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tcp: restrict net.ipv4.tcp_adv_win_scale (#20312)

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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>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexey Dobriyan 2010-11-22 12:54:21 +00:00 committed by David S. Miller
parent 8475ef9fd1
commit 0147fc058d
2 changed files with 6 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
Documentation/networking/ip-sysctl.txt
View File

@ -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

6
net/ipv4/sysctl_net_ipv4.c
View File

@ -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",