xref: /linux/drivers/base/devtmpfs.c (revision 14c897740388216acd59477a382de327d5e27ba4) 
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * devtmpfs - kernel-maintained tmpfs-based /dev
4  *
5  * Copyright (C) 2009, Kay Sievers <kay.sievers@vrfy.org>
6  *
7  * During bootup, before any driver core device is registered,
8  * devtmpfs, a tmpfs-based filesystem is created. Every driver-core
9  * device which requests a device node, will add a node in this
10  * filesystem.
11  * By default, all devices are named after the name of the device,
12  * owned by root and have a default mode of 0600. Subsystems can
13  * overwrite the default setting if needed.
14  */
15 
16 #define pr_fmt(fmt) "devtmpfs: " fmt
17 
18 #include <linux/kernel.h>
19 #include <linux/syscalls.h>
20 #include <linux/mount.h>
21 #include <linux/device.h>
22 #include <linux/blkdev.h>
23 #include <linux/namei.h>
24 #include <linux/fs.h>
25 #include <linux/shmem_fs.h>
26 #include <linux/ramfs.h>
27 #include <linux/sched.h>
28 #include <linux/slab.h>
29 #include <linux/kthread.h>
30 #include <linux/init_syscalls.h>
31 #include <uapi/linux/mount.h>
32 #include "base.h"
33 
34 #ifdef CONFIG_DEVTMPFS_SAFE
35 #define DEVTMPFS_MFLAGS       (MS_SILENT | MS_NOEXEC | MS_NOSUID)
36 #else
37 #define DEVTMPFS_MFLAGS       (MS_SILENT)
38 #endif
39 
40 static struct task_struct *thread;
41 
42 static int __initdata mount_dev = IS_ENABLED(CONFIG_DEVTMPFS_MOUNT);
43 
44 static DEFINE_SPINLOCK(req_lock);
45 
46 static struct req {
47 	struct req *next;
48 	struct completion done;
49 	int err;
50 	const char *name;
51 	umode_t mode;	/* 0 => delete */
52 	kuid_t uid;
53 	kgid_t gid;
54 	struct device *dev;
55 } *requests;
56 
57 static int __init mount_param(char *str)
58 {
59 	return kstrtoint(str, 0, &mount_dev) == 0;
60 }
61 __setup("devtmpfs.mount=", mount_param);
62 
63 static struct vfsmount *mnt;
64 
65 static struct file_system_type internal_fs_type = {
66 	.name = "devtmpfs",
67 #ifdef CONFIG_TMPFS
68 	.init_fs_context = shmem_init_fs_context,
69 #else
70 	.init_fs_context = ramfs_init_fs_context,
71 #endif
72 	.kill_sb = kill_anon_super,
73 };
74 
75 struct devtmpfs_context {
76 	struct fs_context *fc;
77 };
78 
79 static void devtmpfs_free(struct fs_context *fc)
80 {
81 	struct devtmpfs_context *ctx = fc->fs_private;
82 
83 	if (ctx) {
84 		put_fs_context(ctx->fc);
85 		kfree(ctx);
86 	}
87 }
88 
89 static int devtmpfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
90 {
91 	struct devtmpfs_context *ctx = fc->fs_private;
92 
93 	return ctx->fc->ops->parse_param(ctx->fc, param);
94 }
95 
96 static int devtmpfs_parse_monolithic(struct fs_context *fc, void *data)
97 {
98 	struct devtmpfs_context *ctx = fc->fs_private;
99 
100 	if (ctx->fc->ops->parse_monolithic)
101 		return ctx->fc->ops->parse_monolithic(ctx->fc, data);
102 	return generic_parse_monolithic(ctx->fc, data);
103 }
104 
105 static int devtmpfs_get_tree(struct fs_context *fc)
106 {
107 	struct devtmpfs_context *ctx = fc->fs_private;
108 	struct super_block *sb = mnt->mnt_sb;
109 	int err;
110 
111 	atomic_inc(&sb->s_active);
112 	down_write(&sb->s_umount);
113 
114 	if (ctx->fc->ops->reconfigure) {
115 		err = ctx->fc->ops->reconfigure(ctx->fc);
116 		if (err) {
117 			deactivate_locked_super(sb);
118 			return err;
119 		}
120 	}
121 
122 	fc->root = dget(sb->s_root);
123 	return 0;
124 }
125 
126 static const struct fs_context_operations devtmpfs_context_ops = {
127 	.free		  = devtmpfs_free,
128 	.parse_param	  = devtmpfs_parse_param,
129 	.parse_monolithic = devtmpfs_parse_monolithic,
130 	.get_tree	  = devtmpfs_get_tree,
131 };
132 
133 static int devtmpfs_init_fs_context(struct fs_context *fc)
134 {
135 	struct devtmpfs_context *ctx;
136 	int err;
137 
138 	ctx = kzalloc_obj(struct devtmpfs_context);
139 	if (!ctx)
140 		return -ENOMEM;
141 
142 	/* Each mount will reconfigure the shared superblock w/ new options */
143 	ctx->fc = fs_context_for_reconfigure(mnt->mnt_root,
144 					     mnt->mnt_sb->s_flags, MS_RMT_MASK);
145 	if (IS_ERR(ctx->fc)) {
146 		err = PTR_ERR(ctx->fc);
147 		kfree(ctx);
148 		return err;
149 	}
150 
151 	fc->fs_private = ctx;
152 	fc->ops = &devtmpfs_context_ops;
153 
154 	return 0;
155 }
156 
157 static struct file_system_type dev_fs_type = {
158 	.name		 = "devtmpfs",
159 	.init_fs_context = devtmpfs_init_fs_context,
160 };
161 
162 static int devtmpfs_submit_req(struct req *req, const char *tmp)
163 {
164 	init_completion(&req->done);
165 
166 	spin_lock(&req_lock);
167 	req->next = requests;
168 	requests = req;
169 	spin_unlock(&req_lock);
170 
171 	wake_up_process(thread);
172 	wait_for_completion(&req->done);
173 
174 	kfree(tmp);
175 
176 	return req->err;
177 }
178 
179 int devtmpfs_create_node(struct device *dev)
180 {
181 	const char *tmp = NULL;
182 	struct req req;
183 
184 	if (!thread)
185 		return 0;
186 
187 	req.mode = 0;
188 	req.uid = GLOBAL_ROOT_UID;
189 	req.gid = GLOBAL_ROOT_GID;
190 	req.name = device_get_devnode(dev, &req.mode, &req.uid, &req.gid, &tmp);
191 	if (!req.name)
192 		return -ENOMEM;
193 
194 	if (req.mode == 0)
195 		req.mode = 0600;
196 	if (is_blockdev(dev))
197 		req.mode |= S_IFBLK;
198 	else
199 		req.mode |= S_IFCHR;
200 
201 	req.dev = dev;
202 
203 	return devtmpfs_submit_req(&req, tmp);
204 }
205 
206 int devtmpfs_delete_node(struct device *dev)
207 {
208 	const char *tmp = NULL;
209 	struct req req;
210 
211 	if (!thread)
212 		return 0;
213 
214 	req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
215 	if (!req.name)
216 		return -ENOMEM;
217 
218 	req.mode = 0;
219 	req.dev = dev;
220 
221 	return devtmpfs_submit_req(&req, tmp);
222 }
223 
224 static int dev_mkdir(const char *name, umode_t mode)
225 {
226 	struct dentry *dentry;
227 	struct path path;
228 
229 	dentry = start_creating_path(AT_FDCWD, name, &path, LOOKUP_DIRECTORY);
230 	if (IS_ERR(dentry))
231 		return PTR_ERR(dentry);
232 
233 	dentry = vfs_mkdir(&nop_mnt_idmap, d_inode(path.dentry), dentry, mode, NULL);
234 	if (!IS_ERR(dentry))
235 		/* mark as kernel-created inode */
236 		d_inode(dentry)->i_private = &thread;
237 	end_creating_path(&path, dentry);
238 	return PTR_ERR_OR_ZERO(dentry);
239 }
240 
241 static int create_path(const char *nodepath)
242 {
243 	char *path;
244 	char *s;
245 	int err = 0;
246 
247 	/* parent directories do not exist, create them */
248 	path = kstrdup(nodepath, GFP_KERNEL);
249 	if (!path)
250 		return -ENOMEM;
251 
252 	s = path;
253 	for (;;) {
254 		s = strchr(s, '/');
255 		if (!s)
256 			break;
257 		s[0] = '\0';
258 		err = dev_mkdir(path, 0755);
259 		if (err && err != -EEXIST)
260 			break;
261 		s[0] = '/';
262 		s++;
263 	}
264 	kfree(path);
265 	return err;
266 }
267 
268 static int handle_create(const char *nodename, umode_t mode, kuid_t uid,
269 			 kgid_t gid, struct device *dev)
270 {
271 	struct dentry *dentry;
272 	struct path path;
273 	int err;
274 
275 	dentry = start_creating_path(AT_FDCWD, nodename, &path, 0);
276 	if (dentry == ERR_PTR(-ENOENT)) {
277 		create_path(nodename);
278 		dentry = start_creating_path(AT_FDCWD, nodename, &path, 0);
279 	}
280 	if (IS_ERR(dentry))
281 		return PTR_ERR(dentry);
282 
283 	err = vfs_mknod(&nop_mnt_idmap, d_inode(path.dentry), dentry, mode,
284 			dev->devt, NULL);
285 	if (!err) {
286 		struct iattr newattrs;
287 
288 		newattrs.ia_mode = mode;
289 		newattrs.ia_uid = uid;
290 		newattrs.ia_gid = gid;
291 		newattrs.ia_valid = ATTR_MODE|ATTR_UID|ATTR_GID;
292 		inode_lock(d_inode(dentry));
293 		notify_change(&nop_mnt_idmap, dentry, &newattrs, NULL);
294 		inode_unlock(d_inode(dentry));
295 
296 		/* mark as kernel-created inode */
297 		d_inode(dentry)->i_private = &thread;
298 	}
299 	end_creating_path(&path, dentry);
300 	return err;
301 }
302 
303 static int dev_rmdir(const char *name)
304 {
305 	struct path parent;
306 	struct dentry *dentry;
307 	int err;
308 
309 	dentry = start_removing_path(name, &parent);
310 	if (IS_ERR(dentry))
311 		return PTR_ERR(dentry);
312 	if (d_inode(dentry)->i_private == &thread)
313 		err = vfs_rmdir(&nop_mnt_idmap, d_inode(parent.dentry),
314 				dentry, NULL);
315 	else
316 		err = -EPERM;
317 
318 	end_removing_path(&parent, dentry);
319 	return err;
320 }
321 
322 static int delete_path(const char *nodepath)
323 {
324 	char *path;
325 	int err = 0;
326 
327 	path = kstrdup(nodepath, GFP_KERNEL);
328 	if (!path)
329 		return -ENOMEM;
330 
331 	for (;;) {
332 		char *base;
333 
334 		base = strrchr(path, '/');
335 		if (!base)
336 			break;
337 		base[0] = '\0';
338 		err = dev_rmdir(path);
339 		if (err)
340 			break;
341 	}
342 
343 	kfree(path);
344 	return err;
345 }
346 
347 static int dev_mynode(struct device *dev, struct inode *inode)
348 {
349 	/* did we create it */
350 	if (inode->i_private != &thread)
351 		return 0;
352 
353 	/* does the dev_t match */
354 	if (is_blockdev(dev)) {
355 		if (!S_ISBLK(inode->i_mode))
356 			return 0;
357 	} else {
358 		if (!S_ISCHR(inode->i_mode))
359 			return 0;
360 	}
361 	if (inode->i_rdev != dev->devt)
362 		return 0;
363 
364 	/* ours */
365 	return 1;
366 }
367 
368 static int handle_remove(const char *nodename, struct device *dev)
369 {
370 	struct path parent;
371 	struct dentry *dentry;
372 	struct inode *inode;
373 	int deleted = 0;
374 	int err = 0;
375 
376 	dentry = start_removing_path(nodename, &parent);
377 	if (IS_ERR(dentry))
378 		return PTR_ERR(dentry);
379 
380 	inode = d_inode(dentry);
381 	if (dev_mynode(dev, inode)) {
382 		struct iattr newattrs;
383 		/*
384 		 * before unlinking this node, reset permissions
385 		 * of possible references like hardlinks
386 		 */
387 		newattrs.ia_uid = GLOBAL_ROOT_UID;
388 		newattrs.ia_gid = GLOBAL_ROOT_GID;
389 		newattrs.ia_mode = inode->i_mode & ~0777;
390 		newattrs.ia_valid =
391 			ATTR_UID|ATTR_GID|ATTR_MODE;
392 		inode_lock(d_inode(dentry));
393 		notify_change(&nop_mnt_idmap, dentry, &newattrs, NULL);
394 		inode_unlock(d_inode(dentry));
395 		err = vfs_unlink(&nop_mnt_idmap, d_inode(parent.dentry),
396 				 dentry, NULL);
397 		if (!err || err == -ENOENT)
398 			deleted = 1;
399 	}
400 	end_removing_path(&parent, dentry);
401 
402 	if (deleted && strchr(nodename, '/'))
403 		delete_path(nodename);
404 	return err;
405 }
406 
407 /*
408  * If configured, or requested by the commandline, devtmpfs will be
409  * auto-mounted after the kernel mounted the root filesystem.
410  */
411 int __init devtmpfs_mount(void)
412 {
413 	int err;
414 
415 	if (!mount_dev)
416 		return 0;
417 
418 	if (!thread)
419 		return 0;
420 
421 	err = init_mount("devtmpfs", "dev", "devtmpfs", DEVTMPFS_MFLAGS, NULL);
422 	if (err)
423 		pr_info("error mounting %d\n", err);
424 	else
425 		pr_info("mounted\n");
426 	return err;
427 }
428 
429 static __initdata DECLARE_COMPLETION(setup_done);
430 
431 static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
432 		  struct device *dev)
433 {
434 	if (mode)
435 		return handle_create(name, mode, uid, gid, dev);
436 	else
437 		return handle_remove(name, dev);
438 }
439 
440 static void __noreturn devtmpfs_work_loop(void)
441 {
442 	while (1) {
443 		spin_lock(&req_lock);
444 		while (requests) {
445 			struct req *req = requests;
446 			requests = NULL;
447 			spin_unlock(&req_lock);
448 			while (req) {
449 				struct req *next = req->next;
450 				req->err = handle(req->name, req->mode,
451 						  req->uid, req->gid, req->dev);
452 				complete(&req->done);
453 				req = next;
454 			}
455 			spin_lock(&req_lock);
456 		}
457 		__set_current_state(TASK_INTERRUPTIBLE);
458 		spin_unlock(&req_lock);
459 		schedule();
460 	}
461 }
462 
463 static noinline int __init devtmpfs_setup(void *p)
464 {
465 	int err;
466 
467 	err = ksys_unshare(UNSHARE_EMPTY_MNTNS);
468 	if (err)
469 		goto out;
470 	err = init_mount("devtmpfs", "/", "devtmpfs", DEVTMPFS_MFLAGS, NULL);
471 	if (err)
472 		goto out;
473 	init_chdir("/.."); /* will traverse into overmounted root */
474 	init_chroot(".");
475 out:
476 	*(int *)p = err;
477 	return err;
478 }
479 
480 /*
481  * The __ref is because devtmpfs_setup needs to be __init for the routines it
482  * calls.  That call is done while devtmpfs_init, which is marked __init,
483  * synchronously waits for it to complete.
484  */
485 static int __ref devtmpfsd(void *p)
486 {
487 	int err = devtmpfs_setup(p);
488 
489 	complete(&setup_done);
490 	if (err)
491 		return err;
492 	devtmpfs_work_loop();
493 	return 0;
494 }
495 
496 /*
497  * Create devtmpfs instance, driver-core devices will add their device
498  * nodes here.
499  */
500 int __init devtmpfs_init(void)
501 {
502 	char opts[] = "mode=0755";
503 	int err;
504 
505 	mnt = vfs_kern_mount(&internal_fs_type, 0, "devtmpfs", opts);
506 	if (IS_ERR(mnt)) {
507 		pr_err("unable to create devtmpfs %ld\n", PTR_ERR(mnt));
508 		return PTR_ERR(mnt);
509 	}
510 
511 	err = register_filesystem(&dev_fs_type);
512 	if (err) {
513 		pr_err("unable to register devtmpfs type %d\n", err);
514 		return err;
515 	}
516 
517 	thread = kthread_run(devtmpfsd, &err, "kdevtmpfs");
518 	if (!IS_ERR(thread)) {
519 		wait_for_completion(&setup_done);
520 	} else {
521 		err = PTR_ERR(thread);
522 		thread = NULL;
523 	}
524 
525 	if (err) {
526 		pr_err("unable to create devtmpfs %d\n", err);
527 		unregister_filesystem(&dev_fs_type);
528 		thread = NULL;
529 		return err;
530 	}
531 
532 	pr_info("initialized\n");
533 	return 0;
534 }
535