Subject: [PATCH 2/2] NetLabel: fix a cache race condition

From: [email-masked]
Date: Wed, 04 Oct 2006 11:46:31 -0400

Testing revealed a problem with the NetLabel cache where a cached entry could
be freed while in use by the LSM layer causing an oops and other problems.
This patch fixes that problem by introducing a reference counter to the cache
entry so that it is only freed when it is no longer in use.

Signed-off-by: Paul Moore <[email-masked]>
---
 include/net/netlabel.h         |   62 +++++++++++++++++++++++++++++++----------
 net/ipv4/cipso_ipv4.c          |   18 ++++++-----
 net/netlabel/netlabel_kapi.c   |    2 -
 security/selinux/ss/services.c |   37 +++++++++++++-----------
 4 files changed, 79 insertions(+), 40 deletions(-)

Index: net-2.6/include/net/netlabel.h
===================================================================
--- net-2.6.orig/include/net/netlabel.h
+++ net-2.6/include/net/netlabel.h
@@ -34,6 +34,7 @@
 #include <linux/net.h>
 #include <linux/skbuff.h>
 #include <net/netlink.h>
+#include <asm/atomic.h>
 
 /*
  * NetLabel - A management interface for maintaining network packet label
@@ -106,6 +107,7 @@ int netlbl_domhsh_remove(const char *dom
 
 /* LSM security attributes */
 struct netlbl_lsm_cache {
+	atomic_t refcount;
 	void (*free) (const void *data);
 	void *data;
 };
@@ -117,7 +119,7 @@ struct netlbl_lsm_secattr {
 	unsigned char *mls_cat;
 	size_t mls_cat_len;
 
-	struct netlbl_lsm_cache cache;
+	struct netlbl_lsm_cache *cache;
 };
 
 /*
@@ -126,6 +128,43 @@ struct netlbl_lsm_secattr {

 /**
+ * netlbl_secattr_cache_alloc - Allocate and initialize a secattr cache
+ * @flags: the memory allocation flags
+ *
+ * Description:
+ * Allocate and initialize a netlbl_lsm_cache structure.  Returns a pointer
+ * on success, NULL on failure.
+ *
+ */
+static inline struct netlbl_lsm_cache *netlbl_secattr_cache_alloc(int flags)
+{
+	struct netlbl_lsm_cache *cache;
+
+	cache = kzalloc(sizeof(*cache), flags);
+	if (cache)
+		atomic_set(&cache->refcount, 1);
+	return cache;
+}
+
+/**
+ * netlbl_secattr_cache_free - Frees a netlbl_lsm_cache struct
+ * @cache: the struct to free
+ *
+ * Description:
+ * Frees @secattr including all of the internal buffers.
+ *
+ */
+static inline void netlbl_secattr_cache_free(struct netlbl_lsm_cache *cache)
+{
+	if (!atomic_dec_and_test(&cache->refcount))
+		return;
+
+	if (cache->free)
+		cache->free(cache->data);
+	kfree(cache);
+}
+
+/**
  * netlbl_secattr_init - Initialize a netlbl_lsm_secattr struct
  * @secattr: the struct to initialize
  *
@@ -143,20 +182,16 @@ static inline int netlbl_secattr_init(st
 /**
  * netlbl_secattr_destroy - Clears a netlbl_lsm_secattr struct
  * @secattr: the struct to clear
- * @clear_cache: cache clear flag
  *
  * Description:
  * Destroys the @secattr struct, including freeing all of the internal buffers.
- * If @clear_cache is true then free the cache fields, otherwise leave them
- * intact.  The struct must be reset with a call to netlbl_secattr_init()
- * before reuse.
+ * The struct must be reset with a call to netlbl_secattr_init() before reuse.
  *
  */
-static inline void netlbl_secattr_destroy(struct netlbl_lsm_secattr *secattr,
-					  u32 clear_cache)
+static inline void netlbl_secattr_destroy(struct netlbl_lsm_secattr *secattr)
 {
-	if (clear_cache && secattr->cache.data != NULL && secattr->cache.free)
-		secattr->cache.free(secattr->cache.data);
+	if (secattr->cache)
+		netlbl_secattr_cache_free(secattr->cache);
 	kfree(secattr->domain);
 	kfree(secattr->mls_cat);
 }
@@ -178,17 +213,14 @@ static inline struct netlbl_lsm_secattr 
 /**
  * netlbl_secattr_free - Frees a netlbl_lsm_secattr struct
  * @secattr: the struct to free
- * @clear_cache: cache clear flag
  *
  * Description:
- * Frees @secattr including all of the internal buffers.  If @clear_cache is
- * true then free the cache fields, otherwise leave them intact.
+ * Frees @secattr including all of the internal buffers.
  *
  */
-static inline void netlbl_secattr_free(struct netlbl_lsm_secattr *secattr,
-				       u32 clear_cache)
+static inline void netlbl_secattr_free(struct netlbl_lsm_secattr *secattr)
 {
-	netlbl_secattr_destroy(secattr, clear_cache);
+	netlbl_secattr_destroy(secattr);
 	kfree(secattr);
 }
 
Index: net-2.6/net/ipv4/cipso_ipv4.c
===================================================================
--- net-2.6.orig/net/ipv4/cipso_ipv4.c
+++ net-2.6/net/ipv4/cipso_ipv4.c
@@ -43,6 +43,7 @@
 #include <net/tcp.h>
 #include <net/netlabel.h>
 #include <net/cipso_ipv4.h>
+#include <asm/atomic.h>
 #include <asm/bug.h>
 
 struct cipso_v4_domhsh_entry {
@@ -79,7 +80,7 @@ struct cipso_v4_map_cache_entry {
 	unsigned char *key;
 	size_t key_len;
 
-	struct netlbl_lsm_cache lsm_data;
+	struct netlbl_lsm_cache *lsm_data;
 
 	u32 activity;
 	struct list_head list;
@@ -188,13 +189,14 @@ static void cipso_v4_doi_domhsh_free(str
  * @entry: the entry to free
  *
  * Description:
- * This function frees the memory associated with a cache entry.
+ * This function frees the memory associated with a cache entry including the
+ * LSM cache data if there are no longer any users, i.e. reference count == 0.
  *
  */
 static void cipso_v4_cache_entry_free(struct cipso_v4_map_cache_entry *entry)
 {
-	if (entry->lsm_data.free)
-		entry->lsm_data.free(entry->lsm_data.data);
+	if (entry->lsm_data)
+		netlbl_secattr_cache_free(entry->lsm_data);
 	kfree(entry->key);
 	kfree(entry);
 }
@@ -315,8 +317,8 @@ static int cipso_v4_cache_check(const un
 		    entry->key_len == key_len &&
 		    memcmp(entry->key, key, key_len) == 0) {
 			entry->activity += 1;
-			secattr->cache.free = entry->lsm_data.free;
-			secattr->cache.data = entry->lsm_data.data;
+			atomic_inc(&entry->lsm_data->refcount);
+			secattr->cache = entry->lsm_data;
 			if (prev_entry == NULL) {
 				spin_unlock_bh(&cipso_v4_cache[bkt].lock);
 				return 0;
@@ -383,8 +385,8 @@ int cipso_v4_cache_add(const struct sk_b
 	memcpy(entry->key, cipso_ptr, cipso_ptr_len);
 	entry->key_len = cipso_ptr_len;
 	entry->hash = cipso_v4_map_cache_hash(cipso_ptr, cipso_ptr_len);
-	entry->lsm_data.free = secattr->cache.free;
-	entry->lsm_data.data = secattr->cache.data;
+	atomic_inc(&secattr->cache->refcount);
+	entry->lsm_data = secattr->cache;
 
 	bkt = entry->hash & (CIPSO_V4_CACHE_BUCKETBITS - 1);
 	spin_lock_bh(&cipso_v4_cache[bkt].lock);
Index: net-2.6/net/netlabel/netlabel_kapi.c
===================================================================
--- net-2.6.orig/net/netlabel/netlabel_kapi.c
+++ net-2.6/net/netlabel/netlabel_kapi.c
@@ -200,7 +200,7 @@ void netlbl_cache_invalidate(void)
 int netlbl_cache_add(const struct sk_buff *skb,
 		     const struct netlbl_lsm_secattr *secattr)
 {
-	if (secattr->cache.data == NULL)
+	if (secattr->cache == NULL)
 		return -ENOMSG;
 
 	if (CIPSO_V4_OPTEXIST(skb))
Index: net-2.6/security/selinux/ss/services.c
===================================================================
--- net-2.6.orig/security/selinux/ss/services.c
+++ net-2.6/security/selinux/ss/services.c
@@ -2173,7 +2173,12 @@ struct netlbl_cache {
  */
 static void selinux_netlbl_cache_free(const void *data)
 {
-	struct netlbl_cache *cache = NETLBL_CACHE(data);
+	struct netlbl_cache *cache;
+
+	if (data == NULL)
+		return;
+
+	cache = NETLBL_CACHE(data);
 	switch (cache->type) {
 	case NETLBL_CACHE_T_MLS:
 		ebitmap_destroy(&cache->data.mls_label.level[0].cat);
@@ -2198,17 +2203,20 @@ static void selinux_netlbl_cache_add(str
 	struct netlbl_lsm_secattr secattr;
 
 	netlbl_secattr_init(&secattr);
+	secattr.cache = netlbl_secattr_cache_alloc(GFP_ATOMIC);
+	if (secattr.cache == NULL)
+		goto netlbl_cache_add_return;
 
 	cache = kzalloc(sizeof(*cache),	GFP_ATOMIC);
 	if (cache == NULL)
-		goto netlbl_cache_add_failure;
-	secattr.cache.free = selinux_netlbl_cache_free;
-	secattr.cache.data = (void *)cache;
+		goto netlbl_cache_add_return;
+	secattr.cache->free = selinux_netlbl_cache_free;
+	secattr.cache->data = (void *)cache;
 
 	cache->type = NETLBL_CACHE_T_MLS;
 	if (ebitmap_cpy(&cache->data.mls_label.level[0].cat,
 			&ctx->range.level[0].cat) != 0)
-		goto netlbl_cache_add_failure;
+		goto netlbl_cache_add_return;
 	cache->data.mls_label.level[1].cat.highbit =
 		cache->data.mls_label.level[0].cat.highbit;
 	cache->data.mls_label.level[1].cat.node =
@@ -2216,13 +2224,10 @@ static void selinux_netlbl_cache_add(str
 	cache->data.mls_label.level[0].sens = ctx->range.level[0].sens;
 	cache->data.mls_label.level[1].sens = ctx->range.level[0].sens;
 
-	if (netlbl_cache_add(skb, &secattr) != 0)
-		goto netlbl_cache_add_failure;
-
-	return;
+	netlbl_cache_add(skb, &secattr);
 
-netlbl_cache_add_failure:
-	netlbl_secattr_destroy(&secattr, 1);
+netlbl_cache_add_return:
+	netlbl_secattr_destroy(&secattr);
 }
 
 /**
@@ -2264,8 +2269,8 @@ static int selinux_netlbl_secattr_to_sid
 
 	POLICY_RDLOCK;
 
-	if (secattr->cache.data) {
-		cache = NETLBL_CACHE(secattr->cache.data);
+	if (secattr->cache) {
+		cache = NETLBL_CACHE(secattr->cache->data);
 		switch (cache->type) {
 		case NETLBL_CACHE_T_SID:
 			*sid = cache->data.sid;
@@ -2370,7 +2375,7 @@ static int selinux_netlbl_skbuff_getsid(
 						   &secattr,
 						   base_sid,
 						   sid);
-	netlbl_secattr_destroy(&secattr, 0);
+	netlbl_secattr_destroy(&secattr);
 
 	return rc;
 }
@@ -2416,7 +2421,7 @@ static int selinux_netlbl_socket_setsid(
 	if (rc == 0)
 		sksec->nlbl_state = NLBL_LABELED;
 
-	netlbl_secattr_destroy(&secattr, 0);
+	netlbl_secattr_destroy(&secattr);
 
 netlbl_socket_setsid_return:
 	POLICY_RDUNLOCK;
@@ -2512,7 +2517,7 @@ void selinux_netlbl_sock_graft(struct so
 						  sksec->sid,
 						  &nlbl_peer_sid) == 0)
 			sksec->peer_sid = nlbl_peer_sid;
-		netlbl_secattr_destroy(&secattr, 0);
+		netlbl_secattr_destroy(&secattr);
 	}
 
 	sksec->nlbl_state = NLBL_REQUIRE;

--
paul moore
linux security @ hp