xfrm: Set transport header to fix UDP GRO handling

The referenced commit replaced a call to __xfrm4|6_udp_encap_rcv() with
a custom check for non-ESP markers.  But what the called function also
did was setting the transport header to the ESP header.  The function
that follows, esp4|6_gro_receive(), relies on that being set when it calls
xfrm_parse_spi().  We have to set the full offset as the skb's head was
not moved yet so adding just the UDP header length won't work.

Fixes: e3fd057 ("xfrm: Fix UDP GRO handling for some corner cases")
Signed-off-by: Tobias Brunner <tobias@strongswan.org>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

Author: tobiasbrunner

net/ipv4/xfrm4_input.c

@@ -202,6 +202,9 @@ struct sk_buff *xfrm4_gro_udp_encap_rcv(struct sock *sk, struct list_head *head,
 	if (len <= sizeof(struct ip_esp_hdr) || udpdata32[0] == 0)
 		goto out;
 
+	/* set the transport header to ESP */
+	skb_set_transport_header(skb, offset);
+
 	NAPI_GRO_CB(skb)->proto = IPPROTO_UDP;
 
 	pp = call_gro_receive(ops->callbacks.gro_receive, head, skb);

net/ipv6/xfrm6_input.c

@@ -202,6 +202,9 @@ struct sk_buff *xfrm6_gro_udp_encap_rcv(struct sock *sk, struct list_head *head,
 	if (len <= sizeof(struct ip_esp_hdr) || udpdata32[0] == 0)
 		goto out;
 
+	/* set the transport header to ESP */
+	skb_set_transport_header(skb, offset);
+
 	NAPI_GRO_CB(skb)->proto = IPPROTO_UDP;
 
 	pp = call_gro_receive(ops->callbacks.gro_receive, head, skb);