xref: /openbmc/linux/drivers/base/devtmpfs.c (revision 66c98360)
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 	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_really_is_positive(dentry)) {
249 		if (d_inode(dentry)->i_private == &thread)
250 			err = vfs_rmdir(&nop_mnt_idmap, d_inode(parent.dentry),
251 					dentry);
252 		else
253 			err = -EPERM;
254 	} else {
255 		err = -ENOENT;
256 	}
257 	dput(dentry);
258 	inode_unlock(d_inode(parent.dentry));
259 	path_put(&parent);
260 	return err;
261 }
262 
263 static int delete_path(const char *nodepath)
264 {
265 	char *path;
266 	int err = 0;
267 
268 	path = kstrdup(nodepath, GFP_KERNEL);
269 	if (!path)
270 		return -ENOMEM;
271 
272 	for (;;) {
273 		char *base;
274 
275 		base = strrchr(path, '/');
276 		if (!base)
277 			break;
278 		base[0] = '\0';
279 		err = dev_rmdir(path);
280 		if (err)
281 			break;
282 	}
283 
284 	kfree(path);
285 	return err;
286 }
287 
288 static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
289 {
290 	/* did we create it */
291 	if (inode->i_private != &thread)
292 		return 0;
293 
294 	/* does the dev_t match */
295 	if (is_blockdev(dev)) {
296 		if (!S_ISBLK(stat->mode))
297 			return 0;
298 	} else {
299 		if (!S_ISCHR(stat->mode))
300 			return 0;
301 	}
302 	if (stat->rdev != dev->devt)
303 		return 0;
304 
305 	/* ours */
306 	return 1;
307 }
308 
309 static int handle_remove(const char *nodename, struct device *dev)
310 {
311 	struct path parent;
312 	struct dentry *dentry;
313 	int deleted = 0;
314 	int err;
315 
316 	dentry = kern_path_locked(nodename, &parent);
317 	if (IS_ERR(dentry))
318 		return PTR_ERR(dentry);
319 
320 	if (d_really_is_positive(dentry)) {
321 		struct kstat stat;
322 		struct path p = {.mnt = parent.mnt, .dentry = dentry};
323 		err = vfs_getattr(&p, &stat, STATX_TYPE | STATX_MODE,
324 				  AT_STATX_SYNC_AS_STAT);
325 		if (!err && dev_mynode(dev, d_inode(dentry), &stat)) {
326 			struct iattr newattrs;
327 			/*
328 			 * before unlinking this node, reset permissions
329 			 * of possible references like hardlinks
330 			 */
331 			newattrs.ia_uid = GLOBAL_ROOT_UID;
332 			newattrs.ia_gid = GLOBAL_ROOT_GID;
333 			newattrs.ia_mode = stat.mode & ~0777;
334 			newattrs.ia_valid =
335 				ATTR_UID|ATTR_GID|ATTR_MODE;
336 			inode_lock(d_inode(dentry));
337 			notify_change(&nop_mnt_idmap, dentry, &newattrs, NULL);
338 			inode_unlock(d_inode(dentry));
339 			err = vfs_unlink(&nop_mnt_idmap, d_inode(parent.dentry),
340 					 dentry, NULL);
341 			if (!err || err == -ENOENT)
342 				deleted = 1;
343 		}
344 	} else {
345 		err = -ENOENT;
346 	}
347 	dput(dentry);
348 	inode_unlock(d_inode(parent.dentry));
349 
350 	path_put(&parent);
351 	if (deleted && strchr(nodename, '/'))
352 		delete_path(nodename);
353 	return err;
354 }
355 
356 /*
357  * If configured, or requested by the commandline, devtmpfs will be
358  * auto-mounted after the kernel mounted the root filesystem.
359  */
360 int __init devtmpfs_mount(void)
361 {
362 	int err;
363 
364 	if (!mount_dev)
365 		return 0;
366 
367 	if (!thread)
368 		return 0;
369 
370 	err = init_mount("devtmpfs", "dev", "devtmpfs", DEVTMPFS_MFLAGS, NULL);
371 	if (err)
372 		pr_info("error mounting %d\n", err);
373 	else
374 		pr_info("mounted\n");
375 	return err;
376 }
377 
378 static __initdata DECLARE_COMPLETION(setup_done);
379 
380 static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
381 		  struct device *dev)
382 {
383 	if (mode)
384 		return handle_create(name, mode, uid, gid, dev);
385 	else
386 		return handle_remove(name, dev);
387 }
388 
389 static void __noreturn devtmpfs_work_loop(void)
390 {
391 	while (1) {
392 		spin_lock(&req_lock);
393 		while (requests) {
394 			struct req *req = requests;
395 			requests = NULL;
396 			spin_unlock(&req_lock);
397 			while (req) {
398 				struct req *next = req->next;
399 				req->err = handle(req->name, req->mode,
400 						  req->uid, req->gid, req->dev);
401 				complete(&req->done);
402 				req = next;
403 			}
404 			spin_lock(&req_lock);
405 		}
406 		__set_current_state(TASK_INTERRUPTIBLE);
407 		spin_unlock(&req_lock);
408 		schedule();
409 	}
410 }
411 
412 static noinline int __init devtmpfs_setup(void *p)
413 {
414 	int err;
415 
416 	err = ksys_unshare(CLONE_NEWNS);
417 	if (err)
418 		goto out;
419 	err = init_mount("devtmpfs", "/", "devtmpfs", DEVTMPFS_MFLAGS, NULL);
420 	if (err)
421 		goto out;
422 	init_chdir("/.."); /* will traverse into overmounted root */
423 	init_chroot(".");
424 out:
425 	*(int *)p = err;
426 	return err;
427 }
428 
429 /*
430  * The __ref is because devtmpfs_setup needs to be __init for the routines it
431  * calls.  That call is done while devtmpfs_init, which is marked __init,
432  * synchronously waits for it to complete.
433  */
434 static int __ref devtmpfsd(void *p)
435 {
436 	int err = devtmpfs_setup(p);
437 
438 	complete(&setup_done);
439 	if (err)
440 		return err;
441 	devtmpfs_work_loop();
442 	return 0;
443 }
444 
445 /*
446  * Create devtmpfs instance, driver-core devices will add their device
447  * nodes here.
448  */
449 int __init devtmpfs_init(void)
450 {
451 	char opts[] = "mode=0755";
452 	int err;
453 
454 	mnt = vfs_kern_mount(&internal_fs_type, 0, "devtmpfs", opts);
455 	if (IS_ERR(mnt)) {
456 		pr_err("unable to create devtmpfs %ld\n", PTR_ERR(mnt));
457 		return PTR_ERR(mnt);
458 	}
459 	err = register_filesystem(&dev_fs_type);
460 	if (err) {
461 		pr_err("unable to register devtmpfs type %d\n", err);
462 		return err;
463 	}
464 
465 	thread = kthread_run(devtmpfsd, &err, "kdevtmpfs");
466 	if (!IS_ERR(thread)) {
467 		wait_for_completion(&setup_done);
468 	} else {
469 		err = PTR_ERR(thread);
470 		thread = NULL;
471 	}
472 
473 	if (err) {
474 		pr_err("unable to create devtmpfs %d\n", err);
475 		unregister_filesystem(&dev_fs_type);
476 		thread = NULL;
477 		return err;
478 	}
479 
480 	pr_info("initialized\n");
481 	return 0;
482 }
483