Commit 0cda345d authored Apr 30, 2014 by Liu Yu Committed by David S. Miller Apr 30, 2014

tcp_cubic: fix the range of delayed_ack



commit b9f47a3a (tcp_cubic: limit delayed_ack ratio to prevent
divide error) try to prevent divide error, but there is still a little
chance that delayed_ack can reach zero. In case the param cnt get
negative value, then ratio+cnt would overflow and may happen to be zero.
As a result, min(ratio, ACK_RATIO_LIMIT) will calculate to be zero.

In some old kernels, such as 2.6.32, there is a bug that would
pass negative param, which then ultimately leads to this divide error.

commit 5b35e1e6 (tcp: fix tcp_trim_head() to adjust segment count
with skb MSS) fixed the negative param issue. However,
it's safe that we fix the range of delayed_ack as well,
to make sure we do not hit a divide by zero.

CC: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Liu Yu <allanyuliu@tencent.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent e5744fe9

net/ipv4/tcp_cubic.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -409,7 +409,7 @@ static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
		ratio -= ca->delayed_ack >> ACK_RATIO_SHIFT;
		ratio += cnt;

		ca->delayed_ack = min(ratio, ACK_RATIO_LIMIT);
		ca->delayed_ack = clamp(ratio, 1U, ACK_RATIO_LIMIT);
		}

		/* Some calls are for duplicates without timetamps */

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