2 * Implementation of the kernel access vector cache (AVC).
4 * Authors: Stephen Smalley, <sds@epoch.ncsc.mil>
5 * James Morris <jmorris@redhat.com>
7 * Update: KaiGai, Kohei <kaigai@ak.jp.nec.com>
8 * Replaced the avc_lock spinlock by RCU.
10 * Copyright (C) 2003 Red Hat, Inc., James Morris <jmorris@redhat.com>
12 * This program is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU General Public License version 2,
14 * as published by the Free Software Foundation.
16 #include <linux/types.h>
17 #include <linux/stddef.h>
18 #include <linux/kernel.h>
19 #include <linux/slab.h>
21 #include <linux/dcache.h>
22 #include <linux/init.h>
23 #include <linux/skbuff.h>
24 #include <linux/percpu.h>
27 #include <net/af_unix.h>
29 #include <linux/audit.h>
30 #include <linux/ipv6.h>
36 #define AVC_CACHE_SLOTS 512
37 #define AVC_DEF_CACHE_THRESHOLD 512
38 #define AVC_CACHE_RECLAIM 16
40 #ifdef CONFIG_SECURITY_SELINUX_AVC_STATS
41 #define avc_cache_stats_incr(field) this_cpu_inc(avc_cache_stats.field)
43 #define avc_cache_stats_incr(field) do {} while (0)
50 struct av_decision avd
;
55 struct hlist_node list
; /* anchored in avc_cache->slots[i] */
56 struct rcu_head rhead
;
60 struct hlist_head slots
[AVC_CACHE_SLOTS
]; /* head for avc_node->list */
61 spinlock_t slots_lock
[AVC_CACHE_SLOTS
]; /* lock for writes */
62 atomic_t lru_hint
; /* LRU hint for reclaim scan */
63 atomic_t active_nodes
;
64 u32 latest_notif
; /* latest revocation notification */
67 struct avc_callback_node
{
68 int (*callback
) (u32 event
);
70 struct avc_callback_node
*next
;
73 /* Exported via selinufs */
74 unsigned int avc_cache_threshold
= AVC_DEF_CACHE_THRESHOLD
;
76 #ifdef CONFIG_SECURITY_SELINUX_AVC_STATS
77 DEFINE_PER_CPU(struct avc_cache_stats
, avc_cache_stats
) = { 0 };
80 static struct avc_cache avc_cache
;
81 static struct avc_callback_node
*avc_callbacks
;
82 static struct kmem_cache
*avc_node_cachep
;
84 static inline int avc_hash(u32 ssid
, u32 tsid
, u16 tclass
)
86 return (ssid
^ (tsid
<<2) ^ (tclass
<<4)) & (AVC_CACHE_SLOTS
- 1);
90 * avc_dump_av - Display an access vector in human-readable form.
91 * @tclass: target security class
94 static void avc_dump_av(struct audit_buffer
*ab
, u16 tclass
, u32 av
)
100 audit_log_format(ab
, " null");
104 perms
= secclass_map
[tclass
-1].perms
;
106 audit_log_format(ab
, " {");
109 while (i
< (sizeof(av
) * 8)) {
110 if ((perm
& av
) && perms
[i
]) {
111 audit_log_format(ab
, " %s", perms
[i
]);
119 audit_log_format(ab
, " 0x%x", av
);
121 audit_log_format(ab
, " }");
125 * avc_dump_query - Display a SID pair and a class in human-readable form.
126 * @ssid: source security identifier
127 * @tsid: target security identifier
128 * @tclass: target security class
130 static void avc_dump_query(struct audit_buffer
*ab
, u32 ssid
, u32 tsid
, u16 tclass
)
136 rc
= security_sid_to_context(ssid
, &scontext
, &scontext_len
);
138 audit_log_format(ab
, "ssid=%d", ssid
);
140 audit_log_format(ab
, "scontext=%s", scontext
);
144 rc
= security_sid_to_context(tsid
, &scontext
, &scontext_len
);
146 audit_log_format(ab
, " tsid=%d", tsid
);
148 audit_log_format(ab
, " tcontext=%s", scontext
);
152 BUG_ON(tclass
>= ARRAY_SIZE(secclass_map
));
153 audit_log_format(ab
, " tclass=%s", secclass_map
[tclass
-1].name
);
157 * avc_init - Initialize the AVC.
159 * Initialize the access vector cache.
161 void __init
avc_init(void)
165 for (i
= 0; i
< AVC_CACHE_SLOTS
; i
++) {
166 INIT_HLIST_HEAD(&avc_cache
.slots
[i
]);
167 spin_lock_init(&avc_cache
.slots_lock
[i
]);
169 atomic_set(&avc_cache
.active_nodes
, 0);
170 atomic_set(&avc_cache
.lru_hint
, 0);
172 avc_node_cachep
= kmem_cache_create("avc_node", sizeof(struct avc_node
),
173 0, SLAB_PANIC
, NULL
);
175 audit_log(current
->audit_context
, GFP_KERNEL
, AUDIT_KERNEL
, "AVC INITIALIZED\n");
178 int avc_get_hash_stats(char *page
)
180 int i
, chain_len
, max_chain_len
, slots_used
;
181 struct avc_node
*node
;
182 struct hlist_head
*head
;
188 for (i
= 0; i
< AVC_CACHE_SLOTS
; i
++) {
189 head
= &avc_cache
.slots
[i
];
190 if (!hlist_empty(head
)) {
191 struct hlist_node
*next
;
195 hlist_for_each_entry_rcu(node
, next
, head
, list
)
197 if (chain_len
> max_chain_len
)
198 max_chain_len
= chain_len
;
204 return scnprintf(page
, PAGE_SIZE
, "entries: %d\nbuckets used: %d/%d\n"
205 "longest chain: %d\n",
206 atomic_read(&avc_cache
.active_nodes
),
207 slots_used
, AVC_CACHE_SLOTS
, max_chain_len
);
210 static void avc_node_free(struct rcu_head
*rhead
)
212 struct avc_node
*node
= container_of(rhead
, struct avc_node
, rhead
);
213 kmem_cache_free(avc_node_cachep
, node
);
214 avc_cache_stats_incr(frees
);
217 static void avc_node_delete(struct avc_node
*node
)
219 hlist_del_rcu(&node
->list
);
220 call_rcu(&node
->rhead
, avc_node_free
);
221 atomic_dec(&avc_cache
.active_nodes
);
224 static void avc_node_kill(struct avc_node
*node
)
226 kmem_cache_free(avc_node_cachep
, node
);
227 avc_cache_stats_incr(frees
);
228 atomic_dec(&avc_cache
.active_nodes
);
231 static void avc_node_replace(struct avc_node
*new, struct avc_node
*old
)
233 hlist_replace_rcu(&old
->list
, &new->list
);
234 call_rcu(&old
->rhead
, avc_node_free
);
235 atomic_dec(&avc_cache
.active_nodes
);
238 static inline int avc_reclaim_node(void)
240 struct avc_node
*node
;
241 int hvalue
, try, ecx
;
243 struct hlist_head
*head
;
244 struct hlist_node
*next
;
247 for (try = 0, ecx
= 0; try < AVC_CACHE_SLOTS
; try++) {
248 hvalue
= atomic_inc_return(&avc_cache
.lru_hint
) & (AVC_CACHE_SLOTS
- 1);
249 head
= &avc_cache
.slots
[hvalue
];
250 lock
= &avc_cache
.slots_lock
[hvalue
];
252 if (!spin_trylock_irqsave(lock
, flags
))
256 hlist_for_each_entry(node
, next
, head
, list
) {
257 avc_node_delete(node
);
258 avc_cache_stats_incr(reclaims
);
260 if (ecx
>= AVC_CACHE_RECLAIM
) {
262 spin_unlock_irqrestore(lock
, flags
);
267 spin_unlock_irqrestore(lock
, flags
);
273 static struct avc_node
*avc_alloc_node(void)
275 struct avc_node
*node
;
277 node
= kmem_cache_zalloc(avc_node_cachep
, GFP_ATOMIC
);
281 INIT_HLIST_NODE(&node
->list
);
282 avc_cache_stats_incr(allocations
);
284 if (atomic_inc_return(&avc_cache
.active_nodes
) > avc_cache_threshold
)
291 static void avc_node_populate(struct avc_node
*node
, u32 ssid
, u32 tsid
, u16 tclass
, struct av_decision
*avd
)
293 node
->ae
.ssid
= ssid
;
294 node
->ae
.tsid
= tsid
;
295 node
->ae
.tclass
= tclass
;
296 memcpy(&node
->ae
.avd
, avd
, sizeof(node
->ae
.avd
));
299 static inline struct avc_node
*avc_search_node(u32 ssid
, u32 tsid
, u16 tclass
)
301 struct avc_node
*node
, *ret
= NULL
;
303 struct hlist_head
*head
;
304 struct hlist_node
*next
;
306 hvalue
= avc_hash(ssid
, tsid
, tclass
);
307 head
= &avc_cache
.slots
[hvalue
];
308 hlist_for_each_entry_rcu(node
, next
, head
, list
) {
309 if (ssid
== node
->ae
.ssid
&&
310 tclass
== node
->ae
.tclass
&&
311 tsid
== node
->ae
.tsid
) {
321 * avc_lookup - Look up an AVC entry.
322 * @ssid: source security identifier
323 * @tsid: target security identifier
324 * @tclass: target security class
326 * Look up an AVC entry that is valid for the
327 * (@ssid, @tsid), interpreting the permissions
328 * based on @tclass. If a valid AVC entry exists,
329 * then this function returns the avc_node.
330 * Otherwise, this function returns NULL.
332 static struct avc_node
*avc_lookup(u32 ssid
, u32 tsid
, u16 tclass
)
334 struct avc_node
*node
;
336 avc_cache_stats_incr(lookups
);
337 node
= avc_search_node(ssid
, tsid
, tclass
);
342 avc_cache_stats_incr(misses
);
346 static int avc_latest_notif_update(int seqno
, int is_insert
)
349 static DEFINE_SPINLOCK(notif_lock
);
352 spin_lock_irqsave(¬if_lock
, flag
);
354 if (seqno
< avc_cache
.latest_notif
) {
355 printk(KERN_WARNING
"SELinux: avc: seqno %d < latest_notif %d\n",
356 seqno
, avc_cache
.latest_notif
);
360 if (seqno
> avc_cache
.latest_notif
)
361 avc_cache
.latest_notif
= seqno
;
363 spin_unlock_irqrestore(¬if_lock
, flag
);
369 * avc_insert - Insert an AVC entry.
370 * @ssid: source security identifier
371 * @tsid: target security identifier
372 * @tclass: target security class
373 * @avd: resulting av decision
375 * Insert an AVC entry for the SID pair
376 * (@ssid, @tsid) and class @tclass.
377 * The access vectors and the sequence number are
378 * normally provided by the security server in
379 * response to a security_compute_av() call. If the
380 * sequence number @avd->seqno is not less than the latest
381 * revocation notification, then the function copies
382 * the access vectors into a cache entry, returns
383 * avc_node inserted. Otherwise, this function returns NULL.
385 static struct avc_node
*avc_insert(u32 ssid
, u32 tsid
, u16 tclass
, struct av_decision
*avd
)
387 struct avc_node
*pos
, *node
= NULL
;
391 if (avc_latest_notif_update(avd
->seqno
, 1))
394 node
= avc_alloc_node();
396 struct hlist_head
*head
;
397 struct hlist_node
*next
;
400 hvalue
= avc_hash(ssid
, tsid
, tclass
);
401 avc_node_populate(node
, ssid
, tsid
, tclass
, avd
);
403 head
= &avc_cache
.slots
[hvalue
];
404 lock
= &avc_cache
.slots_lock
[hvalue
];
406 spin_lock_irqsave(lock
, flag
);
407 hlist_for_each_entry(pos
, next
, head
, list
) {
408 if (pos
->ae
.ssid
== ssid
&&
409 pos
->ae
.tsid
== tsid
&&
410 pos
->ae
.tclass
== tclass
) {
411 avc_node_replace(node
, pos
);
415 hlist_add_head_rcu(&node
->list
, head
);
417 spin_unlock_irqrestore(lock
, flag
);
424 * avc_audit_pre_callback - SELinux specific information
425 * will be called by generic audit code
426 * @ab: the audit buffer
429 static void avc_audit_pre_callback(struct audit_buffer
*ab
, void *a
)
431 struct common_audit_data
*ad
= a
;
432 audit_log_format(ab
, "avc: %s ",
433 ad
->selinux_audit_data
->denied
? "denied" : "granted");
434 avc_dump_av(ab
, ad
->selinux_audit_data
->tclass
,
435 ad
->selinux_audit_data
->audited
);
436 audit_log_format(ab
, " for ");
440 * avc_audit_post_callback - SELinux specific information
441 * will be called by generic audit code
442 * @ab: the audit buffer
445 static void avc_audit_post_callback(struct audit_buffer
*ab
, void *a
)
447 struct common_audit_data
*ad
= a
;
448 audit_log_format(ab
, " ");
449 avc_dump_query(ab
, ad
->selinux_audit_data
->ssid
,
450 ad
->selinux_audit_data
->tsid
,
451 ad
->selinux_audit_data
->tclass
);
454 /* This is the slow part of avc audit with big stack footprint */
455 noinline
int slow_avc_audit(u32 ssid
, u32 tsid
, u16 tclass
,
456 u32 requested
, u32 audited
, u32 denied
,
457 struct common_audit_data
*a
,
460 struct common_audit_data stack_data
;
461 struct selinux_audit_data sad
;
465 a
->type
= LSM_AUDIT_DATA_NONE
;
469 * When in a RCU walk do the audit on the RCU retry. This is because
470 * the collection of the dname in an inode audit message is not RCU
471 * safe. Note this may drop some audits when the situation changes
472 * during retry. However this is logically just as if the operation
473 * happened a little later.
475 if ((a
->type
== LSM_AUDIT_DATA_INODE
) &&
476 (flags
& MAY_NOT_BLOCK
))
480 sad
.requested
= requested
;
483 sad
.audited
= audited
;
486 a
->selinux_audit_data
= &sad
;
488 common_lsm_audit(a
, avc_audit_pre_callback
, avc_audit_post_callback
);
493 * avc_add_callback - Register a callback for security events.
494 * @callback: callback function
495 * @events: security events
497 * Register a callback function for events in the set @events.
498 * Returns %0 on success or -%ENOMEM if insufficient memory
499 * exists to add the callback.
501 int __init
avc_add_callback(int (*callback
)(u32 event
), u32 events
)
503 struct avc_callback_node
*c
;
506 c
= kmalloc(sizeof(*c
), GFP_KERNEL
);
512 c
->callback
= callback
;
514 c
->next
= avc_callbacks
;
520 static inline int avc_sidcmp(u32 x
, u32 y
)
522 return (x
== y
|| x
== SECSID_WILD
|| y
== SECSID_WILD
);
526 * avc_update_node Update an AVC entry
527 * @event : Updating event
528 * @perms : Permission mask bits
529 * @ssid,@tsid,@tclass : identifier of an AVC entry
530 * @seqno : sequence number when decision was made
532 * if a valid AVC entry doesn't exist,this function returns -ENOENT.
533 * if kmalloc() called internal returns NULL, this function returns -ENOMEM.
534 * otherwise, this function updates the AVC entry. The original AVC-entry object
535 * will release later by RCU.
537 static int avc_update_node(u32 event
, u32 perms
, u32 ssid
, u32 tsid
, u16 tclass
,
542 struct avc_node
*pos
, *node
, *orig
= NULL
;
543 struct hlist_head
*head
;
544 struct hlist_node
*next
;
547 node
= avc_alloc_node();
553 /* Lock the target slot */
554 hvalue
= avc_hash(ssid
, tsid
, tclass
);
556 head
= &avc_cache
.slots
[hvalue
];
557 lock
= &avc_cache
.slots_lock
[hvalue
];
559 spin_lock_irqsave(lock
, flag
);
561 hlist_for_each_entry(pos
, next
, head
, list
) {
562 if (ssid
== pos
->ae
.ssid
&&
563 tsid
== pos
->ae
.tsid
&&
564 tclass
== pos
->ae
.tclass
&&
565 seqno
== pos
->ae
.avd
.seqno
){
578 * Copy and replace original node.
581 avc_node_populate(node
, ssid
, tsid
, tclass
, &orig
->ae
.avd
);
584 case AVC_CALLBACK_GRANT
:
585 node
->ae
.avd
.allowed
|= perms
;
587 case AVC_CALLBACK_TRY_REVOKE
:
588 case AVC_CALLBACK_REVOKE
:
589 node
->ae
.avd
.allowed
&= ~perms
;
591 case AVC_CALLBACK_AUDITALLOW_ENABLE
:
592 node
->ae
.avd
.auditallow
|= perms
;
594 case AVC_CALLBACK_AUDITALLOW_DISABLE
:
595 node
->ae
.avd
.auditallow
&= ~perms
;
597 case AVC_CALLBACK_AUDITDENY_ENABLE
:
598 node
->ae
.avd
.auditdeny
|= perms
;
600 case AVC_CALLBACK_AUDITDENY_DISABLE
:
601 node
->ae
.avd
.auditdeny
&= ~perms
;
604 avc_node_replace(node
, orig
);
606 spin_unlock_irqrestore(lock
, flag
);
612 * avc_flush - Flush the cache
614 static void avc_flush(void)
616 struct hlist_head
*head
;
617 struct hlist_node
*next
;
618 struct avc_node
*node
;
623 for (i
= 0; i
< AVC_CACHE_SLOTS
; i
++) {
624 head
= &avc_cache
.slots
[i
];
625 lock
= &avc_cache
.slots_lock
[i
];
627 spin_lock_irqsave(lock
, flag
);
629 * With preemptable RCU, the outer spinlock does not
630 * prevent RCU grace periods from ending.
633 hlist_for_each_entry(node
, next
, head
, list
)
634 avc_node_delete(node
);
636 spin_unlock_irqrestore(lock
, flag
);
641 * avc_ss_reset - Flush the cache and revalidate migrated permissions.
642 * @seqno: policy sequence number
644 int avc_ss_reset(u32 seqno
)
646 struct avc_callback_node
*c
;
651 for (c
= avc_callbacks
; c
; c
= c
->next
) {
652 if (c
->events
& AVC_CALLBACK_RESET
) {
653 tmprc
= c
->callback(AVC_CALLBACK_RESET
);
654 /* save the first error encountered for the return
655 value and continue processing the callbacks */
661 avc_latest_notif_update(seqno
, 0);
666 * Slow-path helper function for avc_has_perm_noaudit,
667 * when the avc_node lookup fails. We get called with
668 * the RCU read lock held, and need to return with it
669 * still held, but drop if for the security compute.
671 * Don't inline this, since it's the slow-path and just
672 * results in a bigger stack frame.
674 static noinline
struct avc_node
*avc_compute_av(u32 ssid
, u32 tsid
,
675 u16 tclass
, struct av_decision
*avd
)
678 security_compute_av(ssid
, tsid
, tclass
, avd
);
680 return avc_insert(ssid
, tsid
, tclass
, avd
);
683 static noinline
int avc_denied(u32 ssid
, u32 tsid
,
684 u16 tclass
, u32 requested
,
686 struct av_decision
*avd
)
688 if (flags
& AVC_STRICT
)
691 if (selinux_enforcing
&& !(avd
->flags
& AVD_FLAGS_PERMISSIVE
))
694 avc_update_node(AVC_CALLBACK_GRANT
, requested
, ssid
,
695 tsid
, tclass
, avd
->seqno
);
701 * avc_has_perm_noaudit - Check permissions but perform no auditing.
702 * @ssid: source security identifier
703 * @tsid: target security identifier
704 * @tclass: target security class
705 * @requested: requested permissions, interpreted based on @tclass
706 * @flags: AVC_STRICT or 0
707 * @avd: access vector decisions
709 * Check the AVC to determine whether the @requested permissions are granted
710 * for the SID pair (@ssid, @tsid), interpreting the permissions
711 * based on @tclass, and call the security server on a cache miss to obtain
712 * a new decision and add it to the cache. Return a copy of the decisions
713 * in @avd. Return %0 if all @requested permissions are granted,
714 * -%EACCES if any permissions are denied, or another -errno upon
715 * other errors. This function is typically called by avc_has_perm(),
716 * but may also be called directly to separate permission checking from
717 * auditing, e.g. in cases where a lock must be held for the check but
718 * should be released for the auditing.
720 inline int avc_has_perm_noaudit(u32 ssid
, u32 tsid
,
721 u16 tclass
, u32 requested
,
723 struct av_decision
*avd
)
725 struct avc_node
*node
;
733 node
= avc_lookup(ssid
, tsid
, tclass
);
734 if (unlikely(!node
)) {
735 node
= avc_compute_av(ssid
, tsid
, tclass
, avd
);
737 memcpy(avd
, &node
->ae
.avd
, sizeof(*avd
));
741 denied
= requested
& ~(avd
->allowed
);
742 if (unlikely(denied
))
743 rc
= avc_denied(ssid
, tsid
, tclass
, requested
, flags
, avd
);
750 * avc_has_perm - Check permissions and perform any appropriate auditing.
751 * @ssid: source security identifier
752 * @tsid: target security identifier
753 * @tclass: target security class
754 * @requested: requested permissions, interpreted based on @tclass
755 * @auditdata: auxiliary audit data
756 * @flags: VFS walk flags
758 * Check the AVC to determine whether the @requested permissions are granted
759 * for the SID pair (@ssid, @tsid), interpreting the permissions
760 * based on @tclass, and call the security server on a cache miss to obtain
761 * a new decision and add it to the cache. Audit the granting or denial of
762 * permissions in accordance with the policy. Return %0 if all @requested
763 * permissions are granted, -%EACCES if any permissions are denied, or
764 * another -errno upon other errors.
766 int avc_has_perm_flags(u32 ssid
, u32 tsid
, u16 tclass
,
767 u32 requested
, struct common_audit_data
*auditdata
,
770 struct av_decision avd
;
773 rc
= avc_has_perm_noaudit(ssid
, tsid
, tclass
, requested
, 0, &avd
);
775 rc2
= avc_audit(ssid
, tsid
, tclass
, requested
, &avd
, rc
, auditdata
,
782 u32
avc_policy_seqno(void)
784 return avc_cache
.latest_notif
;
787 void avc_disable(void)
790 * If you are looking at this because you have realized that we are
791 * not destroying the avc_node_cachep it might be easy to fix, but
792 * I don't know the memory barrier semantics well enough to know. It's
793 * possible that some other task dereferenced security_ops when
794 * it still pointed to selinux operations. If that is the case it's
795 * possible that it is about to use the avc and is about to need the
796 * avc_node_cachep. I know I could wrap the security.c security_ops call
797 * in an rcu_lock, but seriously, it's not worth it. Instead I just flush
798 * the cache and get that memory back.
800 if (avc_node_cachep
) {
802 /* kmem_cache_destroy(avc_node_cachep); */