[PATCH 3.2 187/221] ipv6: stop sending PTB packets for MTU < 1280

Ben Hutchings
2015-05-05T01:25:17Z

From: Hagen Paul Pfeifer <hagen@jauu.net>

[ 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: Ben Hutchings <ben@decadent.org.uk>
---
net/ipv6/route.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)

--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1018,12 +1018,9 @@ static void ip6_rt_update_pmtu(struct ds

if (mtu < dst_mtu(dst) && rt6->rt6i_dst.plen == 128) {
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);
}
}