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Date: Mon, 30 Jun 2014 17:05:15 +0400
From: Andrey Wagin <avagin@...il.com>
To: Christoph Paasch <christoph.paasch@...ouvain.be>
Cc: David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH net] tcp: Fix divide by zero when pushing during tcp-repair
2014-06-28 20:26 GMT+04:00 Christoph Paasch <christoph.paasch@...ouvain.be>:
> When in repair-mode and TCP_RECV_QUEUE is set, we end up calling
> tcp_push with mss_now being 0. If data is in the send-queue and
> tcp_set_skb_tso_segs gets called, we crash because it will divide by
> mss_now:
>
> [ 347.151939] divide error: 0000 [#1] SMP
> [ 347.152907] Modules linked in:
> [ 347.152907] CPU: 1 PID: 1123 Comm: packetdrill Not tainted 3.16.0-rc2 #4
> [ 347.152907] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
> [ 347.152907] task: f5b88540 ti: f3c82000 task.ti: f3c82000
> [ 347.152907] EIP: 0060:[<c1601359>] EFLAGS: 00210246 CPU: 1
> [ 347.152907] EIP is at tcp_set_skb_tso_segs+0x49/0xa0
> [ 347.152907] EAX: 00000b67 EBX: f5acd080 ECX: 00000000 EDX: 00000000
> [ 347.152907] ESI: f5a28f40 EDI: f3c88f00 EBP: f3c83d10 ESP: f3c83d00
> [ 347.152907] DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
> [ 347.152907] CR0: 80050033 CR2: 083158b0 CR3: 35146000 CR4: 000006b0
> [ 347.152907] Stack:
> [ 347.152907] c167f9d9 f5acd080 000005b4 00000002 f3c83d20 c16013e6 f3c88f00 f5acd080
> [ 347.152907] f3c83da0 c1603b5a f3c83d38 c10a0188 00000000 00000000 f3c83d84 c10acc85
> [ 347.152907] c1ad5ec0 00000000 00000000 c1ad679c 010003e0 00000000 00000000 f3c88fc8
> [ 347.152907] Call Trace:
> [ 347.152907] [<c167f9d9>] ? apic_timer_interrupt+0x2d/0x34
> [ 347.152907] [<c16013e6>] tcp_init_tso_segs+0x36/0x50
> [ 347.152907] [<c1603b5a>] tcp_write_xmit+0x7a/0xbf0
> [ 347.152907] [<c10a0188>] ? up+0x28/0x40
> [ 347.152907] [<c10acc85>] ? console_unlock+0x295/0x480
> [ 347.152907] [<c10ad24f>] ? vprintk_emit+0x1ef/0x4b0
> [ 347.152907] [<c1605716>] __tcp_push_pending_frames+0x36/0xd0
> [ 347.152907] [<c15f4860>] tcp_push+0xf0/0x120
> [ 347.152907] [<c15f7641>] tcp_sendmsg+0xf1/0xbf0
> [ 347.152907] [<c116d920>] ? kmem_cache_free+0xf0/0x120
> [ 347.152907] [<c106a682>] ? __sigqueue_free+0x32/0x40
> [ 347.152907] [<c106a682>] ? __sigqueue_free+0x32/0x40
> [ 347.152907] [<c114f0f0>] ? do_wp_page+0x3e0/0x850
> [ 347.152907] [<c161c36a>] inet_sendmsg+0x4a/0xb0
> [ 347.152907] [<c1150269>] ? handle_mm_fault+0x709/0xfb0
> [ 347.152907] [<c15a006b>] sock_aio_write+0xbb/0xd0
> [ 347.152907] [<c1180b79>] do_sync_write+0x69/0xa0
> [ 347.152907] [<c1181023>] vfs_write+0x123/0x160
> [ 347.152907] [<c1181d55>] SyS_write+0x55/0xb0
> [ 347.152907] [<c167f0d8>] sysenter_do_call+0x12/0x28
>
> This can easily be reproduced with the following packetdrill-script (the
> "magic" with netem, sk_pacing and limit_output_bytes is done to prevent
> the kernel from pushing all segments, because hitting the limit without
> doing this is not so easy with packetdrill):
>
> 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
> +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
>
> +0 bind(3, ..., ...) = 0
> +0 listen(3, 1) = 0
>
> +0 < S 0:0(0) win 32792 <mss 1460>
> +0 > S. 0:0(0) ack 1 <mss 1460>
> +0.1 < . 1:1(0) ack 1 win 65000
>
> +0 accept(3, ..., ...) = 4
>
> // This forces that not all segments of the snd-queue will be pushed
> +0 `tc qdisc add dev tun0 root netem delay 10ms`
> +0 `sysctl -w net.ipv4.tcp_limit_output_bytes=2`
> +0 setsockopt(4, SOL_SOCKET, 47, [2], 4) = 0
>
> +0 write(4,...,10000) = 10000
> +0 write(4,...,10000) = 10000
>
> // Set tcp-repair stuff, particularly TCP_RECV_QUEUE
> +0 setsockopt(4, SOL_TCP, 19, [1], 4) = 0
> +0 setsockopt(4, SOL_TCP, 20, [1], 4) = 0
>
> // This now will make the write push the remaining segments
> +0 setsockopt(4, SOL_SOCKET, 47, [20000], 4) = 0
> +0 `sysctl -w net.ipv4.tcp_limit_output_bytes=130000`
>
> // Now we will crash
> +0 write(4,...,1000) = 1000
>
> This happens since ec3423257508 (tcp: fix retransmission in repair
> mode). Prior to that, the call to tcp_push was prevented by a check for
> tp->repair.
>
> The patch fixes it, by adding the new goto-label out_nopush. When exiting
> tcp_sendmsg and a push is not required, which is the case for tp->repair,
> we go to this label.
>
> When repairing and calling send() with TCP_RECV_QUEUE, the data is
> actually put in the receive-queue. So, no push is required because no
> data has been added to the send-queue.
Acked-by: Andrew Vagin <avagin@...nvz.org>
Thanks.
>
> Cc: Andrew Vagin <avagin@...nvz.org>
> Cc: Pavel Emelyanov <xemul@...allels.com>
> Fixes: ec3423257508 (tcp: fix retransmission in repair mode)
> Signed-off-by: Christoph Paasch <christoph.paasch@...ouvain.be>
> ---
> net/ipv4/tcp.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index eb1dde37e678..9d2118e5fbc7 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1108,7 +1108,7 @@ int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
> if (unlikely(tp->repair)) {
> if (tp->repair_queue == TCP_RECV_QUEUE) {
> copied = tcp_send_rcvq(sk, msg, size);
> - goto out;
> + goto out_nopush;
> }
>
> err = -EINVAL;
> @@ -1282,6 +1282,7 @@ wait_for_memory:
> out:
> if (copied)
> tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
> +out_nopush:
> release_sock(sk);
> return copied + copied_syn;
>
> --
> 1.9.3
>
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