From 14c137ce30cd40caff4fb7efe0a651590b64d695 Mon Sep 17 00:00:00 2001 From: Sabrina Dubroca Date: Tue, 9 Oct 2018 17:48:15 +0200 Subject: net: ipv4: don't let PMTU updates increase route MTU [ Upstream commit 28d35bcdd3925e7293408cdb8aa5f2aac5f0d6e3 ] 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: d52e5a7e7ca4 ("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 Signed-off-by: Sasha Levin --- net/ipv4/route.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'net') diff --git a/net/ipv4/route.c b/net/ipv4/route.c index 6058dbc4e2c1..8f5c6fa54ac0 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -991,21 +991,22 @@ 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; -- cgit v1.2.3