| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.10 62/86] tcp_cubic: fix the range of delayed_ack | Date | Wed, 28 May 2014 21:37:37 -0700 |
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3.10-stable review patch. If anyone has any objections, please let me know.
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From: Liu Yu <allanyuliu@tencent.com>
[ Upstream commit 0cda345d1b2201dd15591b163e3c92bad5191745 ]
commit b9f47a3aaeab (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 5b35e1e6e9c (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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- net/ipv4/tcp_cubic.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -408,7 +408,7 @@ static void bictcp_acked(struct sock *sk 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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