[MLSXFRM]: Fix build with SECURITY_NETWORK_XFRM disabled.

The following patch will fix the build problem (encountered by Andrew
Morton) when SECURITY_NETWORK_XFRM is not enabled.

As compared to git-net-selinux_xfrm_decode_session-build-fix.patch in
-mm, this patch sets the return parameter sid to SECSID_NULL in
selinux_xfrm_decode_session() and handles this value in the caller
selinux_inet_conn_request() appropriately.

Signed-off-by: Venkat Yekkirala <vyekkirala@TrustedCS.com>
Acked-by: James Morris <jmorris@namei.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

security/selinux/hooks.c

@@ -3591,6 +3591,11 @@ int selinux_inet_conn_request(struct sock *sk, struct sk_buff *skb,
 	err = selinux_xfrm_decode_session(skb, &peersid, 0);
 	BUG_ON(err);
 
+	if (peersid == SECSID_NULL) {
+		req->secid = sksec->sid;
+		return 0;
+	}
+
 	err = security_sid_mls_copy(sksec->sid, peersid, &newsid);
 	if (err)
 		return err;

security/selinux/include/xfrm.h

@@ -20,7 +20,6 @@ int selinux_xfrm_policy_lookup(struct xfrm_policy *xp, u32 fl_secid, u8 dir);
 int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x,
 			struct xfrm_policy *xp, struct flowi *fl);
 int selinux_xfrm_flow_state_match(struct flowi *fl, struct xfrm_state *xfrm);
-int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *fl, int ckall);
 
 
 /*
@@ -41,6 +40,7 @@ int selinux_xfrm_postroute_last(u32 isec_sid, struct sk_buff *skb,
 			struct avc_audit_data *ad);
 u32 selinux_socket_getpeer_stream(struct sock *sk);
 u32 selinux_socket_getpeer_dgram(struct sk_buff *skb);
+int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall);
 #else
 static inline int selinux_xfrm_sock_rcv_skb(u32 isec_sid, struct sk_buff *skb,
 			struct avc_audit_data *ad)
@@ -63,6 +63,11 @@ static inline int selinux_socket_getpeer_dgram(struct sk_buff *skb)
 {
 	return SECSID_NULL;
 }
+static inline int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
+{
+	*sid = SECSID_NULL;
+	return 0;
+}
 #endif
 
 #endif /* _SELINUX_XFRM_H_ */