cc-ing netdev
On Fri, Oct 31, 2014 at 7:50 AM, Chen Weilong <chenweil...@huawei.com> wrote:
> From: Weilong Chen <chenweil...@huawei.com>
>
> We got a problem like this:
> [ffff8801c1a05570] machine_kexec at ffffffff81025039
> [ffff8801c1a055d0] crash_kexec at ffffffff8109b253
> [ffff8801c1a056a0] oops_end at ffffffff81442aed
> [ffff8801c1a056d0] die at ffffffff81005603
> [ffff8801c1a05700] do_trap at ffffffff81442448
> [ffff8801c1a05760] do_divide_error at ffffffff81002c10
> [ffff8801c1a05888] tcp_send_dupack at ffffffff81385e44
> [ffff8801c1a058c8] tcp_validate_incoming at ffffffff813886b5
> [ffff8801c1a05908] tcp_rcv_state_process at ffffffff8138d0b7
> [ffff8801c1a05958] tcp_child_process at ffffffff81397255
> [ffff8801c1a05988] tcp_v4_do_rcv at ffffffff81395a70
> [ffff8801c1a059d8] tcp_v4_rcv at ffffffff81396fc8
> [ffff8801c1a05a48] ip_local_deliver_finish at ffffffff813746e9
> [ffff8801c1a05a78] ip_local_deliver at ffffffff81374a20
> [ffff8801c1a05aa8] ip_rcv_finish at ffffffff81374389
> [ffff8801c1a05ad8] ip_rcv at ffffffff81374c78
> There was a wrong ack packet coming during TCP handshake. The socket's state
> was TCP_SYN_RECV, its rcv_mss was not initialize yet. So
> tcp_send_dupack -> tcp_enter_quickack_mode got a divide 0 error.
> This patch add a state check before tcp_enter_quickack_mode.
ouch. Is it remote exploitable?
> Signed-off-by: Weilong Chen <chenweil...@huawei.com>
> ---
> net/ipv4/tcp_input.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 4e4617e..9eb56dc 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -3986,7 +3986,8 @@ static void tcp_send_dupack(struct sock *sk, const
> struct sk_buff *skb)
> if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
> before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
> NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
> - tcp_enter_quickack_mode(sk);
> + if (sk->sk_state != TCP_SYN_RECV)
> + tcp_enter_quickack_mode(sk);
>
> if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
> u32 end_seq = TCP_SKB_CB(skb)->end_seq;
> --
> 1.7.12
>
>
> --
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