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Date: Tue, 19 Mar 2013 21:16:21 -0700 (PDT)
From: dormando <dormando@...ia.net>
To: Eric Dumazet <eric.dumazet@...il.com>
cc: David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] tcp: dont handle MTU reduction on LISTEN socket
> From: Eric Dumazet <edumazet@...gle.com>
>
> 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@...ia.net>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
> 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 4a8ec45..d09203c 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -274,13 +274,6 @@ 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;
> @@ -408,6 +401,13 @@ 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 9b64600..f6d629f 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);
>
>
>
Thanks! We are all incredibly appreciative of your quick help with this.
I have 3.8.3 + this patch running on our machine for 20 hours so far. We
haven't had a kernel newer than 3.2 go for a full day before. I'm giving
it another peak cycle before calling it dead but it looks like you nailed
it.
I assume you no longer need the kernel disassembly?
thanks again,
-Dormando
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