[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, 12 insertions, 14 deletions

diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 84f43a3..2d05c41 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -112,14 +112,19 @@ static void ip_cmsg_recv_retopts(struct msghdr *msg, struct sk_buff *skb)
 static void ip_cmsg_recv_security(struct msghdr *msg, struct sk_buff *skb)
 {
 	char *secdata;
-	u32 seclen;
+	u32 seclen, secid;
 	int err;
 
-	err = security_socket_getpeersec_dgram(skb, &secdata, &seclen);
+	err = security_socket_getpeersec_dgram(NULL, skb, &secid);
+	if (err)
+		return;
+
+	err = security_secid_to_secctx(secid, &secdata, &seclen);
 	if (err)
 		return;
 
 	put_cmsg(msg, SOL_IP, SCM_SECURITY, seclen, secdata);
+	security_release_secctx(secdata, seclen);
 }
 
 
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 6f29092..de6ec51 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -128,23 +128,17 @@ static atomic_t unix_nr_socks = ATOMIC_INIT(0);
 #define UNIX_ABSTRACT(sk)	(unix_sk(sk)->addr->hash != UNIX_HASH_SIZE)
 
 #ifdef CONFIG_SECURITY_NETWORK
-static void unix_get_peersec_dgram(struct sk_buff *skb)
+static void unix_get_secdata(struct scm_cookie *scm, struct sk_buff *skb)
 {
-	int err;
-
-	err = security_socket_getpeersec_dgram(skb, UNIXSECDATA(skb),
-					       UNIXSECLEN(skb));
-	if (err)
-		*(UNIXSECDATA(skb)) = NULL;
+	memcpy(UNIXSID(skb), &scm->secid, sizeof(u32));
 }
 
 static inline void unix_set_secdata(struct scm_cookie *scm, struct sk_buff *skb)
 {
-	scm->secdata = *UNIXSECDATA(skb);
-	scm->seclen = *UNIXSECLEN(skb);
+	scm->secid = *UNIXSID(skb);
 }
 #else
-static inline void unix_get_peersec_dgram(struct sk_buff *skb)
+static inline void unix_get_secdata(struct scm_cookie *scm, struct sk_buff *skb)
 { }
 
 static inline void unix_set_secdata(struct scm_cookie *scm, struct sk_buff *skb)
@@ -1322,8 +1316,7 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	memcpy(UNIXCREDS(skb), &siocb->scm->creds, sizeof(struct ucred));
 	if (siocb->scm->fp)
 		unix_attach_fds(siocb->scm, skb);
-
-	unix_get_peersec_dgram(skb);
+	unix_get_secdata(siocb->scm, skb);
 
 	skb->h.raw = skb->data;
 	err = memcpy_fromiovec(skb_put(skb,len), msg->msg_iov, len);