xref: /linux/ipc/util.c (revision 3932b9ca55b0be314a36d3e84faff3e823c081f5)
1 /*
2  * linux/ipc/util.c
3  * Copyright (C) 1992 Krishna Balasubramanian
4  *
5  * Sep 1997 - Call suser() last after "normal" permission checks so we
6  *            get BSD style process accounting right.
7  *            Occurs in several places in the IPC code.
8  *            Chris Evans, <chris@ferret.lmh.ox.ac.uk>
9  * Nov 1999 - ipc helper functions, unified SMP locking
10  *	      Manfred Spraul <manfred@colorfullife.com>
11  * Oct 2002 - One lock per IPC id. RCU ipc_free for lock-free grow_ary().
12  *            Mingming Cao <cmm@us.ibm.com>
13  * Mar 2006 - support for audit of ipc object properties
14  *            Dustin Kirkland <dustin.kirkland@us.ibm.com>
15  * Jun 2006 - namespaces ssupport
16  *            OpenVZ, SWsoft Inc.
17  *            Pavel Emelianov <xemul@openvz.org>
18  *
19  * General sysv ipc locking scheme:
20  *	rcu_read_lock()
21  *          obtain the ipc object (kern_ipc_perm) by looking up the id in an idr
22  *	    tree.
23  *	    - perform initial checks (capabilities, auditing and permission,
24  *	      etc).
25  *	    - perform read-only operations, such as STAT, INFO commands.
26  *	      acquire the ipc lock (kern_ipc_perm.lock) through
27  *	      ipc_lock_object()
28  *		- perform data updates, such as SET, RMID commands and
29  *		  mechanism-specific operations (semop/semtimedop,
30  *		  msgsnd/msgrcv, shmat/shmdt).
31  *	    drop the ipc lock, through ipc_unlock_object().
32  *	rcu_read_unlock()
33  *
34  *  The ids->rwsem must be taken when:
35  *	- creating, removing and iterating the existing entries in ipc
36  *	  identifier sets.
37  *	- iterating through files under /proc/sysvipc/
38  *
39  *  Note that sems have a special fast path that avoids kern_ipc_perm.lock -
40  *  see sem_lock().
41  */
42 
43 #include <linux/mm.h>
44 #include <linux/shm.h>
45 #include <linux/init.h>
46 #include <linux/msg.h>
47 #include <linux/vmalloc.h>
48 #include <linux/slab.h>
49 #include <linux/notifier.h>
50 #include <linux/capability.h>
51 #include <linux/highuid.h>
52 #include <linux/security.h>
53 #include <linux/rcupdate.h>
54 #include <linux/workqueue.h>
55 #include <linux/seq_file.h>
56 #include <linux/proc_fs.h>
57 #include <linux/audit.h>
58 #include <linux/nsproxy.h>
59 #include <linux/rwsem.h>
60 #include <linux/memory.h>
61 #include <linux/ipc_namespace.h>
62 
63 #include <asm/unistd.h>
64 
65 #include "util.h"
66 
67 struct ipc_proc_iface {
68 	const char *path;
69 	const char *header;
70 	int ids;
71 	int (*show)(struct seq_file *, void *);
72 };
73 
74 static void ipc_memory_notifier(struct work_struct *work)
75 {
76 	ipcns_notify(IPCNS_MEMCHANGED);
77 }
78 
79 static int ipc_memory_callback(struct notifier_block *self,
80 				unsigned long action, void *arg)
81 {
82 	static DECLARE_WORK(ipc_memory_wq, ipc_memory_notifier);
83 
84 	switch (action) {
85 	case MEM_ONLINE:    /* memory successfully brought online */
86 	case MEM_OFFLINE:   /* or offline: it's time to recompute msgmni */
87 		/*
88 		 * This is done by invoking the ipcns notifier chain with the
89 		 * IPC_MEMCHANGED event.
90 		 * In order not to keep the lock on the hotplug memory chain
91 		 * for too long, queue a work item that will, when waken up,
92 		 * activate the ipcns notification chain.
93 		 */
94 		schedule_work(&ipc_memory_wq);
95 		break;
96 	case MEM_GOING_ONLINE:
97 	case MEM_GOING_OFFLINE:
98 	case MEM_CANCEL_ONLINE:
99 	case MEM_CANCEL_OFFLINE:
100 	default:
101 		break;
102 	}
103 
104 	return NOTIFY_OK;
105 }
106 
107 static struct notifier_block ipc_memory_nb = {
108 	.notifier_call = ipc_memory_callback,
109 	.priority = IPC_CALLBACK_PRI,
110 };
111 
112 /**
113  * ipc_init - initialise ipc subsystem
114  *
115  * The various sysv ipc resources (semaphores, messages and shared
116  * memory) are initialised.
117  *
118  * A callback routine is registered into the memory hotplug notifier
119  * chain: since msgmni scales to lowmem this callback routine will be
120  * called upon successful memory add / remove to recompute msmgni.
121  */
122 static int __init ipc_init(void)
123 {
124 	sem_init();
125 	msg_init();
126 	shm_init();
127 	register_hotmemory_notifier(&ipc_memory_nb);
128 	register_ipcns_notifier(&init_ipc_ns);
129 	return 0;
130 }
131 device_initcall(ipc_init);
132 
133 /**
134  * ipc_init_ids	- initialise ipc identifiers
135  * @ids: ipc identifier set
136  *
137  * Set up the sequence range to use for the ipc identifier range (limited
138  * below IPCMNI) then initialise the ids idr.
139  */
140 void ipc_init_ids(struct ipc_ids *ids)
141 {
142 	ids->in_use = 0;
143 	ids->seq = 0;
144 	ids->next_id = -1;
145 	init_rwsem(&ids->rwsem);
146 	idr_init(&ids->ipcs_idr);
147 }
148 
149 #ifdef CONFIG_PROC_FS
150 static const struct file_operations sysvipc_proc_fops;
151 /**
152  * ipc_init_proc_interface -  create a proc interface for sysipc types using a seq_file interface.
153  * @path: Path in procfs
154  * @header: Banner to be printed at the beginning of the file.
155  * @ids: ipc id table to iterate.
156  * @show: show routine.
157  */
158 void __init ipc_init_proc_interface(const char *path, const char *header,
159 		int ids, int (*show)(struct seq_file *, void *))
160 {
161 	struct proc_dir_entry *pde;
162 	struct ipc_proc_iface *iface;
163 
164 	iface = kmalloc(sizeof(*iface), GFP_KERNEL);
165 	if (!iface)
166 		return;
167 	iface->path	= path;
168 	iface->header	= header;
169 	iface->ids	= ids;
170 	iface->show	= show;
171 
172 	pde = proc_create_data(path,
173 			       S_IRUGO,        /* world readable */
174 			       NULL,           /* parent dir */
175 			       &sysvipc_proc_fops,
176 			       iface);
177 	if (!pde)
178 		kfree(iface);
179 }
180 #endif
181 
182 /**
183  * ipc_findkey	- find a key in an ipc identifier set
184  * @ids: ipc identifier set
185  * @key: key to find
186  *
187  * Returns the locked pointer to the ipc structure if found or NULL
188  * otherwise. If key is found ipc points to the owning ipc structure
189  *
190  * Called with ipc_ids.rwsem held.
191  */
192 static struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key)
193 {
194 	struct kern_ipc_perm *ipc;
195 	int next_id;
196 	int total;
197 
198 	for (total = 0, next_id = 0; total < ids->in_use; next_id++) {
199 		ipc = idr_find(&ids->ipcs_idr, next_id);
200 
201 		if (ipc == NULL)
202 			continue;
203 
204 		if (ipc->key != key) {
205 			total++;
206 			continue;
207 		}
208 
209 		rcu_read_lock();
210 		ipc_lock_object(ipc);
211 		return ipc;
212 	}
213 
214 	return NULL;
215 }
216 
217 /**
218  * ipc_get_maxid - get the last assigned id
219  * @ids: ipc identifier set
220  *
221  * Called with ipc_ids.rwsem held.
222  */
223 int ipc_get_maxid(struct ipc_ids *ids)
224 {
225 	struct kern_ipc_perm *ipc;
226 	int max_id = -1;
227 	int total, id;
228 
229 	if (ids->in_use == 0)
230 		return -1;
231 
232 	if (ids->in_use == IPCMNI)
233 		return IPCMNI - 1;
234 
235 	/* Look for the last assigned id */
236 	total = 0;
237 	for (id = 0; id < IPCMNI && total < ids->in_use; id++) {
238 		ipc = idr_find(&ids->ipcs_idr, id);
239 		if (ipc != NULL) {
240 			max_id = id;
241 			total++;
242 		}
243 	}
244 	return max_id;
245 }
246 
247 /**
248  * ipc_addid - add an ipc identifier
249  * @ids: ipc identifier set
250  * @new: new ipc permission set
251  * @size: limit for the number of used ids
252  *
253  * Add an entry 'new' to the ipc ids idr. The permissions object is
254  * initialised and the first free entry is set up and the id assigned
255  * is returned. The 'new' entry is returned in a locked state on success.
256  * On failure the entry is not locked and a negative err-code is returned.
257  *
258  * Called with writer ipc_ids.rwsem held.
259  */
260 int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size)
261 {
262 	kuid_t euid;
263 	kgid_t egid;
264 	int id;
265 	int next_id = ids->next_id;
266 
267 	if (size > IPCMNI)
268 		size = IPCMNI;
269 
270 	if (ids->in_use >= size)
271 		return -ENOSPC;
272 
273 	idr_preload(GFP_KERNEL);
274 
275 	spin_lock_init(&new->lock);
276 	new->deleted = false;
277 	rcu_read_lock();
278 	spin_lock(&new->lock);
279 
280 	id = idr_alloc(&ids->ipcs_idr, new,
281 		       (next_id < 0) ? 0 : ipcid_to_idx(next_id), 0,
282 		       GFP_NOWAIT);
283 	idr_preload_end();
284 	if (id < 0) {
285 		spin_unlock(&new->lock);
286 		rcu_read_unlock();
287 		return id;
288 	}
289 
290 	ids->in_use++;
291 
292 	current_euid_egid(&euid, &egid);
293 	new->cuid = new->uid = euid;
294 	new->gid = new->cgid = egid;
295 
296 	if (next_id < 0) {
297 		new->seq = ids->seq++;
298 		if (ids->seq > IPCID_SEQ_MAX)
299 			ids->seq = 0;
300 	} else {
301 		new->seq = ipcid_to_seqx(next_id);
302 		ids->next_id = -1;
303 	}
304 
305 	new->id = ipc_buildid(id, new->seq);
306 	return id;
307 }
308 
309 /**
310  * ipcget_new -	create a new ipc object
311  * @ns: ipc namespace
312  * @ids: ipc identifer set
313  * @ops: the actual creation routine to call
314  * @params: its parameters
315  *
316  * This routine is called by sys_msgget, sys_semget() and sys_shmget()
317  * when the key is IPC_PRIVATE.
318  */
319 static int ipcget_new(struct ipc_namespace *ns, struct ipc_ids *ids,
320 		const struct ipc_ops *ops, struct ipc_params *params)
321 {
322 	int err;
323 
324 	down_write(&ids->rwsem);
325 	err = ops->getnew(ns, params);
326 	up_write(&ids->rwsem);
327 	return err;
328 }
329 
330 /**
331  * ipc_check_perms - check security and permissions for an ipc object
332  * @ns: ipc namespace
333  * @ipcp: ipc permission set
334  * @ops: the actual security routine to call
335  * @params: its parameters
336  *
337  * This routine is called by sys_msgget(), sys_semget() and sys_shmget()
338  * when the key is not IPC_PRIVATE and that key already exists in the
339  * ds IDR.
340  *
341  * On success, the ipc id is returned.
342  *
343  * It is called with ipc_ids.rwsem and ipcp->lock held.
344  */
345 static int ipc_check_perms(struct ipc_namespace *ns,
346 			   struct kern_ipc_perm *ipcp,
347 			   const struct ipc_ops *ops,
348 			   struct ipc_params *params)
349 {
350 	int err;
351 
352 	if (ipcperms(ns, ipcp, params->flg))
353 		err = -EACCES;
354 	else {
355 		err = ops->associate(ipcp, params->flg);
356 		if (!err)
357 			err = ipcp->id;
358 	}
359 
360 	return err;
361 }
362 
363 /**
364  * ipcget_public - get an ipc object or create a new one
365  * @ns: ipc namespace
366  * @ids: ipc identifer set
367  * @ops: the actual creation routine to call
368  * @params: its parameters
369  *
370  * This routine is called by sys_msgget, sys_semget() and sys_shmget()
371  * when the key is not IPC_PRIVATE.
372  * It adds a new entry if the key is not found and does some permission
373  * / security checkings if the key is found.
374  *
375  * On success, the ipc id is returned.
376  */
377 static int ipcget_public(struct ipc_namespace *ns, struct ipc_ids *ids,
378 		const struct ipc_ops *ops, struct ipc_params *params)
379 {
380 	struct kern_ipc_perm *ipcp;
381 	int flg = params->flg;
382 	int err;
383 
384 	/*
385 	 * Take the lock as a writer since we are potentially going to add
386 	 * a new entry + read locks are not "upgradable"
387 	 */
388 	down_write(&ids->rwsem);
389 	ipcp = ipc_findkey(ids, params->key);
390 	if (ipcp == NULL) {
391 		/* key not used */
392 		if (!(flg & IPC_CREAT))
393 			err = -ENOENT;
394 		else
395 			err = ops->getnew(ns, params);
396 	} else {
397 		/* ipc object has been locked by ipc_findkey() */
398 
399 		if (flg & IPC_CREAT && flg & IPC_EXCL)
400 			err = -EEXIST;
401 		else {
402 			err = 0;
403 			if (ops->more_checks)
404 				err = ops->more_checks(ipcp, params);
405 			if (!err)
406 				/*
407 				 * ipc_check_perms returns the IPC id on
408 				 * success
409 				 */
410 				err = ipc_check_perms(ns, ipcp, ops, params);
411 		}
412 		ipc_unlock(ipcp);
413 	}
414 	up_write(&ids->rwsem);
415 
416 	return err;
417 }
418 
419 
420 /**
421  * ipc_rmid - remove an ipc identifier
422  * @ids: ipc identifier set
423  * @ipcp: ipc perm structure containing the identifier to remove
424  *
425  * ipc_ids.rwsem (as a writer) and the spinlock for this ID are held
426  * before this function is called, and remain locked on the exit.
427  */
428 void ipc_rmid(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)
429 {
430 	int lid = ipcid_to_idx(ipcp->id);
431 
432 	idr_remove(&ids->ipcs_idr, lid);
433 	ids->in_use--;
434 	ipcp->deleted = true;
435 }
436 
437 /**
438  * ipc_alloc -	allocate ipc space
439  * @size: size desired
440  *
441  * Allocate memory from the appropriate pools and return a pointer to it.
442  * NULL is returned if the allocation fails
443  */
444 void *ipc_alloc(int size)
445 {
446 	void *out;
447 	if (size > PAGE_SIZE)
448 		out = vmalloc(size);
449 	else
450 		out = kmalloc(size, GFP_KERNEL);
451 	return out;
452 }
453 
454 /**
455  * ipc_free - free ipc space
456  * @ptr: pointer returned by ipc_alloc
457  * @size: size of block
458  *
459  * Free a block created with ipc_alloc(). The caller must know the size
460  * used in the allocation call.
461  */
462 void ipc_free(void *ptr, int size)
463 {
464 	if (size > PAGE_SIZE)
465 		vfree(ptr);
466 	else
467 		kfree(ptr);
468 }
469 
470 /**
471  * ipc_rcu_alloc - allocate ipc and rcu space
472  * @size: size desired
473  *
474  * Allocate memory for the rcu header structure +  the object.
475  * Returns the pointer to the object or NULL upon failure.
476  */
477 void *ipc_rcu_alloc(int size)
478 {
479 	/*
480 	 * We prepend the allocation with the rcu struct
481 	 */
482 	struct ipc_rcu *out = ipc_alloc(sizeof(struct ipc_rcu) + size);
483 	if (unlikely(!out))
484 		return NULL;
485 	atomic_set(&out->refcount, 1);
486 	return out + 1;
487 }
488 
489 int ipc_rcu_getref(void *ptr)
490 {
491 	struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
492 
493 	return atomic_inc_not_zero(&p->refcount);
494 }
495 
496 void ipc_rcu_putref(void *ptr, void (*func)(struct rcu_head *head))
497 {
498 	struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
499 
500 	if (!atomic_dec_and_test(&p->refcount))
501 		return;
502 
503 	call_rcu(&p->rcu, func);
504 }
505 
506 void ipc_rcu_free(struct rcu_head *head)
507 {
508 	struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
509 
510 	if (is_vmalloc_addr(p))
511 		vfree(p);
512 	else
513 		kfree(p);
514 }
515 
516 /**
517  * ipcperms - check ipc permissions
518  * @ns: ipc namespace
519  * @ipcp: ipc permission set
520  * @flag: desired permission set
521  *
522  * Check user, group, other permissions for access
523  * to ipc resources. return 0 if allowed
524  *
525  * @flag will most probably be 0 or S_...UGO from <linux/stat.h>
526  */
527 int ipcperms(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp, short flag)
528 {
529 	kuid_t euid = current_euid();
530 	int requested_mode, granted_mode;
531 
532 	audit_ipc_obj(ipcp);
533 	requested_mode = (flag >> 6) | (flag >> 3) | flag;
534 	granted_mode = ipcp->mode;
535 	if (uid_eq(euid, ipcp->cuid) ||
536 	    uid_eq(euid, ipcp->uid))
537 		granted_mode >>= 6;
538 	else if (in_group_p(ipcp->cgid) || in_group_p(ipcp->gid))
539 		granted_mode >>= 3;
540 	/* is there some bit set in requested_mode but not in granted_mode? */
541 	if ((requested_mode & ~granted_mode & 0007) &&
542 	    !ns_capable(ns->user_ns, CAP_IPC_OWNER))
543 		return -1;
544 
545 	return security_ipc_permission(ipcp, flag);
546 }
547 
548 /*
549  * Functions to convert between the kern_ipc_perm structure and the
550  * old/new ipc_perm structures
551  */
552 
553 /**
554  * kernel_to_ipc64_perm	- convert kernel ipc permissions to user
555  * @in: kernel permissions
556  * @out: new style ipc permissions
557  *
558  * Turn the kernel object @in into a set of permissions descriptions
559  * for returning to userspace (@out).
560  */
561 void kernel_to_ipc64_perm(struct kern_ipc_perm *in, struct ipc64_perm *out)
562 {
563 	out->key	= in->key;
564 	out->uid	= from_kuid_munged(current_user_ns(), in->uid);
565 	out->gid	= from_kgid_munged(current_user_ns(), in->gid);
566 	out->cuid	= from_kuid_munged(current_user_ns(), in->cuid);
567 	out->cgid	= from_kgid_munged(current_user_ns(), in->cgid);
568 	out->mode	= in->mode;
569 	out->seq	= in->seq;
570 }
571 
572 /**
573  * ipc64_perm_to_ipc_perm - convert new ipc permissions to old
574  * @in: new style ipc permissions
575  * @out: old style ipc permissions
576  *
577  * Turn the new style permissions object @in into a compatibility
578  * object and store it into the @out pointer.
579  */
580 void ipc64_perm_to_ipc_perm(struct ipc64_perm *in, struct ipc_perm *out)
581 {
582 	out->key	= in->key;
583 	SET_UID(out->uid, in->uid);
584 	SET_GID(out->gid, in->gid);
585 	SET_UID(out->cuid, in->cuid);
586 	SET_GID(out->cgid, in->cgid);
587 	out->mode	= in->mode;
588 	out->seq	= in->seq;
589 }
590 
591 /**
592  * ipc_obtain_object
593  * @ids: ipc identifier set
594  * @id: ipc id to look for
595  *
596  * Look for an id in the ipc ids idr and return associated ipc object.
597  *
598  * Call inside the RCU critical section.
599  * The ipc object is *not* locked on exit.
600  */
601 struct kern_ipc_perm *ipc_obtain_object(struct ipc_ids *ids, int id)
602 {
603 	struct kern_ipc_perm *out;
604 	int lid = ipcid_to_idx(id);
605 
606 	out = idr_find(&ids->ipcs_idr, lid);
607 	if (!out)
608 		return ERR_PTR(-EINVAL);
609 
610 	return out;
611 }
612 
613 /**
614  * ipc_lock - lock an ipc structure without rwsem held
615  * @ids: ipc identifier set
616  * @id: ipc id to look for
617  *
618  * Look for an id in the ipc ids idr and lock the associated ipc object.
619  *
620  * The ipc object is locked on successful exit.
621  */
622 struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
623 {
624 	struct kern_ipc_perm *out;
625 
626 	rcu_read_lock();
627 	out = ipc_obtain_object(ids, id);
628 	if (IS_ERR(out))
629 		goto err1;
630 
631 	spin_lock(&out->lock);
632 
633 	/* ipc_rmid() may have already freed the ID while ipc_lock
634 	 * was spinning: here verify that the structure is still valid
635 	 */
636 	if (ipc_valid_object(out))
637 		return out;
638 
639 	spin_unlock(&out->lock);
640 	out = ERR_PTR(-EINVAL);
641 err1:
642 	rcu_read_unlock();
643 	return out;
644 }
645 
646 /**
647  * ipc_obtain_object_check
648  * @ids: ipc identifier set
649  * @id: ipc id to look for
650  *
651  * Similar to ipc_obtain_object() but also checks
652  * the ipc object reference counter.
653  *
654  * Call inside the RCU critical section.
655  * The ipc object is *not* locked on exit.
656  */
657 struct kern_ipc_perm *ipc_obtain_object_check(struct ipc_ids *ids, int id)
658 {
659 	struct kern_ipc_perm *out = ipc_obtain_object(ids, id);
660 
661 	if (IS_ERR(out))
662 		goto out;
663 
664 	if (ipc_checkid(out, id))
665 		return ERR_PTR(-EIDRM);
666 out:
667 	return out;
668 }
669 
670 /**
671  * ipcget - Common sys_*get() code
672  * @ns: namsepace
673  * @ids: ipc identifier set
674  * @ops: operations to be called on ipc object creation, permission checks
675  *       and further checks
676  * @params: the parameters needed by the previous operations.
677  *
678  * Common routine called by sys_msgget(), sys_semget() and sys_shmget().
679  */
680 int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids,
681 			const struct ipc_ops *ops, struct ipc_params *params)
682 {
683 	if (params->key == IPC_PRIVATE)
684 		return ipcget_new(ns, ids, ops, params);
685 	else
686 		return ipcget_public(ns, ids, ops, params);
687 }
688 
689 /**
690  * ipc_update_perm - update the permissions of an ipc object
691  * @in:  the permission given as input.
692  * @out: the permission of the ipc to set.
693  */
694 int ipc_update_perm(struct ipc64_perm *in, struct kern_ipc_perm *out)
695 {
696 	kuid_t uid = make_kuid(current_user_ns(), in->uid);
697 	kgid_t gid = make_kgid(current_user_ns(), in->gid);
698 	if (!uid_valid(uid) || !gid_valid(gid))
699 		return -EINVAL;
700 
701 	out->uid = uid;
702 	out->gid = gid;
703 	out->mode = (out->mode & ~S_IRWXUGO)
704 		| (in->mode & S_IRWXUGO);
705 
706 	return 0;
707 }
708 
709 /**
710  * ipcctl_pre_down_nolock - retrieve an ipc and check permissions for some IPC_XXX cmd
711  * @ns:  ipc namespace
712  * @ids:  the table of ids where to look for the ipc
713  * @id:   the id of the ipc to retrieve
714  * @cmd:  the cmd to check
715  * @perm: the permission to set
716  * @extra_perm: one extra permission parameter used by msq
717  *
718  * This function does some common audit and permissions check for some IPC_XXX
719  * cmd and is called from semctl_down, shmctl_down and msgctl_down.
720  * It must be called without any lock held and
721  *  - retrieves the ipc with the given id in the given table.
722  *  - performs some audit and permission check, depending on the given cmd
723  *  - returns a pointer to the ipc object or otherwise, the corresponding error.
724  *
725  * Call holding the both the rwsem and the rcu read lock.
726  */
727 struct kern_ipc_perm *ipcctl_pre_down_nolock(struct ipc_namespace *ns,
728 					struct ipc_ids *ids, int id, int cmd,
729 					struct ipc64_perm *perm, int extra_perm)
730 {
731 	kuid_t euid;
732 	int err = -EPERM;
733 	struct kern_ipc_perm *ipcp;
734 
735 	ipcp = ipc_obtain_object_check(ids, id);
736 	if (IS_ERR(ipcp)) {
737 		err = PTR_ERR(ipcp);
738 		goto err;
739 	}
740 
741 	audit_ipc_obj(ipcp);
742 	if (cmd == IPC_SET)
743 		audit_ipc_set_perm(extra_perm, perm->uid,
744 				   perm->gid, perm->mode);
745 
746 	euid = current_euid();
747 	if (uid_eq(euid, ipcp->cuid) || uid_eq(euid, ipcp->uid)  ||
748 	    ns_capable(ns->user_ns, CAP_SYS_ADMIN))
749 		return ipcp; /* successful lookup */
750 err:
751 	return ERR_PTR(err);
752 }
753 
754 #ifdef CONFIG_ARCH_WANT_IPC_PARSE_VERSION
755 
756 
757 /**
758  * ipc_parse_version - ipc call version
759  * @cmd: pointer to command
760  *
761  * Return IPC_64 for new style IPC and IPC_OLD for old style IPC.
762  * The @cmd value is turned from an encoding command and version into
763  * just the command code.
764  */
765 int ipc_parse_version(int *cmd)
766 {
767 	if (*cmd & IPC_64) {
768 		*cmd ^= IPC_64;
769 		return IPC_64;
770 	} else {
771 		return IPC_OLD;
772 	}
773 }
774 
775 #endif /* CONFIG_ARCH_WANT_IPC_PARSE_VERSION */
776 
777 #ifdef CONFIG_PROC_FS
778 struct ipc_proc_iter {
779 	struct ipc_namespace *ns;
780 	struct ipc_proc_iface *iface;
781 };
782 
783 /*
784  * This routine locks the ipc structure found at least at position pos.
785  */
786 static struct kern_ipc_perm *sysvipc_find_ipc(struct ipc_ids *ids, loff_t pos,
787 					      loff_t *new_pos)
788 {
789 	struct kern_ipc_perm *ipc;
790 	int total, id;
791 
792 	total = 0;
793 	for (id = 0; id < pos && total < ids->in_use; id++) {
794 		ipc = idr_find(&ids->ipcs_idr, id);
795 		if (ipc != NULL)
796 			total++;
797 	}
798 
799 	if (total >= ids->in_use)
800 		return NULL;
801 
802 	for (; pos < IPCMNI; pos++) {
803 		ipc = idr_find(&ids->ipcs_idr, pos);
804 		if (ipc != NULL) {
805 			*new_pos = pos + 1;
806 			rcu_read_lock();
807 			ipc_lock_object(ipc);
808 			return ipc;
809 		}
810 	}
811 
812 	/* Out of range - return NULL to terminate iteration */
813 	return NULL;
814 }
815 
816 static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
817 {
818 	struct ipc_proc_iter *iter = s->private;
819 	struct ipc_proc_iface *iface = iter->iface;
820 	struct kern_ipc_perm *ipc = it;
821 
822 	/* If we had an ipc id locked before, unlock it */
823 	if (ipc && ipc != SEQ_START_TOKEN)
824 		ipc_unlock(ipc);
825 
826 	return sysvipc_find_ipc(&iter->ns->ids[iface->ids], *pos, pos);
827 }
828 
829 /*
830  * File positions: pos 0 -> header, pos n -> ipc id = n - 1.
831  * SeqFile iterator: iterator value locked ipc pointer or SEQ_TOKEN_START.
832  */
833 static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
834 {
835 	struct ipc_proc_iter *iter = s->private;
836 	struct ipc_proc_iface *iface = iter->iface;
837 	struct ipc_ids *ids;
838 
839 	ids = &iter->ns->ids[iface->ids];
840 
841 	/*
842 	 * Take the lock - this will be released by the corresponding
843 	 * call to stop().
844 	 */
845 	down_read(&ids->rwsem);
846 
847 	/* pos < 0 is invalid */
848 	if (*pos < 0)
849 		return NULL;
850 
851 	/* pos == 0 means header */
852 	if (*pos == 0)
853 		return SEQ_START_TOKEN;
854 
855 	/* Find the (pos-1)th ipc */
856 	return sysvipc_find_ipc(ids, *pos - 1, pos);
857 }
858 
859 static void sysvipc_proc_stop(struct seq_file *s, void *it)
860 {
861 	struct kern_ipc_perm *ipc = it;
862 	struct ipc_proc_iter *iter = s->private;
863 	struct ipc_proc_iface *iface = iter->iface;
864 	struct ipc_ids *ids;
865 
866 	/* If we had a locked structure, release it */
867 	if (ipc && ipc != SEQ_START_TOKEN)
868 		ipc_unlock(ipc);
869 
870 	ids = &iter->ns->ids[iface->ids];
871 	/* Release the lock we took in start() */
872 	up_read(&ids->rwsem);
873 }
874 
875 static int sysvipc_proc_show(struct seq_file *s, void *it)
876 {
877 	struct ipc_proc_iter *iter = s->private;
878 	struct ipc_proc_iface *iface = iter->iface;
879 
880 	if (it == SEQ_START_TOKEN)
881 		return seq_puts(s, iface->header);
882 
883 	return iface->show(s, it);
884 }
885 
886 static const struct seq_operations sysvipc_proc_seqops = {
887 	.start = sysvipc_proc_start,
888 	.stop  = sysvipc_proc_stop,
889 	.next  = sysvipc_proc_next,
890 	.show  = sysvipc_proc_show,
891 };
892 
893 static int sysvipc_proc_open(struct inode *inode, struct file *file)
894 {
895 	int ret;
896 	struct seq_file *seq;
897 	struct ipc_proc_iter *iter;
898 
899 	ret = -ENOMEM;
900 	iter = kmalloc(sizeof(*iter), GFP_KERNEL);
901 	if (!iter)
902 		goto out;
903 
904 	ret = seq_open(file, &sysvipc_proc_seqops);
905 	if (ret) {
906 		kfree(iter);
907 		goto out;
908 	}
909 
910 	seq = file->private_data;
911 	seq->private = iter;
912 
913 	iter->iface = PDE_DATA(inode);
914 	iter->ns    = get_ipc_ns(current->nsproxy->ipc_ns);
915 out:
916 	return ret;
917 }
918 
919 static int sysvipc_proc_release(struct inode *inode, struct file *file)
920 {
921 	struct seq_file *seq = file->private_data;
922 	struct ipc_proc_iter *iter = seq->private;
923 	put_ipc_ns(iter->ns);
924 	return seq_release_private(inode, file);
925 }
926 
927 static const struct file_operations sysvipc_proc_fops = {
928 	.open    = sysvipc_proc_open,
929 	.read    = seq_read,
930 	.llseek  = seq_lseek,
931 	.release = sysvipc_proc_release,
932 };
933 #endif /* CONFIG_PROC_FS */
934