[PATCH] tcp: restrict net.ipv4.tcp_adv_min_scale (#20312)

[PATCH] tcp: restrict net.ipv4.tcp_adv_min_scale (#20312)

[Alexey Dobriyan]

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",

Re: [PATCH] tcp: restrict net.ipv4.tcp_adv_min_scale (#20312)

[Eric Dumazet]

Le dimanche 14 novembre 2010 à 17:18 +0200, Alexey Dobriyan a écrit :
> 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>
> ---
> 

Please fix your patch title, you speak of adv_min_scale ...

> --- 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;

Please use normal symbols, not starting by underscore.

>  
>  /* 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",

Please change Documentation/networking/ip-sysctl.txt to reflect possible
values of adv_win_scale

Thanks

Re: [PATCH] tcp: restrict net.ipv4.tcp_adv_min_scale (#20312)

[Alexey Dobriyan]

On Sun, Nov 14, 2010 at 08:49:43PM +0100, Eric Dumazet wrote:
> > +static int _minus_31 = -31;
> > +static int _31 = 31;
> 
> Please use normal symbols, not starting by underscore.

static int thirty_one = 31? :-)

Re: [PATCH] tcp: restrict net.ipv4.tcp_adv_min_scale (#20312)

[Ben Hutchings]

On Sun, 2010-11-14 at 22:14 +0200, Alexey Dobriyan wrote:
> On Sun, Nov 14, 2010 at 08:49:43PM +0100, Eric Dumazet wrote:
> > > +static int _minus_31 = -31;
> > > +static int _31 = 31;
> > 
> > Please use normal symbols, not starting by underscore.
> 
> static int thirty_one = 31? :-)

How about, oh, I don't know, adv_win_scale_{min,max}?

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

[PATCH v2] tcp: restrict net.ipv4.tcp_adv_win_scale (#20312)

[Alexey Dobriyan]

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",

Re: [PATCH v2] tcp: restrict net.ipv4.tcp_adv_win_scale (#20312)

[David Miller]

From: Alexey Dobriyan <adobriyan@gmail.com>
Date: Tue, 23 Nov 2010 00:54:21 +0200

> 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>

I'll aply this, thanks Alexey.