selinux: ensure that the cached NetLabel secattr matches the desired SID

In selinux_netlbl_skbuff_setsid() we leverage a cached NetLabel
secattr whenever possible.  However, we never check to ensure that
the desired SID matches the cached NetLabel secattr.  This patch
checks the SID against the secattr before use and only uses the
cached secattr when the SID values match.
Signed-off-by: Paul Moore <pmoore@redhat.com>

security/selinux/netlabel.c

@@ -100,6 +100,32 @@ static struct netlbl_lsm_secattr *selinux_netlbl_sock_genattr(struct sock *sk)
 	return secattr;
 }
 
+/**
+ * selinux_netlbl_sock_getattr - Get the cached NetLabel secattr
+ * @sk: the socket
+ * @sid: the SID
+ *
+ * Query the socket's cached secattr and if the SID matches the cached value
+ * return the cache, otherwise return NULL.
+ *
+ */
+static struct netlbl_lsm_secattr *selinux_netlbl_sock_getattr(
+							const struct sock *sk,
+							u32 sid)
+{
+	struct sk_security_struct *sksec = sk->sk_security;
+	struct netlbl_lsm_secattr *secattr = sksec->nlbl_secattr;
+
+	if (secattr == NULL)
+		return NULL;
+
+	if ((secattr->flags & NETLBL_SECATTR_SECID) &&
+	    (secattr->attr.secid == sid))
+		return secattr;
+
+	return NULL;
+}
+
 /**
  * selinux_netlbl_cache_invalidate - Invalidate the NetLabel cache
  *
@@ -224,7 +250,7 @@ int selinux_netlbl_skbuff_setsid(struct sk_buff *skb,
 		struct sk_security_struct *sksec = sk->sk_security;
 		if (sksec->nlbl_state != NLBL_REQSKB)
 			return 0;
-		secattr = sksec->nlbl_secattr;
+		secattr = selinux_netlbl_sock_getattr(sk, sid);
 	}
 	if (secattr == NULL) {
 		secattr = &secattr_storage;
@@ -410,6 +436,9 @@ int selinux_netlbl_socket_setsockopt(struct socket *sock,
 	     sksec->nlbl_state == NLBL_CONNLABELED)) {
 		netlbl_secattr_init(&secattr);
 		lock_sock(sk);
+		/* call the netlabel function directly as we want to see the
+		 * on-the-wire label that is assigned via the socket's options
+		 * and not the cached netlabel/lsm attributes */
 		rc = netlbl_sock_getattr(sk, &secattr);
 		release_sock(sk);
 		if (rc == 0)