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Linux/security/selinux/avc.c

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  1 /*
  2  * Implementation of the kernel access vector cache (AVC).
  3  *
  4  * Authors:  Stephen Smalley, <sds@epoch.ncsc.mil>
  5  *           James Morris <jmorris@redhat.com>
  6  *
  7  * Update:   KaiGai, Kohei <kaigai@ak.jp.nec.com>
  8  *      Replaced the avc_lock spinlock by RCU.
  9  *
 10  * Copyright (C) 2003 Red Hat, Inc., James Morris <jmorris@redhat.com>
 11  *
 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.
 15  */
 16 #include <linux/types.h>
 17 #include <linux/stddef.h>
 18 #include <linux/kernel.h>
 19 #include <linux/slab.h>
 20 #include <linux/fs.h>
 21 #include <linux/dcache.h>
 22 #include <linux/init.h>
 23 #include <linux/skbuff.h>
 24 #include <linux/percpu.h>
 25 #include <net/sock.h>
 26 #include <linux/un.h>
 27 #include <net/af_unix.h>
 28 #include <linux/ip.h>
 29 #include <linux/audit.h>
 30 #include <linux/ipv6.h>
 31 #include <net/ipv6.h>
 32 #include "avc.h"
 33 #include "avc_ss.h"
 34 #include "classmap.h"
 35 
 36 #define AVC_CACHE_SLOTS                 512
 37 #define AVC_DEF_CACHE_THRESHOLD         512
 38 #define AVC_CACHE_RECLAIM               16
 39 
 40 #ifdef CONFIG_SECURITY_SELINUX_AVC_STATS
 41 #define avc_cache_stats_incr(field)     this_cpu_inc(avc_cache_stats.field)
 42 #else
 43 #define avc_cache_stats_incr(field)     do {} while (0)
 44 #endif
 45 
 46 struct avc_entry {
 47         u32                     ssid;
 48         u32                     tsid;
 49         u16                     tclass;
 50         struct av_decision      avd;
 51 };
 52 
 53 struct avc_node {
 54         struct avc_entry        ae;
 55         struct hlist_node       list; /* anchored in avc_cache->slots[i] */
 56         struct rcu_head         rhead;
 57 };
 58 
 59 struct avc_cache {
 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 */
 65 };
 66 
 67 struct avc_callback_node {
 68         int (*callback) (u32 event);
 69         u32 events;
 70         struct avc_callback_node *next;
 71 };
 72 
 73 /* Exported via selinufs */
 74 unsigned int avc_cache_threshold = AVC_DEF_CACHE_THRESHOLD;
 75 
 76 #ifdef CONFIG_SECURITY_SELINUX_AVC_STATS
 77 DEFINE_PER_CPU(struct avc_cache_stats, avc_cache_stats) = { 0 };
 78 #endif
 79 
 80 static struct avc_cache avc_cache;
 81 static struct avc_callback_node *avc_callbacks;
 82 static struct kmem_cache *avc_node_cachep;
 83 
 84 static inline int avc_hash(u32 ssid, u32 tsid, u16 tclass)
 85 {
 86         return (ssid ^ (tsid<<2) ^ (tclass<<4)) & (AVC_CACHE_SLOTS - 1);
 87 }
 88 
 89 /**
 90  * avc_dump_av - Display an access vector in human-readable form.
 91  * @tclass: target security class
 92  * @av: access vector
 93  */
 94 static void avc_dump_av(struct audit_buffer *ab, u16 tclass, u32 av)
 95 {
 96         const char **perms;
 97         int i, perm;
 98 
 99         if (av == 0) {
100                 audit_log_format(ab, " null");
101                 return;
102         }
103 
104         perms = secclass_map[tclass-1].perms;
105 
106         audit_log_format(ab, " {");
107         i = 0;
108         perm = 1;
109         while (i < (sizeof(av) * 8)) {
110                 if ((perm & av) && perms[i]) {
111                         audit_log_format(ab, " %s", perms[i]);
112                         av &= ~perm;
113                 }
114                 i++;
115                 perm <<= 1;
116         }
117 
118         if (av)
119                 audit_log_format(ab, " 0x%x", av);
120 
121         audit_log_format(ab, " }");
122 }
123 
124 /**
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
129  */
130 static void avc_dump_query(struct audit_buffer *ab, u32 ssid, u32 tsid, u16 tclass)
131 {
132         int rc;
133         char *scontext;
134         u32 scontext_len;
135 
136         rc = security_sid_to_context(ssid, &scontext, &scontext_len);
137         if (rc)
138                 audit_log_format(ab, "ssid=%d", ssid);
139         else {
140                 audit_log_format(ab, "scontext=%s", scontext);
141                 kfree(scontext);
142         }
143 
144         rc = security_sid_to_context(tsid, &scontext, &scontext_len);
145         if (rc)
146                 audit_log_format(ab, " tsid=%d", tsid);
147         else {
148                 audit_log_format(ab, " tcontext=%s", scontext);
149                 kfree(scontext);
150         }
151 
152         BUG_ON(tclass >= ARRAY_SIZE(secclass_map));
153         audit_log_format(ab, " tclass=%s", secclass_map[tclass-1].name);
154 }
155 
156 /**
157  * avc_init - Initialize the AVC.
158  *
159  * Initialize the access vector cache.
160  */
161 void __init avc_init(void)
162 {
163         int i;
164 
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]);
168         }
169         atomic_set(&avc_cache.active_nodes, 0);
170         atomic_set(&avc_cache.lru_hint, 0);
171 
172         avc_node_cachep = kmem_cache_create("avc_node", sizeof(struct avc_node),
173                                              0, SLAB_PANIC, NULL);
174 
175         audit_log(current->audit_context, GFP_KERNEL, AUDIT_KERNEL, "AVC INITIALIZED\n");
176 }
177 
178 int avc_get_hash_stats(char *page)
179 {
180         int i, chain_len, max_chain_len, slots_used;
181         struct avc_node *node;
182         struct hlist_head *head;
183 
184         rcu_read_lock();
185 
186         slots_used = 0;
187         max_chain_len = 0;
188         for (i = 0; i < AVC_CACHE_SLOTS; i++) {
189                 head = &avc_cache.slots[i];
190                 if (!hlist_empty(head)) {
191                         slots_used++;
192                         chain_len = 0;
193                         hlist_for_each_entry_rcu(node, head, list)
194                                 chain_len++;
195                         if (chain_len > max_chain_len)
196                                 max_chain_len = chain_len;
197                 }
198         }
199 
200         rcu_read_unlock();
201 
202         return scnprintf(page, PAGE_SIZE, "entries: %d\nbuckets used: %d/%d\n"
203                          "longest chain: %d\n",
204                          atomic_read(&avc_cache.active_nodes),
205                          slots_used, AVC_CACHE_SLOTS, max_chain_len);
206 }
207 
208 static void avc_node_free(struct rcu_head *rhead)
209 {
210         struct avc_node *node = container_of(rhead, struct avc_node, rhead);
211         kmem_cache_free(avc_node_cachep, node);
212         avc_cache_stats_incr(frees);
213 }
214 
215 static void avc_node_delete(struct avc_node *node)
216 {
217         hlist_del_rcu(&node->list);
218         call_rcu(&node->rhead, avc_node_free);
219         atomic_dec(&avc_cache.active_nodes);
220 }
221 
222 static void avc_node_kill(struct avc_node *node)
223 {
224         kmem_cache_free(avc_node_cachep, node);
225         avc_cache_stats_incr(frees);
226         atomic_dec(&avc_cache.active_nodes);
227 }
228 
229 static void avc_node_replace(struct avc_node *new, struct avc_node *old)
230 {
231         hlist_replace_rcu(&old->list, &new->list);
232         call_rcu(&old->rhead, avc_node_free);
233         atomic_dec(&avc_cache.active_nodes);
234 }
235 
236 static inline int avc_reclaim_node(void)
237 {
238         struct avc_node *node;
239         int hvalue, try, ecx;
240         unsigned long flags;
241         struct hlist_head *head;
242         spinlock_t *lock;
243 
244         for (try = 0, ecx = 0; try < AVC_CACHE_SLOTS; try++) {
245                 hvalue = atomic_inc_return(&avc_cache.lru_hint) & (AVC_CACHE_SLOTS - 1);
246                 head = &avc_cache.slots[hvalue];
247                 lock = &avc_cache.slots_lock[hvalue];
248 
249                 if (!spin_trylock_irqsave(lock, flags))
250                         continue;
251 
252                 rcu_read_lock();
253                 hlist_for_each_entry(node, head, list) {
254                         avc_node_delete(node);
255                         avc_cache_stats_incr(reclaims);
256                         ecx++;
257                         if (ecx >= AVC_CACHE_RECLAIM) {
258                                 rcu_read_unlock();
259                                 spin_unlock_irqrestore(lock, flags);
260                                 goto out;
261                         }
262                 }
263                 rcu_read_unlock();
264                 spin_unlock_irqrestore(lock, flags);
265         }
266 out:
267         return ecx;
268 }
269 
270 static struct avc_node *avc_alloc_node(void)
271 {
272         struct avc_node *node;
273 
274         node = kmem_cache_zalloc(avc_node_cachep, GFP_ATOMIC|__GFP_NOMEMALLOC);
275         if (!node)
276                 goto out;
277 
278         INIT_HLIST_NODE(&node->list);
279         avc_cache_stats_incr(allocations);
280 
281         if (atomic_inc_return(&avc_cache.active_nodes) > avc_cache_threshold)
282                 avc_reclaim_node();
283 
284 out:
285         return node;
286 }
287 
288 static void avc_node_populate(struct avc_node *node, u32 ssid, u32 tsid, u16 tclass, struct av_decision *avd)
289 {
290         node->ae.ssid = ssid;
291         node->ae.tsid = tsid;
292         node->ae.tclass = tclass;
293         memcpy(&node->ae.avd, avd, sizeof(node->ae.avd));
294 }
295 
296 static inline struct avc_node *avc_search_node(u32 ssid, u32 tsid, u16 tclass)
297 {
298         struct avc_node *node, *ret = NULL;
299         int hvalue;
300         struct hlist_head *head;
301 
302         hvalue = avc_hash(ssid, tsid, tclass);
303         head = &avc_cache.slots[hvalue];
304         hlist_for_each_entry_rcu(node, head, list) {
305                 if (ssid == node->ae.ssid &&
306                     tclass == node->ae.tclass &&
307                     tsid == node->ae.tsid) {
308                         ret = node;
309                         break;
310                 }
311         }
312 
313         return ret;
314 }
315 
316 /**
317  * avc_lookup - Look up an AVC entry.
318  * @ssid: source security identifier
319  * @tsid: target security identifier
320  * @tclass: target security class
321  *
322  * Look up an AVC entry that is valid for the
323  * (@ssid, @tsid), interpreting the permissions
324  * based on @tclass.  If a valid AVC entry exists,
325  * then this function returns the avc_node.
326  * Otherwise, this function returns NULL.
327  */
328 static struct avc_node *avc_lookup(u32 ssid, u32 tsid, u16 tclass)
329 {
330         struct avc_node *node;
331 
332         avc_cache_stats_incr(lookups);
333         node = avc_search_node(ssid, tsid, tclass);
334 
335         if (node)
336                 return node;
337 
338         avc_cache_stats_incr(misses);
339         return NULL;
340 }
341 
342 static int avc_latest_notif_update(int seqno, int is_insert)
343 {
344         int ret = 0;
345         static DEFINE_SPINLOCK(notif_lock);
346         unsigned long flag;
347 
348         spin_lock_irqsave(&notif_lock, flag);
349         if (is_insert) {
350                 if (seqno < avc_cache.latest_notif) {
351                         printk(KERN_WARNING "SELinux: avc:  seqno %d < latest_notif %d\n",
352                                seqno, avc_cache.latest_notif);
353                         ret = -EAGAIN;
354                 }
355         } else {
356                 if (seqno > avc_cache.latest_notif)
357                         avc_cache.latest_notif = seqno;
358         }
359         spin_unlock_irqrestore(&notif_lock, flag);
360 
361         return ret;
362 }
363 
364 /**
365  * avc_insert - Insert an AVC entry.
366  * @ssid: source security identifier
367  * @tsid: target security identifier
368  * @tclass: target security class
369  * @avd: resulting av decision
370  *
371  * Insert an AVC entry for the SID pair
372  * (@ssid, @tsid) and class @tclass.
373  * The access vectors and the sequence number are
374  * normally provided by the security server in
375  * response to a security_compute_av() call.  If the
376  * sequence number @avd->seqno is not less than the latest
377  * revocation notification, then the function copies
378  * the access vectors into a cache entry, returns
379  * avc_node inserted. Otherwise, this function returns NULL.
380  */
381 static struct avc_node *avc_insert(u32 ssid, u32 tsid, u16 tclass, struct av_decision *avd)
382 {
383         struct avc_node *pos, *node = NULL;
384         int hvalue;
385         unsigned long flag;
386 
387         if (avc_latest_notif_update(avd->seqno, 1))
388                 goto out;
389 
390         node = avc_alloc_node();
391         if (node) {
392                 struct hlist_head *head;
393                 spinlock_t *lock;
394 
395                 hvalue = avc_hash(ssid, tsid, tclass);
396                 avc_node_populate(node, ssid, tsid, tclass, avd);
397 
398                 head = &avc_cache.slots[hvalue];
399                 lock = &avc_cache.slots_lock[hvalue];
400 
401                 spin_lock_irqsave(lock, flag);
402                 hlist_for_each_entry(pos, head, list) {
403                         if (pos->ae.ssid == ssid &&
404                             pos->ae.tsid == tsid &&
405                             pos->ae.tclass == tclass) {
406                                 avc_node_replace(node, pos);
407                                 goto found;
408                         }
409                 }
410                 hlist_add_head_rcu(&node->list, head);
411 found:
412                 spin_unlock_irqrestore(lock, flag);
413         }
414 out:
415         return node;
416 }
417 
418 /**
419  * avc_audit_pre_callback - SELinux specific information
420  * will be called by generic audit code
421  * @ab: the audit buffer
422  * @a: audit_data
423  */
424 static void avc_audit_pre_callback(struct audit_buffer *ab, void *a)
425 {
426         struct common_audit_data *ad = a;
427         audit_log_format(ab, "avc:  %s ",
428                          ad->selinux_audit_data->denied ? "denied" : "granted");
429         avc_dump_av(ab, ad->selinux_audit_data->tclass,
430                         ad->selinux_audit_data->audited);
431         audit_log_format(ab, " for ");
432 }
433 
434 /**
435  * avc_audit_post_callback - SELinux specific information
436  * will be called by generic audit code
437  * @ab: the audit buffer
438  * @a: audit_data
439  */
440 static void avc_audit_post_callback(struct audit_buffer *ab, void *a)
441 {
442         struct common_audit_data *ad = a;
443         audit_log_format(ab, " ");
444         avc_dump_query(ab, ad->selinux_audit_data->ssid,
445                            ad->selinux_audit_data->tsid,
446                            ad->selinux_audit_data->tclass);
447         if (ad->selinux_audit_data->denied) {
448                 audit_log_format(ab, " permissive=%u",
449                                  ad->selinux_audit_data->result ? 0 : 1);
450         }
451 }
452 
453 /* This is the slow part of avc audit with big stack footprint */
454 noinline int slow_avc_audit(u32 ssid, u32 tsid, u16 tclass,
455                 u32 requested, u32 audited, u32 denied, int result,
456                 struct common_audit_data *a,
457                 unsigned flags)
458 {
459         struct common_audit_data stack_data;
460         struct selinux_audit_data sad;
461 
462         if (!a) {
463                 a = &stack_data;
464                 a->type = LSM_AUDIT_DATA_NONE;
465         }
466 
467         /*
468          * When in a RCU walk do the audit on the RCU retry.  This is because
469          * the collection of the dname in an inode audit message is not RCU
470          * safe.  Note this may drop some audits when the situation changes
471          * during retry. However this is logically just as if the operation
472          * happened a little later.
473          */
474         if ((a->type == LSM_AUDIT_DATA_INODE) &&
475             (flags & MAY_NOT_BLOCK))
476                 return -ECHILD;
477 
478         sad.tclass = tclass;
479         sad.requested = requested;
480         sad.ssid = ssid;
481         sad.tsid = tsid;
482         sad.audited = audited;
483         sad.denied = denied;
484         sad.result = result;
485 
486         a->selinux_audit_data = &sad;
487 
488         common_lsm_audit(a, avc_audit_pre_callback, avc_audit_post_callback);
489         return 0;
490 }
491 
492 /**
493  * avc_add_callback - Register a callback for security events.
494  * @callback: callback function
495  * @events: security events
496  *
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.
500  */
501 int __init avc_add_callback(int (*callback)(u32 event), u32 events)
502 {
503         struct avc_callback_node *c;
504         int rc = 0;
505 
506         c = kmalloc(sizeof(*c), GFP_KERNEL);
507         if (!c) {
508                 rc = -ENOMEM;
509                 goto out;
510         }
511 
512         c->callback = callback;
513         c->events = events;
514         c->next = avc_callbacks;
515         avc_callbacks = c;
516 out:
517         return rc;
518 }
519 
520 /**
521  * avc_update_node Update an AVC entry
522  * @event : Updating event
523  * @perms : Permission mask bits
524  * @ssid,@tsid,@tclass : identifier of an AVC entry
525  * @seqno : sequence number when decision was made
526  *
527  * if a valid AVC entry doesn't exist,this function returns -ENOENT.
528  * if kmalloc() called internal returns NULL, this function returns -ENOMEM.
529  * otherwise, this function updates the AVC entry. The original AVC-entry object
530  * will release later by RCU.
531  */
532 static int avc_update_node(u32 event, u32 perms, u32 ssid, u32 tsid, u16 tclass,
533                            u32 seqno)
534 {
535         int hvalue, rc = 0;
536         unsigned long flag;
537         struct avc_node *pos, *node, *orig = NULL;
538         struct hlist_head *head;
539         spinlock_t *lock;
540 
541         node = avc_alloc_node();
542         if (!node) {
543                 rc = -ENOMEM;
544                 goto out;
545         }
546 
547         /* Lock the target slot */
548         hvalue = avc_hash(ssid, tsid, tclass);
549 
550         head = &avc_cache.slots[hvalue];
551         lock = &avc_cache.slots_lock[hvalue];
552 
553         spin_lock_irqsave(lock, flag);
554 
555         hlist_for_each_entry(pos, head, list) {
556                 if (ssid == pos->ae.ssid &&
557                     tsid == pos->ae.tsid &&
558                     tclass == pos->ae.tclass &&
559                     seqno == pos->ae.avd.seqno){
560                         orig = pos;
561                         break;
562                 }
563         }
564 
565         if (!orig) {
566                 rc = -ENOENT;
567                 avc_node_kill(node);
568                 goto out_unlock;
569         }
570 
571         /*
572          * Copy and replace original node.
573          */
574 
575         avc_node_populate(node, ssid, tsid, tclass, &orig->ae.avd);
576 
577         switch (event) {
578         case AVC_CALLBACK_GRANT:
579                 node->ae.avd.allowed |= perms;
580                 break;
581         case AVC_CALLBACK_TRY_REVOKE:
582         case AVC_CALLBACK_REVOKE:
583                 node->ae.avd.allowed &= ~perms;
584                 break;
585         case AVC_CALLBACK_AUDITALLOW_ENABLE:
586                 node->ae.avd.auditallow |= perms;
587                 break;
588         case AVC_CALLBACK_AUDITALLOW_DISABLE:
589                 node->ae.avd.auditallow &= ~perms;
590                 break;
591         case AVC_CALLBACK_AUDITDENY_ENABLE:
592                 node->ae.avd.auditdeny |= perms;
593                 break;
594         case AVC_CALLBACK_AUDITDENY_DISABLE:
595                 node->ae.avd.auditdeny &= ~perms;
596                 break;
597         }
598         avc_node_replace(node, orig);
599 out_unlock:
600         spin_unlock_irqrestore(lock, flag);
601 out:
602         return rc;
603 }
604 
605 /**
606  * avc_flush - Flush the cache
607  */
608 static void avc_flush(void)
609 {
610         struct hlist_head *head;
611         struct avc_node *node;
612         spinlock_t *lock;
613         unsigned long flag;
614         int i;
615 
616         for (i = 0; i < AVC_CACHE_SLOTS; i++) {
617                 head = &avc_cache.slots[i];
618                 lock = &avc_cache.slots_lock[i];
619 
620                 spin_lock_irqsave(lock, flag);
621                 /*
622                  * With preemptable RCU, the outer spinlock does not
623                  * prevent RCU grace periods from ending.
624                  */
625                 rcu_read_lock();
626                 hlist_for_each_entry(node, head, list)
627                         avc_node_delete(node);
628                 rcu_read_unlock();
629                 spin_unlock_irqrestore(lock, flag);
630         }
631 }
632 
633 /**
634  * avc_ss_reset - Flush the cache and revalidate migrated permissions.
635  * @seqno: policy sequence number
636  */
637 int avc_ss_reset(u32 seqno)
638 {
639         struct avc_callback_node *c;
640         int rc = 0, tmprc;
641 
642         avc_flush();
643 
644         for (c = avc_callbacks; c; c = c->next) {
645                 if (c->events & AVC_CALLBACK_RESET) {
646                         tmprc = c->callback(AVC_CALLBACK_RESET);
647                         /* save the first error encountered for the return
648                            value and continue processing the callbacks */
649                         if (!rc)
650                                 rc = tmprc;
651                 }
652         }
653 
654         avc_latest_notif_update(seqno, 0);
655         return rc;
656 }
657 
658 /*
659  * Slow-path helper function for avc_has_perm_noaudit,
660  * when the avc_node lookup fails. We get called with
661  * the RCU read lock held, and need to return with it
662  * still held, but drop if for the security compute.
663  *
664  * Don't inline this, since it's the slow-path and just
665  * results in a bigger stack frame.
666  */
667 static noinline struct avc_node *avc_compute_av(u32 ssid, u32 tsid,
668                          u16 tclass, struct av_decision *avd)
669 {
670         rcu_read_unlock();
671         security_compute_av(ssid, tsid, tclass, avd);
672         rcu_read_lock();
673         return avc_insert(ssid, tsid, tclass, avd);
674 }
675 
676 static noinline int avc_denied(u32 ssid, u32 tsid,
677                          u16 tclass, u32 requested,
678                          unsigned flags,
679                          struct av_decision *avd)
680 {
681         if (flags & AVC_STRICT)
682                 return -EACCES;
683 
684         if (selinux_enforcing && !(avd->flags & AVD_FLAGS_PERMISSIVE))
685                 return -EACCES;
686 
687         avc_update_node(AVC_CALLBACK_GRANT, requested, ssid,
688                                 tsid, tclass, avd->seqno);
689         return 0;
690 }
691 
692 
693 /**
694  * avc_has_perm_noaudit - Check permissions but perform no auditing.
695  * @ssid: source security identifier
696  * @tsid: target security identifier
697  * @tclass: target security class
698  * @requested: requested permissions, interpreted based on @tclass
699  * @flags:  AVC_STRICT or 0
700  * @avd: access vector decisions
701  *
702  * Check the AVC to determine whether the @requested permissions are granted
703  * for the SID pair (@ssid, @tsid), interpreting the permissions
704  * based on @tclass, and call the security server on a cache miss to obtain
705  * a new decision and add it to the cache.  Return a copy of the decisions
706  * in @avd.  Return %0 if all @requested permissions are granted,
707  * -%EACCES if any permissions are denied, or another -errno upon
708  * other errors.  This function is typically called by avc_has_perm(),
709  * but may also be called directly to separate permission checking from
710  * auditing, e.g. in cases where a lock must be held for the check but
711  * should be released for the auditing.
712  */
713 inline int avc_has_perm_noaudit(u32 ssid, u32 tsid,
714                          u16 tclass, u32 requested,
715                          unsigned flags,
716                          struct av_decision *avd)
717 {
718         struct avc_node *node;
719         int rc = 0;
720         u32 denied;
721 
722         BUG_ON(!requested);
723 
724         rcu_read_lock();
725 
726         node = avc_lookup(ssid, tsid, tclass);
727         if (unlikely(!node)) {
728                 node = avc_compute_av(ssid, tsid, tclass, avd);
729         } else {
730                 memcpy(avd, &node->ae.avd, sizeof(*avd));
731                 avd = &node->ae.avd;
732         }
733 
734         denied = requested & ~(avd->allowed);
735         if (unlikely(denied))
736                 rc = avc_denied(ssid, tsid, tclass, requested, flags, avd);
737 
738         rcu_read_unlock();
739         return rc;
740 }
741 
742 /**
743  * avc_has_perm - Check permissions and perform any appropriate auditing.
744  * @ssid: source security identifier
745  * @tsid: target security identifier
746  * @tclass: target security class
747  * @requested: requested permissions, interpreted based on @tclass
748  * @auditdata: auxiliary audit data
749  *
750  * Check the AVC to determine whether the @requested permissions are granted
751  * for the SID pair (@ssid, @tsid), interpreting the permissions
752  * based on @tclass, and call the security server on a cache miss to obtain
753  * a new decision and add it to the cache.  Audit the granting or denial of
754  * permissions in accordance with the policy.  Return %0 if all @requested
755  * permissions are granted, -%EACCES if any permissions are denied, or
756  * another -errno upon other errors.
757  */
758 int avc_has_perm(u32 ssid, u32 tsid, u16 tclass,
759                  u32 requested, struct common_audit_data *auditdata)
760 {
761         struct av_decision avd;
762         int rc, rc2;
763 
764         rc = avc_has_perm_noaudit(ssid, tsid, tclass, requested, 0, &avd);
765 
766         rc2 = avc_audit(ssid, tsid, tclass, requested, &avd, rc, auditdata);
767         if (rc2)
768                 return rc2;
769         return rc;
770 }
771 
772 u32 avc_policy_seqno(void)
773 {
774         return avc_cache.latest_notif;
775 }
776 
777 void avc_disable(void)
778 {
779         /*
780          * If you are looking at this because you have realized that we are
781          * not destroying the avc_node_cachep it might be easy to fix, but
782          * I don't know the memory barrier semantics well enough to know.  It's
783          * possible that some other task dereferenced security_ops when
784          * it still pointed to selinux operations.  If that is the case it's
785          * possible that it is about to use the avc and is about to need the
786          * avc_node_cachep.  I know I could wrap the security.c security_ops call
787          * in an rcu_lock, but seriously, it's not worth it.  Instead I just flush
788          * the cache and get that memory back.
789          */
790         if (avc_node_cachep) {
791                 avc_flush();
792                 /* kmem_cache_destroy(avc_node_cachep); */
793         }
794 }
795 

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