net: core: handle encapsulation offloads when computing segment lengths

if ->encapsulation is set we have to use inner_tcp_hdrlen and add the
size of the inner network headers too.

This is 'mostly harmless'; tbf might send skb that is slightly over
quota or drop skb even if it would have fit.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -4070,15 +4070,22 @@ EXPORT_SYMBOL_GPL(skb_scrub_packet);
 unsigned int skb_gso_transport_seglen(const struct sk_buff *skb)
 {
 	const struct skb_shared_info *shinfo = skb_shinfo(skb);
+	unsigned int thlen = 0;
 
-	if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)))
-		return tcp_hdrlen(skb) + shinfo->gso_size;
+	if (skb->encapsulation) {
+		thlen = skb_inner_transport_header(skb) -
+			skb_transport_header(skb);
 
+		if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)))
+			thlen += inner_tcp_hdrlen(skb);
+	} else if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))) {
+		thlen = tcp_hdrlen(skb);
+	}
 	/* UFO sets gso_size to the size of the fragmentation
 	 * payload, i.e. the size of the L4 (UDP) header is already
 	 * accounted for.
 	 */
-	return shinfo->gso_size;
+	return thlen + shinfo->gso_size;
 }
 EXPORT_SYMBOL_GPL(skb_gso_transport_seglen);