This is a note to let you know that I've just added the patch titled
tcp: don't update snd_nxt, when a socket is switched from repair mode
to the 3.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tcp-don-t-update-snd_nxt-when-a-socket-is-switched-from-repair-mode.patch
and it can be found in the queue-3.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Thu Dec 5 16:16:39 PST 2013
From: Andrey Vagin <avagin@xxxxxxxxxx>
Date: Tue, 19 Nov 2013 22:10:06 +0400
Subject: tcp: don't update snd_nxt, when a socket is switched from repair mode
From: Andrey Vagin <avagin@xxxxxxxxxx>
[ Upstream commit dbde497966804e63a38fdedc1e3815e77097efc2 ]
snd_nxt must be updated synchronously with sk_send_head. Otherwise
tp->packets_out may be updated incorrectly, what may bring a kernel panic.
Here is a kernel panic from my host.
[ 103.043194] BUG: unable to handle kernel NULL pointer dereference at 0000000000000048
[ 103.044025] IP: [<ffffffff815aaaaf>] tcp_rearm_rto+0xcf/0x150
...
[ 146.301158] Call Trace:
[ 146.301158] [<ffffffff815ab7f0>] tcp_ack+0xcc0/0x12c0
Before this panic a tcp socket was restored. This socket had sent and
unsent data in the write queue. Sent data was restored in repair mode,
then the socket was switched from reapair mode and unsent data was
restored. After that the socket was switched back into repair mode.
In that moment we had a socket where write queue looks like this:
snd_una snd_nxt write_seq
|_________|________|
|
sk_send_head
After a second switching from repair mode the state of socket was
changed:
snd_una snd_nxt, write_seq
|_________ ________|
|
sk_send_head
This state is inconsistent, because snd_nxt and sk_send_head are not
synchronized.
Bellow you can find a call trace, how packets_out can be incremented
twice for one skb, if snd_nxt and sk_send_head are not synchronized.
In this case packets_out will be always positive, even when
sk_write_queue is empty.
tcp_write_wakeup
skb = tcp_send_head(sk);
tcp_fragment
if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq))
tcp_adjust_pcount(sk, skb, diff);
tcp_event_new_data_sent
tp->packets_out += tcp_skb_pcount(skb);
I think update of snd_nxt isn't required, when a socket is switched from
repair mode. Because it's initialized in tcp_connect_init. Then when a
write queue is restored, snd_nxt is incremented in tcp_event_new_data_sent,
so it's always is in consistent state.
I have checked, that the bug is not reproduced with this patch and
all tests about restoring tcp connections work fine.
Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Hideaki YOSHIFUJI <yoshfuji@xxxxxxxxxxxxxx>
Cc: Patrick McHardy <kaber@xxxxxxxxx>
Signed-off-by: Andrey Vagin <avagin@xxxxxxxxxx>
Acked-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Acked-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv4/tcp_output.c | 1 -
1 file changed, 1 deletion(-)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3112,7 +3112,6 @@ void tcp_send_window_probe(struct sock *
{
if (sk->sk_state == TCP_ESTABLISHED) {
tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
- tcp_sk(sk)->snd_nxt = tcp_sk(sk)->write_seq;
tcp_xmit_probe_skb(sk, 0);
}
}
Patches currently in stable-queue which might be from avagin@xxxxxxxxxx are
queue-3.12/tcp-don-t-update-snd_nxt-when-a-socket-is-switched-from-repair-mode.patch
queue-3.12/net-x86-bpf-don-t-forget-to-free-sk_filter-v2.patch
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