From: "D.S. Ljungmark" <ljungmark@xxxxxxxx>
This patch has been added to the 3.18 stable tree. If you have any
objections, please let us know.
===============
[ Upstream commit 6fd99094de2b83d1d4c8457f2c83483b2828e75a ]
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 <ljungmark@xxxxxxxx>
Acked-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
---
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 4cb45c1..a46c504 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1215,7 +1215,14 @@ 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);
--
2.1.0
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