1 /*
2 * device_cgroup.c - device cgroup subsystem
3 *
4 * Copyright 2007 IBM Corp
5 */
6
7 #include <linux/device_cgroup.h>
8 #include <linux/cgroup.h>
9 #include <linux/ctype.h>
10 #include <linux/list.h>
11 #include <linux/uaccess.h>
12 #include <linux/seq_file.h>
13 #include <linux/rcupdate.h>
14 #include <linux/mutex.h>
15
16 #define ACC_MKNOD 1
17 #define ACC_READ 2
18 #define ACC_WRITE 4
19 #define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
20
21 #define DEV_BLOCK 1
22 #define DEV_CHAR 2
23 #define DEV_ALL 4 /* this represents all devices */
24
25 static DEFINE_MUTEX(devcgroup_mutex);
26
27 /*
28 * whitelist locking rules:
29 * hold devcgroup_mutex for update/read.
30 * hold rcu_read_lock() for read.
31 */
32
33 struct dev_whitelist_item {
34 u32 major, minor;
35 short type;
36 short access;
37 struct list_head list;
38 struct rcu_head rcu;
39 };
40
41 struct dev_cgroup {
42 struct cgroup_subsys_state css;
43 struct list_head whitelist;
44 };
45
46 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
47 {
48 return container_of(s, struct dev_cgroup, css);
49 }
50
51 static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
52 {
53 return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));
54 }
55
56 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
57 {
58 return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
59 }
60
61 struct cgroup_subsys devices_subsys;
62
63 static int devcgroup_can_attach(struct cgroup_subsys *ss,
64 struct cgroup *new_cgroup, struct task_struct *task)
65 {
66 if (current != task && !capable(CAP_SYS_ADMIN))
67 return -EPERM;
68
69 return 0;
70 }
71
72 /*
73 * called under devcgroup_mutex
74 */
75 static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)
76 {
77 struct dev_whitelist_item *wh, *tmp, *new;
78
79 list_for_each_entry(wh, orig, list) {
80 new = kmemdup(wh, sizeof(*wh), GFP_KERNEL);
81 if (!new)
82 goto free_and_exit;
83 list_add_tail(&new->list, dest);
84 }
85
86 return 0;
87
88 free_and_exit:
89 list_for_each_entry_safe(wh, tmp, dest, list) {
90 list_del(&wh->list);
91 kfree(wh);
92 }
93 return -ENOMEM;
94 }
95
96 /* Stupid prototype - don't bother combining existing entries */
97 /*
98 * called under devcgroup_mutex
99 */
100 static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
101 struct dev_whitelist_item *wh)
102 {
103 struct dev_whitelist_item *whcopy, *walk;
104
105 whcopy = kmemdup(wh, sizeof(*wh), GFP_KERNEL);
106 if (!whcopy)
107 return -ENOMEM;
108
109 list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
110 if (walk->type != wh->type)
111 continue;
112 if (walk->major != wh->major)
113 continue;
114 if (walk->minor != wh->minor)
115 continue;
116
117 walk->access |= wh->access;
118 kfree(whcopy);
119 whcopy = NULL;
120 }
121
122 if (whcopy != NULL)
123 list_add_tail_rcu(&whcopy->list, &dev_cgroup->whitelist);
124 return 0;
125 }
126
127 static void whitelist_item_free(struct rcu_head *rcu)
128 {
129 struct dev_whitelist_item *item;
130
131 item = container_of(rcu, struct dev_whitelist_item, rcu);
132 kfree(item);
133 }
134
135 /*
136 * called under devcgroup_mutex
137 */
138 static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
139 struct dev_whitelist_item *wh)
140 {
141 struct dev_whitelist_item *walk, *tmp;
142
143 list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
144 if (walk->type == DEV_ALL)
145 goto remove;
146 if (walk->type != wh->type)
147 continue;
148 if (walk->major != ~0 && walk->major != wh->major)
149 continue;
150 if (walk->minor != ~0 && walk->minor != wh->minor)
151 continue;
152
153 remove:
154 walk->access &= ~wh->access;
155 if (!walk->access) {
156 list_del_rcu(&walk->list);
157 call_rcu(&walk->rcu, whitelist_item_free);
158 }
159 }
160 }
161
162 /*
163 * called from kernel/cgroup.c with cgroup_lock() held.
164 */
165 static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss,
166 struct cgroup *cgroup)
167 {
168 struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
169 struct cgroup *parent_cgroup;
170 int ret;
171
172 dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
173 if (!dev_cgroup)
174 return ERR_PTR(-ENOMEM);
175 INIT_LIST_HEAD(&dev_cgroup->whitelist);
176 parent_cgroup = cgroup->parent;
177
178 if (parent_cgroup == NULL) {
179 struct dev_whitelist_item *wh;
180 wh = kmalloc(sizeof(*wh), GFP_KERNEL);
181 if (!wh) {
182 kfree(dev_cgroup);
183 return ERR_PTR(-ENOMEM);
184 }
185 wh->minor = wh->major = ~0;
186 wh->type = DEV_ALL;
187 wh->access = ACC_MASK;
188 list_add(&wh->list, &dev_cgroup->whitelist);
189 } else {
190 parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
191 mutex_lock(&devcgroup_mutex);
192 ret = dev_whitelist_copy(&dev_cgroup->whitelist,
193 &parent_dev_cgroup->whitelist);
194 mutex_unlock(&devcgroup_mutex);
195 if (ret) {
196 kfree(dev_cgroup);
197 return ERR_PTR(ret);
198 }
199 }
200
201 return &dev_cgroup->css;
202 }
203
204 static void devcgroup_destroy(struct cgroup_subsys *ss,
205 struct cgroup *cgroup)
206 {
207 struct dev_cgroup *dev_cgroup;
208 struct dev_whitelist_item *wh, *tmp;
209
210 dev_cgroup = cgroup_to_devcgroup(cgroup);
211 list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
212 list_del(&wh->list);
213 kfree(wh);
214 }
215 kfree(dev_cgroup);
216 }
217
218 #define DEVCG_ALLOW 1
219 #define DEVCG_DENY 2
220 #define DEVCG_LIST 3
221
222 #define MAJMINLEN 13
223 #define ACCLEN 4
224
225 static void set_access(char *acc, short access)
226 {
227 int idx = 0;
228 memset(acc, 0, ACCLEN);
229 if (access & ACC_READ)
230 acc[idx++] = 'r';
231 if (access & ACC_WRITE)
232 acc[idx++] = 'w';
233 if (access & ACC_MKNOD)
234 acc[idx++] = 'm';
235 }
236
237 static char type_to_char(short type)
238 {
239 if (type == DEV_ALL)
240 return 'a';
241 if (type == DEV_CHAR)
242 return 'c';
243 if (type == DEV_BLOCK)
244 return 'b';
245 return 'X';
246 }
247
248 static void set_majmin(char *str, unsigned m)
249 {
250 if (m == ~0)
251 strcpy(str, "*");
252 else
253 sprintf(str, "%u", m);
254 }
255
256 static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
257 struct seq_file *m)
258 {
259 struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
260 struct dev_whitelist_item *wh;
261 char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
262
263 rcu_read_lock();
264 list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) {
265 set_access(acc, wh->access);
266 set_majmin(maj, wh->major);
267 set_majmin(min, wh->minor);
268 seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type),
269 maj, min, acc);
270 }
271 rcu_read_unlock();
272
273 return 0;
274 }
275
276 /*
277 * may_access_whitelist:
278 * does the access granted to dev_cgroup c contain the access
279 * requested in whitelist item refwh.
280 * return 1 if yes, 0 if no.
281 * call with devcgroup_mutex held
282 */
283 static int may_access_whitelist(struct dev_cgroup *c,
284 struct dev_whitelist_item *refwh)
285 {
286 struct dev_whitelist_item *whitem;
287
288 list_for_each_entry(whitem, &c->whitelist, list) {
289 if (whitem->type & DEV_ALL)
290 return 1;
291 if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
292 continue;
293 if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
294 continue;
295 if (whitem->major != ~0 && whitem->major != refwh->major)
296 continue;
297 if (whitem->minor != ~0 && whitem->minor != refwh->minor)
298 continue;
299 if (refwh->access & (~whitem->access))
300 continue;
301 return 1;
302 }
303 return 0;
304 }
305
306 /*
307 * parent_has_perm:
308 * when adding a new allow rule to a device whitelist, the rule
309 * must be allowed in the parent device
310 */
311 static int parent_has_perm(struct dev_cgroup *childcg,
312 struct dev_whitelist_item *wh)
313 {
314 struct cgroup *pcg = childcg->css.cgroup->parent;
315 struct dev_cgroup *parent;
316
317 if (!pcg)
318 return 1;
319 parent = cgroup_to_devcgroup(pcg);
320 return may_access_whitelist(parent, wh);
321 }
322
323 /*
324 * Modify the whitelist using allow/deny rules.
325 * CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD
326 * so we can give a container CAP_MKNOD to let it create devices but not
327 * modify the whitelist.
328 * It seems likely we'll want to add a CAP_CONTAINER capability to allow
329 * us to also grant CAP_SYS_ADMIN to containers without giving away the
330 * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN
331 *
332 * Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting
333 * new access is only allowed if you're in the top-level cgroup, or your
334 * parent cgroup has the access you're asking for.
335 */
336 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
337 int filetype, const char *buffer)
338 {
339 const char *b;
340 char *endp;
341 int count;
342 struct dev_whitelist_item wh;
343
344 if (!capable(CAP_SYS_ADMIN))
345 return -EPERM;
346
347 memset(&wh, 0, sizeof(wh));
348 b = buffer;
349
350 switch (*b) {
351 case 'a':
352 wh.type = DEV_ALL;
353 wh.access = ACC_MASK;
354 wh.major = ~0;
355 wh.minor = ~0;
356 goto handle;
357 case 'b':
358 wh.type = DEV_BLOCK;
359 break;
360 case 'c':
361 wh.type = DEV_CHAR;
362 break;
363 default:
364 return -EINVAL;
365 }
366 b++;
367 if (!isspace(*b))
368 return -EINVAL;
369 b++;
370 if (*b == '*') {
371 wh.major = ~0;
372 b++;
373 } else if (isdigit(*b)) {
374 wh.major = simple_strtoul(b, &endp, 10);
375 b = endp;
376 } else {
377 return -EINVAL;
378 }
379 if (*b != ':')
380 return -EINVAL;
381 b++;
382
383 /* read minor */
384 if (*b == '*') {
385 wh.minor = ~0;
386 b++;
387 } else if (isdigit(*b)) {
388 wh.minor = simple_strtoul(b, &endp, 10);
389 b = endp;
390 } else {
391 return -EINVAL;
392 }
393 if (!isspace(*b))
394 return -EINVAL;
395 for (b++, count = 0; count < 3; count++, b++) {
396 switch (*b) {
397 case 'r':
398 wh.access |= ACC_READ;
399 break;
400 case 'w':
401 wh.access |= ACC_WRITE;
402 break;
403 case 'm':
404 wh.access |= ACC_MKNOD;
405 break;
406 case '\n':
407 case '\0':
408 count = 3;
409 break;
410 default:
411 return -EINVAL;
412 }
413 }
414
415 handle:
416 switch (filetype) {
417 case DEVCG_ALLOW:
418 if (!parent_has_perm(devcgroup, &wh))
419 return -EPERM;
420 return dev_whitelist_add(devcgroup, &wh);
421 case DEVCG_DENY:
422 dev_whitelist_rm(devcgroup, &wh);
423 break;
424 default:
425 return -EINVAL;
426 }
427 return 0;
428 }
429
430 static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
431 const char *buffer)
432 {
433 int retval;
434
435 mutex_lock(&devcgroup_mutex);
436 retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
437 cft->private, buffer);
438 mutex_unlock(&devcgroup_mutex);
439 return retval;
440 }
441
442 static struct cftype dev_cgroup_files[] = {
443 {
444 .name = "allow",
445 .write_string = devcgroup_access_write,
446 .private = DEVCG_ALLOW,
447 },
448 {
449 .name = "deny",
450 .write_string = devcgroup_access_write,
451 .private = DEVCG_DENY,
452 },
453 {
454 .name = "list",
455 .read_seq_string = devcgroup_seq_read,
456 .private = DEVCG_LIST,
457 },
458 };
459
460 static int devcgroup_populate(struct cgroup_subsys *ss,
461 struct cgroup *cgroup)
462 {
463 return cgroup_add_files(cgroup, ss, dev_cgroup_files,
464 ARRAY_SIZE(dev_cgroup_files));
465 }
466
467 struct cgroup_subsys devices_subsys = {
468 .name = "devices",
469 .can_attach = devcgroup_can_attach,
470 .create = devcgroup_create,
471 .destroy = devcgroup_destroy,
472 .populate = devcgroup_populate,
473 .subsys_id = devices_subsys_id,
474 };
475
476 int devcgroup_inode_permission(struct inode *inode, int mask)
477 {
478 struct dev_cgroup *dev_cgroup;
479 struct dev_whitelist_item *wh;
480
481 dev_t device = inode->i_rdev;
482 if (!device)
483 return 0;
484 if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
485 return 0;
486
487 rcu_read_lock();
488
489 dev_cgroup = task_devcgroup(current);
490
491 list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
492 if (wh->type & DEV_ALL)
493 goto found;
494 if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode))
495 continue;
496 if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
497 continue;
498 if (wh->major != ~0 && wh->major != imajor(inode))
499 continue;
500 if (wh->minor != ~0 && wh->minor != iminor(inode))
501 continue;
502
503 if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
504 continue;
505 if ((mask & MAY_READ) && !(wh->access & ACC_READ))
506 continue;
507 found:
508 rcu_read_unlock();
509 return 0;
510 }
511
512 rcu_read_unlock();
513
514 return -EPERM;
515 }
516
517 int devcgroup_inode_mknod(int mode, dev_t dev)
518 {
519 struct dev_cgroup *dev_cgroup;
520 struct dev_whitelist_item *wh;
521
522 if (!S_ISBLK(mode) && !S_ISCHR(mode))
523 return 0;
524
525 rcu_read_lock();
526
527 dev_cgroup = task_devcgroup(current);
528
529 list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
530 if (wh->type & DEV_ALL)
531 goto found;
532 if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
533 continue;
534 if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
535 continue;
536 if (wh->major != ~0 && wh->major != MAJOR(dev))
537 continue;
538 if (wh->minor != ~0 && wh->minor != MINOR(dev))
539 continue;
540
541 if (!(wh->access & ACC_MKNOD))
542 continue;
543 found:
544 rcu_read_unlock();
545 return 0;
546 }
547
548 rcu_read_unlock();
549
550 return -EPERM;
551 }
552
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