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