From 5e016cbf6cffd4a53b7922e0c91b775399d7fe47 Mon Sep 17 00:00:00 2001 From: Guenter Roeck Date: Sun, 21 Mar 2010 20:55:13 -0700 Subject: [PATCH] ipv4: Don't drop redirected route cache entry unless PTMU actually expired TCP sessions over IPv4 can get stuck if routers between endpoints do not fragment packets but implement PMTU instead, and we are using those routers because of an ICMP redirect. Setup is as follows MTU1 MTU2 MTU1 A--------B------C------D with MTU1 > MTU2. A and D are endpoints, B and C are routers. B and C implement PMTU and drop packets larger than MTU2 (for example because DF is set on all packets). TCP sessions are initiated between A and D. There is packet loss between A and D, causing frequent TCP retransmits. After the number of retransmits on a TCP session reaches tcp_retries1, tcp calls dst_negative_advice() prior to each retransmit. This results in route cache entries for the peer to be deleted in ipv4_negative_advice() if the Path MTU is set. If the outstanding data on an affected TCP session is larger than MTU2, packets sent from the endpoints will be dropped by B or C, and ICMP NEEDFRAG will be returned. A and D receive NEEDFRAG messages and update PMTU. Before the next retransmit, tcp will again call dst_negative_advice(), causing the route cache entry (with correct PMTU) to be deleted. The retransmitted packet will be larger than MTU2, causing it to be dropped again. This sequence repeats until the TCP session aborts or is terminated. Problem is fixed by removing redirected route cache entries in ipv4_negative_advice() only if the PMTU is expired. Signed-off-by: Guenter Roeck Signed-off-by: David S. Miller --- net/ipv4/route.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/ipv4/route.c b/net/ipv4/route.c index 32d3961..54fd68c 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -1510,7 +1510,8 @@ static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst) ip_rt_put(rt); ret = NULL; } else if ((rt->rt_flags & RTCF_REDIRECTED) || - rt->u.dst.expires) { + (rt->u.dst.expires && + time_after_eq(jiffies, rt->u.dst.expires))) { unsigned hash = rt_hash(rt->fl.fl4_dst, rt->fl.fl4_src, rt->fl.oif, rt_genid(dev_net(dst->dev))); -- 1.8.2.3