1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * device_cgroup.c - device cgroup subsystem
4 *
5 * Copyright 2007 IBM Corp
6 */
7
8 #include <linux/bpf-cgroup.h>
9 #include <linux/device_cgroup.h>
10 #include <linux/cgroup.h>
11 #include <linux/ctype.h>
12 #include <linux/list.h>
13 #include <linux/uaccess.h>
14 #include <linux/seq_file.h>
15 #include <linux/slab.h>
16 #include <linux/rcupdate.h>
17 #include <linux/mutex.h>
18
19 #ifdef CONFIG_CGROUP_DEVICE
20
21 static DEFINE_MUTEX(devcgroup_mutex);
22
23 enum devcg_behavior {
24 DEVCG_DEFAULT_NONE,
25 DEVCG_DEFAULT_ALLOW,
26 DEVCG_DEFAULT_DENY,
27 };
28
29 /*
30 * exception list locking rules:
31 * hold devcgroup_mutex for update/read.
32 * hold rcu_read_lock() for read.
33 */
34
35 struct dev_exception_item {
36 u32 major, minor;
37 short type;
38 short access;
39 struct list_head list;
40 struct rcu_head rcu;
41 };
42
43 struct dev_cgroup {
44 struct cgroup_subsys_state css;
45 struct list_head exceptions;
46 enum devcg_behavior behavior;
47 };
48
css_to_devcgroup(struct cgroup_subsys_state * s)49 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
50 {
51 return s ? container_of(s, struct dev_cgroup, css) : NULL;
52 }
53
task_devcgroup(struct task_struct * task)54 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
55 {
56 return css_to_devcgroup(task_css(task, devices_cgrp_id));
57 }
58
59 /*
60 * called under devcgroup_mutex
61 */
dev_exceptions_copy(struct list_head * dest,struct list_head * orig)62 static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
63 {
64 struct dev_exception_item *ex, *tmp, *new;
65
66 lockdep_assert_held(&devcgroup_mutex);
67
68 list_for_each_entry(ex, orig, list) {
69 new = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
70 if (!new)
71 goto free_and_exit;
72 list_add_tail(&new->list, dest);
73 }
74
75 return 0;
76
77 free_and_exit:
78 list_for_each_entry_safe(ex, tmp, dest, list) {
79 list_del(&ex->list);
80 kfree(ex);
81 }
82 return -ENOMEM;
83 }
84
85 /*
86 * called under devcgroup_mutex
87 */
dev_exception_add(struct dev_cgroup * dev_cgroup,struct dev_exception_item * ex)88 static int dev_exception_add(struct dev_cgroup *dev_cgroup,
89 struct dev_exception_item *ex)
90 {
91 struct dev_exception_item *excopy, *walk;
92
93 lockdep_assert_held(&devcgroup_mutex);
94
95 excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
96 if (!excopy)
97 return -ENOMEM;
98
99 list_for_each_entry(walk, &dev_cgroup->exceptions, list) {
100 if (walk->type != ex->type)
101 continue;
102 if (walk->major != ex->major)
103 continue;
104 if (walk->minor != ex->minor)
105 continue;
106
107 walk->access |= ex->access;
108 kfree(excopy);
109 excopy = NULL;
110 }
111
112 if (excopy != NULL)
113 list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions);
114 return 0;
115 }
116
117 /*
118 * called under devcgroup_mutex
119 */
dev_exception_rm(struct dev_cgroup * dev_cgroup,struct dev_exception_item * ex)120 static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
121 struct dev_exception_item *ex)
122 {
123 struct dev_exception_item *walk, *tmp;
124
125 lockdep_assert_held(&devcgroup_mutex);
126
127 list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
128 if (walk->type != ex->type)
129 continue;
130 if (walk->major != ex->major)
131 continue;
132 if (walk->minor != ex->minor)
133 continue;
134
135 walk->access &= ~ex->access;
136 if (!walk->access) {
137 list_del_rcu(&walk->list);
138 kfree_rcu(walk, rcu);
139 }
140 }
141 }
142
__dev_exception_clean(struct dev_cgroup * dev_cgroup)143 static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
144 {
145 struct dev_exception_item *ex, *tmp;
146
147 list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
148 list_del_rcu(&ex->list);
149 kfree_rcu(ex, rcu);
150 }
151 }
152
153 /**
154 * dev_exception_clean - frees all entries of the exception list
155 * @dev_cgroup: dev_cgroup with the exception list to be cleaned
156 *
157 * called under devcgroup_mutex
158 */
dev_exception_clean(struct dev_cgroup * dev_cgroup)159 static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
160 {
161 lockdep_assert_held(&devcgroup_mutex);
162
163 __dev_exception_clean(dev_cgroup);
164 }
165
is_devcg_online(const struct dev_cgroup * devcg)166 static inline bool is_devcg_online(const struct dev_cgroup *devcg)
167 {
168 return (devcg->behavior != DEVCG_DEFAULT_NONE);
169 }
170
171 /**
172 * devcgroup_online - initializes devcgroup's behavior and exceptions based on
173 * parent's
174 * @css: css getting online
175 * returns 0 in case of success, error code otherwise
176 */
devcgroup_online(struct cgroup_subsys_state * css)177 static int devcgroup_online(struct cgroup_subsys_state *css)
178 {
179 struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
180 struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css->parent);
181 int ret = 0;
182
183 mutex_lock(&devcgroup_mutex);
184
185 if (parent_dev_cgroup == NULL)
186 dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
187 else {
188 ret = dev_exceptions_copy(&dev_cgroup->exceptions,
189 &parent_dev_cgroup->exceptions);
190 if (!ret)
191 dev_cgroup->behavior = parent_dev_cgroup->behavior;
192 }
193 mutex_unlock(&devcgroup_mutex);
194
195 return ret;
196 }
197
devcgroup_offline(struct cgroup_subsys_state * css)198 static void devcgroup_offline(struct cgroup_subsys_state *css)
199 {
200 struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
201
202 mutex_lock(&devcgroup_mutex);
203 dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
204 mutex_unlock(&devcgroup_mutex);
205 }
206
207 /*
208 * called from kernel/cgroup.c with cgroup_lock() held.
209 */
210 static struct cgroup_subsys_state *
devcgroup_css_alloc(struct cgroup_subsys_state * parent_css)211 devcgroup_css_alloc(struct cgroup_subsys_state *parent_css)
212 {
213 struct dev_cgroup *dev_cgroup;
214
215 dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
216 if (!dev_cgroup)
217 return ERR_PTR(-ENOMEM);
218 INIT_LIST_HEAD(&dev_cgroup->exceptions);
219 dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
220
221 return &dev_cgroup->css;
222 }
223
devcgroup_css_free(struct cgroup_subsys_state * css)224 static void devcgroup_css_free(struct cgroup_subsys_state *css)
225 {
226 struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
227
228 __dev_exception_clean(dev_cgroup);
229 kfree(dev_cgroup);
230 }
231
232 #define DEVCG_ALLOW 1
233 #define DEVCG_DENY 2
234 #define DEVCG_LIST 3
235
236 #define MAJMINLEN 13
237 #define ACCLEN 4
238
set_access(char * acc,short access)239 static void set_access(char *acc, short access)
240 {
241 int idx = 0;
242 memset(acc, 0, ACCLEN);
243 if (access & DEVCG_ACC_READ)
244 acc[idx++] = 'r';
245 if (access & DEVCG_ACC_WRITE)
246 acc[idx++] = 'w';
247 if (access & DEVCG_ACC_MKNOD)
248 acc[idx++] = 'm';
249 }
250
type_to_char(short type)251 static char type_to_char(short type)
252 {
253 if (type == DEVCG_DEV_ALL)
254 return 'a';
255 if (type == DEVCG_DEV_CHAR)
256 return 'c';
257 if (type == DEVCG_DEV_BLOCK)
258 return 'b';
259 return 'X';
260 }
261
set_majmin(char * str,unsigned m)262 static void set_majmin(char *str, unsigned m)
263 {
264 if (m == ~0)
265 strcpy(str, "*");
266 else
267 sprintf(str, "%u", m);
268 }
269
devcgroup_seq_show(struct seq_file * m,void * v)270 static int devcgroup_seq_show(struct seq_file *m, void *v)
271 {
272 struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m));
273 struct dev_exception_item *ex;
274 char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
275
276 rcu_read_lock();
277 /*
278 * To preserve the compatibility:
279 * - Only show the "all devices" when the default policy is to allow
280 * - List the exceptions in case the default policy is to deny
281 * This way, the file remains as a "whitelist of devices"
282 */
283 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
284 set_access(acc, DEVCG_ACC_MASK);
285 set_majmin(maj, ~0);
286 set_majmin(min, ~0);
287 seq_printf(m, "%c %s:%s %s\n", type_to_char(DEVCG_DEV_ALL),
288 maj, min, acc);
289 } else {
290 list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
291 set_access(acc, ex->access);
292 set_majmin(maj, ex->major);
293 set_majmin(min, ex->minor);
294 seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
295 maj, min, acc);
296 }
297 }
298 rcu_read_unlock();
299
300 return 0;
301 }
302
303 /**
304 * match_exception - iterates the exception list trying to find a complete match
305 * @exceptions: list of exceptions
306 * @type: device type (DEVCG_DEV_BLOCK or DEVCG_DEV_CHAR)
307 * @major: device file major number, ~0 to match all
308 * @minor: device file minor number, ~0 to match all
309 * @access: permission mask (DEVCG_ACC_READ, DEVCG_ACC_WRITE, DEVCG_ACC_MKNOD)
310 *
311 * It is considered a complete match if an exception is found that will
312 * contain the entire range of provided parameters.
313 *
314 * Return: true in case it matches an exception completely
315 */
match_exception(struct list_head * exceptions,short type,u32 major,u32 minor,short access)316 static bool match_exception(struct list_head *exceptions, short type,
317 u32 major, u32 minor, short access)
318 {
319 struct dev_exception_item *ex;
320
321 list_for_each_entry_rcu(ex, exceptions, list) {
322 if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
323 continue;
324 if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
325 continue;
326 if (ex->major != ~0 && ex->major != major)
327 continue;
328 if (ex->minor != ~0 && ex->minor != minor)
329 continue;
330 /* provided access cannot have more than the exception rule */
331 if (access & (~ex->access))
332 continue;
333 return true;
334 }
335 return false;
336 }
337
338 /**
339 * match_exception_partial - iterates the exception list trying to find a partial match
340 * @exceptions: list of exceptions
341 * @type: device type (DEVCG_DEV_BLOCK or DEVCG_DEV_CHAR)
342 * @major: device file major number, ~0 to match all
343 * @minor: device file minor number, ~0 to match all
344 * @access: permission mask (DEVCG_ACC_READ, DEVCG_ACC_WRITE, DEVCG_ACC_MKNOD)
345 *
346 * It is considered a partial match if an exception's range is found to
347 * contain *any* of the devices specified by provided parameters. This is
348 * used to make sure no extra access is being granted that is forbidden by
349 * any of the exception list.
350 *
351 * Return: true in case the provided range mat matches an exception completely
352 */
match_exception_partial(struct list_head * exceptions,short type,u32 major,u32 minor,short access)353 static bool match_exception_partial(struct list_head *exceptions, short type,
354 u32 major, u32 minor, short access)
355 {
356 struct dev_exception_item *ex;
357
358 list_for_each_entry_rcu(ex, exceptions, list,
359 lockdep_is_held(&devcgroup_mutex)) {
360 if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
361 continue;
362 if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))
363 continue;
364 /*
365 * We must be sure that both the exception and the provided
366 * range aren't masking all devices
367 */
368 if (ex->major != ~0 && major != ~0 && ex->major != major)
369 continue;
370 if (ex->minor != ~0 && minor != ~0 && ex->minor != minor)
371 continue;
372 /*
373 * In order to make sure the provided range isn't matching
374 * an exception, all its access bits shouldn't match the
375 * exception's access bits
376 */
377 if (!(access & ex->access))
378 continue;
379 return true;
380 }
381 return false;
382 }
383
384 /**
385 * verify_new_ex - verifies if a new exception is allowed by parent cgroup's permissions
386 * @dev_cgroup: dev cgroup to be tested against
387 * @refex: new exception
388 * @behavior: behavior of the exception's dev_cgroup
389 *
390 * This is used to make sure a child cgroup won't have more privileges
391 * than its parent
392 */
verify_new_ex(struct dev_cgroup * dev_cgroup,struct dev_exception_item * refex,enum devcg_behavior behavior)393 static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
394 struct dev_exception_item *refex,
395 enum devcg_behavior behavior)
396 {
397 bool match = false;
398
399 RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
400 !lockdep_is_held(&devcgroup_mutex),
401 "device_cgroup:verify_new_ex called without proper synchronization");
402
403 if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
404 if (behavior == DEVCG_DEFAULT_ALLOW) {
405 /*
406 * new exception in the child doesn't matter, only
407 * adding extra restrictions
408 */
409 return true;
410 } else {
411 /*
412 * new exception in the child will add more devices
413 * that can be acessed, so it can't match any of
414 * parent's exceptions, even slightly
415 */
416 match = match_exception_partial(&dev_cgroup->exceptions,
417 refex->type,
418 refex->major,
419 refex->minor,
420 refex->access);
421
422 if (match)
423 return false;
424 return true;
425 }
426 } else {
427 /*
428 * Only behavior == DEVCG_DEFAULT_DENY allowed here, therefore
429 * the new exception will add access to more devices and must
430 * be contained completely in an parent's exception to be
431 * allowed
432 */
433 match = match_exception(&dev_cgroup->exceptions, refex->type,
434 refex->major, refex->minor,
435 refex->access);
436
437 if (match)
438 /* parent has an exception that matches the proposed */
439 return true;
440 else
441 return false;
442 }
443 return false;
444 }
445
446 /*
447 * parent_has_perm:
448 * when adding a new allow rule to a device exception list, the rule
449 * must be allowed in the parent device
450 */
parent_has_perm(struct dev_cgroup * childcg,struct dev_exception_item * ex)451 static int parent_has_perm(struct dev_cgroup *childcg,
452 struct dev_exception_item *ex)
453 {
454 struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
455
456 if (!parent)
457 return 1;
458 return verify_new_ex(parent, ex, childcg->behavior);
459 }
460
461 /**
462 * parent_allows_removal - verify if it's ok to remove an exception
463 * @childcg: child cgroup from where the exception will be removed
464 * @ex: exception being removed
465 *
466 * When removing an exception in cgroups with default ALLOW policy, it must
467 * be checked if removing it will give the child cgroup more access than the
468 * parent.
469 *
470 * Return: true if it's ok to remove exception, false otherwise
471 */
parent_allows_removal(struct dev_cgroup * childcg,struct dev_exception_item * ex)472 static bool parent_allows_removal(struct dev_cgroup *childcg,
473 struct dev_exception_item *ex)
474 {
475 struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
476
477 if (!parent)
478 return true;
479
480 /* It's always allowed to remove access to devices */
481 if (childcg->behavior == DEVCG_DEFAULT_DENY)
482 return true;
483
484 /*
485 * Make sure you're not removing part or a whole exception existing in
486 * the parent cgroup
487 */
488 return !match_exception_partial(&parent->exceptions, ex->type,
489 ex->major, ex->minor, ex->access);
490 }
491
492 /**
493 * may_allow_all - checks if it's possible to change the behavior to
494 * allow based on parent's rules.
495 * @parent: device cgroup's parent
496 * returns: != 0 in case it's allowed, 0 otherwise
497 */
may_allow_all(struct dev_cgroup * parent)498 static inline int may_allow_all(struct dev_cgroup *parent)
499 {
500 if (!parent)
501 return 1;
502 return parent->behavior == DEVCG_DEFAULT_ALLOW;
503 }
504
505 /**
506 * revalidate_active_exceptions - walks through the active exception list and
507 * revalidates the exceptions based on parent's
508 * behavior and exceptions. The exceptions that
509 * are no longer valid will be removed.
510 * Called with devcgroup_mutex held.
511 * @devcg: cgroup which exceptions will be checked
512 *
513 * This is one of the three key functions for hierarchy implementation.
514 * This function is responsible for re-evaluating all the cgroup's active
515 * exceptions due to a parent's exception change.
516 * Refer to Documentation/admin-guide/cgroup-v1/devices.rst for more details.
517 */
revalidate_active_exceptions(struct dev_cgroup * devcg)518 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
519 {
520 struct dev_exception_item *ex;
521 struct list_head *this, *tmp;
522
523 list_for_each_safe(this, tmp, &devcg->exceptions) {
524 ex = container_of(this, struct dev_exception_item, list);
525 if (!parent_has_perm(devcg, ex))
526 dev_exception_rm(devcg, ex);
527 }
528 }
529
530 /**
531 * propagate_exception - propagates a new exception to the children
532 * @devcg_root: device cgroup that added a new exception
533 * @ex: new exception to be propagated
534 *
535 * returns: 0 in case of success, != 0 in case of error
536 */
propagate_exception(struct dev_cgroup * devcg_root,struct dev_exception_item * ex)537 static int propagate_exception(struct dev_cgroup *devcg_root,
538 struct dev_exception_item *ex)
539 {
540 struct cgroup_subsys_state *pos;
541 int rc = 0;
542
543 rcu_read_lock();
544
545 css_for_each_descendant_pre(pos, &devcg_root->css) {
546 struct dev_cgroup *devcg = css_to_devcgroup(pos);
547
548 /*
549 * Because devcgroup_mutex is held, no devcg will become
550 * online or offline during the tree walk (see on/offline
551 * methods), and online ones are safe to access outside RCU
552 * read lock without bumping refcnt.
553 */
554 if (pos == &devcg_root->css || !is_devcg_online(devcg))
555 continue;
556
557 rcu_read_unlock();
558
559 /*
560 * in case both root's behavior and devcg is allow, a new
561 * restriction means adding to the exception list
562 */
563 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
564 devcg->behavior == DEVCG_DEFAULT_ALLOW) {
565 rc = dev_exception_add(devcg, ex);
566 if (rc)
567 return rc;
568 } else {
569 /*
570 * in the other possible cases:
571 * root's behavior: allow, devcg's: deny
572 * root's behavior: deny, devcg's: deny
573 * the exception will be removed
574 */
575 dev_exception_rm(devcg, ex);
576 }
577 revalidate_active_exceptions(devcg);
578
579 rcu_read_lock();
580 }
581
582 rcu_read_unlock();
583 return rc;
584 }
585
586 /*
587 * Modify the exception list using allow/deny rules.
588 * CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD
589 * so we can give a container CAP_MKNOD to let it create devices but not
590 * modify the exception list.
591 * It seems likely we'll want to add a CAP_CONTAINER capability to allow
592 * us to also grant CAP_SYS_ADMIN to containers without giving away the
593 * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
594 *
595 * Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting
596 * new access is only allowed if you're in the top-level cgroup, or your
597 * parent cgroup has the access you're asking for.
598 */
devcgroup_update_access(struct dev_cgroup * devcgroup,int filetype,char * buffer)599 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
600 int filetype, char *buffer)
601 {
602 const char *b;
603 char temp[12]; /* 11 + 1 characters needed for a u32 */
604 int count, rc = 0;
605 struct dev_exception_item ex;
606 struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
607
608 if (!capable(CAP_SYS_ADMIN))
609 return -EPERM;
610
611 memset(&ex, 0, sizeof(ex));
612 b = buffer;
613
614 switch (*b) {
615 case 'a':
616 switch (filetype) {
617 case DEVCG_ALLOW:
618 if (css_has_online_children(&devcgroup->css))
619 return -EINVAL;
620
621 if (!may_allow_all(parent))
622 return -EPERM;
623 dev_exception_clean(devcgroup);
624 devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
625 if (!parent)
626 break;
627
628 rc = dev_exceptions_copy(&devcgroup->exceptions,
629 &parent->exceptions);
630 if (rc)
631 return rc;
632 break;
633 case DEVCG_DENY:
634 if (css_has_online_children(&devcgroup->css))
635 return -EINVAL;
636
637 dev_exception_clean(devcgroup);
638 devcgroup->behavior = DEVCG_DEFAULT_DENY;
639 break;
640 default:
641 return -EINVAL;
642 }
643 return 0;
644 case 'b':
645 ex.type = DEVCG_DEV_BLOCK;
646 break;
647 case 'c':
648 ex.type = DEVCG_DEV_CHAR;
649 break;
650 default:
651 return -EINVAL;
652 }
653 b++;
654 if (!isspace(*b))
655 return -EINVAL;
656 b++;
657 if (*b == '*') {
658 ex.major = ~0;
659 b++;
660 } else if (isdigit(*b)) {
661 memset(temp, 0, sizeof(temp));
662 for (count = 0; count < sizeof(temp) - 1; count++) {
663 temp[count] = *b;
664 b++;
665 if (!isdigit(*b))
666 break;
667 }
668 rc = kstrtou32(temp, 10, &ex.major);
669 if (rc)
670 return -EINVAL;
671 } else {
672 return -EINVAL;
673 }
674 if (*b != ':')
675 return -EINVAL;
676 b++;
677
678 /* read minor */
679 if (*b == '*') {
680 ex.minor = ~0;
681 b++;
682 } else if (isdigit(*b)) {
683 memset(temp, 0, sizeof(temp));
684 for (count = 0; count < sizeof(temp) - 1; count++) {
685 temp[count] = *b;
686 b++;
687 if (!isdigit(*b))
688 break;
689 }
690 rc = kstrtou32(temp, 10, &ex.minor);
691 if (rc)
692 return -EINVAL;
693 } else {
694 return -EINVAL;
695 }
696 if (!isspace(*b))
697 return -EINVAL;
698 for (b++, count = 0; count < 3; count++, b++) {
699 switch (*b) {
700 case 'r':
701 ex.access |= DEVCG_ACC_READ;
702 break;
703 case 'w':
704 ex.access |= DEVCG_ACC_WRITE;
705 break;
706 case 'm':
707 ex.access |= DEVCG_ACC_MKNOD;
708 break;
709 case '\n':
710 case '\0':
711 count = 3;
712 break;
713 default:
714 return -EINVAL;
715 }
716 }
717
718 switch (filetype) {
719 case DEVCG_ALLOW:
720 /*
721 * If the default policy is to allow by default, try to remove
722 * an matching exception instead. And be silent about it: we
723 * don't want to break compatibility
724 */
725 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
726 /* Check if the parent allows removing it first */
727 if (!parent_allows_removal(devcgroup, &ex))
728 return -EPERM;
729 dev_exception_rm(devcgroup, &ex);
730 break;
731 }
732
733 if (!parent_has_perm(devcgroup, &ex))
734 return -EPERM;
735 rc = dev_exception_add(devcgroup, &ex);
736 break;
737 case DEVCG_DENY:
738 /*
739 * If the default policy is to deny by default, try to remove
740 * an matching exception instead. And be silent about it: we
741 * don't want to break compatibility
742 */
743 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
744 dev_exception_rm(devcgroup, &ex);
745 else
746 rc = dev_exception_add(devcgroup, &ex);
747
748 if (rc)
749 break;
750 /* we only propagate new restrictions */
751 rc = propagate_exception(devcgroup, &ex);
752 break;
753 default:
754 rc = -EINVAL;
755 }
756 return rc;
757 }
758
devcgroup_access_write(struct kernfs_open_file * of,char * buf,size_t nbytes,loff_t off)759 static ssize_t devcgroup_access_write(struct kernfs_open_file *of,
760 char *buf, size_t nbytes, loff_t off)
761 {
762 int retval;
763
764 mutex_lock(&devcgroup_mutex);
765 retval = devcgroup_update_access(css_to_devcgroup(of_css(of)),
766 of_cft(of)->private, strstrip(buf));
767 mutex_unlock(&devcgroup_mutex);
768 return retval ?: nbytes;
769 }
770
771 static struct cftype dev_cgroup_files[] = {
772 {
773 .name = "allow",
774 .write = devcgroup_access_write,
775 .private = DEVCG_ALLOW,
776 },
777 {
778 .name = "deny",
779 .write = devcgroup_access_write,
780 .private = DEVCG_DENY,
781 },
782 {
783 .name = "list",
784 .seq_show = devcgroup_seq_show,
785 .private = DEVCG_LIST,
786 },
787 { } /* terminate */
788 };
789
790 struct cgroup_subsys devices_cgrp_subsys = {
791 .css_alloc = devcgroup_css_alloc,
792 .css_free = devcgroup_css_free,
793 .css_online = devcgroup_online,
794 .css_offline = devcgroup_offline,
795 .legacy_cftypes = dev_cgroup_files,
796 };
797
798 /**
799 * devcgroup_legacy_check_permission - checks if an inode operation is permitted
800 * @dev_cgroup: the dev cgroup to be tested against
801 * @type: device type
802 * @major: device major number
803 * @minor: device minor number
804 * @access: combination of DEVCG_ACC_WRITE, DEVCG_ACC_READ and DEVCG_ACC_MKNOD
805 *
806 * returns 0 on success, -EPERM case the operation is not permitted
807 */
devcgroup_legacy_check_permission(short type,u32 major,u32 minor,short access)808 static int devcgroup_legacy_check_permission(short type, u32 major, u32 minor,
809 short access)
810 {
811 struct dev_cgroup *dev_cgroup;
812 bool rc;
813
814 rcu_read_lock();
815 dev_cgroup = task_devcgroup(current);
816 if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW)
817 /* Can't match any of the exceptions, even partially */
818 rc = !match_exception_partial(&dev_cgroup->exceptions,
819 type, major, minor, access);
820 else
821 /* Need to match completely one exception to be allowed */
822 rc = match_exception(&dev_cgroup->exceptions, type, major,
823 minor, access);
824 rcu_read_unlock();
825
826 if (!rc)
827 return -EPERM;
828
829 return 0;
830 }
831
832 #endif /* CONFIG_CGROUP_DEVICE */
833
834 #if defined(CONFIG_CGROUP_DEVICE) || defined(CONFIG_CGROUP_BPF)
835
devcgroup_check_permission(short type,u32 major,u32 minor,short access)836 int devcgroup_check_permission(short type, u32 major, u32 minor, short access)
837 {
838 int rc = BPF_CGROUP_RUN_PROG_DEVICE_CGROUP(type, major, minor, access);
839
840 if (rc)
841 return rc;
842
843 #ifdef CONFIG_CGROUP_DEVICE
844 return devcgroup_legacy_check_permission(type, major, minor, access);
845
846 #else /* CONFIG_CGROUP_DEVICE */
847 return 0;
848
849 #endif /* CONFIG_CGROUP_DEVICE */
850 }
851 EXPORT_SYMBOL(devcgroup_check_permission);
852 #endif /* defined(CONFIG_CGROUP_DEVICE) || defined(CONFIG_CGROUP_BPF) */
853
