1 /*
2 * devtmpfs - kernel-maintained tmpfs-based /dev
3 *
4 * Copyright (C) 2009, Kay Sievers <kay.sievers@vrfy.org>
5 *
6 * During bootup, before any driver core device is registered,
7 * devtmpfs, a tmpfs-based filesystem is created. Every driver-core
8 * device which requests a device node, will add a node in this
9 * filesystem.
10 * By default, all devices are named after the name of the device,
11 * owned by root and have a default mode of 0600. Subsystems can
12 * overwrite the default setting if needed.
13 */
14
15 #include <linux/kernel.h>
16 #include <linux/syscalls.h>
17 #include <linux/mount.h>
18 #include <linux/device.h>
19 #include <linux/genhd.h>
20 #include <linux/namei.h>
21 #include <linux/fs.h>
22 #include <linux/shmem_fs.h>
23 #include <linux/ramfs.h>
24 #include <linux/sched.h>
25 #include <linux/slab.h>
26 #include <linux/kthread.h>
27 #include "base.h"
28
29 static struct task_struct *thread;
30
31 #if defined CONFIG_DEVTMPFS_MOUNT
32 static int mount_dev = 1;
33 #else
34 static int mount_dev;
35 #endif
36
37 static DEFINE_SPINLOCK(req_lock);
38
39 static struct req {
40 struct req *next;
41 struct completion done;
42 int err;
43 const char *name;
44 umode_t mode; /* 0 => delete */
45 kuid_t uid;
46 kgid_t gid;
47 struct device *dev;
48 } *requests;
49
mount_param(char * str)50 static int __init mount_param(char *str)
51 {
52 mount_dev = simple_strtoul(str, NULL, 0);
53 return 1;
54 }
55 __setup("devtmpfs.mount=", mount_param);
56
dev_mount(struct file_system_type * fs_type,int flags,const char * dev_name,void * data)57 static struct dentry *dev_mount(struct file_system_type *fs_type, int flags,
58 const char *dev_name, void *data)
59 {
60 #ifdef CONFIG_TMPFS
61 return mount_single(fs_type, flags, data, shmem_fill_super);
62 #else
63 return mount_single(fs_type, flags, data, ramfs_fill_super);
64 #endif
65 }
66
67 static struct file_system_type dev_fs_type = {
68 .name = "devtmpfs",
69 .mount = dev_mount,
70 .kill_sb = kill_litter_super,
71 };
72
73 #ifdef CONFIG_BLOCK
is_blockdev(struct device * dev)74 static inline int is_blockdev(struct device *dev)
75 {
76 return dev->class == &block_class;
77 }
78 #else
is_blockdev(struct device * dev)79 static inline int is_blockdev(struct device *dev) { return 0; }
80 #endif
81
devtmpfs_create_node(struct device * dev)82 int devtmpfs_create_node(struct device *dev)
83 {
84 const char *tmp = NULL;
85 struct req req;
86
87 if (!thread)
88 return 0;
89
90 req.mode = 0;
91 req.uid = GLOBAL_ROOT_UID;
92 req.gid = GLOBAL_ROOT_GID;
93 req.name = device_get_devnode(dev, &req.mode, &req.uid, &req.gid, &tmp);
94 if (!req.name)
95 return -ENOMEM;
96
97 if (req.mode == 0)
98 req.mode = 0600;
99 if (is_blockdev(dev))
100 req.mode |= S_IFBLK;
101 else
102 req.mode |= S_IFCHR;
103
104 req.dev = dev;
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_delete_node(struct device * dev)121 int devtmpfs_delete_node(struct device *dev)
122 {
123 const char *tmp = NULL;
124 struct req req;
125
126 if (!thread)
127 return 0;
128
129 req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
130 if (!req.name)
131 return -ENOMEM;
132
133 req.mode = 0;
134 req.dev = dev;
135
136 init_completion(&req.done);
137
138 spin_lock(&req_lock);
139 req.next = requests;
140 requests = &req;
141 spin_unlock(&req_lock);
142
143 wake_up_process(thread);
144 wait_for_completion(&req.done);
145
146 kfree(tmp);
147 return req.err;
148 }
149
dev_mkdir(const char * name,umode_t mode)150 static int dev_mkdir(const char *name, umode_t mode)
151 {
152 struct dentry *dentry;
153 struct path path;
154 int err;
155
156 dentry = kern_path_create(AT_FDCWD, name, &path, LOOKUP_DIRECTORY);
157 if (IS_ERR(dentry))
158 return PTR_ERR(dentry);
159
160 err = vfs_mkdir(d_inode(path.dentry), dentry, mode);
161 if (!err)
162 /* mark as kernel-created inode */
163 d_inode(dentry)->i_private = &thread;
164 done_path_create(&path, dentry);
165 return err;
166 }
167
create_path(const char * nodepath)168 static int create_path(const char *nodepath)
169 {
170 char *path;
171 char *s;
172 int err = 0;
173
174 /* parent directories do not exist, create them */
175 path = kstrdup(nodepath, GFP_KERNEL);
176 if (!path)
177 return -ENOMEM;
178
179 s = path;
180 for (;;) {
181 s = strchr(s, '/');
182 if (!s)
183 break;
184 s[0] = '\0';
185 err = dev_mkdir(path, 0755);
186 if (err && err != -EEXIST)
187 break;
188 s[0] = '/';
189 s++;
190 }
191 kfree(path);
192 return err;
193 }
194
handle_create(const char * nodename,umode_t mode,kuid_t uid,kgid_t gid,struct device * dev)195 static int handle_create(const char *nodename, umode_t mode, kuid_t uid,
196 kgid_t gid, struct device *dev)
197 {
198 struct dentry *dentry;
199 struct path path;
200 int err;
201
202 dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
203 if (dentry == ERR_PTR(-ENOENT)) {
204 create_path(nodename);
205 dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
206 }
207 if (IS_ERR(dentry))
208 return PTR_ERR(dentry);
209
210 err = vfs_mknod(d_inode(path.dentry), dentry, mode, dev->devt);
211 if (!err) {
212 struct iattr newattrs;
213
214 newattrs.ia_mode = mode;
215 newattrs.ia_uid = uid;
216 newattrs.ia_gid = gid;
217 newattrs.ia_valid = ATTR_MODE|ATTR_UID|ATTR_GID;
218 mutex_lock(&d_inode(dentry)->i_mutex);
219 notify_change(dentry, &newattrs, NULL);
220 mutex_unlock(&d_inode(dentry)->i_mutex);
221
222 /* mark as kernel-created inode */
223 d_inode(dentry)->i_private = &thread;
224 }
225 done_path_create(&path, dentry);
226 return err;
227 }
228
dev_rmdir(const char * name)229 static int dev_rmdir(const char *name)
230 {
231 struct path parent;
232 struct dentry *dentry;
233 int err;
234
235 dentry = kern_path_locked(name, &parent);
236 if (IS_ERR(dentry))
237 return PTR_ERR(dentry);
238 if (d_really_is_positive(dentry)) {
239 if (d_inode(dentry)->i_private == &thread)
240 err = vfs_rmdir(d_inode(parent.dentry), dentry);
241 else
242 err = -EPERM;
243 } else {
244 err = -ENOENT;
245 }
246 dput(dentry);
247 mutex_unlock(&d_inode(parent.dentry)->i_mutex);
248 path_put(&parent);
249 return err;
250 }
251
delete_path(const char * nodepath)252 static int delete_path(const char *nodepath)
253 {
254 const char *path;
255 int err = 0;
256
257 path = kstrdup(nodepath, GFP_KERNEL);
258 if (!path)
259 return -ENOMEM;
260
261 for (;;) {
262 char *base;
263
264 base = strrchr(path, '/');
265 if (!base)
266 break;
267 base[0] = '\0';
268 err = dev_rmdir(path);
269 if (err)
270 break;
271 }
272
273 kfree(path);
274 return err;
275 }
276
dev_mynode(struct device * dev,struct inode * inode,struct kstat * stat)277 static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
278 {
279 /* did we create it */
280 if (inode->i_private != &thread)
281 return 0;
282
283 /* does the dev_t match */
284 if (is_blockdev(dev)) {
285 if (!S_ISBLK(stat->mode))
286 return 0;
287 } else {
288 if (!S_ISCHR(stat->mode))
289 return 0;
290 }
291 if (stat->rdev != dev->devt)
292 return 0;
293
294 /* ours */
295 return 1;
296 }
297
handle_remove(const char * nodename,struct device * dev)298 static int handle_remove(const char *nodename, struct device *dev)
299 {
300 struct path parent;
301 struct dentry *dentry;
302 int deleted = 0;
303 int err;
304
305 dentry = kern_path_locked(nodename, &parent);
306 if (IS_ERR(dentry))
307 return PTR_ERR(dentry);
308
309 if (d_really_is_positive(dentry)) {
310 struct kstat stat;
311 struct path p = {.mnt = parent.mnt, .dentry = dentry};
312 err = vfs_getattr(&p, &stat);
313 if (!err && dev_mynode(dev, d_inode(dentry), &stat)) {
314 struct iattr newattrs;
315 /*
316 * before unlinking this node, reset permissions
317 * of possible references like hardlinks
318 */
319 newattrs.ia_uid = GLOBAL_ROOT_UID;
320 newattrs.ia_gid = GLOBAL_ROOT_GID;
321 newattrs.ia_mode = stat.mode & ~0777;
322 newattrs.ia_valid =
323 ATTR_UID|ATTR_GID|ATTR_MODE;
324 mutex_lock(&d_inode(dentry)->i_mutex);
325 notify_change(dentry, &newattrs, NULL);
326 mutex_unlock(&d_inode(dentry)->i_mutex);
327 err = vfs_unlink(d_inode(parent.dentry), dentry, NULL);
328 if (!err || err == -ENOENT)
329 deleted = 1;
330 }
331 } else {
332 err = -ENOENT;
333 }
334 dput(dentry);
335 mutex_unlock(&d_inode(parent.dentry)->i_mutex);
336
337 path_put(&parent);
338 if (deleted && strchr(nodename, '/'))
339 delete_path(nodename);
340 return err;
341 }
342
343 /*
344 * If configured, or requested by the commandline, devtmpfs will be
345 * auto-mounted after the kernel mounted the root filesystem.
346 */
devtmpfs_mount(const char * mntdir)347 int devtmpfs_mount(const char *mntdir)
348 {
349 int err;
350
351 if (!mount_dev)
352 return 0;
353
354 if (!thread)
355 return 0;
356
357 err = sys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT, NULL);
358 if (err)
359 printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
360 else
361 printk(KERN_INFO "devtmpfs: mounted\n");
362 return err;
363 }
364
365 static DECLARE_COMPLETION(setup_done);
366
handle(const char * name,umode_t mode,kuid_t uid,kgid_t gid,struct device * dev)367 static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
368 struct device *dev)
369 {
370 if (mode)
371 return handle_create(name, mode, uid, gid, dev);
372 else
373 return handle_remove(name, dev);
374 }
375
devtmpfsd(void * p)376 static int devtmpfsd(void *p)
377 {
378 char options[] = "mode=0755";
379 int *err = p;
380 *err = sys_unshare(CLONE_NEWNS);
381 if (*err)
382 goto out;
383 *err = sys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, options);
384 if (*err)
385 goto out;
386 sys_chdir("/.."); /* will traverse into overmounted root */
387 sys_chroot(".");
388 complete(&setup_done);
389 while (1) {
390 spin_lock(&req_lock);
391 while (requests) {
392 struct req *req = requests;
393 requests = NULL;
394 spin_unlock(&req_lock);
395 while (req) {
396 struct req *next = req->next;
397 req->err = handle(req->name, req->mode,
398 req->uid, req->gid, req->dev);
399 complete(&req->done);
400 req = next;
401 }
402 spin_lock(&req_lock);
403 }
404 __set_current_state(TASK_INTERRUPTIBLE);
405 spin_unlock(&req_lock);
406 schedule();
407 }
408 return 0;
409 out:
410 complete(&setup_done);
411 return *err;
412 }
413
414 /*
415 * Create devtmpfs instance, driver-core devices will add their device
416 * nodes here.
417 */
devtmpfs_init(void)418 int __init devtmpfs_init(void)
419 {
420 int err = register_filesystem(&dev_fs_type);
421 if (err) {
422 printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
423 "type %i\n", err);
424 return err;
425 }
426
427 thread = kthread_run(devtmpfsd, &err, "kdevtmpfs");
428 if (!IS_ERR(thread)) {
429 wait_for_completion(&setup_done);
430 } else {
431 err = PTR_ERR(thread);
432 thread = NULL;
433 }
434
435 if (err) {
436 printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
437 unregister_filesystem(&dev_fs_type);
438 return err;
439 }
440
441 printk(KERN_INFO "devtmpfs: initialized\n");
442 return 0;
443 }
444