Messages in this thread | | | Date | Fri, 31 Oct 2014 09:24:42 -0700 | Subject | Re: [PATCH] ipv4: avoid divide 0 error in tcp_incr_quickack | From | Alexei Starovoitov <> |
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cc-ing netdev
On Fri, Oct 31, 2014 at 7:50 AM, Chen Weilong <chenweilong@huawei.com> wrote: > From: Weilong Chen <chenweilong@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 <chenweilong@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 > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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