net/packet: recvmsg: write back namelen only if name required

kernel/drivers/net/stack/packet/af_packet.c

@@ -351,12 +351,6 @@ rt_packet_recvmsg(struct rtdm_fd *fd, struct user_msghdr *u_msg, int msg_flags)
     rtskb = rtskb_dequeue_chain(&sock->incoming);
     RTNET_ASSERT(rtskb != NULL, return -EFAULT;);
 
-    /* copy the address */
-    namelen = sizeof(sll);
-    ret = rtnet_put_arg(fd, &msg->msg_namelen, &namelen, sizeof(namelen));
-    if (ret)
-	    goto fail;
-
     /* copy the address if required. */
     if (msg->msg_name) {
 	struct rtnet_device *rtdev = rtskb->rtdev;
@@ -373,6 +367,11 @@ rt_packet_recvmsg(struct rtdm_fd *fd, struct user_msghdr *u_msg, int msg_flags)
 	ret = rtnet_put_arg(fd, msg->msg_name, &sll, sizeof(sll));
 	if (ret)
 		goto fail;
+
+	namelen = sizeof(sll);
+	ret = rtnet_put_arg(fd, &u_msg->msg_namelen, &namelen, sizeof(namelen));
+	if (ret)
+		goto fail;
     }
 
     /* Include the header in raw delivery */