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    Subject[PATCH 4.9 13/51] ip6_tunnel: Account for tunnel header in tunnel MTU
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jakub Sitnicki <jkbs@redhat.com>


    [ 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.

    Fixes: b05229f44228 ("gre6: Cleanup GREv6 transmit path, call common GRE functions")
    Signed-off-by: Jakub Sitnicki <jkbs@redhat.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv6/ip6_tunnel.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/net/ipv6/ip6_tunnel.c
    +++ b/net/ipv6/ip6_tunnel.c
    @@ -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;

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