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/slab.h>
14 #include <linux/rcupdate.h>
15 #include <linux/mutex.h>
16
17 #define ACC_MKNOD 1
18 #define ACC_READ 2
19 #define ACC_WRITE 4
20 #define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
21
22 #define DEV_BLOCK 1
23 #define DEV_CHAR 2
24 #define DEV_ALL 4 /* this represents all devices */
25
26 static DEFINE_MUTEX(devcgroup_mutex);
27
28 enum devcg_behavior {
29 DEVCG_DEFAULT_NONE,
30 DEVCG_DEFAULT_ALLOW,
31 DEVCG_DEFAULT_DENY,
32 };
33
34 /*
35 * exception list locking rules:
36 * hold devcgroup_mutex for update/read.
37 * hold rcu_read_lock() for read.
38 */
39
40 struct dev_exception_item {
41 u32 major, minor;
42 short type;
43 short access;
44 struct list_head list;
45 struct rcu_head rcu;
46 };
47
48 struct dev_cgroup {
49 struct cgroup_subsys_state css;
50 struct list_head exceptions;
51 enum devcg_behavior behavior;
52 };
53
css_to_devcgroup(struct cgroup_subsys_state * s)54 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
55 {
56 return s ? container_of(s, struct dev_cgroup, css) : NULL;
57 }
58
task_devcgroup(struct task_struct * task)59 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
60 {
61 return css_to_devcgroup(task_css(task, devices_cgrp_id));
62 }
63
64 /*
65 * called under devcgroup_mutex
66 */
dev_exceptions_copy(struct list_head * dest,struct list_head * orig)67 static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
68 {
69 struct dev_exception_item *ex, *tmp, *new;
70
71 lockdep_assert_held(&devcgroup_mutex);
72
73 list_for_each_entry(ex, orig, list) {
74 new = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
75 if (!new)
76 goto free_and_exit;
77 list_add_tail(&new->list, dest);
78 }
79
80 return 0;
81
82 free_and_exit:
83 list_for_each_entry_safe(ex, tmp, dest, list) {
84 list_del(&ex->list);
85 kfree(ex);
86 }
87 return -ENOMEM;
88 }
89
90 /*
91 * called under devcgroup_mutex
92 */
dev_exception_add(struct dev_cgroup * dev_cgroup,struct dev_exception_item * ex)93 static int dev_exception_add(struct dev_cgroup *dev_cgroup,
94 struct dev_exception_item *ex)
95 {
96 struct dev_exception_item *excopy, *walk;
97
98 lockdep_assert_held(&devcgroup_mutex);
99
100 excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
101 if (!excopy)
102 return -ENOMEM;
103
104 list_for_each_entry(walk, &dev_cgroup->exceptions, list) {
105 if (walk->type != ex->type)
106 continue;
107 if (walk->major != ex->major)
108 continue;
109 if (walk->minor != ex->minor)
110 continue;
111
112 walk->access |= ex->access;
113 kfree(excopy);
114 excopy = NULL;
115 }
116
117 if (excopy != NULL)
118 list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions);
119 return 0;
120 }
121
122 /*
123 * called under devcgroup_mutex
124 */
dev_exception_rm(struct dev_cgroup * dev_cgroup,struct dev_exception_item * ex)125 static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
126 struct dev_exception_item *ex)
127 {
128 struct dev_exception_item *walk, *tmp;
129
130 lockdep_assert_held(&devcgroup_mutex);
131
132 list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
133 if (walk->type != ex->type)
134 continue;
135 if (walk->major != ex->major)
136 continue;
137 if (walk->minor != ex->minor)
138 continue;
139
140 walk->access &= ~ex->access;
141 if (!walk->access) {
142 list_del_rcu(&walk->list);
143 kfree_rcu(walk, rcu);
144 }
145 }
146 }
147
__dev_exception_clean(struct dev_cgroup * dev_cgroup)148 static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
149 {
150 struct dev_exception_item *ex, *tmp;
151
152 list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
153 list_del_rcu(&ex->list);
154 kfree_rcu(ex, rcu);
155 }
156 }
157
158 /**
159 * dev_exception_clean - frees all entries of the exception list
160 * @dev_cgroup: dev_cgroup with the exception list to be cleaned
161 *
162 * called under devcgroup_mutex
163 */
dev_exception_clean(struct dev_cgroup * dev_cgroup)164 static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
165 {
166 lockdep_assert_held(&devcgroup_mutex);
167
168 __dev_exception_clean(dev_cgroup);
169 }
170
is_devcg_online(const struct dev_cgroup * devcg)171 static inline bool is_devcg_online(const struct dev_cgroup *devcg)
172 {
173 return (devcg->behavior != DEVCG_DEFAULT_NONE);
174 }
175
176 /**
177 * devcgroup_online - initializes devcgroup's behavior and exceptions based on
178 * parent's
179 * @css: css getting online
180 * returns 0 in case of success, error code otherwise
181 */
devcgroup_online(struct cgroup_subsys_state * css)182 static int devcgroup_online(struct cgroup_subsys_state *css)
183 {
184 struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
185 struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css->parent);
186 int ret = 0;
187
188 mutex_lock(&devcgroup_mutex);
189
190 if (parent_dev_cgroup == NULL)
191 dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
192 else {
193 ret = dev_exceptions_copy(&dev_cgroup->exceptions,
194 &parent_dev_cgroup->exceptions);
195 if (!ret)
196 dev_cgroup->behavior = parent_dev_cgroup->behavior;
197 }
198 mutex_unlock(&devcgroup_mutex);
199
200 return ret;
201 }
202
devcgroup_offline(struct cgroup_subsys_state * css)203 static void devcgroup_offline(struct cgroup_subsys_state *css)
204 {
205 struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
206
207 mutex_lock(&devcgroup_mutex);
208 dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
209 mutex_unlock(&devcgroup_mutex);
210 }
211
212 /*
213 * called from kernel/cgroup.c with cgroup_lock() held.
214 */
215 static struct cgroup_subsys_state *
devcgroup_css_alloc(struct cgroup_subsys_state * parent_css)216 devcgroup_css_alloc(struct cgroup_subsys_state *parent_css)
217 {
218 struct dev_cgroup *dev_cgroup;
219
220 dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
221 if (!dev_cgroup)
222 return ERR_PTR(-ENOMEM);
223 INIT_LIST_HEAD(&dev_cgroup->exceptions);
224 dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
225
226 return &dev_cgroup->css;
227 }
228
devcgroup_css_free(struct cgroup_subsys_state * css)229 static void devcgroup_css_free(struct cgroup_subsys_state *css)
230 {
231 struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
232
233 __dev_exception_clean(dev_cgroup);
234 kfree(dev_cgroup);
235 }
236
237 #define DEVCG_ALLOW 1
238 #define DEVCG_DENY 2
239 #define DEVCG_LIST 3
240
241 #define MAJMINLEN 13
242 #define ACCLEN 4
243
set_access(char * acc,short access)244 static void set_access(char *acc, short access)
245 {
246 int idx = 0;
247 memset(acc, 0, ACCLEN);
248 if (access & ACC_READ)
249 acc[idx++] = 'r';
250 if (access & ACC_WRITE)
251 acc[idx++] = 'w';
252 if (access & ACC_MKNOD)
253 acc[idx++] = 'm';
254 }
255
type_to_char(short type)256 static char type_to_char(short type)
257 {
258 if (type == DEV_ALL)
259 return 'a';
260 if (type == DEV_CHAR)
261 return 'c';
262 if (type == DEV_BLOCK)
263 return 'b';
264 return 'X';
265 }
266
set_majmin(char * str,unsigned m)267 static void set_majmin(char *str, unsigned m)
268 {
269 if (m == ~0)
270 strcpy(str, "*");
271 else
272 sprintf(str, "%u", m);
273 }
274
devcgroup_seq_show(struct seq_file * m,void * v)275 static int devcgroup_seq_show(struct seq_file *m, void *v)
276 {
277 struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m));
278 struct dev_exception_item *ex;
279 char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
280
281 rcu_read_lock();
282 /*
283 * To preserve the compatibility:
284 * - Only show the "all devices" when the default policy is to allow
285 * - List the exceptions in case the default policy is to deny
286 * This way, the file remains as a "whitelist of devices"
287 */
288 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
289 set_access(acc, ACC_MASK);
290 set_majmin(maj, ~0);
291 set_majmin(min, ~0);
292 seq_printf(m, "%c %s:%s %s\n", type_to_char(DEV_ALL),
293 maj, min, acc);
294 } else {
295 list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
296 set_access(acc, ex->access);
297 set_majmin(maj, ex->major);
298 set_majmin(min, ex->minor);
299 seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
300 maj, min, acc);
301 }
302 }
303 rcu_read_unlock();
304
305 return 0;
306 }
307
308 /**
309 * match_exception - iterates the exception list trying to find a complete match
310 * @exceptions: list of exceptions
311 * @type: device type (DEV_BLOCK or DEV_CHAR)
312 * @major: device file major number, ~0 to match all
313 * @minor: device file minor number, ~0 to match all
314 * @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD)
315 *
316 * It is considered a complete match if an exception is found that will
317 * contain the entire range of provided parameters.
318 *
319 * Return: true in case it matches an exception completely
320 */
match_exception(struct list_head * exceptions,short type,u32 major,u32 minor,short access)321 static bool match_exception(struct list_head *exceptions, short type,
322 u32 major, u32 minor, short access)
323 {
324 struct dev_exception_item *ex;
325
326 list_for_each_entry_rcu(ex, exceptions, list) {
327 if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
328 continue;
329 if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR))
330 continue;
331 if (ex->major != ~0 && ex->major != major)
332 continue;
333 if (ex->minor != ~0 && ex->minor != minor)
334 continue;
335 /* provided access cannot have more than the exception rule */
336 if (access & (~ex->access))
337 continue;
338 return true;
339 }
340 return false;
341 }
342
343 /**
344 * match_exception_partial - iterates the exception list trying to find a partial match
345 * @exceptions: list of exceptions
346 * @type: device type (DEV_BLOCK or DEV_CHAR)
347 * @major: device file major number, ~0 to match all
348 * @minor: device file minor number, ~0 to match all
349 * @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD)
350 *
351 * It is considered a partial match if an exception's range is found to
352 * contain *any* of the devices specified by provided parameters. This is
353 * used to make sure no extra access is being granted that is forbidden by
354 * any of the exception list.
355 *
356 * Return: true in case the provided range mat matches an exception completely
357 */
match_exception_partial(struct list_head * exceptions,short type,u32 major,u32 minor,short access)358 static bool match_exception_partial(struct list_head *exceptions, short type,
359 u32 major, u32 minor, short access)
360 {
361 struct dev_exception_item *ex;
362
363 list_for_each_entry_rcu(ex, exceptions, list) {
364 if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
365 continue;
366 if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR))
367 continue;
368 /*
369 * We must be sure that both the exception and the provided
370 * range aren't masking all devices
371 */
372 if (ex->major != ~0 && major != ~0 && ex->major != major)
373 continue;
374 if (ex->minor != ~0 && minor != ~0 && ex->minor != minor)
375 continue;
376 /*
377 * In order to make sure the provided range isn't matching
378 * an exception, all its access bits shouldn't match the
379 * exception's access bits
380 */
381 if (!(access & ex->access))
382 continue;
383 return true;
384 }
385 return false;
386 }
387
388 /**
389 * verify_new_ex - verifies if a new exception is allowed by parent cgroup's permissions
390 * @dev_cgroup: dev cgroup to be tested against
391 * @refex: new exception
392 * @behavior: behavior of the exception's dev_cgroup
393 *
394 * This is used to make sure a child cgroup won't have more privileges
395 * than its parent
396 */
verify_new_ex(struct dev_cgroup * dev_cgroup,struct dev_exception_item * refex,enum devcg_behavior behavior)397 static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
398 struct dev_exception_item *refex,
399 enum devcg_behavior behavior)
400 {
401 bool match = false;
402
403 RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
404 !lockdep_is_held(&devcgroup_mutex),
405 "device_cgroup:verify_new_ex called without proper synchronization");
406
407 if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
408 if (behavior == DEVCG_DEFAULT_ALLOW) {
409 /*
410 * new exception in the child doesn't matter, only
411 * adding extra restrictions
412 */
413 return true;
414 } else {
415 /*
416 * new exception in the child will add more devices
417 * that can be acessed, so it can't match any of
418 * parent's exceptions, even slightly
419 */
420 match = match_exception_partial(&dev_cgroup->exceptions,
421 refex->type,
422 refex->major,
423 refex->minor,
424 refex->access);
425
426 if (match)
427 return false;
428 return true;
429 }
430 } else {
431 /*
432 * Only behavior == DEVCG_DEFAULT_DENY allowed here, therefore
433 * the new exception will add access to more devices and must
434 * be contained completely in an parent's exception to be
435 * allowed
436 */
437 match = match_exception(&dev_cgroup->exceptions, refex->type,
438 refex->major, refex->minor,
439 refex->access);
440
441 if (match)
442 /* parent has an exception that matches the proposed */
443 return true;
444 else
445 return false;
446 }
447 return false;
448 }
449
450 /*
451 * parent_has_perm:
452 * when adding a new allow rule to a device exception list, the rule
453 * must be allowed in the parent device
454 */
parent_has_perm(struct dev_cgroup * childcg,struct dev_exception_item * ex)455 static int parent_has_perm(struct dev_cgroup *childcg,
456 struct dev_exception_item *ex)
457 {
458 struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
459
460 if (!parent)
461 return 1;
462 return verify_new_ex(parent, ex, childcg->behavior);
463 }
464
465 /**
466 * parent_allows_removal - verify if it's ok to remove an exception
467 * @childcg: child cgroup from where the exception will be removed
468 * @ex: exception being removed
469 *
470 * When removing an exception in cgroups with default ALLOW policy, it must
471 * be checked if removing it will give the child cgroup more access than the
472 * parent.
473 *
474 * Return: true if it's ok to remove exception, false otherwise
475 */
parent_allows_removal(struct dev_cgroup * childcg,struct dev_exception_item * ex)476 static bool parent_allows_removal(struct dev_cgroup *childcg,
477 struct dev_exception_item *ex)
478 {
479 struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
480
481 if (!parent)
482 return true;
483
484 /* It's always allowed to remove access to devices */
485 if (childcg->behavior == DEVCG_DEFAULT_DENY)
486 return true;
487
488 /*
489 * Make sure you're not removing part or a whole exception existing in
490 * the parent cgroup
491 */
492 return !match_exception_partial(&parent->exceptions, ex->type,
493 ex->major, ex->minor, ex->access);
494 }
495
496 /**
497 * may_allow_all - checks if it's possible to change the behavior to
498 * allow based on parent's rules.
499 * @parent: device cgroup's parent
500 * returns: != 0 in case it's allowed, 0 otherwise
501 */
may_allow_all(struct dev_cgroup * parent)502 static inline int may_allow_all(struct dev_cgroup *parent)
503 {
504 if (!parent)
505 return 1;
506 return parent->behavior == DEVCG_DEFAULT_ALLOW;
507 }
508
509 /**
510 * revalidate_active_exceptions - walks through the active exception list and
511 * revalidates the exceptions based on parent's
512 * behavior and exceptions. The exceptions that
513 * are no longer valid will be removed.
514 * Called with devcgroup_mutex held.
515 * @devcg: cgroup which exceptions will be checked
516 *
517 * This is one of the three key functions for hierarchy implementation.
518 * This function is responsible for re-evaluating all the cgroup's active
519 * exceptions due to a parent's exception change.
520 * Refer to Documentation/cgroups/devices.txt for more details.
521 */
revalidate_active_exceptions(struct dev_cgroup * devcg)522 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
523 {
524 struct dev_exception_item *ex;
525 struct list_head *this, *tmp;
526
527 list_for_each_safe(this, tmp, &devcg->exceptions) {
528 ex = container_of(this, struct dev_exception_item, list);
529 if (!parent_has_perm(devcg, ex))
530 dev_exception_rm(devcg, ex);
531 }
532 }
533
534 /**
535 * propagate_exception - propagates a new exception to the children
536 * @devcg_root: device cgroup that added a new exception
537 * @ex: new exception to be propagated
538 *
539 * returns: 0 in case of success, != 0 in case of error
540 */
propagate_exception(struct dev_cgroup * devcg_root,struct dev_exception_item * ex)541 static int propagate_exception(struct dev_cgroup *devcg_root,
542 struct dev_exception_item *ex)
543 {
544 struct cgroup_subsys_state *pos;
545 int rc = 0;
546
547 rcu_read_lock();
548
549 css_for_each_descendant_pre(pos, &devcg_root->css) {
550 struct dev_cgroup *devcg = css_to_devcgroup(pos);
551
552 /*
553 * Because devcgroup_mutex is held, no devcg will become
554 * online or offline during the tree walk (see on/offline
555 * methods), and online ones are safe to access outside RCU
556 * read lock without bumping refcnt.
557 */
558 if (pos == &devcg_root->css || !is_devcg_online(devcg))
559 continue;
560
561 rcu_read_unlock();
562
563 /*
564 * in case both root's behavior and devcg is allow, a new
565 * restriction means adding to the exception list
566 */
567 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
568 devcg->behavior == DEVCG_DEFAULT_ALLOW) {
569 rc = dev_exception_add(devcg, ex);
570 if (rc)
571 return rc;
572 } else {
573 /*
574 * in the other possible cases:
575 * root's behavior: allow, devcg's: deny
576 * root's behavior: deny, devcg's: deny
577 * the exception will be removed
578 */
579 dev_exception_rm(devcg, ex);
580 }
581 revalidate_active_exceptions(devcg);
582
583 rcu_read_lock();
584 }
585
586 rcu_read_unlock();
587 return rc;
588 }
589
590 /*
591 * Modify the exception list using allow/deny rules.
592 * CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD
593 * so we can give a container CAP_MKNOD to let it create devices but not
594 * modify the exception list.
595 * It seems likely we'll want to add a CAP_CONTAINER capability to allow
596 * us to also grant CAP_SYS_ADMIN to containers without giving away the
597 * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
598 *
599 * Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting
600 * new access is only allowed if you're in the top-level cgroup, or your
601 * parent cgroup has the access you're asking for.
602 */
devcgroup_update_access(struct dev_cgroup * devcgroup,int filetype,char * buffer)603 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
604 int filetype, char *buffer)
605 {
606 const char *b;
607 char temp[12]; /* 11 + 1 characters needed for a u32 */
608 int count, rc = 0;
609 struct dev_exception_item ex;
610 struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
611
612 if (!capable(CAP_SYS_ADMIN))
613 return -EPERM;
614
615 memset(&ex, 0, sizeof(ex));
616 b = buffer;
617
618 switch (*b) {
619 case 'a':
620 switch (filetype) {
621 case DEVCG_ALLOW:
622 if (css_has_online_children(&devcgroup->css))
623 return -EINVAL;
624
625 if (!may_allow_all(parent))
626 return -EPERM;
627 dev_exception_clean(devcgroup);
628 devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
629 if (!parent)
630 break;
631
632 rc = dev_exceptions_copy(&devcgroup->exceptions,
633 &parent->exceptions);
634 if (rc)
635 return rc;
636 break;
637 case DEVCG_DENY:
638 if (css_has_online_children(&devcgroup->css))
639 return -EINVAL;
640
641 dev_exception_clean(devcgroup);
642 devcgroup->behavior = DEVCG_DEFAULT_DENY;
643 break;
644 default:
645 return -EINVAL;
646 }
647 return 0;
648 case 'b':
649 ex.type = DEV_BLOCK;
650 break;
651 case 'c':
652 ex.type = DEV_CHAR;
653 break;
654 default:
655 return -EINVAL;
656 }
657 b++;
658 if (!isspace(*b))
659 return -EINVAL;
660 b++;
661 if (*b == '*') {
662 ex.major = ~0;
663 b++;
664 } else if (isdigit(*b)) {
665 memset(temp, 0, sizeof(temp));
666 for (count = 0; count < sizeof(temp) - 1; count++) {
667 temp[count] = *b;
668 b++;
669 if (!isdigit(*b))
670 break;
671 }
672 rc = kstrtou32(temp, 10, &ex.major);
673 if (rc)
674 return -EINVAL;
675 } else {
676 return -EINVAL;
677 }
678 if (*b != ':')
679 return -EINVAL;
680 b++;
681
682 /* read minor */
683 if (*b == '*') {
684 ex.minor = ~0;
685 b++;
686 } else if (isdigit(*b)) {
687 memset(temp, 0, sizeof(temp));
688 for (count = 0; count < sizeof(temp) - 1; count++) {
689 temp[count] = *b;
690 b++;
691 if (!isdigit(*b))
692 break;
693 }
694 rc = kstrtou32(temp, 10, &ex.minor);
695 if (rc)
696 return -EINVAL;
697 } else {
698 return -EINVAL;
699 }
700 if (!isspace(*b))
701 return -EINVAL;
702 for (b++, count = 0; count < 3; count++, b++) {
703 switch (*b) {
704 case 'r':
705 ex.access |= ACC_READ;
706 break;
707 case 'w':
708 ex.access |= ACC_WRITE;
709 break;
710 case 'm':
711 ex.access |= ACC_MKNOD;
712 break;
713 case '\n':
714 case '\0':
715 count = 3;
716 break;
717 default:
718 return -EINVAL;
719 }
720 }
721
722 switch (filetype) {
723 case DEVCG_ALLOW:
724 /*
725 * If the default policy is to allow by default, try to remove
726 * an matching exception instead. And be silent about it: we
727 * don't want to break compatibility
728 */
729 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
730 /* Check if the parent allows removing it first */
731 if (!parent_allows_removal(devcgroup, &ex))
732 return -EPERM;
733 dev_exception_rm(devcgroup, &ex);
734 break;
735 }
736
737 if (!parent_has_perm(devcgroup, &ex))
738 return -EPERM;
739 rc = dev_exception_add(devcgroup, &ex);
740 break;
741 case DEVCG_DENY:
742 /*
743 * If the default policy is to deny by default, try to remove
744 * an matching exception instead. And be silent about it: we
745 * don't want to break compatibility
746 */
747 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
748 dev_exception_rm(devcgroup, &ex);
749 else
750 rc = dev_exception_add(devcgroup, &ex);
751
752 if (rc)
753 break;
754 /* we only propagate new restrictions */
755 rc = propagate_exception(devcgroup, &ex);
756 break;
757 default:
758 rc = -EINVAL;
759 }
760 return rc;
761 }
762
devcgroup_access_write(struct kernfs_open_file * of,char * buf,size_t nbytes,loff_t off)763 static ssize_t devcgroup_access_write(struct kernfs_open_file *of,
764 char *buf, size_t nbytes, loff_t off)
765 {
766 int retval;
767
768 mutex_lock(&devcgroup_mutex);
769 retval = devcgroup_update_access(css_to_devcgroup(of_css(of)),
770 of_cft(of)->private, strstrip(buf));
771 mutex_unlock(&devcgroup_mutex);
772 return retval ?: nbytes;
773 }
774
775 static struct cftype dev_cgroup_files[] = {
776 {
777 .name = "allow",
778 .write = devcgroup_access_write,
779 .private = DEVCG_ALLOW,
780 },
781 {
782 .name = "deny",
783 .write = devcgroup_access_write,
784 .private = DEVCG_DENY,
785 },
786 {
787 .name = "list",
788 .seq_show = devcgroup_seq_show,
789 .private = DEVCG_LIST,
790 },
791 { } /* terminate */
792 };
793
794 struct cgroup_subsys devices_cgrp_subsys = {
795 .css_alloc = devcgroup_css_alloc,
796 .css_free = devcgroup_css_free,
797 .css_online = devcgroup_online,
798 .css_offline = devcgroup_offline,
799 .legacy_cftypes = dev_cgroup_files,
800 };
801
802 /**
803 * __devcgroup_check_permission - checks if an inode operation is permitted
804 * @dev_cgroup: the dev cgroup to be tested against
805 * @type: device type
806 * @major: device major number
807 * @minor: device minor number
808 * @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD
809 *
810 * returns 0 on success, -EPERM case the operation is not permitted
811 */
__devcgroup_check_permission(short type,u32 major,u32 minor,short access)812 static int __devcgroup_check_permission(short type, u32 major, u32 minor,
813 short access)
814 {
815 struct dev_cgroup *dev_cgroup;
816 bool rc;
817
818 rcu_read_lock();
819 dev_cgroup = task_devcgroup(current);
820 if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW)
821 /* Can't match any of the exceptions, even partially */
822 rc = !match_exception_partial(&dev_cgroup->exceptions,
823 type, major, minor, access);
824 else
825 /* Need to match completely one exception to be allowed */
826 rc = match_exception(&dev_cgroup->exceptions, type, major,
827 minor, access);
828 rcu_read_unlock();
829
830 if (!rc)
831 return -EPERM;
832
833 return 0;
834 }
835
__devcgroup_inode_permission(struct inode * inode,int mask)836 int __devcgroup_inode_permission(struct inode *inode, int mask)
837 {
838 short type, access = 0;
839
840 if (S_ISBLK(inode->i_mode))
841 type = DEV_BLOCK;
842 if (S_ISCHR(inode->i_mode))
843 type = DEV_CHAR;
844 if (mask & MAY_WRITE)
845 access |= ACC_WRITE;
846 if (mask & MAY_READ)
847 access |= ACC_READ;
848
849 return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
850 access);
851 }
852
devcgroup_inode_mknod(int mode,dev_t dev)853 int devcgroup_inode_mknod(int mode, dev_t dev)
854 {
855 short type;
856
857 if (!S_ISBLK(mode) && !S_ISCHR(mode))
858 return 0;
859
860 if (S_ISBLK(mode))
861 type = DEV_BLOCK;
862 else
863 type = DEV_CHAR;
864
865 return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
866 ACC_MKNOD);
867
868 }
869