From 345c70e52cde2b3396189d7f3404499a093dd26e Mon Sep 17 00:00:00 2001 From: Sabrina Dubroca Date: Tue, 9 Oct 2018 17:48:15 +0200 Subject: [PATCH] net: ipv4: don't let PMTU updates increase route MTU When an MTU update with PMTU smaller than net.ipv4.route.min_pmtu is received, we must clamp its value. However, we can receive a PMTU exception with PMTU < old_mtu < ip_rt_min_pmtu, which would lead to an increase in PMTU. To fix this, take the smallest of the old MTU and ip_rt_min_pmtu. Before this patch, in case of an update, the exception's MTU would always change. Now, an exception can have only its lock flag updated, but not the MTU, so we need to add a check on locking to the following "is this exception getting updated, or close to expiring?" test. Fixes: f4f42a6066e0 ("ipv4: lock mtu in fnhe when received PMTU < net.ipv4.route.min_pmtu") Signed-off-by: Sabrina Dubroca Reviewed-by: Stefano Brivio Signed-off-by: David S. Miller --- net/ipv4/route.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/net/ipv4/route.c b/net/ipv4/route.c index b678466da451c..8501554e96a4a 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -1001,21 +1001,22 @@ out: kfree_skb(skb); static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu) { struct dst_entry *dst = &rt->dst; + u32 old_mtu = ipv4_mtu(dst); struct fib_result res; bool lock = false; if (ip_mtu_locked(dst)) return; - if (ipv4_mtu(dst) < mtu) + if (old_mtu < mtu) return; if (mtu < ip_rt_min_pmtu) { lock = true; - mtu = ip_rt_min_pmtu; + mtu = min(old_mtu, ip_rt_min_pmtu); } - if (rt->rt_pmtu == mtu && + if (rt->rt_pmtu == mtu && !lock && time_before(jiffies, dst->expires - ip_rt_mtu_expires / 2)) return; -- 2.39.5