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) \
43 per_cpu(avc_cache_stats, get_cpu()).field++; \
47 #define avc_cache_stats_incr(field) do {} while (0)
54 struct av_decision avd;
59 struct hlist_node list; /* anchored in avc_cache->slots[i] */
60 struct rcu_head rhead;
64 struct hlist_head slots[AVC_CACHE_SLOTS]; /* head for avc_node->list */
65 spinlock_t slots_lock[AVC_CACHE_SLOTS]; /* lock for writes */
66 atomic_t lru_hint; /* LRU hint for reclaim scan */
67 atomic_t active_nodes;
68 u32 latest_notif; /* latest revocation notification */
71 struct avc_callback_node {
72 int (*callback) (u32 event, u32 ssid, u32 tsid,
73 u16 tclass, u32 perms,
80 struct avc_callback_node *next;
83 /* Exported via selinufs */
84 unsigned int avc_cache_threshold = AVC_DEF_CACHE_THRESHOLD;
86 #ifdef CONFIG_SECURITY_SELINUX_AVC_STATS
87 DEFINE_PER_CPU(struct avc_cache_stats, avc_cache_stats) = { 0 };
90 static struct avc_cache avc_cache;
91 static struct avc_callback_node *avc_callbacks;
92 static struct kmem_cache *avc_node_cachep;
94 static inline int avc_hash(u32 ssid, u32 tsid, u16 tclass)
96 return (ssid ^ (tsid<<2) ^ (tclass<<4)) & (AVC_CACHE_SLOTS - 1);
100 * avc_dump_av - Display an access vector in human-readable form.
101 * @tclass: target security class
104 static void avc_dump_av(struct audit_buffer *ab, u16 tclass, u32 av)
110 audit_log_format(ab, " null");
114 perms = secclass_map[tclass-1].perms;
116 audit_log_format(ab, " {");
119 while (i < (sizeof(av) * 8)) {
120 if ((perm & av) && perms[i]) {
121 audit_log_format(ab, " %s", perms[i]);
129 audit_log_format(ab, " 0x%x", av);
131 audit_log_format(ab, " }");
135 * avc_dump_query - Display a SID pair and a class in human-readable form.
136 * @ssid: source security identifier
137 * @tsid: target security identifier
138 * @tclass: target security class
140 static void avc_dump_query(struct audit_buffer *ab, u32 ssid, u32 tsid, u16 tclass)
146 rc = security_sid_to_context(ssid, &scontext, &scontext_len);
148 audit_log_format(ab, "ssid=%d", ssid);
150 audit_log_format(ab, "scontext=%s", scontext);
154 rc = security_sid_to_context(tsid, &scontext, &scontext_len);
156 audit_log_format(ab, " tsid=%d", tsid);
158 audit_log_format(ab, " tcontext=%s", scontext);
162 BUG_ON(tclass >= ARRAY_SIZE(secclass_map));
163 audit_log_format(ab, " tclass=%s", secclass_map[tclass-1].name);
167 * avc_init - Initialize the AVC.
169 * Initialize the access vector cache.
171 void __init avc_init(void)
175 for (i = 0; i < AVC_CACHE_SLOTS; i++) {
176 INIT_HLIST_HEAD(&avc_cache.slots[i]);
177 spin_lock_init(&avc_cache.slots_lock[i]);
179 atomic_set(&avc_cache.active_nodes, 0);
180 atomic_set(&avc_cache.lru_hint, 0);
182 avc_node_cachep = kmem_cache_create("avc_node", sizeof(struct avc_node),
183 0, SLAB_PANIC, NULL);
185 audit_log(current->audit_context, GFP_KERNEL, AUDIT_KERNEL, "AVC INITIALIZED\n");
188 int avc_get_hash_stats(char *page)
190 int i, chain_len, max_chain_len, slots_used;
191 struct avc_node *node;
192 struct hlist_head *head;
198 for (i = 0; i < AVC_CACHE_SLOTS; i++) {
199 head = &avc_cache.slots[i];
200 if (!hlist_empty(head)) {
201 struct hlist_node *next;
205 hlist_for_each_entry_rcu(node, next, head, list)
207 if (chain_len > max_chain_len)
208 max_chain_len = chain_len;
214 return scnprintf(page, PAGE_SIZE, "entries: %d\nbuckets used: %d/%d\n"
215 "longest chain: %d\n",
216 atomic_read(&avc_cache.active_nodes),
217 slots_used, AVC_CACHE_SLOTS, max_chain_len);
220 static void avc_node_free(struct rcu_head *rhead)
222 struct avc_node *node = container_of(rhead, struct avc_node, rhead);
223 kmem_cache_free(avc_node_cachep, node);
224 avc_cache_stats_incr(frees);
227 static void avc_node_delete(struct avc_node *node)
229 hlist_del_rcu(&node->list);
230 call_rcu(&node->rhead, avc_node_free);
231 atomic_dec(&avc_cache.active_nodes);
234 static void avc_node_kill(struct avc_node *node)
236 kmem_cache_free(avc_node_cachep, node);
237 avc_cache_stats_incr(frees);
238 atomic_dec(&avc_cache.active_nodes);
241 static void avc_node_replace(struct avc_node *new, struct avc_node *old)
243 hlist_replace_rcu(&old->list, &new->list);
244 call_rcu(&old->rhead, avc_node_free);
245 atomic_dec(&avc_cache.active_nodes);
248 static inline int avc_reclaim_node(void)
250 struct avc_node *node;
251 int hvalue, try, ecx;
253 struct hlist_head *head;
254 struct hlist_node *next;
257 for (try = 0, ecx = 0; try < AVC_CACHE_SLOTS; try++) {
258 hvalue = atomic_inc_return(&avc_cache.lru_hint) & (AVC_CACHE_SLOTS - 1);
259 head = &avc_cache.slots[hvalue];
260 lock = &avc_cache.slots_lock[hvalue];
262 if (!spin_trylock_irqsave(lock, flags))
266 hlist_for_each_entry(node, next, head, list) {
267 avc_node_delete(node);
268 avc_cache_stats_incr(reclaims);
270 if (ecx >= AVC_CACHE_RECLAIM) {
272 spin_unlock_irqrestore(lock, flags);
277 spin_unlock_irqrestore(lock, flags);
283 static struct avc_node *avc_alloc_node(void)
285 struct avc_node *node;
287 node = kmem_cache_zalloc(avc_node_cachep, GFP_ATOMIC);
291 INIT_HLIST_NODE(&node->list);
292 avc_cache_stats_incr(allocations);
294 if (atomic_inc_return(&avc_cache.active_nodes) > avc_cache_threshold)
301 static void avc_node_populate(struct avc_node *node, u32 ssid, u32 tsid, u16 tclass, struct av_decision *avd)
303 node->ae.ssid = ssid;
304 node->ae.tsid = tsid;
305 node->ae.tclass = tclass;
306 memcpy(&node->ae.avd, avd, sizeof(node->ae.avd));
309 static inline struct avc_node *avc_search_node(u32 ssid, u32 tsid, u16 tclass)
311 struct avc_node *node, *ret = NULL;
313 struct hlist_head *head;
314 struct hlist_node *next;
316 hvalue = avc_hash(ssid, tsid, tclass);
317 head = &avc_cache.slots[hvalue];
318 hlist_for_each_entry_rcu(node, next, head, list) {
319 if (ssid == node->ae.ssid &&
320 tclass == node->ae.tclass &&
321 tsid == node->ae.tsid) {
331 * avc_lookup - Look up an AVC entry.
332 * @ssid: source security identifier
333 * @tsid: target security identifier
334 * @tclass: target security class
336 * Look up an AVC entry that is valid for the
337 * (@ssid, @tsid), interpreting the permissions
338 * based on @tclass. If a valid AVC entry exists,
339 * then this function returns the avc_node.
340 * Otherwise, this function returns NULL.
342 static struct avc_node *avc_lookup(u32 ssid, u32 tsid, u16 tclass)
344 struct avc_node *node;
346 avc_cache_stats_incr(lookups);
347 node = avc_search_node(ssid, tsid, tclass);
350 avc_cache_stats_incr(hits);
352 avc_cache_stats_incr(misses);
357 static int avc_latest_notif_update(int seqno, int is_insert)
360 static DEFINE_SPINLOCK(notif_lock);
363 spin_lock_irqsave(¬if_lock, flag);
365 if (seqno < avc_cache.latest_notif) {
366 printk(KERN_WARNING "SELinux: avc: seqno %d < latest_notif %d\n",
367 seqno, avc_cache.latest_notif);
371 if (seqno > avc_cache.latest_notif)
372 avc_cache.latest_notif = seqno;
374 spin_unlock_irqrestore(¬if_lock, flag);
380 * avc_insert - Insert an AVC entry.
381 * @ssid: source security identifier
382 * @tsid: target security identifier
383 * @tclass: target security class
384 * @avd: resulting av decision
386 * Insert an AVC entry for the SID pair
387 * (@ssid, @tsid) and class @tclass.
388 * The access vectors and the sequence number are
389 * normally provided by the security server in
390 * response to a security_compute_av() call. If the
391 * sequence number @avd->seqno is not less than the latest
392 * revocation notification, then the function copies
393 * the access vectors into a cache entry, returns
394 * avc_node inserted. Otherwise, this function returns NULL.
396 static struct avc_node *avc_insert(u32 ssid, u32 tsid, u16 tclass, struct av_decision *avd)
398 struct avc_node *pos, *node = NULL;
402 if (avc_latest_notif_update(avd->seqno, 1))
405 node = avc_alloc_node();
407 struct hlist_head *head;
408 struct hlist_node *next;
411 hvalue = avc_hash(ssid, tsid, tclass);
412 avc_node_populate(node, ssid, tsid, tclass, avd);
414 head = &avc_cache.slots[hvalue];
415 lock = &avc_cache.slots_lock[hvalue];
417 spin_lock_irqsave(lock, flag);
418 hlist_for_each_entry(pos, next, head, list) {
419 if (pos->ae.ssid == ssid &&
420 pos->ae.tsid == tsid &&
421 pos->ae.tclass == tclass) {
422 avc_node_replace(node, pos);
426 hlist_add_head_rcu(&node->list, head);
428 spin_unlock_irqrestore(lock, flag);
435 * avc_audit_pre_callback - SELinux specific information
436 * will be called by generic audit code
437 * @ab: the audit buffer
440 static void avc_audit_pre_callback(struct audit_buffer *ab, void *a)
442 struct common_audit_data *ad = a;
443 audit_log_format(ab, "avc: %s ",
444 ad->selinux_audit_data.denied ? "denied" : "granted");
445 avc_dump_av(ab, ad->selinux_audit_data.tclass,
446 ad->selinux_audit_data.audited);
447 audit_log_format(ab, " for ");
451 * avc_audit_post_callback - SELinux specific information
452 * will be called by generic audit code
453 * @ab: the audit buffer
456 static void avc_audit_post_callback(struct audit_buffer *ab, void *a)
458 struct common_audit_data *ad = a;
459 audit_log_format(ab, " ");
460 avc_dump_query(ab, ad->selinux_audit_data.ssid,
461 ad->selinux_audit_data.tsid,
462 ad->selinux_audit_data.tclass);
466 * avc_audit - Audit the granting or denial of permissions.
467 * @ssid: source security identifier
468 * @tsid: target security identifier
469 * @tclass: target security class
470 * @requested: requested permissions
471 * @avd: access vector decisions
472 * @result: result from avc_has_perm_noaudit
473 * @a: auxiliary audit data
474 * @flags: VFS walk flags
476 * Audit the granting or denial of permissions in accordance
477 * with the policy. This function is typically called by
478 * avc_has_perm() after a permission check, but can also be
479 * called directly by callers who use avc_has_perm_noaudit()
480 * in order to separate the permission check from the auditing.
481 * For example, this separation is useful when the permission check must
482 * be performed under a lock, to allow the lock to be released
483 * before calling the auditing code.
485 int avc_audit(u32 ssid, u32 tsid,
486 u16 tclass, u32 requested,
487 struct av_decision *avd, int result, struct common_audit_data *a,
490 struct common_audit_data stack_data;
492 denied = requested & ~avd->allowed;
494 audited = denied & avd->auditdeny;
496 * a->selinux_audit_data.auditdeny is TRICKY! Setting a bit in
497 * this field means that ANY denials should NOT be audited if
498 * the policy contains an explicit dontaudit rule for that
499 * permission. Take notice that this is unrelated to the
500 * actual permissions that were denied. As an example lets
504 * avd.auditdeny & ACCESS == 0 (not set means explicit rule)
505 * selinux_audit_data.auditdeny & ACCESS == 1
507 * We will NOT audit the denial even though the denied
508 * permission was READ and the auditdeny checks were for
512 a->selinux_audit_data.auditdeny &&
513 !(a->selinux_audit_data.auditdeny & avd->auditdeny))
516 audited = denied = requested;
518 audited = requested & avd->auditallow;
524 COMMON_AUDIT_DATA_INIT(a, NONE);
528 * When in a RCU walk do the audit on the RCU retry. This is because
529 * the collection of the dname in an inode audit message is not RCU
530 * safe. Note this may drop some audits when the situation changes
531 * during retry. However this is logically just as if the operation
532 * happened a little later.
534 if ((a->type == LSM_AUDIT_DATA_FS) &&
535 (flags & IPERM_FLAG_RCU))
538 a->selinux_audit_data.tclass = tclass;
539 a->selinux_audit_data.requested = requested;
540 a->selinux_audit_data.ssid = ssid;
541 a->selinux_audit_data.tsid = tsid;
542 a->selinux_audit_data.audited = audited;
543 a->selinux_audit_data.denied = denied;
544 a->lsm_pre_audit = avc_audit_pre_callback;
545 a->lsm_post_audit = avc_audit_post_callback;
551 * avc_add_callback - Register a callback for security events.
552 * @callback: callback function
553 * @events: security events
554 * @ssid: source security identifier or %SECSID_WILD
555 * @tsid: target security identifier or %SECSID_WILD
556 * @tclass: target security class
557 * @perms: permissions
559 * Register a callback function for events in the set @events
560 * related to the SID pair (@ssid, @tsid)
561 * and the permissions @perms, interpreting
562 * @perms based on @tclass. Returns %0 on success or
563 * -%ENOMEM if insufficient memory exists to add the callback.
565 int avc_add_callback(int (*callback)(u32 event, u32 ssid, u32 tsid,
566 u16 tclass, u32 perms,
568 u32 events, u32 ssid, u32 tsid,
569 u16 tclass, u32 perms)
571 struct avc_callback_node *c;
574 c = kmalloc(sizeof(*c), GFP_ATOMIC);
580 c->callback = callback;
585 c->next = avc_callbacks;
591 static inline int avc_sidcmp(u32 x, u32 y)
593 return (x == y || x == SECSID_WILD || y == SECSID_WILD);
597 * avc_update_node Update an AVC entry
598 * @event : Updating event
599 * @perms : Permission mask bits
600 * @ssid,@tsid,@tclass : identifier of an AVC entry
601 * @seqno : sequence number when decision was made
603 * if a valid AVC entry doesn't exist,this function returns -ENOENT.
604 * if kmalloc() called internal returns NULL, this function returns -ENOMEM.
605 * otherwise, this function updates the AVC entry. The original AVC-entry object
606 * will release later by RCU.
608 static int avc_update_node(u32 event, u32 perms, u32 ssid, u32 tsid, u16 tclass,
613 struct avc_node *pos, *node, *orig = NULL;
614 struct hlist_head *head;
615 struct hlist_node *next;
618 node = avc_alloc_node();
624 /* Lock the target slot */
625 hvalue = avc_hash(ssid, tsid, tclass);
627 head = &avc_cache.slots[hvalue];
628 lock = &avc_cache.slots_lock[hvalue];
630 spin_lock_irqsave(lock, flag);
632 hlist_for_each_entry(pos, next, head, list) {
633 if (ssid == pos->ae.ssid &&
634 tsid == pos->ae.tsid &&
635 tclass == pos->ae.tclass &&
636 seqno == pos->ae.avd.seqno){
649 * Copy and replace original node.
652 avc_node_populate(node, ssid, tsid, tclass, &orig->ae.avd);
655 case AVC_CALLBACK_GRANT:
656 node->ae.avd.allowed |= perms;
658 case AVC_CALLBACK_TRY_REVOKE:
659 case AVC_CALLBACK_REVOKE:
660 node->ae.avd.allowed &= ~perms;
662 case AVC_CALLBACK_AUDITALLOW_ENABLE:
663 node->ae.avd.auditallow |= perms;
665 case AVC_CALLBACK_AUDITALLOW_DISABLE:
666 node->ae.avd.auditallow &= ~perms;
668 case AVC_CALLBACK_AUDITDENY_ENABLE:
669 node->ae.avd.auditdeny |= perms;
671 case AVC_CALLBACK_AUDITDENY_DISABLE:
672 node->ae.avd.auditdeny &= ~perms;
675 avc_node_replace(node, orig);
677 spin_unlock_irqrestore(lock, flag);
683 * avc_flush - Flush the cache
685 static void avc_flush(void)
687 struct hlist_head *head;
688 struct hlist_node *next;
689 struct avc_node *node;
694 for (i = 0; i < AVC_CACHE_SLOTS; i++) {
695 head = &avc_cache.slots[i];
696 lock = &avc_cache.slots_lock[i];
698 spin_lock_irqsave(lock, flag);
700 * With preemptable RCU, the outer spinlock does not
701 * prevent RCU grace periods from ending.
704 hlist_for_each_entry(node, next, head, list)
705 avc_node_delete(node);
707 spin_unlock_irqrestore(lock, flag);
712 * avc_ss_reset - Flush the cache and revalidate migrated permissions.
713 * @seqno: policy sequence number
715 int avc_ss_reset(u32 seqno)
717 struct avc_callback_node *c;
722 for (c = avc_callbacks; c; c = c->next) {
723 if (c->events & AVC_CALLBACK_RESET) {
724 tmprc = c->callback(AVC_CALLBACK_RESET,
726 /* save the first error encountered for the return
727 value and continue processing the callbacks */
733 avc_latest_notif_update(seqno, 0);
738 * avc_has_perm_noaudit - Check permissions but perform no auditing.
739 * @ssid: source security identifier
740 * @tsid: target security identifier
741 * @tclass: target security class
742 * @requested: requested permissions, interpreted based on @tclass
743 * @flags: AVC_STRICT or 0
744 * @avd: access vector decisions
746 * Check the AVC to determine whether the @requested permissions are granted
747 * for the SID pair (@ssid, @tsid), interpreting the permissions
748 * based on @tclass, and call the security server on a cache miss to obtain
749 * a new decision and add it to the cache. Return a copy of the decisions
750 * in @avd. Return %0 if all @requested permissions are granted,
751 * -%EACCES if any permissions are denied, or another -errno upon
752 * other errors. This function is typically called by avc_has_perm(),
753 * but may also be called directly to separate permission checking from
754 * auditing, e.g. in cases where a lock must be held for the check but
755 * should be released for the auditing.
757 int avc_has_perm_noaudit(u32 ssid, u32 tsid,
758 u16 tclass, u32 requested,
760 struct av_decision *in_avd)
762 struct avc_node *node;
763 struct av_decision avd_entry, *avd;
771 node = avc_lookup(ssid, tsid, tclass);
780 security_compute_av(ssid, tsid, tclass, avd);
782 node = avc_insert(ssid, tsid, tclass, avd);
785 memcpy(in_avd, &node->ae.avd, sizeof(*in_avd));
789 denied = requested & ~(avd->allowed);
792 if (flags & AVC_STRICT)
794 else if (!selinux_enforcing || (avd->flags & AVD_FLAGS_PERMISSIVE))
795 avc_update_node(AVC_CALLBACK_GRANT, requested, ssid,
796 tsid, tclass, avd->seqno);
806 * avc_has_perm - Check permissions and perform any appropriate auditing.
807 * @ssid: source security identifier
808 * @tsid: target security identifier
809 * @tclass: target security class
810 * @requested: requested permissions, interpreted based on @tclass
811 * @auditdata: auxiliary audit data
812 * @flags: VFS walk flags
814 * Check the AVC to determine whether the @requested permissions are granted
815 * for the SID pair (@ssid, @tsid), interpreting the permissions
816 * based on @tclass, and call the security server on a cache miss to obtain
817 * a new decision and add it to the cache. Audit the granting or denial of
818 * permissions in accordance with the policy. Return %0 if all @requested
819 * permissions are granted, -%EACCES if any permissions are denied, or
820 * another -errno upon other errors.
822 int avc_has_perm_flags(u32 ssid, u32 tsid, u16 tclass,
823 u32 requested, struct common_audit_data *auditdata,
826 struct av_decision avd;
829 rc = avc_has_perm_noaudit(ssid, tsid, tclass, requested, 0, &avd);
831 rc2 = avc_audit(ssid, tsid, tclass, requested, &avd, rc, auditdata,
838 u32 avc_policy_seqno(void)
840 return avc_cache.latest_notif;
843 void avc_disable(void)
846 * If you are looking at this because you have realized that we are
847 * not destroying the avc_node_cachep it might be easy to fix, but
848 * I don't know the memory barrier semantics well enough to know. It's
849 * possible that some other task dereferenced security_ops when
850 * it still pointed to selinux operations. If that is the case it's
851 * possible that it is about to use the avc and is about to need the
852 * avc_node_cachep. I know I could wrap the security.c security_ops call
853 * in an rcu_lock, but seriously, it's not worth it. Instead I just flush
854 * the cache and get that memory back.
856 if (avc_node_cachep) {
858 /* kmem_cache_destroy(avc_node_cachep); */