From: Alexey Dobriyan <adobriyan@gmail•com>
To: davem@davemloft•net
Cc: shemminger@linux-foundation•org, netdev@vger•kernel.org
Subject: [PATCH] tcp: restrict net.ipv4.tcp_adv_min_scale (#20312)
Date: Sun, 14 Nov 2010 17:18:25 +0200 [thread overview]
Message-ID: <20101114151825.GA25137@core2.telecom.by> (raw)
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>
---
--- 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 _minus_31 = -31;
+static int _31 = 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 = &_minus_31,
+ .extra2 = &_31,
},
{
.procname = "tcp_tw_reuse",
next reply other threads:[~2010-11-14 15:18 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-14 15:18 Alexey Dobriyan [this message]
2010-11-14 19:49 ` [PATCH] tcp: restrict net.ipv4.tcp_adv_min_scale (#20312) Eric Dumazet
2010-11-14 20:14 ` Alexey Dobriyan
2010-11-15 14:18 ` Ben Hutchings
2010-11-22 22:54 ` [PATCH v2] tcp: restrict net.ipv4.tcp_adv_win_scale (#20312) Alexey Dobriyan
2010-11-28 18:39 ` David Miller
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