xref: /linux-6.15/drivers/base/devtmpfs.c (revision 1c3cb50b) 
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * devtmpfs - kernel-maintained tmpfs-based /dev
4  *
5  * Copyright (C) 2009, Kay Sievers <[email protected]>
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 	mount_dev = simple_strtoul(str, NULL, 0);
60 	return 1;
61 }
62 __setup("devtmpfs.mount=", mount_param);
63 
64 static struct vfsmount *mnt;
65 
66 static struct dentry *public_dev_mount(struct file_system_type *fs_type, int flags,
67 		      const char *dev_name, void *data)
68 {
69 	struct super_block *s = mnt->mnt_sb;
70 	int err;
71 
72 	atomic_inc(&s->s_active);
73 	down_write(&s->s_umount);
74 	err = reconfigure_single(s, flags, data);
75 	if (err < 0) {
76 		deactivate_locked_super(s);
77 		return ERR_PTR(err);
78 	}
79 	return dget(s->s_root);
80 }
81 
82 static struct file_system_type internal_fs_type = {
83 	.name = "devtmpfs",
84 #ifdef CONFIG_TMPFS
85 	.init_fs_context = shmem_init_fs_context,
86 #else
87 	.init_fs_context = ramfs_init_fs_context,
88 #endif
89 	.kill_sb = kill_litter_super,
90 };
91 
92 static struct file_system_type dev_fs_type = {
93 	.name = "devtmpfs",
94 	.mount = public_dev_mount,
95 };
96 
97 static int devtmpfs_submit_req(struct req *req, const char *tmp)
98 {
99 	init_completion(&req->done);
100 
101 	spin_lock(&req_lock);
102 	req->next = requests;
103 	requests = req;
104 	spin_unlock(&req_lock);
105 
106 	wake_up_process(thread);
107 	wait_for_completion(&req->done);
108 
109 	kfree(tmp);
110 
111 	return req->err;
112 }
113 
114 int devtmpfs_create_node(struct device *dev)
115 {
116 	const char *tmp = NULL;
117 	struct req req;
118 
119 	if (!thread)
120 		return 0;
121 
122 	req.mode = 0;
123 	req.uid = GLOBAL_ROOT_UID;
124 	req.gid = GLOBAL_ROOT_GID;
125 	req.name = device_get_devnode(dev, &req.mode, &req.uid, &req.gid, &tmp);
126 	if (!req.name)
127 		return -ENOMEM;
128 
129 	if (req.mode == 0)
130 		req.mode = 0600;
131 	if (is_blockdev(dev))
132 		req.mode |= S_IFBLK;
133 	else
134 		req.mode |= S_IFCHR;
135 
136 	req.dev = dev;
137 
138 	return devtmpfs_submit_req(&req, tmp);
139 }
140 
141 int devtmpfs_delete_node(struct device *dev)
142 {
143 	const char *tmp = NULL;
144 	struct req req;
145 
146 	if (!thread)
147 		return 0;
148 
149 	req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
150 	if (!req.name)
151 		return -ENOMEM;
152 
153 	req.mode = 0;
154 	req.dev = dev;
155 
156 	return devtmpfs_submit_req(&req, tmp);
157 }
158 
159 static int dev_mkdir(const char *name, umode_t mode)
160 {
161 	struct dentry *dentry;
162 	struct path path;
163 	int err;
164 
165 	dentry = kern_path_create(AT_FDCWD, name, &path, LOOKUP_DIRECTORY);
166 	if (IS_ERR(dentry))
167 		return PTR_ERR(dentry);
168 
169 	err = vfs_mkdir(&nop_mnt_idmap, d_inode(path.dentry), dentry, mode);
170 	if (!err)
171 		/* mark as kernel-created inode */
172 		d_inode(dentry)->i_private = &thread;
173 	done_path_create(&path, dentry);
174 	return err;
175 }
176 
177 static int create_path(const char *nodepath)
178 {
179 	char *path;
180 	char *s;
181 	int err = 0;
182 
183 	/* parent directories do not exist, create them */
184 	path = kstrdup(nodepath, GFP_KERNEL);
185 	if (!path)
186 		return -ENOMEM;
187 
188 	s = path;
189 	for (;;) {
190 		s = strchr(s, '/');
191 		if (!s)
192 			break;
193 		s[0] = '\0';
194 		err = dev_mkdir(path, 0755);
195 		if (err && err != -EEXIST)
196 			break;
197 		s[0] = '/';
198 		s++;
199 	}
200 	kfree(path);
201 	return err;
202 }
203 
204 static int handle_create(const char *nodename, umode_t mode, kuid_t uid,
205 			 kgid_t gid, struct device *dev)
206 {
207 	struct dentry *dentry;
208 	struct path path;
209 	int err;
210 
211 	dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
212 	if (dentry == ERR_PTR(-ENOENT)) {
213 		create_path(nodename);
214 		dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
215 	}
216 	if (IS_ERR(dentry))
217 		return PTR_ERR(dentry);
218 
219 	err = vfs_mknod(&nop_mnt_idmap, d_inode(path.dentry), dentry, mode,
220 			dev->devt);
221 	if (!err) {
222 		struct iattr newattrs;
223 
224 		newattrs.ia_mode = mode;
225 		newattrs.ia_uid = uid;
226 		newattrs.ia_gid = gid;
227 		newattrs.ia_valid = ATTR_MODE|ATTR_UID|ATTR_GID;
228 		inode_lock(d_inode(dentry));
229 		notify_change(&nop_mnt_idmap, dentry, &newattrs, NULL);
230 		inode_unlock(d_inode(dentry));
231 
232 		/* mark as kernel-created inode */
233 		d_inode(dentry)->i_private = &thread;
234 	}
235 	done_path_create(&path, dentry);
236 	return err;
237 }
238 
239 static int dev_rmdir(const char *name)
240 {
241 	struct path parent;
242 	struct dentry *dentry;
243 	int err;
244 
245 	dentry = kern_path_locked(name, &parent);
246 	if (IS_ERR(dentry))
247 		return PTR_ERR(dentry);
248 	if (d_inode(dentry)->i_private == &thread)
249 		err = vfs_rmdir(&nop_mnt_idmap, d_inode(parent.dentry),
250 				dentry);
251 	else
252 		err = -EPERM;
253 
254 	dput(dentry);
255 	inode_unlock(d_inode(parent.dentry));
256 	path_put(&parent);
257 	return err;
258 }
259 
260 static int delete_path(const char *nodepath)
261 {
262 	char *path;
263 	int err = 0;
264 
265 	path = kstrdup(nodepath, GFP_KERNEL);
266 	if (!path)
267 		return -ENOMEM;
268 
269 	for (;;) {
270 		char *base;
271 
272 		base = strrchr(path, '/');
273 		if (!base)
274 			break;
275 		base[0] = '\0';
276 		err = dev_rmdir(path);
277 		if (err)
278 			break;
279 	}
280 
281 	kfree(path);
282 	return err;
283 }
284 
285 static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
286 {
287 	/* did we create it */
288 	if (inode->i_private != &thread)
289 		return 0;
290 
291 	/* does the dev_t match */
292 	if (is_blockdev(dev)) {
293 		if (!S_ISBLK(stat->mode))
294 			return 0;
295 	} else {
296 		if (!S_ISCHR(stat->mode))
297 			return 0;
298 	}
299 	if (stat->rdev != dev->devt)
300 		return 0;
301 
302 	/* ours */
303 	return 1;
304 }
305 
306 static int handle_remove(const char *nodename, struct device *dev)
307 {
308 	struct path parent;
309 	struct dentry *dentry;
310 	struct kstat stat;
311 	struct path p;
312 	int deleted = 0;
313 	int err;
314 
315 	dentry = kern_path_locked(nodename, &parent);
316 	if (IS_ERR(dentry))
317 		return PTR_ERR(dentry);
318 
319 	p.mnt = parent.mnt;
320 	p.dentry = dentry;
321 	err = vfs_getattr(&p, &stat, STATX_TYPE | STATX_MODE,
322 			  AT_STATX_SYNC_AS_STAT);
323 	if (!err && dev_mynode(dev, d_inode(dentry), &stat)) {
324 		struct iattr newattrs;
325 		/*
326 		 * before unlinking this node, reset permissions
327 		 * of possible references like hardlinks
328 		 */
329 		newattrs.ia_uid = GLOBAL_ROOT_UID;
330 		newattrs.ia_gid = GLOBAL_ROOT_GID;
331 		newattrs.ia_mode = stat.mode & ~0777;
332 		newattrs.ia_valid =
333 			ATTR_UID|ATTR_GID|ATTR_MODE;
334 		inode_lock(d_inode(dentry));
335 		notify_change(&nop_mnt_idmap, dentry, &newattrs, NULL);
336 		inode_unlock(d_inode(dentry));
337 		err = vfs_unlink(&nop_mnt_idmap, d_inode(parent.dentry),
338 				 dentry, NULL);
339 		if (!err || err == -ENOENT)
340 			deleted = 1;
341 	}
342 	dput(dentry);
343 	inode_unlock(d_inode(parent.dentry));
344 
345 	path_put(&parent);
346 	if (deleted && strchr(nodename, '/'))
347 		delete_path(nodename);
348 	return err;
349 }
350 
351 /*
352  * If configured, or requested by the commandline, devtmpfs will be
353  * auto-mounted after the kernel mounted the root filesystem.
354  */
355 int __init devtmpfs_mount(void)
356 {
357 	int err;
358 
359 	if (!mount_dev)
360 		return 0;
361 
362 	if (!thread)
363 		return 0;
364 
365 	err = init_mount("devtmpfs", "dev", "devtmpfs", DEVTMPFS_MFLAGS, NULL);
366 	if (err)
367 		pr_info("error mounting %d\n", err);
368 	else
369 		pr_info("mounted\n");
370 	return err;
371 }
372 
373 static __initdata DECLARE_COMPLETION(setup_done);
374 
375 static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
376 		  struct device *dev)
377 {
378 	if (mode)
379 		return handle_create(name, mode, uid, gid, dev);
380 	else
381 		return handle_remove(name, dev);
382 }
383 
384 static void __noreturn devtmpfs_work_loop(void)
385 {
386 	while (1) {
387 		spin_lock(&req_lock);
388 		while (requests) {
389 			struct req *req = requests;
390 			requests = NULL;
391 			spin_unlock(&req_lock);
392 			while (req) {
393 				struct req *next = req->next;
394 				req->err = handle(req->name, req->mode,
395 						  req->uid, req->gid, req->dev);
396 				complete(&req->done);
397 				req = next;
398 			}
399 			spin_lock(&req_lock);
400 		}
401 		__set_current_state(TASK_INTERRUPTIBLE);
402 		spin_unlock(&req_lock);
403 		schedule();
404 	}
405 }
406 
407 static noinline int __init devtmpfs_setup(void *p)
408 {
409 	int err;
410 
411 	err = ksys_unshare(CLONE_NEWNS);
412 	if (err)
413 		goto out;
414 	err = init_mount("devtmpfs", "/", "devtmpfs", DEVTMPFS_MFLAGS, NULL);
415 	if (err)
416 		goto out;
417 	init_chdir("/.."); /* will traverse into overmounted root */
418 	init_chroot(".");
419 out:
420 	*(int *)p = err;
421 	return err;
422 }
423 
424 /*
425  * The __ref is because devtmpfs_setup needs to be __init for the routines it
426  * calls.  That call is done while devtmpfs_init, which is marked __init,
427  * synchronously waits for it to complete.
428  */
429 static int __ref devtmpfsd(void *p)
430 {
431 	int err = devtmpfs_setup(p);
432 
433 	complete(&setup_done);
434 	if (err)
435 		return err;
436 	devtmpfs_work_loop();
437 	return 0;
438 }
439 
440 /*
441  * Create devtmpfs instance, driver-core devices will add their device
442  * nodes here.
443  */
444 int __init devtmpfs_init(void)
445 {
446 	char opts[] = "mode=0755";
447 	int err;
448 
449 	mnt = vfs_kern_mount(&internal_fs_type, 0, "devtmpfs", opts);
450 	if (IS_ERR(mnt)) {
451 		pr_err("unable to create devtmpfs %ld\n", PTR_ERR(mnt));
452 		return PTR_ERR(mnt);
453 	}
454 	err = register_filesystem(&dev_fs_type);
455 	if (err) {
456 		pr_err("unable to register devtmpfs type %d\n", err);
457 		return err;
458 	}
459 
460 	thread = kthread_run(devtmpfsd, &err, "kdevtmpfs");
461 	if (!IS_ERR(thread)) {
462 		wait_for_completion(&setup_done);
463 	} else {
464 		err = PTR_ERR(thread);
465 		thread = NULL;
466 	}
467 
468 	if (err) {
469 		pr_err("unable to create devtmpfs %d\n", err);
470 		unregister_filesystem(&dev_fs_type);
471 		thread = NULL;
472 		return err;
473 	}
474 
475 	pr_info("initialized\n");
476 	return 0;
477 }
478