ipv4: Don't use ufo handling on later transformed packets

We might call ip_ufo_append_data() for packets that will be IPsec
transformed later. This function should be used just for real
udp packets. So we check for rt->dst.header_len which is only
nonzero on IPsec handling and call ip_ufo_append_data() just
if rt->dst.header_len is zero.
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit c146066a)
Signed-off-by: Willy Tarreau <w@1wt.eu>

net/ipv4/ip_output.c

@@ -878,6 +878,7 @@ int ip_append_data(struct sock *sk,
 	if (((length > mtu) || (skb && skb_has_frags(skb))) &&
 	    (sk->sk_protocol == IPPROTO_UDP) &&
 	    (rt->u.dst.dev->features & NETIF_F_UFO)) {
+	    (rt->u.dst.dev->features & NETIF_F_UFO) && !rt->u.dst.header_len) {
 		err = ip_ufo_append_data(sk, getfrag, from, length, hh_len,
 					 fragheaderlen, transhdrlen, mtu,
 					 flags);