2 * device_cgroup.c - device cgroup subsystem
4 * Copyright 2007 IBM Corp
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>
20 #define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
24 #define DEV_ALL 4 /* this represents all devices */
26 static DEFINE_MUTEX(devcgroup_mutex);
35 * exception list locking rules:
36 * hold devcgroup_mutex for update/read.
37 * hold rcu_read_lock() for read.
40 struct dev_exception_item {
44 struct list_head list;
49 struct cgroup_subsys_state css;
50 struct list_head exceptions;
51 enum devcg_behavior behavior;
54 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
56 return s ? container_of(s, struct dev_cgroup, css) : NULL;
59 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
61 return css_to_devcgroup(task_css(task, devices_cgrp_id));
65 * called under devcgroup_mutex
67 static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
69 struct dev_exception_item *ex, *tmp, *new;
71 lockdep_assert_held(&devcgroup_mutex);
73 list_for_each_entry(ex, orig, list) {
74 new = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
77 list_add_tail(&new->list, dest);
83 list_for_each_entry_safe(ex, tmp, dest, list) {
91 * called under devcgroup_mutex
93 static int dev_exception_add(struct dev_cgroup *dev_cgroup,
94 struct dev_exception_item *ex)
96 struct dev_exception_item *excopy, *walk;
98 lockdep_assert_held(&devcgroup_mutex);
100 excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
104 list_for_each_entry(walk, &dev_cgroup->exceptions, list) {
105 if (walk->type != ex->type)
107 if (walk->major != ex->major)
109 if (walk->minor != ex->minor)
112 walk->access |= ex->access;
118 list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions);
123 * called under devcgroup_mutex
125 static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
126 struct dev_exception_item *ex)
128 struct dev_exception_item *walk, *tmp;
130 lockdep_assert_held(&devcgroup_mutex);
132 list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
133 if (walk->type != ex->type)
135 if (walk->major != ex->major)
137 if (walk->minor != ex->minor)
140 walk->access &= ~ex->access;
142 list_del_rcu(&walk->list);
143 kfree_rcu(walk, rcu);
148 static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
150 struct dev_exception_item *ex, *tmp;
152 list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
153 list_del_rcu(&ex->list);
159 * dev_exception_clean - frees all entries of the exception list
160 * @dev_cgroup: dev_cgroup with the exception list to be cleaned
162 * called under devcgroup_mutex
164 static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
166 lockdep_assert_held(&devcgroup_mutex);
168 __dev_exception_clean(dev_cgroup);
171 static inline bool is_devcg_online(const struct dev_cgroup *devcg)
173 return (devcg->behavior != DEVCG_DEFAULT_NONE);
177 * devcgroup_online - initializes devcgroup's behavior and exceptions based on
179 * @css: css getting online
180 * returns 0 in case of success, error code otherwise
182 static int devcgroup_online(struct cgroup_subsys_state *css)
184 struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
185 struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css_parent(css));
188 mutex_lock(&devcgroup_mutex);
190 if (parent_dev_cgroup == NULL)
191 dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
193 ret = dev_exceptions_copy(&dev_cgroup->exceptions,
194 &parent_dev_cgroup->exceptions);
196 dev_cgroup->behavior = parent_dev_cgroup->behavior;
198 mutex_unlock(&devcgroup_mutex);
203 static void devcgroup_offline(struct cgroup_subsys_state *css)
205 struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
207 mutex_lock(&devcgroup_mutex);
208 dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
209 mutex_unlock(&devcgroup_mutex);
213 * called from kernel/cgroup.c with cgroup_lock() held.
215 static struct cgroup_subsys_state *
216 devcgroup_css_alloc(struct cgroup_subsys_state *parent_css)
218 struct dev_cgroup *dev_cgroup;
220 dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
222 return ERR_PTR(-ENOMEM);
223 INIT_LIST_HEAD(&dev_cgroup->exceptions);
224 dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
226 return &dev_cgroup->css;
229 static void devcgroup_css_free(struct cgroup_subsys_state *css)
231 struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
233 __dev_exception_clean(dev_cgroup);
237 #define DEVCG_ALLOW 1
244 static void set_access(char *acc, short access)
247 memset(acc, 0, ACCLEN);
248 if (access & ACC_READ)
250 if (access & ACC_WRITE)
252 if (access & ACC_MKNOD)
256 static char type_to_char(short type)
260 if (type == DEV_CHAR)
262 if (type == DEV_BLOCK)
267 static void set_majmin(char *str, unsigned m)
272 sprintf(str, "%u", m);
275 static int devcgroup_seq_show(struct seq_file *m, void *v)
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];
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"
288 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
289 set_access(acc, ACC_MASK);
292 seq_printf(m, "%c %s:%s %s\n", type_to_char(DEV_ALL),
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),
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)
316 * It is considered a complete match if an exception is found that will
317 * contain the entire range of provided parameters.
319 * Return: true in case it matches an exception completely
321 static bool match_exception(struct list_head *exceptions, short type,
322 u32 major, u32 minor, short access)
324 struct dev_exception_item *ex;
326 list_for_each_entry_rcu(ex, exceptions, list) {
327 if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
329 if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR))
331 if (ex->major != ~0 && ex->major != major)
333 if (ex->minor != ~0 && ex->minor != minor)
335 /* provided access cannot have more than the exception rule */
336 if (access & (~ex->access))
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)
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.
356 * Return: true in case the provided range mat matches an exception completely
358 static bool match_exception_partial(struct list_head *exceptions, short type,
359 u32 major, u32 minor, short access)
361 struct dev_exception_item *ex;
363 list_for_each_entry_rcu(ex, exceptions, list) {
364 if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
366 if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR))
369 * We must be sure that both the exception and the provided
370 * range aren't masking all devices
372 if (ex->major != ~0 && major != ~0 && ex->major != major)
374 if (ex->minor != ~0 && minor != ~0 && ex->minor != minor)
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
381 if (!(access & ex->access))
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
394 * This is used to make sure a child cgroup won't have more privileges
397 static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
398 struct dev_exception_item *refex,
399 enum devcg_behavior behavior)
403 rcu_lockdep_assert(rcu_read_lock_held() ||
404 lockdep_is_held(&devcgroup_mutex),
405 "device_cgroup:verify_new_ex called without proper synchronization");
407 if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
408 if (behavior == DEVCG_DEFAULT_ALLOW) {
410 * new exception in the child doesn't matter, only
411 * adding extra restrictions
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
420 match = match_exception_partial(&dev_cgroup->exceptions,
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
437 match = match_exception(&dev_cgroup->exceptions, refex->type,
438 refex->major, refex->minor,
442 /* parent has an exception that matches the proposed */
452 * when adding a new allow rule to a device exception list, the rule
453 * must be allowed in the parent device
455 static int parent_has_perm(struct dev_cgroup *childcg,
456 struct dev_exception_item *ex)
458 struct dev_cgroup *parent = css_to_devcgroup(css_parent(&childcg->css));
462 return verify_new_ex(parent, ex, childcg->behavior);
466 * may_allow_all - checks if it's possible to change the behavior to
467 * allow based on parent's rules.
468 * @parent: device cgroup's parent
469 * returns: != 0 in case it's allowed, 0 otherwise
471 static inline int may_allow_all(struct dev_cgroup *parent)
475 return parent->behavior == DEVCG_DEFAULT_ALLOW;
479 * revalidate_active_exceptions - walks through the active exception list and
480 * revalidates the exceptions based on parent's
481 * behavior and exceptions. The exceptions that
482 * are no longer valid will be removed.
483 * Called with devcgroup_mutex held.
484 * @devcg: cgroup which exceptions will be checked
486 * This is one of the three key functions for hierarchy implementation.
487 * This function is responsible for re-evaluating all the cgroup's active
488 * exceptions due to a parent's exception change.
489 * Refer to Documentation/cgroups/devices.txt for more details.
491 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
493 struct dev_exception_item *ex;
494 struct list_head *this, *tmp;
496 list_for_each_safe(this, tmp, &devcg->exceptions) {
497 ex = container_of(this, struct dev_exception_item, list);
498 if (!parent_has_perm(devcg, ex))
499 dev_exception_rm(devcg, ex);
504 * propagate_exception - propagates a new exception to the children
505 * @devcg_root: device cgroup that added a new exception
506 * @ex: new exception to be propagated
508 * returns: 0 in case of success, != 0 in case of error
510 static int propagate_exception(struct dev_cgroup *devcg_root,
511 struct dev_exception_item *ex)
513 struct cgroup_subsys_state *pos;
518 css_for_each_descendant_pre(pos, &devcg_root->css) {
519 struct dev_cgroup *devcg = css_to_devcgroup(pos);
522 * Because devcgroup_mutex is held, no devcg will become
523 * online or offline during the tree walk (see on/offline
524 * methods), and online ones are safe to access outside RCU
525 * read lock without bumping refcnt.
527 if (pos == &devcg_root->css || !is_devcg_online(devcg))
533 * in case both root's behavior and devcg is allow, a new
534 * restriction means adding to the exception list
536 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
537 devcg->behavior == DEVCG_DEFAULT_ALLOW) {
538 rc = dev_exception_add(devcg, ex);
543 * in the other possible cases:
544 * root's behavior: allow, devcg's: deny
545 * root's behavior: deny, devcg's: deny
546 * the exception will be removed
548 dev_exception_rm(devcg, ex);
550 revalidate_active_exceptions(devcg);
559 static inline bool has_children(struct dev_cgroup *devcgroup)
561 struct cgroup *cgrp = devcgroup->css.cgroup;
563 return !list_empty(&cgrp->children);
567 * Modify the exception list using allow/deny rules.
568 * CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD
569 * so we can give a container CAP_MKNOD to let it create devices but not
570 * modify the exception list.
571 * It seems likely we'll want to add a CAP_CONTAINER capability to allow
572 * us to also grant CAP_SYS_ADMIN to containers without giving away the
573 * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
575 * Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting
576 * new access is only allowed if you're in the top-level cgroup, or your
577 * parent cgroup has the access you're asking for.
579 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
580 int filetype, char *buffer)
583 char temp[12]; /* 11 + 1 characters needed for a u32 */
585 struct dev_exception_item ex;
586 struct dev_cgroup *parent = css_to_devcgroup(css_parent(&devcgroup->css));
588 if (!capable(CAP_SYS_ADMIN))
591 memset(&ex, 0, sizeof(ex));
598 if (has_children(devcgroup))
601 if (!may_allow_all(parent))
603 dev_exception_clean(devcgroup);
604 devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
608 rc = dev_exceptions_copy(&devcgroup->exceptions,
609 &parent->exceptions);
614 if (has_children(devcgroup))
617 dev_exception_clean(devcgroup);
618 devcgroup->behavior = DEVCG_DEFAULT_DENY;
640 } else if (isdigit(*b)) {
641 memset(temp, 0, sizeof(temp));
642 for (count = 0; count < sizeof(temp) - 1; count++) {
648 rc = kstrtou32(temp, 10, &ex.major);
662 } else if (isdigit(*b)) {
663 memset(temp, 0, sizeof(temp));
664 for (count = 0; count < sizeof(temp) - 1; count++) {
670 rc = kstrtou32(temp, 10, &ex.minor);
678 for (b++, count = 0; count < 3; count++, b++) {
681 ex.access |= ACC_READ;
684 ex.access |= ACC_WRITE;
687 ex.access |= ACC_MKNOD;
700 if (!parent_has_perm(devcgroup, &ex))
703 * If the default policy is to allow by default, try to remove
704 * an matching exception instead. And be silent about it: we
705 * don't want to break compatibility
707 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
708 dev_exception_rm(devcgroup, &ex);
711 rc = dev_exception_add(devcgroup, &ex);
715 * If the default policy is to deny by default, try to remove
716 * an matching exception instead. And be silent about it: we
717 * don't want to break compatibility
719 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
720 dev_exception_rm(devcgroup, &ex);
722 rc = dev_exception_add(devcgroup, &ex);
726 /* we only propagate new restrictions */
727 rc = propagate_exception(devcgroup, &ex);
735 static int devcgroup_access_write(struct cgroup_subsys_state *css,
736 struct cftype *cft, char *buffer)
740 mutex_lock(&devcgroup_mutex);
741 retval = devcgroup_update_access(css_to_devcgroup(css),
742 cft->private, buffer);
743 mutex_unlock(&devcgroup_mutex);
747 static struct cftype dev_cgroup_files[] = {
750 .write_string = devcgroup_access_write,
751 .private = DEVCG_ALLOW,
755 .write_string = devcgroup_access_write,
756 .private = DEVCG_DENY,
760 .seq_show = devcgroup_seq_show,
761 .private = DEVCG_LIST,
766 struct cgroup_subsys devices_cgrp_subsys = {
767 .css_alloc = devcgroup_css_alloc,
768 .css_free = devcgroup_css_free,
769 .css_online = devcgroup_online,
770 .css_offline = devcgroup_offline,
771 .base_cftypes = dev_cgroup_files,
775 * __devcgroup_check_permission - checks if an inode operation is permitted
776 * @dev_cgroup: the dev cgroup to be tested against
778 * @major: device major number
779 * @minor: device minor number
780 * @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD
782 * returns 0 on success, -EPERM case the operation is not permitted
784 static int __devcgroup_check_permission(short type, u32 major, u32 minor,
787 struct dev_cgroup *dev_cgroup;
791 dev_cgroup = task_devcgroup(current);
792 if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW)
793 /* Can't match any of the exceptions, even partially */
794 rc = !match_exception_partial(&dev_cgroup->exceptions,
795 type, major, minor, access);
797 /* Need to match completely one exception to be allowed */
798 rc = match_exception(&dev_cgroup->exceptions, type, major,
808 int __devcgroup_inode_permission(struct inode *inode, int mask)
810 short type, access = 0;
812 if (S_ISBLK(inode->i_mode))
814 if (S_ISCHR(inode->i_mode))
816 if (mask & MAY_WRITE)
821 return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
825 int devcgroup_inode_mknod(int mode, dev_t dev)
829 if (!S_ISBLK(mode) && !S_ISCHR(mode))
837 return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),