[ 019/171 ] tcp: dont handle MTU reduction on LISTEN socket

[Steven Rostedt]

3.6.11.2 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ Upstream commit 0d4f0608619de59fd8169dd8e72aadc28d80e715 ]

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@xxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 net/ipv4/tcp_ipv4.c |   14 +++++++-------
 net/ipv6/tcp_ipv6.c |    7 +++++++
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index c883f4f..e6ed4ae 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -285,13 +285,6 @@ static void tcp_v4_mtu_reduced(struct sock *sk)
 	struct inet_sock *inet = inet_sk(sk);
 	u32 mtu = tcp_sk(sk)->mtu_info;
 
-	/* 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)
-		return;
-
 	dst = inet_csk_update_pmtu(sk, mtu);
 	if (!dst)
 		return;
@@ -415,6 +408,13 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
 			goto out;
 
 		if (code == ICMP_FRAG_NEEDED) { /* PMTU discovery (RFC1191) */
+			/* 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 = info;
 			if (!sock_owned_by_user(sk)) {
 				tcp_v4_mtu_reduced(sk);
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 8b45fb4..fe48fc9 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -400,6 +400,13 @@ 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);
-- 
1.7.10.4


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