnt_parent, -1);
1577 			if (!disconnect) {
1578 				/* Don't forget about p */
1579 				list_add_tail(&p->mnt_child, &p->mnt_parent->mnt_mounts);
1580 			} else {
1581 				umount_mnt(p);
1582 			}
1583 		}
1584 		change_mnt_propagation(p, MS_PRIVATE);
1585 		if (disconnect)
1586 			hlist_add_head(&p->mnt_umount, &unmounted);
1587 	}
1588 }
1589 
1590 static void shrink_submounts(struct mount *mnt);
1591 
1592 static int do_umount_root(struct super_block *sb)
1593 {
1594 	int ret = 0;
1595 
1596 	down_write(&sb->s_umount);
1597 	if (!sb_rdonly(sb)) {
1598 		struct fs_context *fc;
1599 
1600 		fc = fs_context_for_reconfigure(sb->s_root, SB_RDONLY,
1601 						SB_RDONLY);
1602 		if (IS_ERR(fc)) {
1603 			ret = PTR_ERR(fc);
1604 		} else {
1605 			ret = parse_monolithic_mount_data(fc, NULL);
1606 			if (!ret)
1607 				ret = reconfigure_super(fc);
1608 			put_fs_context(fc);
1609 		}
1610 	}
1611 	up_write(&sb->s_umount);
1612 	return ret;
1613 }
1614 
1615 static int do_umount(struct mount *mnt, int flags)
1616 {
1617 	struct super_block *sb = mnt->mnt.mnt_sb;
1618 	int retval;
1619 
1620 	retval = security_sb_umount(&mnt->mnt, flags);
1621 	if (retval)
1622 		return retval;
1623 
1624 	/*
1625 	 * Allow userspace to request a mountpoint be expired rather than
1626 	 * unmounting unconditionally. Unmount only happens if:
1627 	 *  (1) the mark is already set (the mark is cleared by mntput())
1628 	 *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
1629 	 */
1630 	if (flags & MNT_EXPIRE) {
1631 		if (&mnt->mnt == current->fs->root.mnt ||
1632 		    flags & (MNT_FORCE | MNT_DETACH))
1633 			return -EINVAL;
1634 
1635 		/*
1636 		 * probably don't strictly need the lock here if we examined
1637 		 * all race cases, but it's a slowpath.
1638 		 */
1639 		lock_mount_hash();
1640 		if (mnt_get_count(mnt) != 2) {
1641 			unlock_mount_hash();
1642 			return -EBUSY;
1643 		}
1644 		unlock_mount_hash();
1645 
1646 		if (!xchg(&mnt->mnt_expiry_mark, 1))
1647 			return -EAGAIN;
1648 	}
1649 
1650 	/*
1651 	 * If we may have to abort operations to get out of this
1652 	 * mount, and they will themselves hold resources we must
1653 	 * allow the fs to do things. In the Unix tradition of
1654 	 * 'Gee thats tricky lets do it in userspace' the umount_begin
1655 	 * might fail to complete on the first run through as other tasks
1656 	 * must return, and the like. Thats for the mount program to worry
1657 	 * about for the moment.
1658 	 */
1659 
1660 	if (flags & MNT_FORCE && sb->s_op->umount_begin) {
1661 		sb->s_op->umount_begin(sb);
1662 	}
1663 
1664 	/*
1665 	 * No sense to grab the lock for this test, but test itself looks
1666 	 * somewhat bogus. Suggestions for better replacement?
1667 	 * Ho-hum... In principle, we might treat that as umount + switch
1668 	 * to rootfs. GC would eventually take care of the old vfsmount.
1669 	 * Actually it makes sense, especially if rootfs would contain a
1670 	 * /reboot - static binary that would close all descriptors and
1671 	 * call reboot(9). Then init(8) could umount root and exec /reboot.
1672 	 */
1673 	if (&mnt->mnt == current->fs->root.mnt && !(flags & MNT_DETACH)) {
1674 		/*
1675 		 * Special case for "unmounting" root ...
1676 		 * we just try to remount it readonly.
1677 		 */
1678 		if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
1679 			return -EPERM;
1680 		return do_umount_root(sb);
1681 	}
1682 
1683 	namespace_lock();
1684 	lock_mount_hash();
1685 
1686 	/* Recheck MNT_LOCKED with the locks held */
1687 	retval = -EINVAL;
1688 	if (mnt->mnt.mnt_flags & MNT_LOCKED)
1689 		goto out;
1690 
1691 	event++;
1692 	if (flags & MNT_DETACH) {
1693 		if (!list_empty(&mnt->mnt_list))
1694 			umount_tree(mnt, UMOUNT_PROPAGATE);
1695 		retval = 0;
1696 	} else {
1697 		shrink_submounts(mnt);
1698 		retval = -EBUSY;
1699 		if (!propagate_mount_busy(mnt, 2)) {
1700 			if (!list_empty(&mnt->mnt_list))
1701 				umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
1702 			retval = 0;
1703 		}
1704 	}
1705 out:
1706 	unlock_mount_hash();
1707 	namespace_unlock();
1708 	return retval;
1709 }
1710 
1711 /*
1712  * __detach_mounts - lazily unmount all mounts on the specified dentry
1713  *
1714  * During unlink, rmdir, and d_drop it is possible to loose the path
1715  * to an existing mountpoint, and wind up leaking the mount.
1716  * detach_mounts allows lazily unmounting those mounts instead of
1717  * leaking them.
1718  *
1719  * The caller may hold dentry->d_inode->i_mutex.
1720  */
1721 void __detach_mounts(struct dentry *dentry)
1722 {
1723 	struct mountpoint *mp;
1724 	struct mount *mnt;
1725 
1726 	namespace_lock();
1727 	lock_mount_hash();
1728 	mp = lookup_mountpoint(dentry);
1729 	if (!mp)
1730 		goto out_unlock;
1731 
1732 	event++;
1733 	while (!hlist_empty(&mp->m_list)) {
1734 		mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list);
1735 		if (mnt->mnt.mnt_flags & MNT_UMOUNT) {
1736 			umount_mnt(mnt);
1737 			hlist_add_head(&mnt->mnt_umount, &unmounted);
1738 		}
1739 		else umount_tree(mnt, UMOUNT_CONNECTED);
1740 	}
1741 	put_mountpoint(mp);
1742 out_unlock:
1743 	unlock_mount_hash();
1744 	namespace_unlock();
1745 }
1746 
1747 /*
1748  * Is the caller allowed to modify his namespace?
1749  */
1750 static inline bool may_mount(void)
1751 {
1752 	return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
1753 }
1754 
1755 static void warn_mandlock(void)
1756 {
1757 	pr_warn_once("=======================================================\n"
1758 		     "WARNING: The mand mount option has been deprecated and\n"
1759 		     "         and is ignored by this kernel. Remove the mand\n"
1760 		     "         option from the mount to silence this warning.\n"
1761 		     "=======================================================\n");
1762 }
1763 
1764 static int can_umount(const struct path *path, int flags)
1765 {
1766 	struct mount *mnt = real_mount(path->mnt);
1767 
1768 	if (!may_mount())
1769 		return -EPERM;
1770 	if (path->dentry != path->mnt->mnt_root)
1771 		return -EINVAL;
1772 	if (!check_mnt(mnt))
1773 		return -EINVAL;
1774 	if (mnt->mnt.mnt_flags & MNT_LOCKED) /* Check optimistically */
1775 		return -EINVAL;
1776 	if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
1777 		return -EPERM;
1778 	return 0;
1779 }
1780 
1781 // caller is responsible for flags being sane
1782 int path_umount(struct path *path, int flags)
1783 {
1784 	struct mount *mnt = real_mount(path->mnt);
1785 	int ret;
1786 
1787 	ret = can_umount(path, flags);
1788 	if (!ret)
1789 		ret = do_umount(mnt, flags);
1790 
1791 	/* we mustn't call path_put() as that would clear mnt_expiry_mark */
1792 	dput(path->dentry);
1793 	mntput_no_expire(mnt);
1794 	return ret;
1795 }
1796 
1797 static int ksys_umount(char __user *name, int flags)
1798 {
1799 	int lookup_flags = LOOKUP_MOUNTPOINT;
1800 	struct path path;
1801 	int ret;
1802 
1803 	// basic validity checks done first
1804 	if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
1805 		return -EINVAL;
1806 
1807 	if (!(flags & UMOUNT_NOFOLLOW))
1808 		lookup_flags |= LOOKUP_FOLLOW;
1809 	ret = user_path_at(AT_FDCWD, name, lookup_flags, &path);
1810 	if (ret)
1811 		return ret;
1812 	return path_umount(&path, flags);
1813 }
1814 
1815 SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
1816 {
1817 	return ksys_umount(name, flags);
1818 }
1819 
1820 #ifdef __ARCH_WANT_SYS_OLDUMOUNT
1821 
1822 /*
1823  *	The 2.0 compatible umount. No flags.
1824  */
1825 SYSCALL_DEFINE1(oldumount, char __user *, name)
1826 {
1827 	return ksys_umount(name, 0);
1828 }
1829 
1830 #endif
1831 
1832 static bool is_mnt_ns_file(struct dentry *dentry)
1833 {
1834 	/* Is this a proxy for a mount namespace? */
1835 	return dentry->d_op == &ns_dentry_operations &&
1836 	       dentry->d_fsdata == &mntns_operations;
1837 }
1838 
1839 static struct mnt_namespace *to_mnt_ns(struct ns_common *ns)
1840 {
1841 	return container_of(ns, struct mnt_namespace, ns);
1842 }
1843 
1844 struct ns_common *from_mnt_ns(struct mnt_namespace *mnt)
1845 {
1846 	return &mnt->ns;
1847 }
1848 
1849 static bool mnt_ns_loop(struct dentry *dentry)
1850 {
1851 	/* Could bind mounting the mount namespace inode cause a
1852 	 * mount namespace loop?
1853 	 */
1854 	struct mnt_namespace *mnt_ns;
1855 	if (!is_mnt_ns_file(dentry))
1856 		return false;
1857 
1858 	mnt_ns = to_mnt_ns(get_proc_ns(dentry->d_inode));
1859 	return current->nsproxy->mnt_ns->seq >= mnt_ns->seq;
1860 }
1861 
1862 struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
1863 					int flag)
1864 {
1865 	struct mount *res, *p, *q, *r, *parent;
1866 
1867 	if (!(flag & CL_COPY_UNBINDABLE) && IS_MNT_UNBINDABLE(mnt))
1868 		return ERR_PTR(-EINVAL);
1869 
1870 	if (!(flag & CL_COPY_MNT_NS_FILE) && is_mnt_ns_file(dentry))
1871 		return ERR_PTR(-EINVAL);
1872 
1873 	res = q = clone_mnt(mnt, dentry, flag);
1874 	if (IS_ERR(q))
1875 		return q;
1876 
1877 	q->mnt_mountpoint = mnt->mnt_mountpoint;
1878 
1879 	p = mnt;
1880 	list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
1881 		struct mount *s;
1882 		if (!is_subdir(r->mnt_mountpoint, dentry))
1883 			continue;
1884 
1885 		for (s = r; s; s = next_mnt(s, r)) {
1886 			if (!(flag & CL_COPY_UNBINDABLE) &&
1887 			    IS_MNT_UNBINDABLE(s)) {
1888 				if (s->mnt.mnt_flags & MNT_LOCKED) {
1889 					/* Both unbindable and locked. */
1890 					q = ERR_PTR(-EPERM);
1891 					goto out;
1892 				} else {
1893 					s = skip_mnt_tree(s);
1894 					continue;
1895 				}
1896 			}
1897 			if (!(flag & CL_COPY_MNT_NS_FILE) &&
1898 			    is_mnt_ns_file(s->mnt.mnt_root)) {
1899 				s = skip_mnt_tree(s);
1900 				continue;
1901 			}
1902 			while (p != s->mnt_parent) {
1903 				p = p->mnt_parent;
1904 				q = q->mnt_parent;
1905 			}
1906 			p = s;
1907 			parent = q;
1908 			q = clone_mnt(p, p->mnt.mnt_root, flag);
1909 			if (IS_ERR(q))
1910 				goto out;
1911 			lock_mount_hash();
1912 			list_add_tail(&q->mnt_list, &res->mnt_list);
1913 			attach_mnt(q, parent, p->mnt_mp);
1914 			unlock_mount_hash();
1915 		}
1916 	}
1917 	return res;
1918 out:
1919 	if (res) {
1920 		lock_mount_hash();
1921 		umount_tree(res, UMOUNT_SYNC);
1922 		unlock_mount_hash();
1923 	}
1924 	return q;
1925 }
1926 
1927 /* Caller should check returned pointer for errors */
1928 
1929 struct vfsmount *collect_mounts(const struct path *path)
1930 {
1931 	struct mount *tree;
1932 	namespace_lock();
1933 	if (!check_mnt(real_mount(path->mnt)))
1934 		tree = ERR_PTR(-EINVAL);
1935 	else
1936 		tree = copy_tree(real_mount(path->mnt), path->dentry,
1937 				 CL_COPY_ALL | CL_PRIVATE);
1938 	namespace_unlock();
1939 	if (IS_ERR(tree))
1940 		return ERR_CAST(tree);
1941 	return &tree->mnt;
1942 }
1943 
1944 static void free_mnt_ns(struct mnt_namespace *);
1945 static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *, bool);
1946 
1947 void dissolve_on_fput(struct vfsmount *mnt)
1948 {
1949 	struct mnt_namespace *ns;
1950 	namespace_lock();
1951 	lock_mount_hash();
1952 	ns = real_mount(mnt)->mnt_ns;
1953 	if (ns) {
1954 		if (is_anon_ns(ns))
1955 			umount_tree(real_mount(mnt), UMOUNT_CONNECTED);
1956 		else
1957 			ns = NULL;
1958 	}
1959 	unlock_mount_hash();
1960 	namespace_unlock();
1961 	if (ns)
1962 		free_mnt_ns(ns);
1963 }
1964 
1965 void drop_collected_mounts(struct vfsmount *mnt)
1966 {
1967 	namespace_lock();
1968 	lock_mount_hash();
1969 	umount_tree(real_mount(mnt), 0);
1970 	unlock_mount_hash();
1971 	namespace_unlock();
1972 }
1973 
1974 static bool has_locked_children(struct mount *mnt, struct dentry *dentry)
1975 {
1976 	struct mount *child;
1977 
1978 	list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
1979 		if (!is_subdir(child->mnt_mountpoint, dentry))
1980 			continue;
1981 
1982 		if (child->mnt.mnt_flags & MNT_LOCKED)
1983 			return true;
1984 	}
1985 	return false;
1986 }
1987 
1988 /**
1989  * clone_private_mount - create a private clone of a path
1990  * @path: path to clone
1991  *
1992  * This creates a new vfsmount, which will be the clone of @path.  The new mount
1993  * will not be attached anywhere in the namespace and will be private (i.e.
1994  * changes to the originating mount won't be propagated into this).
1995  *
1996  * Release with mntput().
1997  */
1998 struct vfsmount *clone_private_mount(const struct path *path)
1999 {
2000 	struct mount *old_mnt = real_mount(path->mnt);
2001 	struct mount *new_mnt;
2002 
2003 	down_read(&namespace_sem);
2004 	if (IS_MNT_UNBINDABLE(old_mnt))
2005 		goto invalid;
2006 
2007 	if (!check_mnt(old_mnt))
2008 		goto invalid;
2009 
2010 	if (has_locked_children(old_mnt, path->dentry))
2011 		goto invalid;
2012 
2013 	new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
2014 	up_read(&namespace_sem);
2015 
2016 	if (IS_ERR(new_mnt))
2017 		return ERR_CAST(new_mnt);
2018 
2019 	/* Longterm mount to be removed by kern_unmount*() */
2020 	new_mnt->mnt_ns = MNT_NS_INTERNAL;
2021 
2022 	return &new_mnt->mnt;
2023 
2024 invalid:
2025 	up_read(&namespace_sem);
2026 	return ERR_PTR(-EINVAL);
2027 }
2028 EXPORT_SYMBOL_GPL(clone_private_mount);
2029 
2030 int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
2031 		   struct vfsmount *root)
2032 {
2033 	struct mount *mnt;
2034 	int res = f(root, arg);
2035 	if (res)
2036 		return res;
2037 	list_for_each_entry(mnt, &real_mount(root)->mnt_list, mnt_list) {
2038 		res = f(&mnt->mnt, arg);
2039 		if (res)
2040 			return res;
2041 	}
2042 	return 0;
2043 }
2044 
2045 static void lock_mnt_tree(struct mount *mnt)
2046 {
2047 	struct mount *p;
2048 
2049 	for (p = mnt; p; p = next_mnt(p, mnt)) {
2050 		int flags = p->mnt.mnt_flags;
2051 		/* Don't allow unprivileged users to change mount flags */
2052 		flags |= MNT_LOCK_ATIME;
2053 
2054 		if (flags & MNT_READONLY)
2055 			flags |= MNT_LOCK_READONLY;
2056 
2057 		if (flags & MNT_NODEV)
2058 			flags |= MNT_LOCK_NODEV;
2059 
2060 		if (flags & MNT_NOSUID)
2061 			flags |= MNT_LOCK_NOSUID;
2062 
2063 		if (flags & MNT_NOEXEC)
2064 			flags |= MNT_LOCK_NOEXEC;
2065 		/* Don't allow unprivileged users to reveal what is under a mount */
2066 		if (list_empty(&p->mnt_expire))
2067 			flags |= MNT_LOCKED;
2068 		p->mnt.mnt_flags = flags;
2069 	}
2070 }
2071 
2072 static void cleanup_group_ids(struct mount *mnt, struct mount *end)
2073 {
2074 	struct mount *p;
2075 
2076 	for (p = mnt; p != end; p = next_mnt(p, mnt)) {
2077 		if (p->mnt_group_id && !IS_MNT_SHARED(p))
2078 			mnt_release_group_id(p);
2079 	}
2080 }
2081 
2082 static int invent_group_ids(struct mount *mnt, bool recurse)
2083 {
2084 	struct mount *p;
2085 
2086 	for (p = mnt; p; p = recurse ? next_mnt(p, mnt) : NULL) {
2087 		if (!p->mnt_group_id && !IS_MNT_SHARED(p)) {
2088 			int err = mnt_alloc_group_id(p);
2089 			if (err) {
2090 				cleanup_group_ids(mnt, p);
2091 				return err;
2092 			}
2093 		}
2094 	}
2095 
2096 	return 0;
2097 }
2098 
2099 int count_mounts(struct mnt_namespace *ns, struct mount *mnt)
2100 {
2101 	unsigned int max = READ_ONCE(sysctl_mount_max);
2102 	unsigned int mounts = 0, old, pending, sum;
2103 	struct mount *p;
2104 
2105 	for (p = mnt; p; p = next_mnt(p, mnt))
2106 		mounts++;
2107 
2108 	old = ns->mounts;
2109 	pending = ns->pending_mounts;
2110 	sum = old + pending;
2111 	if ((old > sum) ||
2112 	    (pending > sum) ||
2113 	    (max < sum) ||
2114 	    (mounts > (max - sum)))
2115 		return -ENOSPC;
2116 
2117 	ns->pending_mounts = pending + mounts;
2118 	return 0;
2119 }
2120 
2121 /*
2122  *  @source_mnt : mount tree to be attached
2123  *  @nd         : place the mount tree @source_mnt is attached
2124  *  @parent_nd  : if non-null, detach the source_mnt from its parent and
2125  *  		   store the parent mount and mountpoint dentry.
2126  *  		   (done when source_mnt is moved)
2127  *
2128  *  NOTE: in the table below explains the semantics when a source mount
2129  *  of a given type is attached to a destination mount of a given type.
2130  * ---------------------------------------------------------------------------
2131  * |         BIND MOUNT OPERATION                                            |
2132  * |**************************************************************************
2133  * | source-->| shared        |       private  |       slave    | unbindable |
2134  * | dest     |               |                |                |            |
2135  * |   |      |               |                |                |            |
2136  * |   v      |               |                |                |            |
2137  * |**************************************************************************
2138  * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
2139  * |          |               |                |                |            |
2140  * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
2141  * ***************************************************************************
2142  * A bind operation clones the source mount and mounts the clone on the
2143  * destination mount.
2144  *
2145  * (++)  the cloned mount is propagated to all the mounts in the propagation
2146  * 	 tree of the destination mount and the cloned mount is added to
2147  * 	 the peer group of the source mount.
2148  * (+)   the cloned mount is created under the destination mount and is marked
2149  *       as shared. The cloned mount is added to the peer group of the source
2150  *       mount.
2151  * (+++) the mount is propagated to all the mounts in the propagation tree
2152  *       of the destination mount and the cloned mount is made slave
2153  *       of the same master as that of the source mount. The cloned mount
2154  *       is marked as 'shared and slave'.
2155  * (*)   the cloned mount is made a slave of the same master as that of the
2156  * 	 source mount.
2157  *
2158  * ---------------------------------------------------------------------------
2159  * |         		MOVE MOUNT OPERATION                                 |
2160  * |**************************************************************************
2161  * | source-->| shared        |       private  |       slave    | unbindable |
2162  * | dest     |               |                |                |            |
2163  * |   |      |               |                |                |            |
2164  * |   v      |               |                |                |            |
2165  * |**************************************************************************
2166  * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
2167  * |          |               |                |                |            |
2168  * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
2169  * ***************************************************************************
2170  *
2171  * (+)  the mount is moved to the destination. And is then propagated to
2172  * 	all the mounts in the propagation tree of the destination mount.
2173  * (+*)  the mount is moved to the destination.
2174  * (+++)  the mount is moved to the destination and is then propagated to
2175  * 	all the mounts belonging to the destination mount's propagation tree.
2176  * 	the mount is marked as 'shared and slave'.
2177  * (*)	the mount continues to be a slave at the new location.
2178  *
2179  * if the source mount is a tree, the operations explained above is
2180  * applied to each mount in the tree.
2181  * Must be called without spinlocks held, since this function can sleep
2182  * in allocations.
2183  */
2184 static int attach_recursive_mnt(struct mount *source_mnt,
2185 			struct mount *dest_mnt,
2186 			struct mountpoint *dest_mp,
2187 			bool moving)
2188 {
2189 	struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
2190 	HLIST_HEAD(tree_list);
2191 	struct mnt_namespace *ns = dest_mnt->mnt_ns;
2192 	struct mountpoint *smp;
2193 	struct mount *child, *p;
2194 	struct hlist_node *n;
2195 	int err;
2196 
2197 	/* Preallocate a mountpoint in case the new mounts need
2198 	 * to be tucked under other mounts.
2199 	 */
2200 	smp = get_mountpoint(source_mnt->mnt.mnt_root);
2201 	if (IS_ERR(smp))
2202 		return PTR_ERR(smp);
2203 
2204 	/* Is there space to add these mounts to the mount namespace? */
2205 	if (!moving) {
2206 		err = count_mounts(ns, source_mnt);
2207 		if (err)
2208 			goto out;
2209 	}
2210 
2211 	if (IS_MNT_SHARED(dest_mnt)) {
2212 		err = invent_group_ids(source_mnt, true);
2213 		if (err)
2214 			goto out;
2215 		err = propagate_mnt(dest_mnt, dest_mp, source_mnt, &tree_list);
2216 		lock_mount_hash();
2217 		if (err)
2218 			goto out_cleanup_ids;
2219 		for (p = source_mnt; p; p = next_mnt(p, source_mnt))
2220 			set_mnt_shared(p);
2221 	} else {
2222 		lock_mount_hash();
2223 	}
2224 	if (moving) {
2225 		unhash_mnt(source_mnt);
2226 		attach_mnt(source_mnt, dest_mnt, dest_mp);
2227 		touch_mnt_namespace(source_mnt->mnt_ns);
2228 	} else {
2229 		if (source_mnt->mnt_ns) {
2230 			/* move from anon - the caller will destroy */
2231 			list_del_init(&source_mnt->mnt_ns->list);
2232 		}
2233 		mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
2234 		commit_tree(source_mnt);
2235 	}
2236 
2237 	hlist_for_each_entry_safe(child, n, &tree_list, mnt_hash) {
2238 		struct mount *q;
2239 		hlist_del_init(&child->mnt_hash);
2240 		q = __lookup_mnt(&child->mnt_parent->mnt,
2241 				 child->mnt_mountpoint);
2242 		if (q)
2243 			mnt_change_mountpoint(child, smp, q);
2244 		/* Notice when we are propagating across user namespaces */
2245 		if (child->mnt_parent->mnt_ns->user_ns != user_ns)
2246 			lock_mnt_tree(child);
2247 		child->mnt.mnt_flags &= ~MNT_LOCKED;
2248 		commit_tree(child);
2249 	}
2250 	put_mountpoint(smp);
2251 	unlock_mount_hash();
2252 
2253 	return 0;
2254 
2255  out_cleanup_ids:
2256 	while (!hlist_empty(&tree_list)) {
2257 		child = hlist_entry(tree_list.first, struct mount, mnt_hash);
2258 		child->mnt_parent->mnt_ns->pending_mounts = 0;
2259 		umount_tree(child, UMOUNT_SYNC);
2260 	}
2261 	unlock_mount_hash();
2262 	cleanup_group_ids(source_mnt, NULL);
2263  out:
2264 	ns->pending_mounts = 0;
2265 
2266 	read_seqlock_excl(&mount_lock);
2267 	put_mountpoint(smp);
2268 	read_sequnlock_excl(&mount_lock);
2269 
2270 	return err;
2271 }
2272 
2273 static struct mountpoint *lock_mount(struct path *path)
2274 {
2275 	struct vfsmount *mnt;
2276 	struct dentry *dentry = path->dentry;
2277 retry:
2278 	inode_lock(dentry->d_inode);
2279 	if (unlikely(cant_mount(dentry))) {
2280 		inode_unlock(dentry->d_inode);
2281 		return ERR_PTR(-ENOENT);
2282 	}
2283 	namespace_lock();
2284 	mnt = lookup_mnt(path);
2285 	if (likely(!mnt)) {
2286 		struct mountpoint *mp = get_mountpoint(dentry);
2287 		if (IS_ERR(mp)) {
2288 			namespace_unlock();
2289 			inode_unlock(dentry->d_inode);
2290 			return mp;
2291 		}
2292 		return mp;
2293 	}
2294 	namespace_unlock();
2295 	inode_unlock(path->dentry->d_inode);
2296 	path_put(path);
2297 	path->mnt = mnt;
2298 	dentry = path->dentry = dget(mnt->mnt_root);
2299 	goto retry;
2300 }
2301 
2302 static void unlock_mount(struct mountpoint *where)
2303 {
2304 	struct dentry *dentry = where->m_dentry;
2305 
2306 	read_seqlock_excl(&mount_lock);
2307 	put_mountpoint(where);
2308 	read_sequnlock_excl(&mount_lock);
2309 
2310 	namespace_unlock();
2311 	inode_unlock(dentry->d_inode);
2312 }
2313 
2314 static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp)
2315 {
2316 	if (mnt->mnt.mnt_sb->s_flags & SB_NOUSER)
2317 		return -EINVAL;
2318 
2319 	if (d_is_dir(mp->m_dentry) !=
2320 	      d_is_dir(mnt->mnt.mnt_root))
2321 		return -ENOTDIR;
2322 
2323 	return attach_recursive_mnt(mnt, p, mp, false);
2324 }
2325 
2326 /*
2327  * Sanity check the flags to change_mnt_propagation.
2328  */
2329 
2330 static int flags_to_propagation_type(int ms_flags)
2331 {
2332 	int type = ms_flags & ~(MS_REC | MS_SILENT);
2333 
2334 	/* Fail if any non-propagation flags are set */
2335 	if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
2336 		return 0;
2337 	/* Only one propagation flag should be set */
2338 	if (!is_power_of_2(type))
2339 		return 0;
2340 	return type;
2341 }
2342 
2343 /*
2344  * recursively change the type of the mountpoint.
2345  */
2346 static int do_change_type(struct path *path, int ms_flags)
2347 {
2348 	struct mount *m;
2349 	struct mount *mnt = real_mount(path->mnt);
2350 	int recurse = ms_flags & MS_REC;
2351 	int type;
2352 	int err = 0;
2353 
2354 	if (path->dentry != path->mnt->mnt_root)
2355 		return -EINVAL;
2356 
2357 	type = flags_to_propagation_type(ms_flags);
2358 	if (!type)
2359 		return -EINVAL;
2360 
2361 	namespace_lock();
2362 	if (type == MS_SHARED) {
2363 		err = invent_group_ids(mnt, recurse);
2364 		if (err)
2365 			goto out_unlock;
2366 	}
2367 
2368 	lock_mount_hash();
2369 	for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
2370 		change_mnt_propagation(m, type);
2371 	unlock_mount_hash();
2372 
2373  out_unlock:
2374 	namespace_unlock();
2375 	return err;
2376 }
2377 
2378 static struct mount *__do_loopback(struct path *old_path, int recurse)
2379 {
2380 	struct mount *mnt = ERR_PTR(-EINVAL), *old = real_mount(old_path->mnt);
2381 
2382 	if (IS_MNT_UNBINDABLE(old))
2383 		return mnt;
2384 
2385 	if (!check_mnt(old) && old_path->dentry->d_op != &ns_dentry_operations)
2386 		return mnt;
2387 
2388 	if (!recurse && has_locked_children(old, old_path->dentry))
2389 		return mnt;
2390 
2391 	if (recurse)
2392 		mnt = copy_tree(old, old_path->dentry, CL_COPY_MNT_NS_FILE);
2393 	else
2394 		mnt = clone_mnt(old, old_path->dentry, 0);
2395 
2396 	if (!IS_ERR(mnt))
2397 		mnt->mnt.mnt_flags &= ~MNT_LOCKED;
2398 
2399 	return mnt;
2400 }
2401 
2402 /*
2403  * do loopback mount.
2404  */
2405 static int do_loopback(struct path *path, const char *old_name,
2406 				int recurse)
2407 {
2408 	struct path old_path;
2409 	struct mount *mnt = NULL, *parent;
2410 	struct mountpoint *mp;
2411 	int err;
2412 	if (!old_name || !*old_name)
2413 		return -EINVAL;
2414 	err = kern_path(old_name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &old_path);
2415 	if (err)
2416 		return err;
2417 
2418 	err = -EINVAL;
2419 	if (mnt_ns_loop(old_path.dentry))
2420 		goto out;
2421 
2422 	mp = lock_mount(path);
2423 	if (IS_ERR(mp)) {
2424 		err = PTR_ERR(mp);
2425 		goto out;
2426 	}
2427 
2428 	parent = real_mount(path->mnt);
2429 	if (!check_mnt(parent))
2430 		goto out2;
2431 
2432 	mnt = __do_loopback(&old_path, recurse);
2433 	if (IS_ERR(mnt)) {
2434 		err = PTR_ERR(mnt);
2435 		goto out2;
2436 	}
2437 
2438 	err = graft_tree(mnt, parent, mp);
2439 	if (err) {
2440 		lock_mount_hash();
2441 		umount_tree(mnt, UMOUNT_SYNC);
2442 		unlock_mount_hash();
2443 	}
2444 out2:
2445 	unlock_mount(mp);
2446 out:
2447 	path_put(&old_path);
2448 	return err;
2449 }
2450 
2451 static struct file *open_detached_copy(struct path *path, bool recursive)
2452 {
2453 	struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
2454 	struct mnt_namespace *ns = alloc_mnt_ns(user_ns, true);
2455 	struct mount *mnt, *p;
2456 	struct file *file;
2457 
2458 	if (IS_ERR(ns))
2459 		return ERR_CAST(ns);
2460 
2461 	namespace_lock();
2462 	mnt = __do_loopback(path, recursive);
2463 	if (IS_ERR(mnt)) {
2464 		namespace_unlock();
2465 		free_mnt_ns(ns);
2466 		return ERR_CAST(mnt);
2467 	}
2468 
2469 	lock_mount_hash();
2470 	for (p = mnt; p; p = next_mnt(p, mnt)) {
2471 		p->mnt_ns = ns;
2472 		ns->mounts++;
2473 	}
2474 	ns->root = mnt;
2475 	list_add_tail(&ns->list, &mnt->mnt_list);
2476 	mntget(&mnt->mnt);
2477 	unlock_mount_hash();
2478 	namespace_unlock();
2479 
2480 	mntput(path->mnt);
2481 	path->mnt = &mnt->mnt;
2482 	file = dentry_open(path, O_PATH, current_cred());
2483 	if (IS_ERR(file))
2484 		dissolve_on_fput(path->mnt);
2485 	else
2486 		file->f_mode |= FMODE_NEED_UNMOUNT;
2487 	return file;
2488 }
2489 
2490 SYSCALL_DEFINE3(open_tree, int, dfd, const char __user *, filename, unsigned, flags)
2491 {
2492 	struct file *file;
2493 	struct path path;
2494 	int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW;
2495 	bool detached = flags & OPEN_TREE_CLONE;
2496 	int error;
2497 	int fd;
2498 
2499 	BUILD_BUG_ON(OPEN_TREE_CLOEXEC != O_CLOEXEC);
2500 
2501 	if (flags & ~(AT_EMPTY_PATH | AT_NO_AUTOMOUNT | AT_RECURSIVE |
2502 		      AT_SYMLINK_NOFOLLOW | OPEN_TREE_CLONE |
2503 		      OPEN_TREE_CLOEXEC))
2504 		return -EINVAL;
2505 
2506 	if ((flags & (AT_RECURSIVE | OPEN_TREE_CLONE)) == AT_RECURSIVE)
2507 		return -EINVAL;
2508 
2509 	if (flags & AT_NO_AUTOMOUNT)
2510 		lookup_flags &= ~LOOKUP_AUTOMOUNT;
2511 	if (flags & AT_SYMLINK_NOFOLLOW)
2512 		lookup_flags &= ~LOOKUP_FOLLOW;
2513 	if (flags & AT_EMPTY_PATH)
2514 		lookup_flags |= LOOKUP_EMPTY;
2515 
2516 	if (detached && !may_mount())
2517 		return -EPERM;
2518 
2519 	fd = get_unused_fd_flags(flags & O_CLOEXEC);
2520 	if (fd < 0)
2521 		return fd;
2522 
2523 	error = user_path_at(dfd, filename, lookup_flags, &path);
2524 	if (unlikely(error)) {
2525 		file = ERR_PTR(error);
2526 	} else {
2527 		if (detached)
2528 			file = open_detached_copy(&path, flags & AT_RECURSIVE);
2529 		else
2530 			file = dentry_open(&path, O_PATH, current_cred());
2531 		path_put(&path);
2532 	}
2533 	if (IS_ERR(file)) {
2534 		put_unused_fd(fd);
2535 		return PTR_ERR(file);
2536 	}
2537 	fd_install(fd, file);
2538 	return fd;
2539 }
2540 
2541 /*
2542  * Don't allow locked mount flags to be cleared.
2543  *
2544  * No locks need to be held here while testing the various MNT_LOCK
2545  * flags because those flags can never be cleared once they are set.
2546  */
2547 static bool can_change_locked_flags(struct mount *mnt, unsigned int mnt_flags)
2548 {
2549 	unsigned int fl = mnt->mnt.mnt_flags;
2550 
2551 	if ((fl & MNT_LOCK_READONLY) &&
2552 	    !(mnt_flags & MNT_READONLY))
2553 		return false;
2554 
2555 	if ((fl & MNT_LOCK_NODEV) &&
2556 	    !(mnt_flags & MNT_NODEV))
2557 		return false;
2558 
2559 	if ((fl & MNT_LOCK_NOSUID) &&
2560 	    !(mnt_flags & MNT_NOSUID))
2561 		return false;
2562 
2563 	if ((fl & MNT_LOCK_NOEXEC) &&
2564 	    !(mnt_flags & MNT_NOEXEC))
2565 		return false;
2566 
2567 	if ((fl & MNT_LOCK_ATIME) &&
2568 	    ((fl & MNT_ATIME_MASK) != (mnt_flags & MNT_ATIME_MASK)))
2569 		return false;
2570 
2571 	return true;
2572 }
2573 
2574 static int change_mount_ro_state(struct mount *mnt, unsigned int mnt_flags)
2575 {
2576 	bool readonly_request = (mnt_flags & MNT_READONLY);
2577 
2578 	if (readonly_request == __mnt_is_readonly(&mnt->mnt))
2579 		return 0;
2580 
2581 	if (readonly_request)
2582 		return mnt_make_readonly(mnt);
2583 
2584 	mnt->mnt.mnt_flags &= ~MNT_READONLY;
2585 	return 0;
2586 }
2587 
2588 static void set_mount_attributes(struct mount *mnt, unsigned int mnt_flags)
2589 {
2590 	mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
2591 	mnt->mnt.mnt_flags = mnt_flags;
2592 	touch_mnt_namespace(mnt->mnt_ns);
2593 }
2594 
2595 static void mnt_warn_timestamp_expiry(struct path *mountpoint, struct vfsmount *mnt)
2596 {
2597 	struct super_block *sb = mnt->mnt_sb;
2598 
2599 	if (!__mnt_is_readonly(mnt) &&
2600 	   (ktime_get_real_seconds() + TIME_UPTIME_SEC_MAX > sb->s_time_max)) {
2601 		char *buf = (char *)__get_free_page(GFP_KERNEL);
2602 		char *mntpath = buf ? d_path(mountpoint, buf, PAGE_SIZE) : ERR_PTR(-ENOMEM);
2603 		struct tm tm;
2604 
2605 		time64_to_tm(sb->s_time_max, 0, &tm);
2606 
2607 		pr_warn("%s filesystem being %s at %s supports timestamps until %04ld (0x%llx)\n",
2608 			sb->s_type->name,
2609 			is_mounted(mnt) ? "remounted" : "mounted",
2610 			mntpath,
2611 			tm.tm_year+1900, (unsigned long long)sb->s_time_max);
2612 
2613 		free_page((unsigned long)buf);
2614 	}
2615 }
2616 
2617 /*
2618  * Handle reconfiguration of the mountpoint only without alteration of the
2619  * superblock it refers to.  This is triggered by specifying MS_REMOUNT|MS_BIND
2620  * to mount(2).
2621  */
2622 static int do_reconfigure_mnt(struct path *path, unsigned int mnt_flags)
2623 {
2624 	struct super_block *sb = path->mnt->mnt_sb;
2625 	struct mount *mnt = real_mount(path->mnt);
2626 	int ret;
2627 
2628 	if (!check_mnt(mnt))
2629 		return -EINVAL;
2630 
2631 	if (path->dentry != mnt->mnt.mnt_root)
2632 		return -EINVAL;
2633 
2634 	if (!can_change_locked_flags(mnt, mnt_flags))
2635 		return -EPERM;
2636 
2637 	/*
2638 	 * We're only checking whether the superblock is read-only not
2639 	 * changing it, so only take down_read(&sb->s_umount).
2640 	 */
2641 	down_read(&sb->s_umount);
2642 	lock_mount_hash();
2643 	ret = change_mount_ro_state(mnt, mnt_flags);
2644 	if (ret == 0)
2645 		set_mount_attributes(mnt, mnt_flags);
2646 	unlock_mount_hash();
2647 	up_read(&sb->s_umount);
2648 
2649 	mnt_warn_timestamp_expiry(path, &mnt->mnt);
2650 
2651 	return ret;
2652 }
2653 
2654 /*
2655  * change filesystem flags. dir should be a physical root of filesystem.
2656  * If you've mounted a non-root directory somewhere and want to do remount
2657  * on it - tough luck.
2658  */
2659 static int do_remount(struct path *path, int ms_flags, int sb_flags,
2660 		      int mnt_flags, void *data)
2661 {
2662 	int err;
2663 	struct super_block *sb = path->mnt->mnt_sb;
2664 	struct mount *mnt = real_mount(path->mnt);
2665 	struct fs_context *fc;
2666 
2667 	if (!check_mnt(mnt))
2668 		return -EINVAL;
2669 
2670 	if (path->dentry != path->mnt->mnt_root)
2671 		return -EINVAL;
2672 
2673 	if (!can_change_locked_flags(mnt, mnt_flags))
2674 		return -EPERM;
2675 
2676 	fc = fs_context_for_reconfigure(path->dentry, sb_flags, MS_RMT_MASK);
2677 	if (IS_ERR(fc))
2678 		return PTR_ERR(fc);
2679 
2680 	fc->oldapi = true;
2681 	err = parse_monolithic_mount_data(fc, data);
2682 	if (!err) {
2683 		down_write(&sb->s_umount);
2684 		err = -EPERM;
2685 		if (ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
2686 			err = reconfigure_super(fc);
2687 			if (!err) {
2688 				lock_mount_hash();
2689 				set_mount_attributes(mnt, mnt_flags);
2690 				unlock_mount_hash();
2691 			}
2692 		}
2693 		up_write(&sb->s_umount);
2694 	}
2695 
2696 	mnt_warn_timestamp_expiry(path, &mnt->mnt);
2697 
2698 	put_fs_context(fc);
2699 	return err;
2700 }
2701 
2702 static inline int tree_contains_unbindable(struct mount *mnt)
2703 {
2704 	struct mount *p;
2705 	for (p = mnt; p; p = next_mnt(p, mnt)) {
2706 		if (IS_MNT_UNBINDABLE(p))
2707 			return 1;
2708 	}
2709 	return 0;
2710 }
2711 
2712 /*
2713  * Check that there aren't references to earlier/same mount namespaces in the
2714  * specified subtree.  Such references can act as pins for mount namespaces
2715  * that aren't checked by the mount-cycle checking code, thereby allowing
2716  * cycles to be made.
2717  */
2718 static bool check_for_nsfs_mounts(struct mount *subtree)
2719 {
2720 	struct mount *p;
2721 	bool ret = false;
2722 
2723 	lock_mount_hash();
2724 	for (p = subtree; p; p = next_mnt(p, subtree))
2725 		if (mnt_ns_loop(p->mnt.mnt_root))
2726 			goto out;
2727 
2728 	ret = true;
2729 out:
2730 	unlock_mount_hash();
2731 	return ret;
2732 }
2733 
2734 static int do_set_group(struct path *from_path, struct path *to_path)
2735 {
2736 	struct mount *from, *to;
2737 	int err;
2738 
2739 	from = real_mount(from_path->mnt);
2740 	to = real_mount(to_path->mnt);
2741 
2742 	namespace_lock();
2743 
2744 	err = -EINVAL;
2745 	/* To and From must be mounted */
2746 	if (!is_mounted(&from->mnt))
2747 		goto out;
2748 	if (!is_mounted(&to->mnt))
2749 		goto out;
2750 
2751 	err = -EPERM;
2752 	/* We should be allowed to modify mount namespaces of both mounts */
2753 	if (!ns_capable(from->mnt_ns->user_ns, CAP_SYS_ADMIN))
2754 		goto out;
2755 	if (!ns_capable(to->mnt_ns->user_ns, CAP_SYS_ADMIN))
2756 		goto out;
2757 
2758 	err = -EINVAL;
2759 	/* To and From paths should be mount roots */
2760 	if (from_path->dentry != from_path->mnt->mnt_root)
2761 		goto out;
2762 	if (to_path->dentry != to_path->mnt->mnt_root)
2763 		goto out;
2764 
2765 	/* Setting sharing groups is only allowed across same superblock */
2766 	if (from->mnt.mnt_sb != to->mnt.mnt_sb)
2767 		goto out;
2768 
2769 	/* From mount root should be wider than To mount root */
2770 	if (!is_subdir(to->mnt.mnt_root, from->mnt.mnt_root))
2771 		goto out;
2772 
2773 	/* From mount should not have locked children in place of To's root */
2774 	if (has_locked_children(from, to->mnt.mnt_root))
2775 		goto out;
2776 
2777 	/* Setting sharing groups is only allowed on private mounts */
2778 	if (IS_MNT_SHARED(to) || IS_MNT_SLAVE(to))
2779 		goto out;
2780 
2781 	/* From should not be private */
2782 	if (!IS_MNT_SHARED(from) && !IS_MNT_SLAVE(from))
2783 		goto out;
2784 
2785 	if (IS_MNT_SLAVE(from)) {
2786 		struct mount *m = from->mnt_master;
2787 
2788 		list_add(&to->mnt_slave, &m->mnt_slave_list);
2789 		to->mnt_master = m;
2790 	}
2791 
2792 	if (IS_MNT_SHARED(from)) {
2793 		to->mnt_group_id = from->mnt_group_id;
2794 		list_add(&to->mnt_share, &from->mnt_share);
2795 		lock_mount_hash();
2796 		set_mnt_shared(to);
2797 		unlock_mount_hash();
2798 	}
2799 
2800 	err = 0;
2801 out:
2802 	namespace_unlock();
2803 	return err;
2804 }
2805 
2806 static int do_move_mount(struct path *old_path, struct path *new_path)
2807 {
2808 	struct mnt_namespace *ns;
2809 	struct mount *p;
2810 	struct mount *old;
2811 	struct mount *parent;
2812 	struct mountpoint *mp, *old_mp;
2813 	int err;
2814 	bool attached;
2815 
2816 	mp = lock_mount(new_path);
2817 	if (IS_ERR(mp))
2818 		return PTR_ERR(mp);
2819 
2820 	old = real_mount(old_path->mnt);
2821 	p = real_mount(new_path->mnt);
2822 	parent = old->mnt_parent;
2823 	attached = mnt_has_parent(old);
2824 	old_mp = old->mnt_mp;
2825 	ns = old->mnt_ns;
2826 
2827 	err = -EINVAL;
2828 	/* The mountpoint must be in our namespace. */
2829 	if (!check_mnt(p))
2830 		goto out;
2831 
2832 	/* The thing moved must be mounted... */
2833 	if (!is_mounted(&old->mnt))
2834 		goto out;
2835 
2836 	/* ... and either ours or the root of anon namespace */
2837 	if (!(attached ? check_mnt(old) : is_anon_ns(ns)))
2838 		goto out;
2839 
2840 	if (old->mnt.mnt_flags & MNT_LOCKED)
2841 		goto out;
2842 
2843 	if (old_path->dentry != old_path->mnt->mnt_root)
2844 		goto out;
2845 
2846 	if (d_is_dir(new_path->dentry) !=
2847 	    d_is_dir(old_path->dentry))
2848 		goto out;
2849 	/*
2850 	 * Don't move a mount residing in a shared parent.
2851 	 */
2852 	if (attached && IS_MNT_SHARED(parent))
2853 		goto out;
2854 	/*
2855 	 * Don't move a mount tree containing unbindable mounts to a destination
2856 	 * mount which is shared.
2857 	 */
2858 	if (IS_MNT_SHARED(p) && tree_contains_unbindable(old))
2859 		goto out;
2860 	err = -ELOOP;
2861 	if (!check_for_nsfs_mounts(old))
2862 		goto out;
2863 	for (; mnt_has_parent(p); p = p->mnt_parent)
2864 		if (p == old)
2865 			goto out;
2866 
2867 	err = attach_recursive_mnt(old, real_mount(new_path->mnt), mp,
2868 				   attached);
2869 	if (err)
2870 		goto out;
2871 
2872 	/* if the mount is moved, it should no longer be expire
2873 	 * automatically */
2874 	list_del_init(&old->mnt_expire);
2875 	if (attached)
2876 		put_mountpoint(old_mp);
2877 out:
2878 	unlock_mount(mp);
2879 	if (!err) {
2880 		if (attached)
2881 			mntput_no_expire(parent);
2882 		else
2883 			free_mnt_ns(ns);
2884 	}
2885 	return err;
2886 }
2887 
2888 static int do_move_mount_old(struct path *path, const char *old_name)
2889 {
2890 	struct path old_path;
2891 	int err;
2892 
2893 	if (!old_name || !*old_name)
2894 		return -EINVAL;
2895 
2896 	err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
2897 	if (err)
2898 		return err;
2899 
2900 	err = do_move_mount(&old_path, path);
2901 	path_put(&old_path);
2902 	return err;
2903 }
2904 
2905 /*
2906  * add a mount into a namespace's mount tree
2907  */
2908 static int do_add_mount(struct mount *newmnt, struct mountpoint *mp,
2909 			struct path *path, int mnt_flags)
2910 {
2911 	struct mount *parent = real_mount(path->mnt);
2912 
2913 	mnt_flags &= ~MNT_INTERNAL_FLAGS;
2914 
2915 	if (unlikely(!check_mnt(parent))) {
2916 		/* that's acceptable only for automounts done in private ns */
2917 		if (!(mnt_flags & MNT_SHRINKABLE))
2918 			return -EINVAL;
2919 		/* ... and for those we'd better have mountpoint still alive */
2920 		if (!parent->mnt_ns)
2921 			return -EINVAL;
2922 	}
2923 
2924 	/* Refuse the same filesystem on the same mount point */
2925 	if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb &&
2926 	    path->mnt->mnt_root == path->dentry)
2927 		return -EBUSY;
2928 
2929 	if (d_is_symlink(newmnt->mnt.mnt_root))
2930 		return -EINVAL;
2931 
2932 	newmnt->mnt.mnt_flags = mnt_flags;
2933 	return graft_tree(newmnt, parent, mp);
2934 }
2935 
2936 static bool mount_too_revealing(const struct super_block *sb, int *new_mnt_flags);
2937 
2938 /*
2939  * Create a new mount using a superblock configuration and request it
2940  * be added to the namespace tree.
2941  */
2942 static int do_new_mount_fc(struct fs_context *fc, struct path *mountpoint,
2943 			   unsigned int mnt_flags)
2944 {
2945 	struct vfsmount *mnt;
2946 	struct mountpoint *mp;
2947 	struct super_block *sb = fc->root->d_sb;
2948 	int error;
2949 
2950 	error = security_sb_kern_mount(sb);
2951 	if (!error && mount_too_revealing(sb, &mnt_flags))
2952 		error = -EPERM;
2953 
2954 	if (unlikely(error)) {
2955 		fc_drop_locked(fc);
2956 		return error;
2957 	}
2958 
2959 	up_write(&sb->s_umount);
2960 
2961 	mnt = vfs_create_mount(fc);
2962 	if (IS_ERR(mnt))
2963 		return PTR_ERR(mnt);
2964 
2965 	mnt_warn_timestamp_expiry(mountpoint, mnt);
2966 
2967 	mp = lock_mount(mountpoint);
2968 	if (IS_ERR(mp)) {
2969 		mntput(mnt);
2970 		return PTR_ERR(mp);
2971 	}
2972 	error = do_add_mount(real_mount(mnt), mp, mountpoint, mnt_flags);
2973 	unlock_mount(mp);
2974 	if (error < 0)
2975 		mntput(mnt);
2976 	return error;
2977 }
2978 
2979 /*
2980  * create a new mount for userspace and request it to be added into the
2981  * namespace's tree
2982  */
2983 static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
2984 			int mnt_flags, const char *name, void *data)
2985 {
2986 	struct file_system_type *type;
2987 	struct fs_context *fc;
2988 	const char *subtype = NULL;
2989 	int err = 0;
2990 
2991 	if (!fstype)
2992 		return -EINVAL;
2993 
2994 	type = get_fs_type(fstype);
2995 	if (!type)
2996 		return -ENODEV;
2997 
2998 	if (type->fs_flags & FS_HAS_SUBTYPE) {
2999 		subtype = strchr(fstype, '.');
3000 		if (subtype) {
3001 			subtype++;
3002 			if (!*subtype) {
3003 				put_filesystem(type);
3004 				return -EINVAL;
3005 			}
3006 		}
3007 	}
3008 
3009 	fc = fs_context_for_mount(type, sb_flags);
3010 	put_filesystem(type);
3011 	if (IS_ERR(fc))
3012 		return PTR_ERR(fc);
3013 
3014 	if (subtype)
3015 		err = vfs_parse_fs_string(fc, "subtype",
3016 					  subtype, strlen(subtype));
3017 	if (!err && name)
3018 		err = vfs_parse_fs_string(fc, "source", name, strlen(name));
3019 	if (!err)
3020 		err = parse_monolithic_mount_data(fc, data);
3021 	if (!err && !mount_capable(fc))
3022 		err = -EPERM;
3023 	if (!err)
3024 		err = vfs_get_tree(fc);
3025 	if (!err)
3026 		err = do_new_mount_fc(fc, path, mnt_flags);
3027 
3028 	put_fs_context(fc);
3029 	return err;
3030 }
3031 
3032 int finish_automount(struct vfsmount *m, struct path *path)
3033 {
3034 	struct dentry *dentry = path->dentry;
3035 	struct mountpoint *mp;
3036 	struct mount *mnt;
3037 	int err;
3038 
3039 	if (!m)
3040 		return 0;
3041 	if (IS_ERR(m))
3042 		return PTR_ERR(m);
3043 
3044 	mnt = real_mount(m);
3045 	/* The new mount record should have at least 2 refs to prevent it being
3046 	 * expired before we get a chance to add it
3047 	 */
3048 	BUG_ON(mnt_get_count(mnt) < 2);
3049 
3050 	if (m->mnt_sb == path->mnt->mnt_sb &&
3051 	    m->mnt_root == dentry) {
3052 		err = -ELOOP;
3053 		goto discard;
3054 	}
3055 
3056 	/*
3057 	 * we don't want to use lock_mount() - in this case finding something
3058 	 * that overmounts our mountpoint to be means "quitely drop what we've
3059 	 * got", not "try to mount it on top".
3060 	 */
3061 	inode_lock(dentry->d_inode);
3062 	namespace_lock();
3063 	if (unlikely(cant_mount(dentry))) {
3064 		err = -ENOENT;
3065 		goto discard_locked;
3066 	}
3067 	rcu_read_lock();
3068 	if (unlikely(__lookup_mnt(path->mnt, dentry))) {
3069 		rcu_read_unlock();
3070 		err = 0;
3071 		goto discard_locked;
3072 	}
3073 	rcu_read_unlock();
3074 	mp = get_mountpoint(dentry);
3075 	if (IS_ERR(mp)) {
3076 		err = PTR_ERR(mp);
3077 		goto discard_locked;
3078 	}
3079 
3080 	err = do_add_mount(mnt, mp, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
3081 	unlock_mount(mp);
3082 	if (unlikely(err))
3083 		goto discard;
3084 	mntput(m);
3085 	return 0;
3086 
3087 discard_locked:
3088 	namespace_unlock();
3089 	inode_unlock(dentry->d_inode);
3090 discard:
3091 	/* remove m from any expiration list it may be on */
3092 	if (!list_empty(&mnt->mnt_expire)) {
3093 		namespace_lock();
3094 		list_del_init(&mnt->mnt_expire);
3095 		namespace_unlock();
3096 	}
3097 	mntput(m);
3098 	mntput(m);
3099 	return err;
3100 }
3101 
3102 /**
3103  * mnt_set_expiry - Put a mount on an expiration list
3104  * @mnt: The mount to list.
3105  * @expiry_list: The list to add the mount to.
3106  */
3107 void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
3108 {
3109 	namespace_lock();
3110 
3111 	list_add_tail(&real_mount(mnt)->mnt_expire, expiry_list);
3112 
3113 	namespace_unlock();
3114 }
3115 EXPORT_SYMBOL(mnt_set_expiry);
3116 
3117 /*
3118  * process a list of expirable mountpoints with the intent of discarding any
3119  * mountpoints that aren't in use and haven't been touched since last we came
3120  * here
3121  */
3122 void mark_mounts_for_expiry(struct list_head *mounts)
3123 {
3124 	struct mount *mnt, *next;
3125 	LIST_HEAD(graveyard);
3126 
3127 	if (list_empty(mounts))
3128 		return;
3129 
3130 	namespace_lock();
3131 	lock_mount_hash();
3132 
3133 	/* extract from the expiration list every vfsmount that matches the
3134 	 * following criteria:
3135 	 * - only referenced by its parent vfsmount
3136 	 * - still marked for expiry (marked on the last call here; marks are
3137 	 *   cleared by mntput())
3138 	 */
3139 	list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
3140 		if (!xchg(&mnt->mnt_expiry_mark, 1) ||
3141 			propagate_mount_busy(mnt, 1))
3142 			continue;
3143 		list_move(&mnt->mnt_expire, &graveyard);
3144 	}
3145 	while (!list_empty(&graveyard)) {
3146 		mnt = list_first_entry(&graveyard, struct mount, mnt_expire);
3147 		touch_mnt_namespace(mnt->mnt_ns);
3148 		umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
3149 	}
3150 	unlock_mount_hash();
3151 	namespace_unlock();
3152 }
3153 
3154 EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
3155 
3156 /*
3157  * Ripoff of 'select_parent()'
3158  *
3159  * search the list of submounts for a given mountpoint, and move any
3160  * shrinkable submounts to the 'graveyard' list.
3161  */
3162 static int select_submounts(struct mount *parent, struct list_head *graveyard)
3163 {
3164 	struct mount *this_parent = parent;
3165 	struct list_head *next;
3166 	int found = 0;
3167 
3168 repeat:
3169 	next = this_parent->mnt_mounts.next;
3170 resume:
3171 	while (next != &this_parent->mnt_mounts) {
3172 		struct list_head *tmp = next;
3173 		struct mount *mnt = list_entry(tmp, struct mount, mnt_child);
3174 
3175 		next = tmp->next;
3176 		if (!(mnt->mnt.mnt_flags & MNT_SHRINKABLE))
3177 			continue;
3178 		/*
3179 		 * Descend a level if the d_mounts list is non-empty.
3180 		 */
3181 		if (!list_empty(&mnt->mnt_mounts)) {
3182 			this_parent = mnt;
3183 			goto repeat;
3184 		}
3185 
3186 		if (!propagate_mount_busy(mnt, 1)) {
3187 			list_move_tail(&mnt->mnt_expire, graveyard);
3188 			found++;
3189 		}
3190 	}
3191 	/*
3192 	 * All done at this level ... ascend and resume the search
3193 	 */
3194 	if (this_parent != parent) {
3195 		next = this_parent->mnt_child.next;
3196 		this_parent = this_parent->mnt_parent;
3197 		goto resume;
3198 	}
3199 	return found;
3200 }
3201 
3202 /*
3203  * process a list of expirable mountpoints with the intent of discarding any
3204  * submounts of a specific parent mountpoint
3205  *
3206  * mount_lock must be held for write
3207  */
3208 static void shrink_submounts(struct mount *mnt)
3209 {
3210 	LIST_HEAD(graveyard);
3211 	struct mount *m;
3212 
3213 	/* extract submounts of 'mountpoint' from the expiration list */
3214 	while (select_submounts(mnt, &graveyard)) {
3215 		while (!list_empty(&graveyard)) {
3216 			m = list_first_entry(&graveyard, struct mount,
3217 						mnt_expire);
3218 			touch_mnt_namespace(m->mnt_ns);
3219 			umount_tree(m, UMOUNT_PROPAGATE|UMOUNT_SYNC);
3220 		}
3221 	}
3222 }
3223 
3224 static void *copy_mount_options(const void __user * data)
3225 {
3226 	char *copy;
3227 	unsigned left, offset;
3228 
3229 	if (!data)
3230 		return NULL;
3231 
3232 	copy = kmalloc(PAGE_SIZE, GFP_KERNEL);
3233 	if (!copy)
3234 		return ERR_PTR(-ENOMEM);
3235 
3236 	left = copy_from_user(copy, data, PAGE_SIZE);
3237 
3238 	/*
3239 	 * Not all architectures have an exact copy_from_user(). Resort to
3240 	 * byte at a time.
3241 	 */
3242 	offset = PAGE_SIZE - left;
3243 	while (left) {
3244 		char c;
3245 		if (get_user(c, (const char __user *)data + offset))
3246 			break;
3247 		copy[offset] = c;
3248 		left--;
3249 		offset++;
3250 	}
3251 
3252 	if (left == PAGE_SIZE) {
3253 		kfree(copy);
3254 		return ERR_PTR(-EFAULT);
3255 	}
3256 
3257 	return copy;
3258 }
3259 
3260 static char *copy_mount_string(const void __user *data)
3261 {
3262 	return data ? strndup_user(data, PATH_MAX) : NULL;
3263 }
3264 
3265 /*
3266  * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
3267  * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
3268  *
3269  * data is a (void *) that can point to any structure up to
3270  * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
3271  * information (or be NULL).
3272  *
3273  * Pre-0.97 versions of mount() didn't have a flags word.
3274  * When the flags word was introduced its top half was required
3275  * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
3276  * Therefore, if this magic number is present, it carries no information
3277  * and must be discarded.
3278  */
3279 int path_mount(const char *dev_name, struct path *path,
3280 		const char *type_page, unsigned long flags, void *data_page)
3281 {
3282 	unsigned int mnt_flags = 0, sb_flags;
3283 	int ret;
3284 
3285 	/* Discard magic */
3286 	if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
3287 		flags &= ~MS_MGC_MSK;
3288 
3289 	/* Basic sanity checks */
3290 	if (data_page)
3291 		((char *)data_page)[PAGE_SIZE - 1] = 0;
3292 
3293 	if (flags & MS_NOUSER)
3294 		return -EINVAL;
3295 
3296 	ret = security_sb_mount(dev_name, path, type_page, flags, data_page);
3297 	if (ret)
3298 		return ret;
3299 	if (!may_mount())
3300 		return -EPERM;
3301 	if (flags & SB_MANDLOCK)
3302 		warn_mandlock();
3303 
3304 	/* Default to relatime unless overriden */
3305 	if (!(flags & MS_NOATIME))
3306 		mnt_flags |= MNT_RELATIME;
3307 
3308 	/* Separate the per-mountpoint flags */
3309 	if (flags & MS_NOSUID)
3310 		mnt_flags |= MNT_NOSUID;
3311 	if (flags & MS_NODEV)
3312 		mnt_flags |= MNT_NODEV;
3313 	if (flags & MS_NOEXEC)
3314 		mnt_flags |= MNT_NOEXEC;
3315 	if (flags & MS_NOATIME)
3316 		mnt_flags |= MNT_NOATIME;
3317 	if (flags & MS_NODIRATIME)
3318 		mnt_flags |= MNT_NODIRATIME;
3319 	if (flags & MS_STRICTATIME)
3320 		mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
3321 	if (flags & MS_RDONLY)
3322 		mnt_flags |= MNT_READONLY;
3323 	if (flags & MS_NOSYMFOLLOW)
3324 		mnt_flags |= MNT_NOSYMFOLLOW;
3325 
3326 	/* The default atime for remount is preservation */
3327 	if ((flags & MS_REMOUNT) &&
3328 	    ((flags & (MS_NOATIME | MS_NODIRATIME | MS_RELATIME |
3329 		       MS_STRICTATIME)) == 0)) {
3330 		mnt_flags &= ~MNT_ATIME_MASK;
3331 		mnt_flags |= path->mnt->mnt_flags & MNT_ATIME_MASK;
3332 	}
3333 
3334 	sb_flags = flags & (SB_RDONLY |
3335 			    SB_SYNCHRONOUS |
3336 			    SB_MANDLOCK |
3337 			    SB_DIRSYNC |
3338 			    SB_SILENT |
3339 			    SB_POSIXACL |
3340 			    SB_LAZYTIME |
3341 			    SB_I_VERSION);
3342 
3343 	if ((flags & (MS_REMOUNT | MS_BIND)) == (MS_REMOUNT | MS_BIND))
3344 		return do_reconfigure_mnt(path, mnt_flags);
3345 	if (flags & MS_REMOUNT)
3346 		return do_remount(path, flags, sb_flags, mnt_flags, data_page);
3347 	if (flags & MS_BIND)
3348 		return do_loopback(path, dev_name, flags & MS_REC);
3349 	if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
3350 		return do_change_type(path, flags);
3351 	if (flags & MS_MOVE)
3352 		return do_move_mount_old(path, dev_name);
3353 
3354 	return do_new_mount(path, type_page, sb_flags, mnt_flags, dev_name,
3355 			    data_page);
3356 }
3357 
3358 long do_mount(const char *dev_name, const char __user *dir_name,
3359 		const char *type_page, unsigned long flags, void *data_page)
3360 {
3361 	struct path path;
3362 	int ret;
3363 
3364 	ret = user_path_at(AT_FDCWD, dir_name, LOOKUP_FOLLOW, &path);
3365 	if (ret)
3366 		return ret;
3367 	ret = path_mount(dev_name, &path, type_page, flags, data_page);
3368 	path_put(&path);
3369 	return ret;
3370 }
3371 
3372 static struct ucounts *inc_mnt_namespaces(struct user_namespace *ns)
3373 {
3374 	return inc_ucount(ns, current_euid(), UCOUNT_MNT_NAMESPACES);
3375 }
3376 
3377 static void dec_mnt_namespaces(struct ucounts *ucounts)
3378 {
3379 	dec_ucount(ucounts, UCOUNT_MNT_NAMESPACES);
3380 }
3381 
3382 static void free_mnt_ns(struct mnt_namespace *ns)
3383 {
3384 	if (!is_anon_ns(ns))
3385 		ns_free_inum(&ns->ns);
3386 	dec_mnt_namespaces(ns->ucounts);
3387 	put_user_ns(ns->user_ns);
3388 	kfree(ns);
3389 }
3390 
3391 /*
3392  * Assign a sequence number so we can detect when we attempt to bind
3393  * mount a reference to an older mount namespace into the current
3394  * mount namespace, preventing reference counting loops.  A 64bit
3395  * number incrementing at 10Ghz will take 12,427 years to wrap which
3396  * is effectively never, so we can ignore the possibility.
3397  */
3398 static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
3399 
3400 static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns, bool anon)
3401 {
3402 	struct mnt_namespace *new_ns;
3403 	struct ucounts *ucounts;
3404 	int ret;
3405 
3406 	ucounts = inc_mnt_namespaces(user_ns);
3407 	if (!ucounts)
3408 		return ERR_PTR(-ENOSPC);
3409 
3410 	new_ns = kzalloc(sizeof(struct mnt_namespace), GFP_KERNEL_ACCOUNT);
3411 	if (!new_ns) {
3412 		dec_mnt_namespaces(ucounts);
3413 		return ERR_PTR(-ENOMEM);
3414 	}
3415 	if (!anon) {
3416 		ret = ns_alloc_inum(&new_ns->ns);
3417 		if (ret) {
3418 			kfree(new_ns);
3419 			dec_mnt_namespaces(ucounts);
3420 			return ERR_PTR(ret);
3421 		}
3422 	}
3423 	new_ns->ns.ops = &mntns_operations;
3424 	if (!anon)
3425 		new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
3426 	refcount_set(&new_ns->ns.count, 1);
3427 	INIT_LIST_HEAD(&new_ns->list);
3428 	init_waitqueue_head(&new_ns->poll);
3429 	spin_lock_init(&new_ns->ns_lock);
3430 	new_ns->user_ns = get_user_ns(user_ns);
3431 	new_ns->ucounts = ucounts;
3432 	return new_ns;
3433 }
3434 
3435 __latent_entropy
3436 struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
3437 		struct user_namespace *user_ns, struct fs_struct *new_fs)
3438 {
3439 	struct mnt_namespace *new_ns;
3440 	struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
3441 	struct mount *p, *q;
3442 	struct mount *old;
3443 	struct mount *new;
3444 	int copy_flags;
3445 
3446 	BUG_ON(!ns);
3447 
3448 	if (likely(!(flags & CLONE_NEWNS))) {
3449 		get_mnt_ns(ns);
3450 		return ns;
3451 	}
3452 
3453 	old = ns->root;
3454 
3455 	new_ns = alloc_mnt_ns(user_ns, false);
3456 	if (IS_ERR(new_ns))
3457 		return new_ns;
3458 
3459 	namespace_lock();
3460 	/* First pass: copy the tree topology */
3461 	copy_flags = CL_COPY_UNBINDABLE | CL_EXPIRE;
3462 	if (user_ns != ns->user_ns)
3463 		copy_flags |= CL_SHARED_TO_SLAVE;
3464 	new = copy_tree(old, old->mnt.mnt_root, copy_flags);
3465 	if (IS_ERR(new)) {
3466 		namespace_unlock();
3467 		free_mnt_ns(new_ns);
3468 		return ERR_CAST(new);
3469 	}
3470 	if (user_ns != ns->user_ns) {
3471 		lock_mount_hash();
3472 		lock_mnt_tree(new);
3473 		unlock_mount_hash();
3474 	}
3475 	new_ns->root = new;
3476 	list_add_tail(&new_ns->list, &new->mnt_list);
3477 
3478 	/*
3479 	 * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
3480 	 * as belonging to new namespace.  We have already acquired a private
3481 	 * fs_struct, so tsk->fs->lock is not needed.
3482 	 */
3483 	p = old;
3484 	q = new;
3485 	while (p) {
3486 		q->mnt_ns = new_ns;
3487 		new_ns->mounts++;
3488 		if (new_fs) {
3489 			if (&p->mnt == new_fs->root.mnt) {
3490 				new_fs->root.mnt = mntget(&q->mnt);
3491 				rootmnt = &p->mnt;
3492 			}
3493 			if (&p->mnt == new_fs->pwd.mnt) {
3494 				new_fs->pwd.mnt = mntget(&q->mnt);
3495 				pwdmnt = &p->mnt;
3496 			}
3497 		}
3498 		p = next_mnt(p, old);
3499 		q = next_mnt(q, new);
3500 		if (!q)
3501 			break;
3502 		while (p->mnt.mnt_root != q->mnt.mnt_root)
3503 			p = next_mnt(p, old);
3504 	}
3505 	namespace_unlock();
3506 
3507 	if (rootmnt)
3508 		mntput(rootmnt);
3509 	if (pwdmnt)
3510 		mntput(pwdmnt);
3511 
3512 	return new_ns;
3513 }
3514 
3515 struct dentry *mount_subtree(struct vfsmount *m, const char *name)
3516 {
3517 	struct mount *mnt = real_mount(m);
3518 	struct mnt_namespace *ns;
3519 	struct super_block *s;
3520 	struct path path;
3521 	int err;
3522 
3523 	ns = alloc_mnt_ns(&init_user_ns, true);
3524 	if (IS_ERR(ns)) {
3525 		mntput(m);
3526 		return ERR_CAST(ns);
3527 	}
3528 	mnt->mnt_ns = ns;
3529 	ns->root = mnt;
3530 	ns->mounts++;
3531 	list_add(&mnt->mnt_list, &ns->list);
3532 
3533 	err = vfs_path_lookup(m->mnt_root, m,
3534 			name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
3535 
3536 	put_mnt_ns(ns);
3537 
3538 	if (err)
3539 		return ERR_PTR(err);
3540 
3541 	/* trade a vfsmount reference for active sb one */
3542 	s = path.mnt->mnt_sb;
3543 	atomic_inc(&s->s_active);
3544 	mntput(path.mnt);
3545 	/* lock the sucker */
3546 	down_write(&s->s_umount);
3547 	/* ... and return the root of (sub)tree on it */
3548 	return path.dentry;
3549 }
3550 EXPORT_SYMBOL(mount_subtree);
3551 
3552 SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
3553 		char __user *, type, unsigned long, flags, void __user *, data)
3554 {
3555 	int ret;
3556 	char *kernel_type;
3557 	char *kernel_dev;
3558 	void *options;
3559 
3560 	kernel_type = copy_mount_string(type);
3561 	ret = PTR_ERR(kernel_type);
3562 	if (IS_ERR(kernel_type))
3563 		goto out_type;
3564 
3565 	kernel_dev = copy_mount_string(dev_name);
3566 	ret = PTR_ERR(kernel_dev);
3567 	if (IS_ERR(kernel_dev))
3568 		goto out_dev;
3569 
3570 	options = copy_mount_options(data);
3571 	ret = PTR_ERR(options);
3572 	if (IS_ERR(options))
3573 		goto out_data;
3574 
3575 	ret = do_mount(kernel_dev, dir_name, kernel_type, flags, options);
3576 
3577 	kfree(options);
3578 out_data:
3579 	kfree(kernel_dev);
3580 out_dev:
3581 	kfree(kernel_type);
3582 out_type:
3583 	return ret;
3584 }
3585 
3586 #define FSMOUNT_VALID_FLAGS                                                    \
3587 	(MOUNT_ATTR_RDONLY | MOUNT_ATTR_NOSUID | MOUNT_ATTR_NODEV |            \
3588 	 MOUNT_ATTR_NOEXEC | MOUNT_ATTR__ATIME | MOUNT_ATTR_NODIRATIME |       \
3589 	 MOUNT_ATTR_NOSYMFOLLOW)
3590 
3591 #define MOUNT_SETATTR_VALID_FLAGS (FSMOUNT_VALID_FLAGS | MOUNT_ATTR_IDMAP)
3592 
3593 #define MOUNT_SETATTR_PROPAGATION_FLAGS \
3594 	(MS_UNBINDABLE | MS_PRIVATE | MS_SLAVE | MS_SHARED)
3595 
3596 static unsigned int attr_flags_to_mnt_flags(u64 attr_flags)
3597 {
3598 	unsigned int mnt_flags = 0;
3599 
3600 	if (attr_flags & MOUNT_ATTR_RDONLY)
3601 		mnt_flags |= MNT_READONLY;
3602 	if (attr_flags & MOUNT_ATTR_NOSUID)
3603 		mnt_flags |= MNT_NOSUID;
3604 	if (attr_flags & MOUNT_ATTR_NODEV)
3605 		mnt_flags |= MNT_NODEV;
3606 	if (attr_flags & MOUNT_ATTR_NOEXEC)
3607 		mnt_flags |= MNT_NOEXEC;
3608 	if (attr_flags & MOUNT_ATTR_NODIRATIME)
3609 		mnt_flags |= MNT_NODIRATIME;
3610 	if (attr_flags & MOUNT_ATTR_NOSYMFOLLOW)
3611 		mnt_flags |= MNT_NOSYMFOLLOW;
3612 
3613 	return mnt_flags;
3614 }
3615 
3616 /*
3617  * Create a kernel mount representation for a new, prepared superblock
3618  * (specified by fs_fd) and attach to an open_tree-like file descriptor.
3619  */
3620 SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags,
3621 		unsigned int, attr_flags)
3622 {
3623 	struct mnt_namespace *ns;
3624 	struct fs_context *fc;
3625 	struct file *file;
3626 	struct path newmount;
3627 	struct mount *mnt;
3628 	struct fd f;
3629 	unsigned int mnt_flags = 0;
3630 	long ret;
3631 
3632 	if (!may_mount())
3633 		return -EPERM;
3634 
3635 	if ((flags & ~(FSMOUNT_CLOEXEC)) != 0)
3636 		return -EINVAL;
3637 
3638 	if (attr_flags & ~FSMOUNT_VALID_FLAGS)
3639 		return -EINVAL;
3640 
3641 	mnt_flags = attr_flags_to_mnt_flags(attr_flags);
3642 
3643 	switch (attr_flags & MOUNT_ATTR__ATIME) {
3644 	case MOUNT_ATTR_STRICTATIME:
3645 		break;
3646 	case MOUNT_ATTR_NOATIME:
3647 		mnt_flags |= MNT_NOATIME;
3648 		break;
3649 	case MOUNT_ATTR_RELATIME:
3650 		mnt_flags |= MNT_RELATIME;
3651 		break;
3652 	default:
3653 		return -EINVAL;
3654 	}
3655 
3656 	f = fdget(fs_fd);
3657 	if (!f.file)
3658 		return -EBADF;
3659 
3660 	ret = -EINVAL;
3661 	if (f.file->f_op != &fscontext_fops)
3662 		goto err_fsfd;
3663 
3664 	fc = f.file->private_data;
3665 
3666 	ret = mutex_lock_interruptible(&fc->uapi_mutex);
3667 	if (ret < 0)
3668 		goto err_fsfd;
3669 
3670 	/* There must be a valid superblock or we can't mount it */
3671 	ret = -EINVAL;
3672 	if (!fc->root)
3673 		goto err_unlock;
3674 
3675 	ret = -EPERM;
3676 	if (mount_too_revealing(fc->root->d_sb, &mnt_flags)) {
3677 		pr_warn("VFS: Mount too revealing\n");
3678 		goto err_unlock;
3679 	}
3680 
3681 	ret = -EBUSY;
3682 	if (fc->phase != FS_CONTEXT_AWAITING_MOUNT)
3683 		goto err_unlock;
3684 
3685 	if (fc->sb_flags & SB_MANDLOCK)
3686 		warn_mandlock();
3687 
3688 	newmount.mnt = vfs_create_mount(fc);
3689 	if (IS_ERR(newmount.mnt)) {
3690 		ret = PTR_ERR(newmount.mnt);
3691 		goto err_unlock;
3692 	}
3693 	newmount.dentry = dget(fc->root);
3694 	newmount.mnt->mnt_flags = mnt_flags;
3695 
3696 	/* We've done the mount bit - now move the file context into more or
3697 	 * less the same state as if we'd done an fspick().  We don't want to
3698 	 * do any memory allocation or anything like that at this point as we
3699 	 * don't want to have to handle any errors incurred.
3700 	 */
3701 	vfs_clean_context(fc);
3702 
3703 	ns = alloc_mnt_ns(current->nsproxy->mnt_ns->user_ns, true);
3704 	if (IS_ERR(ns)) {
3705 		ret = PTR_ERR(ns);
3706 		goto err_path;
3707 	}
3708 	mnt = real_mount(newmount.mnt);
3709 	mnt->mnt_ns = ns;
3710 	ns->root = mnt;
3711 	ns->mounts = 1;
3712 	list_add(&mnt->mnt_list, &ns->list);
3713 	mntget(newmount.mnt);
3714 
3715 	/* Attach to an apparent O_PATH fd with a note that we need to unmount
3716 	 * it, not just simply put it.
3717 	 */
3718 	file = dentry_open(&newmount, O_PATH, fc->cred);
3719 	if (IS_ERR(file)) {
3720 		dissolve_on_fput(newmount.mnt);
3721 		ret = PTR_ERR(file);
3722 		goto err_path;
3723 	}
3724 	file->f_mode |= FMODE_NEED_UNMOUNT;
3725 
3726 	ret = get_unused_fd_flags((flags & FSMOUNT_CLOEXEC) ? O_CLOEXEC : 0);
3727 	if (ret >= 0)
3728 		fd_install(ret, file);
3729 	else
3730 		fput(file);
3731 
3732 err_path:
3733 	path_put(&newmount);
3734 err_unlock:
3735 	mutex_unlock(&fc->uapi_mutex);
3736 err_fsfd:
3737 	fdput(f);
3738 	return ret;
3739 }
3740 
3741 /*
3742  * Move a mount from one place to another.  In combination with
3743  * fsopen()/fsmount() this is used to install a new mount and in combination
3744  * with open_tree(OPEN_TREE_CLONE [| AT_RECURSIVE]) it can be used to copy
3745  * a mount subtree.
3746  *
3747  * Note the flags value is a combination of MOVE_MOUNT_* flags.
3748  */
3749 SYSCALL_DEFINE5(move_mount,
3750 		int, from_dfd, const char __user *, from_pathname,
3751 		int, to_dfd, const char __user *, to_pathname,
3752 		unsigned int, flags)
3753 {
3754 	struct path from_path, to_path;
3755 	unsigned int lflags;
3756 	int ret = 0;
3757 
3758 	if (!may_mount())
3759 		return -EPERM;
3760 
3761 	if (flags & ~MOVE_MOUNT__MASK)
3762 		return -EINVAL;
3763 
3764 	/* If someone gives a pathname, they aren't permitted to move
3765 	 * from an fd that requires unmount as we can't get at the flag
3766 	 * to clear it afterwards.
3767 	 */
3768 	lflags = 0;
3769 	if (flags & MOVE_MOUNT_F_SYMLINKS)	lflags |= LOOKUP_FOLLOW;
3770 	if (flags & MOVE_MOUNT_F_AUTOMOUNTS)	lflags |= LOOKUP_AUTOMOUNT;
3771 	if (flags & MOVE_MOUNT_F_EMPTY_PATH)	lflags |= LOOKUP_EMPTY;
3772 
3773 	ret = user_path_at(from_dfd, from_pathname, lflags, &from_path);
3774 	if (ret < 0)
3775 		return ret;
3776 
3777 	lflags = 0;
3778 	if (flags & MOVE_MOUNT_T_SYMLINKS)	lflags |= LOOKUP_FOLLOW;
3779 	if (flags & MOVE_MOUNT_T_AUTOMOUNTS)	lflags |= LOOKUP_AUTOMOUNT;
3780 	if (flags & MOVE_MOUNT_T_EMPTY_PATH)	lflags |= LOOKUP_EMPTY;
3781 
3782 	ret = user_path_at(to_dfd, to_pathname, lflags, &to_path);
3783 	if (ret < 0)
3784 		goto out_from;
3785 
3786 	ret = security_move_mount(&from_path, &to_path);
3787 	if (ret < 0)
3788 		goto out_to;
3789 
3790 	if (flags & MOVE_MOUNT_SET_GROUP)
3791 		ret = do_set_group(&from_path, &to_path);
3792 	else
3793 		ret = do_move_mount(&from_path, &to_path);
3794 
3795 out_to:
3796 	path_put(&to_path);
3797 out_from:
3798 	path_put(&from_path);
3799 	return ret;
3800 }
3801 
3802 /*
3803  * Return true if path is reachable from root
3804  *
3805  * namespace_sem or mount_lock is held
3806  */
3807 bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
3808 			 const struct path *root)
3809 {
3810 	while (&mnt->mnt != root->mnt && mnt_has_parent(mnt)) {
3811 		dentry = mnt->mnt_mountpoint;
3812 		mnt = mnt->mnt_parent;
3813 	}
3814 	return &mnt->mnt == root->mnt && is_subdir(dentry, root->dentry);
3815 }
3816 
3817 bool path_is_under(const struct path *path1, const struct path *path2)
3818 {
3819 	bool res;
3820 	read_seqlock_excl(&mount_lock);
3821 	res = is_path_reachable(real_mount(path1->mnt), path1->dentry, path2);
3822 	read_sequnlock_excl(&mount_lock);
3823 	return res;
3824 }
3825 EXPORT_SYMBOL(path_is_under);
3826 
3827 /*
3828  * pivot_root Semantics:
3829  * Moves the root file system of the current process to the directory put_old,
3830  * makes new_root as the new root file system of the current process, and sets
3831  * root/cwd of all processes which had them on the current root to new_root.
3832  *
3833  * Restrictions:
3834  * The new_root and put_old must be directories, and  must not be on the
3835  * same file  system as the current process root. The put_old  must  be
3836  * underneath new_root,  i.e. adding a non-zero number of /.. to the string
3837  * pointed to by put_old must yield the same directory as new_root. No other
3838  * file system may be mounted on put_old. After all, new_root is a mountpoint.
3839  *
3840  * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
3841  * See Documentation/filesystems/ramfs-rootfs-initramfs.rst for alternatives
3842  * in this situation.
3843  *
3844  * Notes:
3845  *  - we don't move root/cwd if they are not at the root (reason: if something
3846  *    cared enough to change them, it's probably wrong to force them elsewhere)
3847  *  - it's okay to pick a root that isn't the root of a file system, e.g.
3848  *    /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
3849  *    though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
3850  *    first.
3851  */
3852 SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
3853 		const char __user *, put_old)
3854 {
3855 	struct path new, old, root;
3856 	struct mount *new_mnt, *root_mnt, *old_mnt, *root_parent, *ex_parent;
3857 	struct mountpoint *old_mp, *root_mp;
3858 	int error;
3859 
3860 	if (!may_mount())
3861 		return -EPERM;
3862 
3863 	error = user_path_at(AT_FDCWD, new_root,
3864 			     LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &new);
3865 	if (error)
3866 		goto out0;
3867 
3868 	error = user_path_at(AT_FDCWD, put_old,
3869 			     LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &old);
3870 	if (error)
3871 		goto out1;
3872 
3873 	error = security_sb_pivotroot(&old, &new);
3874 	if (error)
3875 		goto out2;
3876 
3877 	get_fs_root(current->fs, &root);
3878 	old_mp = lock_mount(&old);
3879 	error = PTR_ERR(old_mp);
3880 	if (IS_ERR(old_mp))
3881 		goto out3;
3882 
3883 	error = -EINVAL;
3884 	new_mnt = real_mount(new.mnt);
3885 	root_mnt = real_mount(root.mnt);
3886 	old_mnt = real_mount(old.mnt);
3887 	ex_parent = new_mnt->mnt_parent;
3888 	root_parent = root_mnt->mnt_parent;
3889 	if (IS_MNT_SHARED(old_mnt) ||
3890 		IS_MNT_SHARED(ex_parent) ||
3891 		IS_MNT_SHARED(root_parent))
3892 		goto out4;
3893 	if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
3894 		goto out4;
3895 	if (new_mnt->mnt.mnt_flags & MNT_LOCKED)
3896 		goto out4;
3897 	error = -ENOENT;
3898 	if (d_unlinked(new.dentry))
3899 		goto out4;
3900 	error = -EBUSY;
3901 	if (new_mnt == root_mnt || old_mnt == root_mnt)
3902 		goto out4; /* loop, on the same file system  */
3903 	error = -EINVAL;
3904 	if (root.mnt->mnt_root != root.dentry)
3905 		goto out4; /* not a mountpoint */
3906 	if (!mnt_has_parent(root_mnt))
3907 		goto out4; /* not attached */
3908 	if (new.mnt->mnt_root != new.dentry)
3909 		goto out4; /* not a mountpoint */
3910 	if (!mnt_has_parent(new_mnt))
3911 		goto out4; /* not attached */
3912 	/* make sure we can reach put_old from new_root */
3913 	if (!is_path_reachable(old_mnt, old.dentry, &new))
3914 		goto out4;
3915 	/* make certain new is below the root */
3916 	if (!is_path_reachable(new_mnt, new.dentry, &root))
3917 		goto out4;
3918 	lock_mount_hash();
3919 	umount_mnt(new_mnt);
3920 	root_mp = unhash_mnt(root_mnt);  /* we'll need its mountpoint */
3921 	if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {
3922 		new_mnt->mnt.mnt_flags |= MNT_LOCKED;
3923 		root_mnt->mnt.mnt_flags &= ~MNT_LOCKED;
3924 	}
3925 	/* mount old root on put_old */
3926 	attach_mnt(root_mnt, old_mnt, old_mp);
3927 	/* mount new_root on / */
3928 	attach_mnt(new_mnt, root_parent, root_mp);
3929 	mnt_add_count(root_parent, -1);
3930 	touch_mnt_namespace(current->nsproxy->mnt_ns);
3931 	/* A moved mount should not expire automatically */
3932 	list_del_init(&new_mnt->mnt_expire);
3933 	put_mountpoint(root_mp);
3934 	unlock_mount_hash();
3935 	chroot_fs_refs(&root, &new);
3936 	error = 0;
3937 out4:
3938 	unlock_mount(old_mp);
3939 	if (!error)
3940 		mntput_no_expire(ex_parent);
3941 out3:
3942 	path_put(&root);
3943 out2:
3944 	path_put(&old);
3945 out1:
3946 	path_put(&new);
3947 out0:
3948 	return error;
3949 }
3950 
3951 static unsigned int recalc_flags(struct mount_kattr *kattr, struct mount *mnt)
3952 {
3953 	unsigned int flags = mnt->mnt.mnt_flags;
3954 
3955 	/*  flags to clear */
3956 	flags &= ~kattr->attr_clr;
3957 	/* flags to raise */
3958 	flags |= kattr->attr_set;
3959 
3960 	return flags;
3961 }
3962 
3963 static int can_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt)
3964 {
3965 	struct vfsmount *m = &mnt->mnt;
3966 	struct user_namespace *fs_userns = m->mnt_sb->s_user_ns;
3967 
3968 	if (!kattr->mnt_userns)
3969 		return 0;
3970 
3971 	/*
3972 	 * Creating an idmapped mount with the filesystem wide idmapping
3973 	 * doesn't make sense so block that. We don't allow mushy semantics.
3974 	 */
3975 	if (kattr->mnt_userns == fs_userns)
3976 		return -EINVAL;
3977 
3978 	/*
3979 	 * Once a mount has been idmapped we don't allow it to change its
3980 	 * mapping. It makes things simpler and callers can just create
3981 	 * another bind-mount they can idmap if they want to.
3982 	 */
3983 	if (is_idmapped_mnt(m))
3984 		return -EPERM;
3985 
3986 	/* The underlying filesystem doesn't support idmapped mounts yet. */
3987 	if (!(m->mnt_sb->s_type->fs_flags & FS_ALLOW_IDMAP))
3988 		return -EINVAL;
3989 
3990 	/* We're not controlling the superblock. */
3991 	if (!ns_capable(fs_userns, CAP_SYS_ADMIN))
3992 		return -EPERM;
3993 
3994 	/* Mount has already been visible in the filesystem hierarchy. */
3995 	if (!is_anon_ns(mnt->mnt_ns))
3996 		return -EINVAL;
3997 
3998 	return 0;
3999 }
4000 
4001 static struct mount *mount_setattr_prepare(struct mount_kattr *kattr,
4002 					   struct mount *mnt, int *err)
4003 {
4004 	struct mount *m = mnt, *last = NULL;
4005 
4006 	if (!is_mounted(&m->mnt)) {
4007 		*err = -EINVAL;
4008 		goto out;
4009 	}
4010 
4011 	if (!(mnt_has_parent(m) ? check_mnt(m) : is_anon_ns(m->mnt_ns))) {
4012 		*err = -EINVAL;
4013 		goto out;
4014 	}
4015 
4016 	do {
4017 		unsigned int flags;
4018 
4019 		flags = recalc_flags(kattr, m);
4020 		if (!can_change_locked_flags(m, flags)) {
4021 			*err = -EPERM;
4022 			goto out;
4023 		}
4024 
4025 		*err = can_idmap_mount(kattr, m);
4026 		if (*err)
4027 			goto out;
4028 
4029 		last = m;
4030 
4031 		if ((kattr->attr_set & MNT_READONLY) &&
4032 		    !(m->mnt.mnt_flags & MNT_READONLY)) {
4033 			*err = mnt_hold_writers(m);
4034 			if (*err)
4035 				goto out;
4036 		}
4037 	} while (kattr->recurse && (m = next_mnt(m, mnt)));
4038 
4039 out:
4040 	return last;
4041 }
4042 
4043 static void do_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt)
4044 {
4045 	struct user_namespace *mnt_userns, *old_mnt_userns;
4046 
4047 	if (!kattr->mnt_userns)
4048 		return;
4049 
4050 	/*
4051 	 * We're the only ones able to change the mount's idmapping. So
4052 	 * mnt->mnt.mnt_userns is stable and we can retrieve it directly.
4053 	 */
4054 	old_mnt_userns = mnt->mnt.mnt_userns;
4055 
4056 	mnt_userns = get_user_ns(kattr->mnt_userns);
4057 	/* Pairs with smp_load_acquire() in mnt_user_ns(). */
4058 	smp_store_release(&mnt->mnt.mnt_userns, mnt_userns);
4059 
4060 	/*
4061 	 * If this is an idmapped filesystem drop the reference we've taken
4062 	 * in vfs_create_mount() before.
4063 	 */
4064 	if (!initial_idmapping(old_mnt_userns))
4065 		put_user_ns(old_mnt_userns);
4066 }
4067 
4068 static void mount_setattr_commit(struct mount_kattr *kattr,
4069 				 struct mount *mnt, struct mount *last,
4070 				 int err)
4071 {
4072 	struct mount *m = mnt;
4073 
4074 	do {
4075 		if (!err) {
4076 			unsigned int flags;
4077 
4078 			do_idmap_mount(kattr, m);
4079 			flags = recalc_flags(kattr, m);
4080 			WRITE_ONCE(m->mnt.mnt_flags, flags);
4081 		}
4082 
4083 		/*
4084 		 * We either set MNT_READONLY above so make it visible
4085 		 * before ~MNT_WRITE_HOLD or we failed to recursively
4086 		 * apply mount options.
4087 		 */
4088 		if ((kattr->attr_set & MNT_READONLY) &&
4089 		    (m->mnt.mnt_flags & MNT_WRITE_HOLD))
4090 			mnt_unhold_writers(m);
4091 
4092 		if (!err && kattr->propagation)
4093 			change_mnt_propagation(m, kattr->propagation);
4094 
4095 		/*
4096 		 * On failure, only cleanup until we found the first mount
4097 		 * we failed to handle.
4098 		 */
4099 		if (err && m == last)
4100 			break;
4101 	} while (kattr->recurse && (m = next_mnt(m, mnt)));
4102 
4103 	if (!err)
4104 		touch_mnt_namespace(mnt->mnt_ns);
4105 }
4106 
4107 static int do_mount_setattr(struct path *path, struct mount_kattr *kattr)
4108 {
4109 	struct mount *mnt = real_mount(path->mnt), *last = NULL;
4110 	int err = 0;
4111 
4112 	if (path->dentry != mnt->mnt.mnt_root)
4113 		return -EINVAL;
4114 
4115 	if (kattr->propagation) {
4116 		/*
4117 		 * Only take namespace_lock() if we're actually changing
4118 		 * propagation.
4119 		 */
4120 		namespace_lock();
4121 		if (kattr->propagation == MS_SHARED) {
4122 			err = invent_group_ids(mnt, kattr->recurse);
4123 			if (err) {
4124 				namespace_unlock();
4125 				return err;
4126 			}
4127 		}
4128 	}
4129 
4130 	lock_mount_hash();
4131 
4132 	/*
4133 	 * Get the mount tree in a shape where we can change mount
4134 	 * properties without failure.
4135 	 */
4136 	last = mount_setattr_prepare(kattr, mnt, &err);
4137 	if (last) /* Commit all changes or revert to the old state. */
4138 		mount_setattr_commit(kattr, mnt, last, err);
4139 
4140 	unlock_mount_hash();
4141 
4142 	if (kattr->propagation) {
4143 		namespace_unlock();
4144 		if (err)
4145 			cleanup_group_ids(mnt, NULL);
4146 	}
4147 
4148 	return err;
4149 }
4150 
4151 static int build_mount_idmapped(const struct mount_attr *attr, size_t usize,
4152 				struct mount_kattr *kattr, unsigned int flags)
4153 {
4154 	int err = 0;
4155 	struct ns_common *ns;
4156 	struct user_namespace *mnt_userns;
4157 	struct file *file;
4158 
4159 	if (!((attr->attr_set | attr->attr_clr) & MOUNT_ATTR_IDMAP))
4160 		return 0;
4161 
4162 	/*
4163 	 * We currently do not support clearing an idmapped mount. If this ever
4164 	 * is a use-case we can revisit this but for now let's keep it simple
4165 	 * and not allow it.
4166 	 */
4167 	if (attr->attr_clr & MOUNT_ATTR_IDMAP)
4168 		return -EINVAL;
4169 
4170 	if (attr->userns_fd > INT_MAX)
4171 		return -EINVAL;
4172 
4173 	file = fget(attr->userns_fd);
4174 	if (!file)
4175 		return -EBADF;
4176 
4177 	if (!proc_ns_file(file)) {
4178 		err = -EINVAL;
4179 		goto out_fput;
4180 	}
4181 
4182 	ns = get_proc_ns(file_inode(file));
4183 	if (ns->ops->type != CLONE_NEWUSER) {
4184 		err = -EINVAL;
4185 		goto out_fput;
4186 	}
4187 
4188 	/*
4189 	 * The initial idmapping cannot be used to create an idmapped
4190 	 * mount. We use the initial idmapping as an indicator of a mount
4191 	 * that is not idmapped. It can simply be passed into helpers that
4192 	 * are aware of idmapped mounts as a convenient shortcut. A user
4193 	 * can just create a dedicated identity mapping to achieve the same
4194 	 * result.
4195 	 */
4196 	mnt_userns = container_of(ns, struct user_namespace, ns);
4197 	if (initial_idmapping(mnt_userns)) {
4198 		err = -EPERM;
4199 		goto out_fput;
4200 	}
4201 	kattr->mnt_userns = get_user_ns(mnt_userns);
4202 
4203 out_fput:
4204 	fput(file);
4205 	return err;
4206 }
4207 
4208 static int build_mount_kattr(const struct mount_attr *attr, size_t usize,
4209 			     struct mount_kattr *kattr, unsigned int flags)
4210 {
4211 	unsigned int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW;
4212 
4213 	if (flags & AT_NO_AUTOMOUNT)
4214 		lookup_flags &= ~LOOKUP_AUTOMOUNT;
4215 	if (flags & AT_SYMLINK_NOFOLLOW)
4216 		lookup_flags &= ~LOOKUP_FOLLOW;
4217 	if (flags & AT_EMPTY_PATH)
4218 		lookup_flags |= LOOKUP_EMPTY;
4219 
4220 	*kattr = (struct mount_kattr) {
4221 		.lookup_flags	= lookup_flags,
4222 		.recurse	= !!(flags & AT_RECURSIVE),
4223 	};
4224 
4225 	if (attr->propagation & ~MOUNT_SETATTR_PROPAGATION_FLAGS)
4226 		return -EINVAL;
4227 	if (hweight32(attr->propagation & MOUNT_SETATTR_PROPAGATION_FLAGS) > 1)
4228 		return -EINVAL;
4229 	kattr->propagation = attr->propagation;
4230 
4231 	if ((attr->attr_set | attr->attr_clr) & ~MOUNT_SETATTR_VALID_FLAGS)
4232 		return -EINVAL;
4233 
4234 	kattr->attr_set = attr_flags_to_mnt_flags(attr->attr_set);
4235 	kattr->attr_clr = attr_flags_to_mnt_flags(attr->attr_clr);
4236 
4237 	/*
4238 	 * Since the MOUNT_ATTR_<atime> values are an enum, not a bitmap,
4239 	 * users wanting to transition to a different atime setting cannot
4240 	 * simply specify the atime setting in @attr_set, but must also
4241 	 * specify MOUNT_ATTR__ATIME in the @attr_clr field.
4242 	 * So ensure that MOUNT_ATTR__ATIME can't be partially set in
4243 	 * @attr_clr and that @attr_set can't have any atime bits set if
4244 	 * MOUNT_ATTR__ATIME isn't set in @attr_clr.
4245 	 */
4246 	if (attr->attr_clr & MOUNT_ATTR__ATIME) {
4247 		if ((attr->attr_clr & MOUNT_ATTR__ATIME) != MOUNT_ATTR__ATIME)
4248 			return -EINVAL;
4249 
4250 		/*
4251 		 * Clear all previous time settings as they are mutually
4252 		 * exclusive.
4253 		 */
4254 		kattr->attr_clr |= MNT_RELATIME | MNT_NOATIME;
4255 		switch (attr->attr_set & MOUNT_ATTR__ATIME) {
4256 		case MOUNT_ATTR_RELATIME:
4257 			kattr->attr_set |= MNT_RELATIME;
4258 			break;
4259 		case MOUNT_ATTR_NOATIME:
4260 			kattr->attr_set |= MNT_NOATIME;
4261 			break;
4262 		case MOUNT_ATTR_STRICTATIME:
4263 			break;
4264 		default:
4265 			return -EINVAL;
4266 		}
4267 	} else {
4268 		if (attr->attr_set & MOUNT_ATTR__ATIME)
4269 			return -EINVAL;
4270 	}
4271 
4272 	return build_mount_idmapped(attr, usize, kattr, flags);
4273 }
4274 
4275 static void finish_mount_kattr(struct mount_kattr *kattr)
4276 {
4277 	put_user_ns(kattr->mnt_userns);
4278 	kattr->mnt_userns = NULL;
4279 }
4280 
4281 SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path,
4282 		unsigned int, flags, struct mount_attr __user *, uattr,
4283 		size_t, usize)
4284 {
4285 	int err;
4286 	struct path target;
4287 	struct mount_attr attr;
4288 	struct mount_kattr kattr;
4289 
4290 	BUILD_BUG_ON(sizeof(struct mount_attr) != MOUNT_ATTR_SIZE_VER0);
4291 
4292 	if (flags & ~(AT_EMPTY_PATH |
4293 		      AT_RECURSIVE |
4294 		      AT_SYMLINK_NOFOLLOW |
4295 		      AT_NO_AUTOMOUNT))
4296 		return -EINVAL;
4297 
4298 	if (unlikely(usize > PAGE_SIZE))
4299 		return -E2BIG;
4300 	if (unlikely(usize < MOUNT_ATTR_SIZE_VER0))
4301 		return -EINVAL;
4302 
4303 	if (!may_mount())
4304 		return -EPERM;
4305 
4306 	err = copy_struct_from_user(&attr, sizeof(attr), uattr, usize);
4307 	if (err)
4308 		return err;
4309 
4310 	/* Don't bother walking through the mounts if this is a nop. */
4311 	if (attr.attr_set == 0 &&
4312 	    attr.attr_clr == 0 &&
4313 	    attr.propagation == 0)
4314 		return 0;
4315 
4316 	err = build_mount_kattr(&attr, usize, &kattr, flags);
4317 	if (err)
4318 		return err;
4319 
4320 	err = user_path_at(dfd, path, kattr.lookup_flags, &target);
4321 	if (!err) {
4322 		err = do_mount_setattr(&target, &kattr);
4323 		path_put(&target);
4324 	}
4325 	finish_mount_kattr(&kattr);
4326 	return err;
4327 }
4328 
4329 static void __init init_mount_tree(void)
4330 {
4331 	struct vfsmount *mnt;
4332 	struct mount *m;
4333 	struct mnt_namespace *ns;
4334 	struct path root;
4335 
4336 	mnt = vfs_kern_mount(&rootfs_fs_type, 0, "rootfs", NULL);
4337 	if (IS_ERR(mnt))
4338 		panic("Can't create rootfs");
4339 
4340 	ns = alloc_mnt_ns(&init_user_ns, false);
4341 	if (IS_ERR(ns))
4342 		panic("Can't allocate initial namespace");
4343 	m = real_mount(mnt);
4344 	m->mnt_ns = ns;
4345 	ns->root = m;
4346 	ns->mounts = 1;
4347 	list_add(&m->mnt_list, &ns->list);
4348 	init_task.nsproxy->mnt_ns = ns;
4349 	get_mnt_ns(ns);
4350 
4351 	root.mnt = mnt;
4352 	root.dentry = mnt->mnt_root;
4353 	mnt->mnt_flags |= MNT_LOCKED;
4354 
4355 	set_fs_pwd(current->fs, &root);
4356 	set_fs_root(current->fs, &root);
4357 }
4358 
4359 void __init mnt_init(void)
4360 {
4361 	int err;
4362 
4363 	mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct mount),
4364 			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
4365 
4366 	mount_hashtable = alloc_large_system_hash("Mount-cache",
4367 				sizeof(struct hlist_head),
4368 				mhash_entries, 19,
4369 				HASH_ZERO,
4370 				&m_hash_shift, &m_hash_mask, 0, 0);
4371 	mountpoint_hashtable = alloc_large_system_hash("Mountpoint-cache",
4372 				sizeof(struct hlist_head),
4373 				mphash_entries, 19,
4374 				HASH_ZERO,
4375 				&mp_hash_shift, &mp_hash_mask, 0, 0);
4376 
4377 	if (!mount_hashtable || !mountpoint_hashtable)
4378 		panic("Failed to allocate mount hash table\n");
4379 
4380 	kernfs_init();
4381 
4382 	err = sysfs_init();
4383 	if (err)
4384 		printk(KERN_WARNING "%s: sysfs_init error: %d\n",
4385 			__func__, err);
4386 	fs_kobj = kobject_create_and_add("fs", NULL);
4387 	if (!fs_kobj)
4388 		printk(KERN_WARNING "%s: kobj create error\n", __func__);
4389 	shmem_init();
4390 	init_rootfs();
4391 	init_mount_tree();
4392 }
4393 
4394 void put_mnt_ns(struct mnt_namespace *ns)
4395 {
4396 	if (!refcount_dec_and_test(&ns->ns.count))
4397 		return;
4398 	drop_collected_mounts(&ns->root->mnt);
4399 	free_mnt_ns(ns);
4400 }
4401 
4402 struct vfsmount *kern_mount(struct file_system_type *type)
4403 {
4404 	struct vfsmount *mnt;
4405 	mnt = vfs_kern_mount(type, SB_KERNMOUNT, type->name, NULL);
4406 	if (!IS_ERR(mnt)) {
4407 		/*
4408 		 * it is a longterm mount, don't release mnt until
4409 		 * we unmount before file sys is unregistered
4410 		*/
4411 		real_mount(mnt)->mnt_ns = MNT_NS_INTERNAL;
4412 	}
4413 	return mnt;
4414 }
4415 EXPORT_SYMBOL_GPL(kern_mount);
4416 
4417 void kern_unmount(struct vfsmount *mnt)
4418 {
4419 	/* release long term mount so mount point can be released */
4420 	if (!IS_ERR_OR_NULL(mnt)) {
4421 		real_mount(mnt)->mnt_ns = NULL;
4422 		synchronize_rcu();	/* yecchhh... */
4423 		mntput(mnt);
4424 	}
4425 }
4426 EXPORT_SYMBOL(kern_unmount);
4427 
4428 void kern_unmount_array(struct vfsmount *mnt[], unsigned int num)
4429 {
4430 	unsigned int i;
4431 
4432 	for (i = 0; i < num; i++)
4433 		if (mnt[i])
4434 			real_mount(mnt[i])->mnt_ns = NULL;
4435 	synchronize_rcu_expedited();
4436 	for (i = 0; i < num; i++)
4437 		mntput(mnt[i]);
4438 }
4439 EXPORT_SYMBOL(kern_unmount_array);
4440 
4441 bool our_mnt(struct vfsmount *mnt)
4442 {
4443 	return check_mnt(real_mount(mnt));
4444 }
4445 
4446 bool current_chrooted(void)
4447 {
4448 	/* Does the current process have a non-standard root */
4449 	struct path ns_root;
4450 	struct path fs_root;
4451 	bool chrooted;
4452 
4453 	/* Find the namespace root */
4454 	ns_root.mnt = &current->nsproxy->mnt_ns->root->mnt;
4455 	ns_root.dentry = ns_root.mnt->mnt_root;
4456 	path_get(&ns_root);
4457 	while (d_mountpoint(ns_root.dentry) && follow_down_one(&ns_root))
4458 		;
4459 
4460 	get_fs_root(current->fs, &fs_root);
4461 
4462 	chrooted = !path_equal(&fs_root, &ns_root);
4463 
4464 	path_put(&fs_root);
4465 	path_put(&ns_root);
4466 
4467 	return chrooted;
4468 }
4469 
4470 static bool mnt_already_visible(struct mnt_namespace *ns,
4471 				const struct super_block *sb,
4472 				int *new_mnt_flags)
4473 {
4474 	int new_flags = *new_mnt_flags;
4475 	struct mount *mnt;
4476 	bool visible = false;
4477 
4478 	down_read(&namespace_sem);
4479 	lock_ns_list(ns);
4480 	list_for_each_entry(mnt, &ns->list, mnt_list) {
4481 		struct mount *child;
4482 		int mnt_flags;
4483 
4484 		if (mnt_is_cursor(mnt))
4485 			continue;
4486 
4487 		if (mnt->mnt.mnt_sb->s_type != sb->s_type)
4488 			continue;
4489 
4490 		/* This mount is not fully visible if it's root directory
4491 		 * is not the root directory of the filesystem.
4492 		 */
4493 		if (mnt->mnt.mnt_root != mnt->mnt.mnt_sb->s_root)
4494 			continue;
4495 
4496 		/* A local view of the mount flags */
4497 		mnt_flags = mnt->mnt.mnt_flags;
4498 
4499 		/* Don't miss readonly hidden in the superblock flags */
4500 		if (sb_rdonly(mnt->mnt.mnt_sb))
4501 			mnt_flags |= MNT_LOCK_READONLY;
4502 
4503 		/* Verify the mount flags are equal to or more permissive
4504 		 * than the proposed new mount.
4505 		 */
4506 		if ((mnt_flags & MNT_LOCK_READONLY) &&
4507 		    !(new_flags & MNT_READONLY))
4508 			continue;
4509 		if ((mnt_flags & MNT_LOCK_ATIME) &&
4510 		    ((mnt_flags & MNT_ATIME_MASK) != (new_flags & MNT_ATIME_MASK)))
4511 			continue;
4512 
4513 		/* This mount is not fully visible if there are any
4514 		 * locked child mounts that cover anything except for
4515 		 * empty directories.
4516 		 */
4517 		list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
4518 			struct inode *inode = child->mnt_mountpoint->d_inode;
4519 			/* Only worry about locked mounts */
4520 			if (!(child->mnt.mnt_flags & MNT_LOCKED))
4521 				continue;
4522 			/* Is the directory permanetly empty? */
4523 			if (!is_empty_dir_inode(inode))
4524 				goto next;
4525 		}
4526 		/* Preserve the locked attributes */
4527 		*new_mnt_flags |= mnt_flags & (MNT_LOCK_READONLY | \
4528 					       MNT_LOCK_ATIME);
4529 		visible = true;
4530 		goto found;
4531 	next:	;
4532 	}
4533 found:
4534 	unlock_ns_list(ns);
4535 	up_read(&namespace_sem);
4536 	return visible;
4537 }
4538 
4539 static bool mount_too_revealing(const struct super_block *sb, int *new_mnt_flags)
4540 {
4541 	const unsigned long required_iflags = SB_I_NOEXEC | SB_I_NODEV;
4542 	struct mnt_namespace *ns = current->nsproxy->mnt_ns;
4543 	unsigned long s_iflags;
4544 
4545 	if (ns->user_ns == &init_user_ns)
4546 		return false;
4547 
4548 	/* Can this filesystem be too revealing? */
4549 	s_iflags = sb->s_iflags;
4550 	if (!(s_iflags & SB_I_USERNS_VISIBLE))
4551 		return false;
4552 
4553 	if ((s_iflags & required_iflags) != required_iflags) {
4554 		WARN_ONCE(1, "Expected s_iflags to contain 0x%lx\n",
4555 			  required_iflags);
4556 		return true;
4557 	}
4558 
4559 	return !mnt_already_visible(ns, sb, new_mnt_flags);
4560 }
4561 
4562 bool mnt_may_suid(struct vfsmount *mnt)
4563 {
4564 	/*
4565 	 * Foreign mounts (accessed via fchdir or through /proc
4566 	 * symlinks) are always treated as if they are nosuid.  This
4567 	 * prevents namespaces from trusting potentially unsafe
4568 	 * suid/sgid bits, file caps, or security labels that originate
4569 	 * in other namespaces.
4570 	 */
4571 	return !(mnt->mnt_flags & MNT_NOSUID) && check_mnt(real_mount(mnt)) &&
4572 	       current_in_userns(mnt->mnt_sb->s_user_ns);
4573 }
4574 
4575 static struct ns_common *mntns_get(struct task_struct *task)
4576 {
4577 	struct ns_common *ns = NULL;
4578 	struct nsproxy *nsproxy;
4579 
4580 	task_lock(task);
4581 	nsproxy = task->nsproxy;
4582 	if (nsproxy) {
4583 		ns = &nsproxy->mnt_ns->ns;
4584 		get_mnt_ns(to_mnt_ns(ns));
4585 	}
4586 	task_unlock(task);
4587 
4588 	return ns;
4589 }
4590 
4591 static void mntns_put(struct ns_common *ns)
4592 {
4593 	put_mnt_ns(to_mnt_ns(ns));
4594 }
4595 
4596 static int mntns_install(struct nsset *nsset, struct ns_common *ns)
4597 {
4598 	struct nsproxy *nsproxy = nsset->nsproxy;
4599 	struct fs_struct *fs = nsset->fs;
4600 	struct mnt_namespace *mnt_ns = to_mnt_ns(ns), *old_mnt_ns;
4601 	struct user_namespace *user_ns = nsset->cred->user_ns;
4602 	struct path root;
4603 	int err;
4604 
4605 	if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
4606 	    !ns_capable(user_ns, CAP_SYS_CHROOT) ||
4607 	    !ns_capable(user_ns, CAP_SYS_ADMIN))
4608 		return -EPERM;
4609 
4610 	if (is_anon_ns(mnt_ns))
4611 		return -EINVAL;
4612 
4613 	if (fs->users != 1)
4614 		return -EINVAL;
4615 
4616 	get_mnt_ns(mnt_ns);
4617 	old_mnt_ns = nsproxy->mnt_ns;
4618 	nsproxy->mnt_ns = mnt_ns;
4619 
4620 	/* Find the root */
4621 	err = vfs_path_lookup(mnt_ns->root->mnt.mnt_root, &mnt_ns->root->mnt,
4622 				"/", LOOKUP_DOWN, &root);
4623 	if (err) {
4624 		/* revert to old namespace */
4625 		nsproxy->mnt_ns = old_mnt_ns;
4626 		put_mnt_ns(mnt_ns);
4627 		return err;
4628 	}
4629 
4630 	put_mnt_ns(old_mnt_ns);
4631 
4632 	/* Update the pwd and root */
4633 	set_fs_pwd(fs, &root);
4634 	set_fs_root(fs, &root);
4635 
4636 	path_put(&root);
4637 	return 0;
4638 }
4639 
4640 static struct user_namespace *mntns_owner(struct ns_common *ns)
4641 {
4642 	return to_mnt_ns(ns)->user_ns;
4643 }
4644 
4645 const struct proc_ns_operations mntns_operations = {
4646 	.name		= "mnt",
4647 	.type		= CLONE_NEWNS,
4648 	.get		= mntns_get,
4649 	.put		= mntns_put,
4650 	.install	= mntns_install,
4651 	.owner		= mntns_owner,
4652 };
4653 
4654 #ifdef CONFIG_SYSCTL
4655 static struct ctl_table fs_namespace_sysctls[] = {
4656 	{
4657 		.procname	= "mount-max",
4658 		.data		= &sysctl_mount_max,
4659 		.maxlen		= sizeof(unsigned int),
4660 		.mode		= 0644,
4661 		.proc_handler	= proc_dointvec_minmax,
4662 		.extra1		= SYSCTL_ONE,
4663 	},
4664 	{ }
4665 };
4666 
4667 static int __init init_fs_namespace_sysctls(void)
4668 {
4669 	register_sysctl_init("fs", fs_namespace_sysctls);
4670 	return 0;
4671 }
4672 fs_initcall(init_fs_namespace_sysctls);
4673 
4674 #endif /* CONFIG_SYSCTL */
4675