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    Subject[PATCH 3.12 078/122] ipv6: stop sending PTB packets for MTU < 1280
    Date
    From: Hagen Paul Pfeifer <hagen@jauu.net>

    3.12-stable review patch. If anyone has any objections, please let me know.

    ===============

    [ Upstream commit 9d289715eb5c252ae15bd547cb252ca547a3c4f2 ]

    Reduce the attack vector and stop generating IPv6 Fragment Header for
    paths with an MTU smaller than the minimum required IPv6 MTU
    size (1280 byte) - called atomic fragments.

    See IETF I-D "Deprecating the Generation of IPv6 Atomic Fragments" [1]
    for more information and how this "feature" can be misused.

    [1] https://tools.ietf.org/html/draft-ietf-6man-deprecate-atomfrag-generation-00

    Signed-off-by: Fernando Gont <fgont@si6networks.com>
    Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
    Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    ---
    net/ipv6/route.c | 7 ++-----
    1 file changed, 2 insertions(+), 5 deletions(-)

    diff --git a/net/ipv6/route.c b/net/ipv6/route.c
    index b4bb6a29aa16..1d0c5d66d637 100644
    --- a/net/ipv6/route.c
    +++ b/net/ipv6/route.c
    @@ -1144,12 +1144,9 @@ static void ip6_rt_update_pmtu(struct dst_entry *dst, struct sock *sk,
    struct net *net = dev_net(dst->dev);

    rt6->rt6i_flags |= RTF_MODIFIED;
    - if (mtu < IPV6_MIN_MTU) {
    - u32 features = dst_metric(dst, RTAX_FEATURES);
    + if (mtu < IPV6_MIN_MTU)
    mtu = IPV6_MIN_MTU;
    - features |= RTAX_FEATURE_ALLFRAG;
    - dst_metric_set(dst, RTAX_FEATURES, features);
    - }
    +
    dst_metric_set(dst, RTAX_MTU, mtu);
    rt6_update_expires(rt6, net->ipv6.sysctl.ip6_rt_mtu_expires);
    }
    --
    2.2.2


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