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);
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_WARN(!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(childcg->css.parent);
462 return verify_new_ex(parent, ex, childcg->behavior);
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
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
474 * Return: true if it's ok to remove exception, false otherwise
476 static bool parent_allows_removal(struct dev_cgroup *childcg,
477 struct dev_exception_item *ex)
479 struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
484 /* It's always allowed to remove access to devices */
485 if (childcg->behavior == DEVCG_DEFAULT_DENY)
489 * Make sure you're not removing part or a whole exception existing in
492 return !match_exception_partial(&parent->exceptions, ex->type,
493 ex->major, ex->minor, ex->access);
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
502 static inline int may_allow_all(struct dev_cgroup *parent)
506 return parent->behavior == DEVCG_DEFAULT_ALLOW;
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
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.
522 static void revalidate_active_exceptions(struct dev_cgroup *devcg)
524 struct dev_exception_item *ex;
525 struct list_head *this, *tmp;
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);
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
539 * returns: 0 in case of success, != 0 in case of error
541 static int propagate_exception(struct dev_cgroup *devcg_root,
542 struct dev_exception_item *ex)
544 struct cgroup_subsys_state *pos;
549 css_for_each_descendant_pre(pos, &devcg_root->css) {
550 struct dev_cgroup *devcg = css_to_devcgroup(pos);
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.
558 if (pos == &devcg_root->css || !is_devcg_online(devcg))
564 * in case both root's behavior and devcg is allow, a new
565 * restriction means adding to the exception list
567 if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
568 devcg->behavior == DEVCG_DEFAULT_ALLOW) {
569 rc = dev_exception_add(devcg, ex);
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
579 dev_exception_rm(devcg, ex);
581 revalidate_active_exceptions(devcg);
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
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.
603 static int devcgroup_update_access(struct dev_cgroup *devcgroup,
604 int filetype, char *buffer)
607 char temp[12]; /* 11 + 1 characters needed for a u32 */
609 struct dev_exception_item ex;
610 struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
612 if (!capable(CAP_SYS_ADMIN))
615 memset(&ex, 0, sizeof(ex));
622 if (css_has_online_children(&devcgroup->css))
625 if (!may_allow_all(parent))
627 dev_exception_clean(devcgroup);
628 devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
632 rc = dev_exceptions_copy(&devcgroup->exceptions,
633 &parent->exceptions);
638 if (css_has_online_children(&devcgroup->css))
641 dev_exception_clean(devcgroup);
642 devcgroup->behavior = DEVCG_DEFAULT_DENY;
664 } else if (isdigit(*b)) {
665 memset(temp, 0, sizeof(temp));
666 for (count = 0; count < sizeof(temp) - 1; count++) {
672 rc = kstrtou32(temp, 10, &ex.major);
686 } else if (isdigit(*b)) {
687 memset(temp, 0, sizeof(temp));
688 for (count = 0; count < sizeof(temp) - 1; count++) {
694 rc = kstrtou32(temp, 10, &ex.minor);
702 for (b++, count = 0; count < 3; count++, b++) {
705 ex.access |= ACC_READ;
708 ex.access |= ACC_WRITE;
711 ex.access |= ACC_MKNOD;
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
729 if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
730 /* Check if the parent allows removing it first */
731 if (!parent_allows_removal(devcgroup, &ex))
733 dev_exception_rm(devcgroup, &ex);
737 if (!parent_has_perm(devcgroup, &ex))
739 rc = dev_exception_add(devcgroup, &ex);
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
747 if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
748 dev_exception_rm(devcgroup, &ex);
750 rc = dev_exception_add(devcgroup, &ex);
754 /* we only propagate new restrictions */
755 rc = propagate_exception(devcgroup, &ex);
763 static ssize_t devcgroup_access_write(struct kernfs_open_file *of,
764 char *buf, size_t nbytes, loff_t off)
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;
775 static struct cftype dev_cgroup_files[] = {
778 .write = devcgroup_access_write,
779 .private = DEVCG_ALLOW,
783 .write = devcgroup_access_write,
784 .private = DEVCG_DENY,
788 .seq_show = devcgroup_seq_show,
789 .private = DEVCG_LIST,
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,
803 * __devcgroup_check_permission - checks if an inode operation is permitted
804 * @dev_cgroup: the dev cgroup to be tested against
806 * @major: device major number
807 * @minor: device minor number
808 * @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD
810 * returns 0 on success, -EPERM case the operation is not permitted
812 static int __devcgroup_check_permission(short type, u32 major, u32 minor,
815 struct dev_cgroup *dev_cgroup;
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);
825 /* Need to match completely one exception to be allowed */
826 rc = match_exception(&dev_cgroup->exceptions, type, major,
836 int __devcgroup_inode_permission(struct inode *inode, int mask)
838 short type, access = 0;
840 if (S_ISBLK(inode->i_mode))
842 if (S_ISCHR(inode->i_mode))
844 if (mask & MAY_WRITE)
849 return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
853 int devcgroup_inode_mknod(int mode, dev_t dev)
857 if (!S_ISBLK(mode) && !S_ISCHR(mode))
865 return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),