From 0d4f0608619de59fd8169dd8e72aadc28d80e715 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Mon, 18 Mar 2013 07:01:28 +0000
Subject: tcp: dont handle MTU reduction on LISTEN socket

When an ICMP ICMP_FRAG_NEEDED (or ICMPV6_PKT_TOOBIG) message finds a
LISTEN socket, and this socket is currently owned by the user, we
set TCP_MTU_REDUCED_DEFERRED flag in listener tsq_flags.

This is bad because if we clone the parent before it had a chance to
clear the flag, the child inherits the tsq_flags value, and next
tcp_release_cb() on the child will decrement sk_refcnt.

Result is that we might free a live TCP socket, as reported by
Dormando.

IPv4: Attempt to release TCP socket in state 1

Fix this issue by testing sk_state against TCP_LISTEN early, so that we
set TCP_MTU_REDUCED_DEFERRED on appropriate sockets (not a LISTEN one)

This bug was introduced in commit 563d34d05786
(tcp: dont drop MTU reduction indications)

Reported-by: dormando <dormando@rydia.net>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
 net/ipv6/tcp_ipv6.c | 7 +++++++
 1 file changed, 7 insertions(+)

(limited to 'net/ipv6/tcp_ipv6.c')

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 9b6460055df5..f6d629fd6aee 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -389,6 +389,13 @@ static void tcp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 	}
 
 	if (type == ICMPV6_PKT_TOOBIG) {
+		/* We are not interested in TCP_LISTEN and open_requests
+		 * (SYN-ACKs send out by Linux are always <576bytes so
+		 * they should go through unfragmented).
+		 */
+		if (sk->sk_state == TCP_LISTEN)
+			goto out;
+
 		tp->mtu_info = ntohl(info);
 		if (!sock_owned_by_user(sk))
 			tcp_v6_mtu_reduced(sk);
-- 
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