ipv6 : Don't reduce hop limit below current value

["D. S. Ljungmark" <spider@takeit.se>]

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A local route may have a lower hop_limit set than global routes do.


See RFC 3756 Section 4.2.7

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From 846e648ac8ea9325778a61038a09d98c2fb7002a Mon Sep 17 00:00:00 2001
From: "D.S. Ljungmark" <spider@skuggor.se>
Date: Tue, 24 Mar 2015 22:18:47 +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.
See RFC 3756 Section 4.2.7

Signed-off-by: D.S. Ljungmark <ljungmark@modio.se>
---
 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 471ed24..b939652 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);
-- 
2.1.0


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