Patch "ip6_tunnel: Account for tunnel header in tunnel MTU" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

ip6_tunnel: Account for tunnel header in tunnel MTU

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ip6_tunnel-account-for-tunnel-header-in-tunnel-mtu.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jakub Sitnicki <[email protected]>
Date: Fri, 13 Jan 2017 10:12:20 +0100
Subject: ip6_tunnel: Account for tunnel header in tunnel MTU

From: Jakub Sitnicki <[email protected]>

[ Upstream commit 02ca0423fd65a0a9c4d70da0dbb8f4b8503f08c7 ]

With ip6gre we have a tunnel header which also makes the tunnel MTU smaller. We need to reserve room for it. Previously we were using up space reserved for the Tunnel Encapsulation Limit option header (RFC 2473).

Also, after commit b05229f44228 ("gre6: Cleanup GREv6 transmit path, call common GRE functions") our contract with the caller has changed. Now we check if the packet length exceeds the tunnel MTU after the tunnel header has been pushed, unlike before.

This is reflected in the check where we look at the packet length minus the size of the tunnel header, which is already accounted for in tunnel MTU.

---
 net/ipv6/ip6_tunnel.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -1108,7 +1108,7 @@ route_lookup:
 				     t->parms.name);
 		goto tx_err_dst_release;
 	}
-	mtu = dst_mtu(dst) - psh_hlen;
+	mtu = dst_mtu(dst) - psh_hlen - t->tun_hlen;
 	if (encap_limit >= 0) {
 		max_headroom += 8;
 		mtu -= 8;

@@ -1117,7 +1117,7 @@ route_lookup:
 		mtu = IPV6_MIN_MTU;
 	if (skb_dst(skb) && !t->parms.collect_md)
 		skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);
-	if (skb->len > mtu && !skb_is_gso(skb)) {
+	if (skb->len - t->tun_hlen > mtu && !skb_is_gso(skb)) {
 		*pmtu = mtu;
 		err = -EMSGSIZE;
 		goto tx_err_dst_release;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/ip6_tunnel-account-for-tunnel-header-in-tunnel-mtu.patch