[ 21/98] tcp: dont handle MTU reduction on LISTEN socket

Greg Kroah-Hartman
2013-03-26T23:44:10Z

From: Eric Dumazet <edumazet@google.com>

[ 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@rydia.net>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/tcp_ipv4.c | 14 +++++++-------
net/ipv6/tcp_ipv6.c | 7 +++++++
2 files changed, 14 insertions(+), 7 deletions(-)

--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -274,13 +274,6 @@ static void tcp_v4_mtu_reduced(struct so
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;
@@ -408,6 +401,13 @@ void tcp_v4_err(struct sk_buff *icmp_skb
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);
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -389,6 +389,13 @@ static void tcp_v6_err(struct sk_buff *s
}

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);