From 6fd99094de2b83d1d4c8457f2c83483b2828e75a Mon Sep 17 00:00:00 2001 From: "D.S. Ljungmark" Date: Wed, 25 Mar 2015 09:28:15 +0100 Subject: [PATCH] ipv6: Don't reduce hop limit for an interface A local route may have a lower hop_limit set than global routes do. RFC 3756, Section 4.2.7, "Parameter Spoofing" > 1. The attacker includes a Current Hop Limit of one or another small > number which the attacker knows will cause legitimate packets to > be dropped before they reach their destination. > As an example, one possible approach to mitigate this threat is to > ignore very small hop limits. The nodes could implement a > configurable minimum hop limit, and ignore attempts to set it below > said limit. Signed-off-by: D.S. Ljungmark Acked-by: Hannes Frederic Sowa Signed-off-by: David S. Miller --- net/ipv6/ndisc.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c index 471ed24aabaec..14ecdaf06bf74 100644 --- a/net/ipv6/ndisc.c +++ b/net/ipv6/ndisc.c @@ -1218,7 +1218,14 @@ static void ndisc_router_discovery(struct sk_buff *skb) if (rt) rt6_set_expires(rt, jiffies + (HZ * lifetime)); if (ra_msg->icmph.icmp6_hop_limit) { - in6_dev->cnf.hop_limit = ra_msg->icmph.icmp6_hop_limit; + /* Only set hop_limit on the interface if it is higher than + * the current hop_limit. + */ + if (in6_dev->cnf.hop_limit < ra_msg->icmph.icmp6_hop_limit) { + in6_dev->cnf.hop_limit = ra_msg->icmph.icmp6_hop_limit; + } else { + ND_PRINTK(2, warn, "RA: Got route advertisement with lower hop_limit than current\n"); + } if (rt) dst_metric_set(&rt->dst, RTAX_HOPLIMIT, ra_msg->icmph.icmp6_hop_limit);