/*
   * Implementation of the kernel access vector cache (AVC).
   *
   * Authors:  Stephen Smalley, <sds@epoch.ncsc.mil>

   *	     James Morris <jmorris@redhat.com>

   *
   * Update:   KaiGai, Kohei <kaigai@ak.jp.nec.com>

   *	Replaced the avc_lock spinlock by RCU.

   *
   * Copyright (C) 2003 Red Hat, Inc., James Morris <jmorris@redhat.com>
   *
   *	This program is free software; you can redistribute it and/or modify
   *	it under the terms of the GNU General Public License version 2,

   *	as published by the Free Software Foundation.

   */
  #include <linux/types.h>
  #include <linux/stddef.h>
  #include <linux/kernel.h>
  #include <linux/slab.h>
  #include <linux/fs.h>
  #include <linux/dcache.h>
  #include <linux/init.h>
  #include <linux/skbuff.h>
  #include <linux/percpu.h>
  #include <net/sock.h>
  #include <linux/un.h>
  #include <net/af_unix.h>
  #include <linux/ip.h>
  #include <linux/audit.h>
  #include <linux/ipv6.h>
  #include <net/ipv6.h>
  #include "avc.h"
  #include "avc_ss.h"

  #include "classmap.h"

  #define AVC_CACHE_SLOTS			512
  #define AVC_DEF_CACHE_THRESHOLD		512
  #define AVC_CACHE_RECLAIM		16
  
  #ifdef CONFIG_SECURITY_SELINUX_AVC_STATS

  #define avc_cache_stats_incr(field)	this_cpu_inc(avc_cache_stats.field)

  #else
  #define avc_cache_stats_incr(field)	do {} while (0)
  #endif
  
  struct avc_entry {
  	u32			ssid;
  	u32			tsid;
  	u16			tclass;
  	struct av_decision	avd;

  };
  
  struct avc_node {
  	struct avc_entry	ae;

  	struct hlist_node	list; /* anchored in avc_cache->slots[i] */

  	struct rcu_head		rhead;

  };
  
  struct avc_cache {

  	struct hlist_head	slots[AVC_CACHE_SLOTS]; /* head for avc_node->list */

  	spinlock_t		slots_lock[AVC_CACHE_SLOTS]; /* lock for writes */
  	atomic_t		lru_hint;	/* LRU hint for reclaim scan */
  	atomic_t		active_nodes;
  	u32			latest_notif;	/* latest revocation notification */
  };
  
  struct avc_callback_node {
  	int (*callback) (u32 event, u32 ssid, u32 tsid,

  			 u16 tclass, u32 perms,
  			 u32 *out_retained);

  	u32 events;
  	u32 ssid;
  	u32 tsid;
  	u16 tclass;
  	u32 perms;
  	struct avc_callback_node *next;
  };
  
  /* Exported via selinufs */
  unsigned int avc_cache_threshold = AVC_DEF_CACHE_THRESHOLD;
  
  #ifdef CONFIG_SECURITY_SELINUX_AVC_STATS
  DEFINE_PER_CPU(struct avc_cache_stats, avc_cache_stats) = { 0 };
  #endif
  
  static struct avc_cache avc_cache;
  static struct avc_callback_node *avc_callbacks;

  static struct kmem_cache *avc_node_cachep;

  
  static inline int avc_hash(u32 ssid, u32 tsid, u16 tclass)
  {
  	return (ssid ^ (tsid<<2) ^ (tclass<<4)) & (AVC_CACHE_SLOTS - 1);
  }
  
  /**
   * avc_dump_av - Display an access vector in human-readable form.
   * @tclass: target security class
   * @av: access vector
   */

  static void avc_dump_av(struct audit_buffer *ab, u16 tclass, u32 av)

  {

  	const char **perms;
  	int i, perm;

  
  	if (av == 0) {
  		audit_log_format(ab, " null");
  		return;
  	}

  	perms = secclass_map[tclass-1].perms;

  
  	audit_log_format(ab, " {");
  	i = 0;
  	perm = 1;

  	while (i < (sizeof(av) * 8)) {

  		if ((perm & av) && perms[i]) {

  			audit_log_format(ab, " %s", perms[i]);

  			av &= ~perm;
  		}
  		i++;
  		perm <<= 1;
  	}

  	if (av)
  		audit_log_format(ab, " 0x%x", av);
  
  	audit_log_format(ab, " }");
  }
  
  /**
   * avc_dump_query - Display a SID pair and a class in human-readable form.
   * @ssid: source security identifier
   * @tsid: target security identifier
   * @tclass: target security class
   */
  static void avc_dump_query(struct audit_buffer *ab, u32 ssid, u32 tsid, u16 tclass)
  {
  	int rc;
  	char *scontext;
  	u32 scontext_len;

  	rc = security_sid_to_context(ssid, &scontext, &scontext_len);

  	if (rc)
  		audit_log_format(ab, "ssid=%d", ssid);
  	else {
  		audit_log_format(ab, "scontext=%s", scontext);
  		kfree(scontext);
  	}
  
  	rc = security_sid_to_context(tsid, &scontext, &scontext_len);
  	if (rc)
  		audit_log_format(ab, " tsid=%d", tsid);
  	else {
  		audit_log_format(ab, " tcontext=%s", scontext);
  		kfree(scontext);
  	}

  	BUG_ON(tclass >= ARRAY_SIZE(secclass_map));
  	audit_log_format(ab, " tclass=%s", secclass_map[tclass-1].name);

  }
  
  /**
   * avc_init - Initialize the AVC.
   *
   * Initialize the access vector cache.
   */
  void __init avc_init(void)
  {
  	int i;
  
  	for (i = 0; i < AVC_CACHE_SLOTS; i++) {

  		INIT_HLIST_HEAD(&avc_cache.slots[i]);

  		spin_lock_init(&avc_cache.slots_lock[i]);
  	}
  	atomic_set(&avc_cache.active_nodes, 0);
  	atomic_set(&avc_cache.lru_hint, 0);
  
  	avc_node_cachep = kmem_cache_create("avc_node", sizeof(struct avc_node),

  					     0, SLAB_PANIC, NULL);

  	audit_log(current->audit_context, GFP_KERNEL, AUDIT_KERNEL, "AVC INITIALIZED
  ");

  }
  
  int avc_get_hash_stats(char *page)
  {
  	int i, chain_len, max_chain_len, slots_used;
  	struct avc_node *node;

  	struct hlist_head *head;

  
  	rcu_read_lock();
  
  	slots_used = 0;
  	max_chain_len = 0;
  	for (i = 0; i < AVC_CACHE_SLOTS; i++) {

  		head = &avc_cache.slots[i];

  		if (!hlist_empty(head)) {
  			struct hlist_node *next;

  			slots_used++;
  			chain_len = 0;

  			hlist_for_each_entry_rcu(node, next, head, list)

  				chain_len++;
  			if (chain_len > max_chain_len)
  				max_chain_len = chain_len;
  		}
  	}
  
  	rcu_read_unlock();
  
  	return scnprintf(page, PAGE_SIZE, "entries: %d
  buckets used: %d/%d
  "
  			 "longest chain: %d
  ",
  			 atomic_read(&avc_cache.active_nodes),
  			 slots_used, AVC_CACHE_SLOTS, max_chain_len);
  }
  
  static void avc_node_free(struct rcu_head *rhead)
  {
  	struct avc_node *node = container_of(rhead, struct avc_node, rhead);
  	kmem_cache_free(avc_node_cachep, node);
  	avc_cache_stats_incr(frees);
  }
  
  static void avc_node_delete(struct avc_node *node)
  {

  	hlist_del_rcu(&node->list);

  	call_rcu(&node->rhead, avc_node_free);
  	atomic_dec(&avc_cache.active_nodes);
  }
  
  static void avc_node_kill(struct avc_node *node)
  {
  	kmem_cache_free(avc_node_cachep, node);
  	avc_cache_stats_incr(frees);
  	atomic_dec(&avc_cache.active_nodes);
  }
  
  static void avc_node_replace(struct avc_node *new, struct avc_node *old)
  {

  	hlist_replace_rcu(&old->list, &new->list);

  	call_rcu(&old->rhead, avc_node_free);
  	atomic_dec(&avc_cache.active_nodes);
  }
  
  static inline int avc_reclaim_node(void)
  {
  	struct avc_node *node;
  	int hvalue, try, ecx;
  	unsigned long flags;

  	struct hlist_head *head;
  	struct hlist_node *next;

  	spinlock_t *lock;

  	for (try = 0, ecx = 0; try < AVC_CACHE_SLOTS; try++) {

  		hvalue = atomic_inc_return(&avc_cache.lru_hint) & (AVC_CACHE_SLOTS - 1);

  		head = &avc_cache.slots[hvalue];
  		lock = &avc_cache.slots_lock[hvalue];

  		if (!spin_trylock_irqsave(lock, flags))

  			continue;

  		rcu_read_lock();

  		hlist_for_each_entry(node, next, head, list) {

  			avc_node_delete(node);
  			avc_cache_stats_incr(reclaims);
  			ecx++;
  			if (ecx >= AVC_CACHE_RECLAIM) {
  				rcu_read_unlock();

  				spin_unlock_irqrestore(lock, flags);

  				goto out;

  			}
  		}

  		rcu_read_unlock();

  		spin_unlock_irqrestore(lock, flags);

  	}
  out:
  	return ecx;
  }
  
  static struct avc_node *avc_alloc_node(void)
  {
  	struct avc_node *node;

  	node = kmem_cache_zalloc(avc_node_cachep, GFP_ATOMIC);

  	if (!node)
  		goto out;

  	INIT_HLIST_NODE(&node->list);

  	avc_cache_stats_incr(allocations);
  
  	if (atomic_inc_return(&avc_cache.active_nodes) > avc_cache_threshold)
  		avc_reclaim_node();
  
  out:
  	return node;
  }

  static void avc_node_populate(struct avc_node *node, u32 ssid, u32 tsid, u16 tclass, struct av_decision *avd)

  {
  	node->ae.ssid = ssid;
  	node->ae.tsid = tsid;
  	node->ae.tclass = tclass;

  	memcpy(&node->ae.avd, avd, sizeof(node->ae.avd));

  }
  
  static inline struct avc_node *avc_search_node(u32 ssid, u32 tsid, u16 tclass)
  {
  	struct avc_node *node, *ret = NULL;
  	int hvalue;

  	struct hlist_head *head;
  	struct hlist_node *next;

  
  	hvalue = avc_hash(ssid, tsid, tclass);

  	head = &avc_cache.slots[hvalue];

  	hlist_for_each_entry_rcu(node, next, head, list) {

  		if (ssid == node->ae.ssid &&
  		    tclass == node->ae.tclass &&
  		    tsid == node->ae.tsid) {
  			ret = node;
  			break;
  		}
  	}

  	return ret;
  }
  
  /**
   * avc_lookup - Look up an AVC entry.
   * @ssid: source security identifier
   * @tsid: target security identifier
   * @tclass: target security class

   *
   * Look up an AVC entry that is valid for the

   * (@ssid, @tsid), interpreting the permissions
   * based on @tclass.  If a valid AVC entry exists,

   * then this function returns the avc_node.

   * Otherwise, this function returns NULL.
   */

  static struct avc_node *avc_lookup(u32 ssid, u32 tsid, u16 tclass)

  {
  	struct avc_node *node;
  
  	avc_cache_stats_incr(lookups);
  	node = avc_search_node(ssid, tsid, tclass);

  	if (node)

  		return node;

  	avc_cache_stats_incr(misses);
  	return NULL;

  }
  
  static int avc_latest_notif_update(int seqno, int is_insert)
  {
  	int ret = 0;
  	static DEFINE_SPINLOCK(notif_lock);
  	unsigned long flag;
  
  	spin_lock_irqsave(&notif_lock, flag);
  	if (is_insert) {
  		if (seqno < avc_cache.latest_notif) {

  			printk(KERN_WARNING "SELinux: avc:  seqno %d < latest_notif %d
  ",

  			       seqno, avc_cache.latest_notif);
  			ret = -EAGAIN;
  		}
  	} else {
  		if (seqno > avc_cache.latest_notif)
  			avc_cache.latest_notif = seqno;
  	}
  	spin_unlock_irqrestore(&notif_lock, flag);
  
  	return ret;
  }
  
  /**
   * avc_insert - Insert an AVC entry.
   * @ssid: source security identifier
   * @tsid: target security identifier
   * @tclass: target security class

   * @avd: resulting av decision

   *
   * Insert an AVC entry for the SID pair
   * (@ssid, @tsid) and class @tclass.
   * The access vectors and the sequence number are
   * normally provided by the security server in
   * response to a security_compute_av() call.  If the

   * sequence number @avd->seqno is not less than the latest

   * revocation notification, then the function copies
   * the access vectors into a cache entry, returns
   * avc_node inserted. Otherwise, this function returns NULL.
   */

  static struct avc_node *avc_insert(u32 ssid, u32 tsid, u16 tclass, struct av_decision *avd)

  {
  	struct avc_node *pos, *node = NULL;
  	int hvalue;
  	unsigned long flag;

  	if (avc_latest_notif_update(avd->seqno, 1))

  		goto out;
  
  	node = avc_alloc_node();
  	if (node) {

  		struct hlist_head *head;
  		struct hlist_node *next;

  		spinlock_t *lock;

  		hvalue = avc_hash(ssid, tsid, tclass);

  		avc_node_populate(node, ssid, tsid, tclass, avd);

  		head = &avc_cache.slots[hvalue];
  		lock = &avc_cache.slots_lock[hvalue];
  
  		spin_lock_irqsave(lock, flag);

  		hlist_for_each_entry(pos, next, head, list) {

  			if (pos->ae.ssid == ssid &&
  			    pos->ae.tsid == tsid &&
  			    pos->ae.tclass == tclass) {

  				avc_node_replace(node, pos);

  				goto found;
  			}
  		}

  		hlist_add_head_rcu(&node->list, head);

  found:

  		spin_unlock_irqrestore(lock, flag);

  	}
  out:
  	return node;
  }

  /**
   * avc_audit_pre_callback - SELinux specific information
   * will be called by generic audit code
   * @ab: the audit buffer
   * @a: audit_data
   */
  static void avc_audit_pre_callback(struct audit_buffer *ab, void *a)

  {

  	struct common_audit_data *ad = a;
  	audit_log_format(ab, "avc:  %s ",
  			 ad->selinux_audit_data.denied ? "denied" : "granted");
  	avc_dump_av(ab, ad->selinux_audit_data.tclass,
  			ad->selinux_audit_data.audited);
  	audit_log_format(ab, " for ");

  }

  /**
   * avc_audit_post_callback - SELinux specific information
   * will be called by generic audit code
   * @ab: the audit buffer
   * @a: audit_data
   */
  static void avc_audit_post_callback(struct audit_buffer *ab, void *a)

  {

  	struct common_audit_data *ad = a;
  	audit_log_format(ab, " ");
  	avc_dump_query(ab, ad->selinux_audit_data.ssid,
  			   ad->selinux_audit_data.tsid,
  			   ad->selinux_audit_data.tclass);

  }
  
  /**
   * avc_audit - Audit the granting or denial of permissions.
   * @ssid: source security identifier
   * @tsid: target security identifier
   * @tclass: target security class
   * @requested: requested permissions
   * @avd: access vector decisions
   * @result: result from avc_has_perm_noaudit
   * @a:  auxiliary audit data

   * @flags: VFS walk flags

   *
   * Audit the granting or denial of permissions in accordance
   * with the policy.  This function is typically called by
   * avc_has_perm() after a permission check, but can also be
   * called directly by callers who use avc_has_perm_noaudit()
   * in order to separate the permission check from the auditing.
   * For example, this separation is useful when the permission check must
   * be performed under a lock, to allow the lock to be released
   * before calling the auditing code.
   */

  int avc_audit(u32 ssid, u32 tsid,

  	       u16 tclass, u32 requested,

  	       struct av_decision *avd, int result, struct common_audit_data *a,
  	       unsigned flags)

  {

  	struct common_audit_data stack_data;

  	u32 denied, audited;

  	denied = requested & ~avd->allowed;

  	if (denied) {

  		audited = denied & avd->auditdeny;

  		/*
  		 * a->selinux_audit_data.auditdeny is TRICKY!  Setting a bit in
  		 * this field means that ANY denials should NOT be audited if
  		 * the policy contains an explicit dontaudit rule for that
  		 * permission.  Take notice that this is unrelated to the
  		 * actual permissions that were denied.  As an example lets
  		 * assume:
  		 *
  		 * denied == READ
  		 * avd.auditdeny & ACCESS == 0 (not set means explicit rule)
  		 * selinux_audit_data.auditdeny & ACCESS == 1
  		 *
  		 * We will NOT audit the denial even though the denied
  		 * permission was READ and the auditdeny checks were for
  		 * ACCESS
  		 */
  		if (a &&
  		    a->selinux_audit_data.auditdeny &&
  		    !(a->selinux_audit_data.auditdeny & avd->auditdeny))
  			audited = 0;
  	} else if (result)

  		audited = denied = requested;

  	else
  		audited = requested & avd->auditallow;
  	if (!audited)

  		return 0;

  	if (!a) {
  		a = &stack_data;

  		COMMON_AUDIT_DATA_INIT(a, NONE);

  	}

  
  	/*
  	 * When in a RCU walk do the audit on the RCU retry.  This is because
  	 * the collection of the dname in an inode audit message is not RCU
  	 * safe.  Note this may drop some audits when the situation changes
  	 * during retry. However this is logically just as if the operation
  	 * happened a little later.
  	 */

  	if ((a->type == LSM_AUDIT_DATA_INODE) &&

  	    (flags & MAY_NOT_BLOCK))

  		return -ECHILD;

  	a->selinux_audit_data.tclass = tclass;
  	a->selinux_audit_data.requested = requested;
  	a->selinux_audit_data.ssid = ssid;
  	a->selinux_audit_data.tsid = tsid;
  	a->selinux_audit_data.audited = audited;
  	a->selinux_audit_data.denied = denied;
  	a->lsm_pre_audit = avc_audit_pre_callback;
  	a->lsm_post_audit = avc_audit_post_callback;
  	common_lsm_audit(a);

  	return 0;

  }
  
  /**
   * avc_add_callback - Register a callback for security events.
   * @callback: callback function
   * @events: security events
   * @ssid: source security identifier or %SECSID_WILD
   * @tsid: target security identifier or %SECSID_WILD
   * @tclass: target security class
   * @perms: permissions
   *
   * Register a callback function for events in the set @events

   * related to the SID pair (@ssid, @tsid) 

   * and the permissions @perms, interpreting
   * @perms based on @tclass.  Returns %0 on success or
   * -%ENOMEM if insufficient memory exists to add the callback.
   */
  int avc_add_callback(int (*callback)(u32 event, u32 ssid, u32 tsid,

  				     u16 tclass, u32 perms,
  				     u32 *out_retained),
  		     u32 events, u32 ssid, u32 tsid,
  		     u16 tclass, u32 perms)

  {
  	struct avc_callback_node *c;
  	int rc = 0;
  
  	c = kmalloc(sizeof(*c), GFP_ATOMIC);
  	if (!c) {
  		rc = -ENOMEM;
  		goto out;
  	}
  
  	c->callback = callback;
  	c->events = events;
  	c->ssid = ssid;
  	c->tsid = tsid;
  	c->perms = perms;
  	c->next = avc_callbacks;
  	avc_callbacks = c;
  out:
  	return rc;
  }
  
  static inline int avc_sidcmp(u32 x, u32 y)
  {
  	return (x == y || x == SECSID_WILD || y == SECSID_WILD);
  }
  
  /**
   * avc_update_node Update an AVC entry
   * @event : Updating event
   * @perms : Permission mask bits
   * @ssid,@tsid,@tclass : identifier of an AVC entry

   * @seqno : sequence number when decision was made

   *
   * if a valid AVC entry doesn't exist,this function returns -ENOENT.
   * if kmalloc() called internal returns NULL, this function returns -ENOMEM.

   * otherwise, this function updates the AVC entry. The original AVC-entry object

   * will release later by RCU.
   */

  static int avc_update_node(u32 event, u32 perms, u32 ssid, u32 tsid, u16 tclass,
  			   u32 seqno)

  {
  	int hvalue, rc = 0;
  	unsigned long flag;
  	struct avc_node *pos, *node, *orig = NULL;

  	struct hlist_head *head;
  	struct hlist_node *next;

  	spinlock_t *lock;

  
  	node = avc_alloc_node();
  	if (!node) {
  		rc = -ENOMEM;
  		goto out;
  	}
  
  	/* Lock the target slot */
  	hvalue = avc_hash(ssid, tsid, tclass);

  	head = &avc_cache.slots[hvalue];
  	lock = &avc_cache.slots_lock[hvalue];
  
  	spin_lock_irqsave(lock, flag);

  	hlist_for_each_entry(pos, next, head, list) {

  		if (ssid == pos->ae.ssid &&
  		    tsid == pos->ae.tsid &&

  		    tclass == pos->ae.tclass &&
  		    seqno == pos->ae.avd.seqno){

  			orig = pos;
  			break;
  		}
  	}
  
  	if (!orig) {
  		rc = -ENOENT;
  		avc_node_kill(node);
  		goto out_unlock;
  	}
  
  	/*
  	 * Copy and replace original node.
  	 */

  	avc_node_populate(node, ssid, tsid, tclass, &orig->ae.avd);

  
  	switch (event) {
  	case AVC_CALLBACK_GRANT:
  		node->ae.avd.allowed |= perms;
  		break;
  	case AVC_CALLBACK_TRY_REVOKE:
  	case AVC_CALLBACK_REVOKE:
  		node->ae.avd.allowed &= ~perms;
  		break;
  	case AVC_CALLBACK_AUDITALLOW_ENABLE:
  		node->ae.avd.auditallow |= perms;
  		break;
  	case AVC_CALLBACK_AUDITALLOW_DISABLE:
  		node->ae.avd.auditallow &= ~perms;
  		break;
  	case AVC_CALLBACK_AUDITDENY_ENABLE:
  		node->ae.avd.auditdeny |= perms;
  		break;
  	case AVC_CALLBACK_AUDITDENY_DISABLE:
  		node->ae.avd.auditdeny &= ~perms;
  		break;
  	}
  	avc_node_replace(node, orig);
  out_unlock:

  	spin_unlock_irqrestore(lock, flag);

  out:
  	return rc;
  }
  
  /**

   * avc_flush - Flush the cache

   */

  static void avc_flush(void)

  {

  	struct hlist_head *head;
  	struct hlist_node *next;

  	struct avc_node *node;

  	spinlock_t *lock;

  	unsigned long flag;
  	int i;

  
  	for (i = 0; i < AVC_CACHE_SLOTS; i++) {

  		head = &avc_cache.slots[i];
  		lock = &avc_cache.slots_lock[i];
  
  		spin_lock_irqsave(lock, flag);

  		/*
  		 * With preemptable RCU, the outer spinlock does not
  		 * prevent RCU grace periods from ending.
  		 */
  		rcu_read_lock();

  		hlist_for_each_entry(node, next, head, list)

  			avc_node_delete(node);

  		rcu_read_unlock();

  		spin_unlock_irqrestore(lock, flag);

  	}

  }
  
  /**
   * avc_ss_reset - Flush the cache and revalidate migrated permissions.
   * @seqno: policy sequence number
   */
  int avc_ss_reset(u32 seqno)
  {
  	struct avc_callback_node *c;
  	int rc = 0, tmprc;
  
  	avc_flush();

  
  	for (c = avc_callbacks; c; c = c->next) {
  		if (c->events & AVC_CALLBACK_RESET) {

  			tmprc = c->callback(AVC_CALLBACK_RESET,

  					    0, 0, 0, 0, NULL);

  			/* save the first error encountered for the return
  			   value and continue processing the callbacks */
  			if (!rc)
  				rc = tmprc;

  		}
  	}
  
  	avc_latest_notif_update(seqno, 0);

  	return rc;
  }
  
  /**
   * avc_has_perm_noaudit - Check permissions but perform no auditing.
   * @ssid: source security identifier
   * @tsid: target security identifier
   * @tclass: target security class
   * @requested: requested permissions, interpreted based on @tclass

   * @flags:  AVC_STRICT or 0

   * @avd: access vector decisions
   *
   * Check the AVC to determine whether the @requested permissions are granted
   * for the SID pair (@ssid, @tsid), interpreting the permissions
   * based on @tclass, and call the security server on a cache miss to obtain
   * a new decision and add it to the cache.  Return a copy of the decisions
   * in @avd.  Return %0 if all @requested permissions are granted,
   * -%EACCES if any permissions are denied, or another -errno upon
   * other errors.  This function is typically called by avc_has_perm(),
   * but may also be called directly to separate permission checking from
   * auditing, e.g. in cases where a lock must be held for the check but
   * should be released for the auditing.
   */
  int avc_has_perm_noaudit(u32 ssid, u32 tsid,

  			 u16 tclass, u32 requested,
  			 unsigned flags,

  			 struct av_decision *avd)

  {
  	struct avc_node *node;

  	int rc = 0;
  	u32 denied;

  	BUG_ON(!requested);

  	rcu_read_lock();

  	node = avc_lookup(ssid, tsid, tclass);

  	if (unlikely(!node)) {

  		rcu_read_unlock();

  		security_compute_av(ssid, tsid, tclass, avd);

  		rcu_read_lock();

  		node = avc_insert(ssid, tsid, tclass, avd);
  	} else {

  		memcpy(avd, &node->ae.avd, sizeof(*avd));

  		avd = &node->ae.avd;

  	}

  	denied = requested & ~(avd->allowed);

  	if (denied) {

  		if (flags & AVC_STRICT)

  			rc = -EACCES;

  		else if (!selinux_enforcing || (avd->flags & AVD_FLAGS_PERMISSIVE))

  			avc_update_node(AVC_CALLBACK_GRANT, requested, ssid,

  					tsid, tclass, avd->seqno);

  		else

  			rc = -EACCES;

  	}
  
  	rcu_read_unlock();

  	return rc;
  }
  
  /**
   * avc_has_perm - Check permissions and perform any appropriate auditing.
   * @ssid: source security identifier
   * @tsid: target security identifier
   * @tclass: target security class
   * @requested: requested permissions, interpreted based on @tclass
   * @auditdata: auxiliary audit data

   * @flags: VFS walk flags

   *
   * Check the AVC to determine whether the @requested permissions are granted
   * for the SID pair (@ssid, @tsid), interpreting the permissions
   * based on @tclass, and call the security server on a cache miss to obtain
   * a new decision and add it to the cache.  Audit the granting or denial of
   * permissions in accordance with the policy.  Return %0 if all @requested
   * permissions are granted, -%EACCES if any permissions are denied, or
   * another -errno upon other errors.
   */

  int avc_has_perm_flags(u32 ssid, u32 tsid, u16 tclass,
  		       u32 requested, struct common_audit_data *auditdata,
  		       unsigned flags)

  {
  	struct av_decision avd;

  	int rc, rc2;

  	rc = avc_has_perm_noaudit(ssid, tsid, tclass, requested, 0, &avd);

  
  	rc2 = avc_audit(ssid, tsid, tclass, requested, &avd, rc, auditdata,
  			flags);
  	if (rc2)
  		return rc2;

  	return rc;
  }

  
  u32 avc_policy_seqno(void)
  {
  	return avc_cache.latest_notif;
  }

  
  void avc_disable(void)
  {

  	/*
  	 * If you are looking at this because you have realized that we are
  	 * not destroying the avc_node_cachep it might be easy to fix, but
  	 * I don't know the memory barrier semantics well enough to know.  It's
  	 * possible that some other task dereferenced security_ops when
  	 * it still pointed to selinux operations.  If that is the case it's
  	 * possible that it is about to use the avc and is about to need the
  	 * avc_node_cachep.  I know I could wrap the security.c security_ops call
  	 * in an rcu_lock, but seriously, it's not worth it.  Instead I just flush
  	 * the cache and get that memory back.
  	 */
  	if (avc_node_cachep) {
  		avc_flush();
  		/* kmem_cache_destroy(avc_node_cachep); */
  	}

  }