projects/linux·blob v4.14 · refs

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