[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, 27 insertions, 8 deletions

diff --git a/include/net/af_unix.h b/include/net/af_unix.h
index 2fec827..c0398f5 100644
--- a/include/net/af_unix.h
+++ b/include/net/af_unix.h
@@ -54,15 +54,13 @@ struct unix_skb_parms {
 	struct ucred		creds;		/* Skb credentials	*/
 	struct scm_fp_list	*fp;		/* Passed files		*/
 #ifdef CONFIG_SECURITY_NETWORK
-	char			*secdata;	/* Security context	*/
-	u32			seclen;		/* Security length	*/
+	u32			secid;		/* Security ID		*/
 #endif
 };
 
 #define UNIXCB(skb) 	(*(struct unix_skb_parms*)&((skb)->cb))
 #define UNIXCREDS(skb)	(&UNIXCB((skb)).creds)
-#define UNIXSECDATA(skb)	(&UNIXCB((skb)).secdata)
-#define UNIXSECLEN(skb)		(&UNIXCB((skb)).seclen)
+#define UNIXSID(skb)	(&UNIXCB((skb)).secid)
 
 #define unix_state_rlock(s)	spin_lock(&unix_sk(s)->lock)
 #define unix_state_runlock(s)	spin_unlock(&unix_sk(s)->lock)
diff --git a/include/net/scm.h b/include/net/scm.h
index 02daa09..5637d5e 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -3,6 +3,7 @@
 
 #include <linux/limits.h>
 #include <linux/net.h>
+#include <linux/security.h>
 
 /* Well, we should have at least one descriptor open
  * to accept passed FDs 8)
@@ -20,8 +21,7 @@ struct scm_cookie
 	struct ucred		creds;		/* Skb credentials	*/
 	struct scm_fp_list	*fp;		/* Passed files		*/
 #ifdef CONFIG_SECURITY_NETWORK
-	char			*secdata;	/* Security context	*/
-	u32			seclen;		/* Security length	*/
+	u32			secid;		/* Passed security ID 	*/
 #endif
 	unsigned long		seq;		/* Connection seqno	*/
 };
@@ -32,6 +32,16 @@ extern int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie
 extern void __scm_destroy(struct scm_cookie *scm);
 extern struct scm_fp_list * scm_fp_dup(struct scm_fp_list *fpl);
 
+#ifdef CONFIG_SECURITY_NETWORK
+static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_cookie *scm)
+{
+	security_socket_getpeersec_dgram(sock, NULL, &scm->secid);
+}
+#else
+static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_cookie *scm)
+{ }
+#endif /* CONFIG_SECURITY_NETWORK */
+
 static __inline__ void scm_destroy(struct scm_cookie *scm)
 {
 	if (scm && scm->fp)
@@ -47,6 +57,7 @@ static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
 	scm->creds.pid = p->tgid;
 	scm->fp = NULL;
 	scm->seq = 0;
+	unix_get_peersec_dgram(sock, scm);
 	if (msg->msg_controllen <= 0)
 		return 0;
 	return __scm_send(sock, msg, scm);
@@ -55,8 +66,18 @@ static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
 #ifdef CONFIG_SECURITY_NETWORK
 static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
 {
-	if (test_bit(SOCK_PASSSEC, &sock->flags) && scm->secdata != NULL)
-		put_cmsg(msg, SOL_SOCKET, SCM_SECURITY, scm->seclen, scm->secdata);
+	char *secdata;
+	u32 seclen;
+	int err;
+
+	if (test_bit(SOCK_PASSSEC, &sock->flags)) {
+		err = security_secid_to_secctx(scm->secid, &secdata, &seclen);
+
+		if (!err) {
+			put_cmsg(msg, SOL_SOCKET, SCM_SECURITY, seclen, secdata);
+			security_release_secctx(secdata, seclen);
+		}
+	}
 }
 #else
 static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)