| From foo@baz Wed May 28 21:03:54 PDT 2014 |
| From: Liu Yu <allanyuliu@tencent.com> |
| Date: Wed, 30 Apr 2014 17:34:09 +0800 |
| Subject: tcp_cubic: fix the range of delayed_ack |
| |
| 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 |
| @@ -409,7 +409,7 @@ 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 */ |
