From: Alexey Dobriyan <adobriyan@gmail•com>
To: davem@davemloft•net
Cc: Eric Dumazet <eric.dumazet@gmail•com>,
shemminger@linux-foundation•org, netdev@vger•kernel.org,
Ben Hutchings <bhutchings@solarflare•com>
Subject: [PATCH v2] tcp: restrict net.ipv4.tcp_adv_win_scale (#20312)
Date: Tue, 23 Nov 2010 00:54:21 +0200 [thread overview]
Message-ID: <20101122225421.GA7372@core2.telecom.by> (raw)
In-Reply-To: <1289830722.2586.5.camel@bwh-desktop>
tcp_win_from_space() does the following:
if (sysctl_tcp_adv_win_scale <= 0)
return space >> (-sysctl_tcp_adv_win_scale);
else
return space - (space >> sysctl_tcp_adv_win_scale);
"space" is int.
As per C99 6.5.7 (3) shifting int for 32 or more bits is
undefined behaviour.
Indeed, if sysctl_tcp_adv_win_scale is exactly 32,
space >> 32 equals space and function returns 0.
Which means we busyloop in tcp_fixup_rcvbuf().
Restrict net.ipv4.tcp_adv_win_scale to [-31, 31].
Fix https://bugzilla.kernel.org/show_bug.cgi?id=20312
Steps to reproduce:
echo 32 >/proc/sys/net/ipv4/tcp_adv_win_scale
wget www.kernel.org
[softlockup]
Signed-off-by: Alexey Dobriyan <adobriyan@gmail•com>
---
Documentation/networking/ip-sysctl.txt | 1 +
net/ipv4/sysctl_net_ipv4.c | 6 +++++-
2 files changed, 6 insertions(+), 1 deletion(-)
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -144,6 +144,7 @@ tcp_adv_win_scale - INTEGER
Count buffering overhead as bytes/2^tcp_adv_win_scale
(if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
if it is <= 0.
+ Possible values are [-31, 31], inclusive.
Default: 2
tcp_allowed_congestion_control - STRING
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -26,6 +26,8 @@ static int zero;
static int tcp_retr1_max = 255;
static int ip_local_port_range_min[] = { 1, 1 };
static int ip_local_port_range_max[] = { 65535, 65535 };
+static int tcp_adv_win_scale_min = -31;
+static int tcp_adv_win_scale_max = 31;
/* Update system visible IP port range */
static void set_local_port_range(int range[2])
@@ -426,7 +428,9 @@ static struct ctl_table ipv4_table[] = {
.data = &sysctl_tcp_adv_win_scale,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &tcp_adv_win_scale_min,
+ .extra2 = &tcp_adv_win_scale_max,
},
{
.procname = "tcp_tw_reuse",
next prev parent reply other threads:[~2010-11-22 22:54 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-14 15:18 [PATCH] tcp: restrict net.ipv4.tcp_adv_min_scale (#20312) Alexey Dobriyan
2010-11-14 19:49 ` Eric Dumazet
2010-11-14 20:14 ` Alexey Dobriyan
2010-11-15 14:18 ` Ben Hutchings
2010-11-22 22:54 ` Alexey Dobriyan [this message]
2010-11-28 18:39 ` [PATCH v2] tcp: restrict net.ipv4.tcp_adv_win_scale (#20312) David Miller
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