net/tcp: save fd before sending the conn to main

Save local fd of the connection before sending it to TCP main, to make
sure we it won't get overwritten by main, and we close somebody else's
file descriptor.

net/net_tcp.c

@@ -933,18 +933,20 @@ struct tcp_connection* tcp_conn_new(int sock, union sockaddr_union* su,
 int tcp_conn_send(struct tcp_connection *c)
 {
 	long response[2];
-	int n;
+	int n, fd;
 
 	/* inform TCP main about this new connection */
 	if (c->state==S_CONN_CONNECTING) {
+		/* store the local fd now, before TCP main overwrites it */
+		fd = c->s;
 		response[0]=(long)c;
 		response[1]=ASYNC_CONNECT;
-		n=send_fd(unix_tcp_sock, response, sizeof(response), c->s);
+		n=send_fd(unix_tcp_sock, response, sizeof(response), fd);
 		if (n<=0) {
 			LM_ERR("Failed to send the socket to main for async connection\n");
 			goto error;
 		}
-		close(c->s);
+		close(fd);
 	} else {
 		response[0]=(long)c;
 		response[1]=CONN_NEW;