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