avc.c

linux 内核源代码

/*
 * Implementation of the kernel access vector cache (AVC).
 *
 * Authors:  Stephen Smalley, <[e-mail]>
 *           James Morris <[e-mail]>
 *
 * Update:   KaiGai, Kohei <[e-mail]>
 *     Replaced the avc_lock spinlock by RCU.
 *
 * Copyright (C) 2003 Red Hat, Inc., James Morris <[e-mail]>
 *
 *	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"

static const struct av_perm_to_string av_perm_to_string[] = {
#define S_(c, v, s) { c, v, s },
#include "av_perm_to_string.h"
#undef S_
};

static const char *class_to_string[] = {
#define S_(s) s,
#include "class_to_string.h"
#undef S_
};

#define TB_(s) static const char * s [] = {
#define TE_(s) };
#define S_(s) s,
#include "common_perm_to_string.h"
#undef TB_
#undef TE_
#undef S_

static const struct av_inherit av_inherit[] = {
#define S_(c, i, b) { c, common_##i##_perm_to_string, b },
#include "av_inherit.h"
#undef S_
};

const struct selinux_class_perm selinux_class_perm = {
	av_perm_to_string,
	ARRAY_SIZE(av_perm_to_string),
	class_to_string,
	ARRAY_SIZE(class_to_string),
	av_inherit,
	ARRAY_SIZE(av_inherit)
};

#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) 				\
do {								\
	per_cpu(avc_cache_stats, get_cpu()).field++;		\
	put_cpu();						\
} while (0)
#else
#define avc_cache_stats_incr(field)	do {} while (0)
#endif

struct avc_entry {
	u32			ssid;
	u32			tsid;
	u16			tclass;
	struct av_decision	avd;
	atomic_t		used;	/* used recently */
};

struct avc_node {
	struct avc_entry	ae;
	struct list_head	list;
	struct rcu_head         rhead;
};

struct avc_cache {
	struct list_head	slots[AVC_CACHE_SLOTS];
	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 **common_pts = NULL;
	u32 common_base = 0;
	int i, i2, perm;

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

	for (i = 0; i < ARRAY_SIZE(av_inherit); i++) {
		if (av_inherit[i].tclass == tclass) {
			common_pts = av_inherit[i].common_pts;
			common_base = av_inherit[i].common_base;
			break;
		}
	}

	audit_log_format(ab, " {");
	i = 0;
	perm = 1;
	while (perm < common_base) {
		if (perm & av) {
			audit_log_format(ab, " %s", common_pts[i]);
			av &= ~perm;
		}
		i++;
		perm <<= 1;
	}

	while (i < sizeof(av) * 8) {
		if (perm & av) {
			for (i2 = 0; i2 < ARRAY_SIZE(av_perm_to_string); i2++) {
				if ((av_perm_to_string[i2].tclass == tclass) &&
				    (av_perm_to_string[i2].value == perm))
					break;
			}
			if (i2 < ARRAY_SIZE(av_perm_to_string)) {
				audit_log_format(ab, " %s",
						 av_perm_to_string[i2].name);
				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(class_to_string) || !class_to_string[tclass]);
	audit_log_format(ab, " tclass=%s", class_to_string[tclass]);
}

/**
 * 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_LIST_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\n");
}

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

	rcu_read_lock();

	slots_used = 0;
	max_chain_len = 0;
	for (i = 0; i < AVC_CACHE_SLOTS; i++) {
		if (!list_empty(&avc_cache.slots[i])) {
			slots_used++;
			chain_len = 0;
			list_for_each_entry_rcu(node, &avc_cache.slots[i], list)
				chain_len++;
			if (chain_len > max_chain_len)
				max_chain_len = chain_len;
		}
	}

	rcu_read_unlock();

	return scnprintf(page, PAGE_SIZE, "entries: %d\nbuckets used: %d/%d\n"
			 "longest chain: %d\n",
			 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)
{
	list_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)
{
	list_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;

	for (try = 0, ecx = 0; try < AVC_CACHE_SLOTS; try++ ) {
		hvalue = atomic_inc_return(&avc_cache.lru_hint) & (AVC_CACHE_SLOTS - 1);

		if (!spin_trylock_irqsave(&avc_cache.slots_lock[hvalue], flags))
			continue;

		list_for_each_entry(node, &avc_cache.slots[hvalue], list) {
			if (atomic_dec_and_test(&node->ae.used)) {
				/* Recently Unused */
				avc_node_delete(node);
				avc_cache_stats_incr(reclaims);
				ecx++;
				if (ecx >= AVC_CACHE_RECLAIM) {
					spin_unlock_irqrestore(&avc_cache.slots_lock[hvalue], flags);
					goto out;
				}
			}
		}
		spin_unlock_irqrestore(&avc_cache.slots_lock[hvalue], 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_RCU_HEAD(&node->rhead);
	INIT_LIST_HEAD(&node->list);
	atomic_set(&node->ae.used, 1);
	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 avc_entry *ae)
{
	node->ae.ssid = ssid;
	node->ae.tsid = tsid;
	node->ae.tclass = tclass;
	memcpy(&node->ae.avd, &ae->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;

	hvalue = avc_hash(ssid, tsid, tclass);
	list_for_each_entry_rcu(node, &avc_cache.slots[hvalue], list) {
		if (ssid == node->ae.ssid &&
		    tclass == node->ae.tclass &&
		    tsid == node->ae.tsid) {
			ret = node;
			break;
		}
	}

	if (ret == NULL) {
		/* cache miss */
		goto out;
	}

	/* cache hit */
	if (atomic_read(&ret->ae.used) != 1)
		atomic_set(&ret->ae.used, 1);
out:
	return ret;
}

/**
 * avc_lookup - Look up an AVC entry.
 * @ssid: source security identifier
 * @tsid: target security identifier
 * @tclass: target security class
 * @requested: requested permissions, interpreted based on @tclass
 *
 * Look up an AVC entry that is valid for the
 * @requested permissions between the SID pair
 * (@ssid, @tsid), interpreting the permissions
 * based on @tclass.  If a valid AVC entry exists,
 * then this function return the avc_node.
 * Otherwise, this function returns NULL.
 */
static struct avc_node *avc_lookup(u32 ssid, u32 tsid, u16 tclass, u32 requested)
{
	struct avc_node *node;

	avc_cache_stats_incr(lookups);
	node = avc_search_node(ssid, tsid, tclass);

	if (node && ((node->ae.avd.decided & requested) == requested)) {
		avc_cache_stats_incr(hits);
		goto out;
	}

	node = NULL;
	avc_cache_stats_incr(misses);
out:
	return node;
}

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 "avc:  seqno %d < latest_notif %d\n",
			       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
 * @ae: AVC entry
 *
 * 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 @ae->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 avc_entry *ae)
{
	struct avc_node *pos, *node = NULL;
	int hvalue;