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 * may_access - verifies if a new exception is part of what is allowed
310 * by a dev cgroup based on the default policy +
311 * exceptions. This is used to make sure a child cgroup
312 * won't have more privileges than its parent or to
313 * verify if a certain access is allowed.
314 * @dev_cgroup: dev cgroup to be tested against
315 * @refex: new exception
316 * @behavior: behavior of the exception
318 static bool may_access(struct dev_cgroup
*dev_cgroup
,
319 struct dev_exception_item
*refex
,
320 enum devcg_behavior behavior
)
322 struct dev_exception_item
*ex
;
325 rcu_lockdep_assert(rcu_read_lock_held() ||
326 lockdep_is_held(&devcgroup_mutex
),
327 "device_cgroup::may_access() called without proper synchronization");
329 list_for_each_entry_rcu(ex
, &dev_cgroup
->exceptions
, list
) {
330 if ((refex
->type
& DEV_BLOCK
) && !(ex
->type
& DEV_BLOCK
))
332 if ((refex
->type
& DEV_CHAR
) && !(ex
->type
& DEV_CHAR
))
334 if (ex
->major
!= ~0 && ex
->major
!= refex
->major
)
336 if (ex
->minor
!= ~0 && ex
->minor
!= refex
->minor
)
338 if (refex
->access
& (~ex
->access
))
344 if (dev_cgroup
->behavior
== DEVCG_DEFAULT_ALLOW
) {
345 if (behavior
== DEVCG_DEFAULT_ALLOW
) {
346 /* the exception will deny access to certain devices */
349 /* the exception will allow access to certain devices */
352 * a new exception allowing access shouldn't
353 * match an parent's exception
359 /* only behavior == DEVCG_DEFAULT_DENY allowed here */
361 /* parent has an exception that matches the proposed */
371 * when adding a new allow rule to a device exception list, the rule
372 * must be allowed in the parent device
374 static int parent_has_perm(struct dev_cgroup
*childcg
,
375 struct dev_exception_item
*ex
)
377 struct dev_cgroup
*parent
= css_to_devcgroup(css_parent(&childcg
->css
));
381 return may_access(parent
, ex
, childcg
->behavior
);
385 * may_allow_all - checks if it's possible to change the behavior to
386 * allow based on parent's rules.
387 * @parent: device cgroup's parent
388 * returns: != 0 in case it's allowed, 0 otherwise
390 static inline int may_allow_all(struct dev_cgroup
*parent
)
394 return parent
->behavior
== DEVCG_DEFAULT_ALLOW
;
398 * revalidate_active_exceptions - walks through the active exception list and
399 * revalidates the exceptions based on parent's
400 * behavior and exceptions. The exceptions that
401 * are no longer valid will be removed.
402 * Called with devcgroup_mutex held.
403 * @devcg: cgroup which exceptions will be checked
405 * This is one of the three key functions for hierarchy implementation.
406 * This function is responsible for re-evaluating all the cgroup's active
407 * exceptions due to a parent's exception change.
408 * Refer to Documentation/cgroups/devices.txt for more details.
410 static void revalidate_active_exceptions(struct dev_cgroup
*devcg
)
412 struct dev_exception_item
*ex
;
413 struct list_head
*this, *tmp
;
415 list_for_each_safe(this, tmp
, &devcg
->exceptions
) {
416 ex
= container_of(this, struct dev_exception_item
, list
);
417 if (!parent_has_perm(devcg
, ex
))
418 dev_exception_rm(devcg
, ex
);
423 * propagate_exception - propagates a new exception to the children
424 * @devcg_root: device cgroup that added a new exception
425 * @ex: new exception to be propagated
427 * returns: 0 in case of success, != 0 in case of error
429 static int propagate_exception(struct dev_cgroup
*devcg_root
,
430 struct dev_exception_item
*ex
)
432 struct cgroup_subsys_state
*pos
;
437 css_for_each_descendant_pre(pos
, &devcg_root
->css
) {
438 struct dev_cgroup
*devcg
= css_to_devcgroup(pos
);
441 * Because devcgroup_mutex is held, no devcg will become
442 * online or offline during the tree walk (see on/offline
443 * methods), and online ones are safe to access outside RCU
444 * read lock without bumping refcnt.
446 if (pos
== &devcg_root
->css
|| !is_devcg_online(devcg
))
452 * in case both root's behavior and devcg is allow, a new
453 * restriction means adding to the exception list
455 if (devcg_root
->behavior
== DEVCG_DEFAULT_ALLOW
&&
456 devcg
->behavior
== DEVCG_DEFAULT_ALLOW
) {
457 rc
= dev_exception_add(devcg
, ex
);
462 * in the other possible cases:
463 * root's behavior: allow, devcg's: deny
464 * root's behavior: deny, devcg's: deny
465 * the exception will be removed
467 dev_exception_rm(devcg
, ex
);
469 revalidate_active_exceptions(devcg
);
478 static inline bool has_children(struct dev_cgroup
*devcgroup
)
480 struct cgroup
*cgrp
= devcgroup
->css
.cgroup
;
482 return !list_empty(&cgrp
->children
);
486 * Modify the exception list using allow/deny rules.
487 * CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD
488 * so we can give a container CAP_MKNOD to let it create devices but not
489 * modify the exception list.
490 * It seems likely we'll want to add a CAP_CONTAINER capability to allow
491 * us to also grant CAP_SYS_ADMIN to containers without giving away the
492 * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
494 * Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting
495 * new access is only allowed if you're in the top-level cgroup, or your
496 * parent cgroup has the access you're asking for.
498 static int devcgroup_update_access(struct dev_cgroup
*devcgroup
,
499 int filetype
, char *buffer
)
502 char temp
[12]; /* 11 + 1 characters needed for a u32 */
504 struct dev_exception_item ex
;
505 struct dev_cgroup
*parent
= css_to_devcgroup(css_parent(&devcgroup
->css
));
507 if (!capable(CAP_SYS_ADMIN
))
510 memset(&ex
, 0, sizeof(ex
));
517 if (has_children(devcgroup
))
520 if (!may_allow_all(parent
))
522 dev_exception_clean(devcgroup
);
523 devcgroup
->behavior
= DEVCG_DEFAULT_ALLOW
;
527 rc
= dev_exceptions_copy(&devcgroup
->exceptions
,
528 &parent
->exceptions
);
533 if (has_children(devcgroup
))
536 dev_exception_clean(devcgroup
);
537 devcgroup
->behavior
= DEVCG_DEFAULT_DENY
;
559 } else if (isdigit(*b
)) {
560 memset(temp
, 0, sizeof(temp
));
561 for (count
= 0; count
< sizeof(temp
) - 1; count
++) {
567 rc
= kstrtou32(temp
, 10, &ex
.major
);
581 } else if (isdigit(*b
)) {
582 memset(temp
, 0, sizeof(temp
));
583 for (count
= 0; count
< sizeof(temp
) - 1; count
++) {
589 rc
= kstrtou32(temp
, 10, &ex
.minor
);
597 for (b
++, count
= 0; count
< 3; count
++, b
++) {
600 ex
.access
|= ACC_READ
;
603 ex
.access
|= ACC_WRITE
;
606 ex
.access
|= ACC_MKNOD
;
619 if (!parent_has_perm(devcgroup
, &ex
))
622 * If the default policy is to allow by default, try to remove
623 * an matching exception instead. And be silent about it: we
624 * don't want to break compatibility
626 if (devcgroup
->behavior
== DEVCG_DEFAULT_ALLOW
) {
627 dev_exception_rm(devcgroup
, &ex
);
630 rc
= dev_exception_add(devcgroup
, &ex
);
634 * If the default policy is to deny by default, try to remove
635 * an matching exception instead. And be silent about it: we
636 * don't want to break compatibility
638 if (devcgroup
->behavior
== DEVCG_DEFAULT_DENY
)
639 dev_exception_rm(devcgroup
, &ex
);
641 rc
= dev_exception_add(devcgroup
, &ex
);
645 /* we only propagate new restrictions */
646 rc
= propagate_exception(devcgroup
, &ex
);
654 static int devcgroup_access_write(struct cgroup_subsys_state
*css
,
655 struct cftype
*cft
, char *buffer
)
659 mutex_lock(&devcgroup_mutex
);
660 retval
= devcgroup_update_access(css_to_devcgroup(css
),
661 cft
->private, buffer
);
662 mutex_unlock(&devcgroup_mutex
);
666 static struct cftype dev_cgroup_files
[] = {
669 .write_string
= devcgroup_access_write
,
670 .private = DEVCG_ALLOW
,
674 .write_string
= devcgroup_access_write
,
675 .private = DEVCG_DENY
,
679 .seq_show
= devcgroup_seq_show
,
680 .private = DEVCG_LIST
,
685 struct cgroup_subsys devices_cgrp_subsys
= {
686 .css_alloc
= devcgroup_css_alloc
,
687 .css_free
= devcgroup_css_free
,
688 .css_online
= devcgroup_online
,
689 .css_offline
= devcgroup_offline
,
690 .base_cftypes
= dev_cgroup_files
,
694 * __devcgroup_check_permission - checks if an inode operation is permitted
695 * @dev_cgroup: the dev cgroup to be tested against
697 * @major: device major number
698 * @minor: device minor number
699 * @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD
701 * returns 0 on success, -EPERM case the operation is not permitted
703 static int __devcgroup_check_permission(short type
, u32 major
, u32 minor
,
706 struct dev_cgroup
*dev_cgroup
;
707 struct dev_exception_item ex
;
710 memset(&ex
, 0, sizeof(ex
));
717 dev_cgroup
= task_devcgroup(current
);
718 rc
= may_access(dev_cgroup
, &ex
, dev_cgroup
->behavior
);
727 int __devcgroup_inode_permission(struct inode
*inode
, int mask
)
729 short type
, access
= 0;
731 if (S_ISBLK(inode
->i_mode
))
733 if (S_ISCHR(inode
->i_mode
))
735 if (mask
& MAY_WRITE
)
740 return __devcgroup_check_permission(type
, imajor(inode
), iminor(inode
),
744 int devcgroup_inode_mknod(int mode
, dev_t dev
)
748 if (!S_ISBLK(mode
) && !S_ISCHR(mode
))
756 return __devcgroup_check_permission(type
, MAJOR(dev
), MINOR(dev
),