[PATCH 3.16.y-ckt 27/58] ipv6: stop sending PTB packets for MTU < 1280

From: Luis Henriques
Date: Thu Feb 19 2015 - 09:02:37 EST

3.16.7-ckt7 -stable review patch. If anyone has any objections, please let me know.


From: Hagen Paul Pfeifer <hagen@xxxxxxxx>

commit 9d289715eb5c252ae15bd547cb252ca547a3c4f2 upstream.

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@xxxxxxxxxxxxxxx>
Signed-off-by: Hagen Paul Pfeifer <hagen@xxxxxxxx>
Acked-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
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 bafde82324c5..920616d05758 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1152,12 +1152,9 @@ 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;
- 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);

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