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Message-ID: <CAADnVQLe+Xs22sbdy7=8KW2+LscFOiFWdKxSFFuPTWSPTHbSow@mail.gmail.com> Date: Fri, 31 Oct 2014 09:24:42 -0700 From: Alexei Starovoitov <alexei.starovoitov@...il.com> To: Chen Weilong <chenweilong@...wei.com>, Eric Dumazet <eric.dumazet@...il.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org> Cc: "David S. Miller" <davem@...emloft.net>, Alexey Kuznetsov <kuznet@....inr.ac.ru>, James Morris <jmorris@...ei.org>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>, Patrick McHardy <kaber@...sh.net>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] ipv4: avoid divide 0 error in tcp_incr_quickack cc-ing netdev On Fri, Oct 31, 2014 at 7:50 AM, Chen Weilong <chenweilong@...wei.com> wrote: > From: Weilong Chen <chenweilong@...wei.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@...wei.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@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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