[AF_UNIX]: Kernel memory leak fix for af_unix datagram getpeersec patch

From: Catherine Zhang <cxzhang@watson.ibm.com>

This patch implements a cleaner fix for the memory leak problem of the
original unix datagram getpeersec patch.  Instead of creating a
security context each time a unix datagram is sent, we only create the
security context when the receiver requests it.

This new design requires modification of the current
unix_getsecpeer_dgram LSM hook and addition of two new hooks, namely,
secid_to_secctx and release_secctx.  The former retrieves the security
context and the latter releases it.  A hook is required for releasing
the security context because it is up to the security module to decide
how that's done.  In the case of Selinux, it's a simple kfree
operation.

Acked-by:  Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 36 insertions, 16 deletions

diff --git a/security/dummy.c b/security/dummy.c
index bbbfda7..58c6d39 100644
--- a/security/dummy.c
+++ b/security/dummy.c
@@ -791,8 +791,7 @@ static int dummy_socket_getpeersec_stream(struct socket *sock, char __user *optv
 	return -ENOPROTOOPT;
 }
 
-static int dummy_socket_getpeersec_dgram(struct sk_buff *skb, char **secdata,
-					 u32 *seclen)
+static int dummy_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, u32 *secid)
 {
 	return -ENOPROTOOPT;
 }
@@ -876,6 +875,15 @@ static int dummy_setprocattr(struct task_struct *p, char *name, void *value, siz
 	return -EINVAL;
 }
 
+static int dummy_secid_to_secctx(u32 secid, char **secdata, u32 *seclen)
+{
+	return -EOPNOTSUPP;
+}
+
+static void dummy_release_secctx(char *secdata, u32 seclen)
+{
+}
+
 #ifdef CONFIG_KEYS
 static inline int dummy_key_alloc(struct key *key, struct task_struct *ctx,
 				  unsigned long flags)
@@ -1028,6 +1036,8 @@ void security_fixup_ops (struct security_operations *ops)
 	set_to_dummy_if_null(ops, d_instantiate);
  	set_to_dummy_if_null(ops, getprocattr);
  	set_to_dummy_if_null(ops, setprocattr);
+ 	set_to_dummy_if_null(ops, secid_to_secctx);
+ 	set_to_dummy_if_null(ops, release_secctx);
 #ifdef CONFIG_SECURITY_NETWORK
 	set_to_dummy_if_null(ops, unix_stream_connect);
 	set_to_dummy_if_null(ops, unix_may_send);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index a91c961..5d1b8c7 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3524,25 +3524,21 @@ out:
 	return err;
 }
 
-static int selinux_socket_getpeersec_dgram(struct sk_buff *skb, char **secdata, u32 *seclen)
+static int selinux_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, u32 *secid)
 {
+	u32 peer_secid = SECSID_NULL;
 	int err = 0;
-	u32 peer_sid;
 
-	if (skb->sk->sk_family == PF_UNIX)
-		selinux_get_inode_sid(SOCK_INODE(skb->sk->sk_socket),
-				      &peer_sid);
-	else
-		peer_sid = selinux_socket_getpeer_dgram(skb);
-
-	if (peer_sid == SECSID_NULL)
-		return -EINVAL;
+	if (sock && (sock->sk->sk_family == PF_UNIX))
+		selinux_get_inode_sid(SOCK_INODE(sock), &peer_secid);
+	else if (skb)
+		peer_secid = selinux_socket_getpeer_dgram(skb);
 
-	err = security_sid_to_context(peer_sid, secdata, seclen);
-	if (err)
-		return err;
+	if (peer_secid == SECSID_NULL)
+		err = -EINVAL;
+	*secid = peer_secid;
 
-	return 0;
+	return err;
 }
 
 static int selinux_sk_alloc_security(struct sock *sk, int family, gfp_t priority)
@@ -4407,6 +4403,17 @@ static int selinux_setprocattr(struct task_struct *p,
 	return size;
 }
 
+static int selinux_secid_to_secctx(u32 secid, char **secdata, u32 *seclen)
+{
+	return security_sid_to_context(secid, secdata, seclen);
+}
+
+static void selinux_release_secctx(char *secdata, u32 seclen)
+{
+	if (secdata)
+		kfree(secdata);
+}
+
 #ifdef CONFIG_KEYS
 
 static int selinux_key_alloc(struct key *k, struct task_struct *tsk,
@@ -4587,6 +4594,9 @@ static struct security_operations selinux_ops = {
 	.getprocattr =                  selinux_getprocattr,
 	.setprocattr =                  selinux_setprocattr,
 
+	.secid_to_secctx =		selinux_secid_to_secctx,
+	.release_secctx =		selinux_release_secctx,
+
         .unix_stream_connect =		selinux_socket_unix_stream_connect,
 	.unix_may_send =		selinux_socket_unix_may_send,