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