Re: [PATCH] ipv4: avoid divide 0 error in tcp_incr_quickack
From: Eric Dumazet <hidden>
Date: 2014-11-03 03:42:11
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On Mon, 2014-11-03 at 09:29 +0800, Chen Weilong wrote:
From: Weilong Chen <redacted> We got a problem like this:
quoted hunk ↗ jump to hunk
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. Signed-off-by: Weilong Chen <redacted> --- 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;
Sorry I do not think this is the right fix. We have to not simply avoid the divide, but fix this issue by understanding the missing steps.