PATCH: Fix poor pointer math in devinet_sysctl_register

PATCH: Fix poor pointer math in devinet_sysctl_register

[Jordan Crouse]

This patch fixes pointer math that under certain circumstances, results
in really bad pointers. This was encountered on a system compiled for i486, so
other compilers may differ, but I don't think it hurts anyone.

Signed-off-by: Jordan Crouse <jordan.crouse@amd.com>
---

 net/ipv4/devinet.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 4ec4b2c..7585fce 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1454,7 +1454,7 @@ static void devinet_sysctl_register(stru
 		return;
 	memcpy(t, &devinet_sysctl, sizeof(*t));
 	for (i = 0; i < ARRAY_SIZE(t->devinet_vars) - 1; i++) {
-		t->devinet_vars[i].data += (char *)p - (char *)&ipv4_devconf;
+		t->devinet_vars[i].data += (int)((char *)p - (char *)&ipv4_devconf);
 		t->devinet_vars[i].de = NULL;
 	}
 

Re: PATCH: Fix poor pointer math in devinet_sysctl_register

[Andrew Morton]

"Jordan Crouse" <jordan.crouse@amd.com> wrote:
>
> This patch fixes pointer math that under certain circumstances, results
>  in really bad pointers. This was encountered on a system compiled for i486, so
>  other compilers may differ, but I don't think it hurts anyone.
> 
>  Signed-off-by: Jordan Crouse <jordan.crouse@amd.com>
>  ---
> 
>   net/ipv4/devinet.c |    2 +-
>   1 files changed, 1 insertions(+), 1 deletions(-)
> 
>  diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
>  index 4ec4b2c..7585fce 100644
>  --- a/net/ipv4/devinet.c
>  +++ b/net/ipv4/devinet.c
>  @@ -1454,7 +1454,7 @@ static void devinet_sysctl_register(stru
>   		return;
>   	memcpy(t, &devinet_sysctl, sizeof(*t));
>   	for (i = 0; i < ARRAY_SIZE(t->devinet_vars) - 1; i++) {
>  -		t->devinet_vars[i].data += (char *)p - (char *)&ipv4_devconf;
>  +		t->devinet_vars[i].data += (int)((char *)p - (char *)&ipv4_devconf);

Confused.  These appear to be equivalent (on 32-bit CPUs, anyway).

Re: PATCH: Fix poor pointer math in devinet_sysctl_register

[David S. Miller]

From: Andrew Morton <akpm@osdl.org>
Date: Wed, 16 Nov 2005 22:14:12 -0800

> "Jordan Crouse" <jordan.crouse@amd.com> wrote:
> >  @@ -1454,7 +1454,7 @@ static void devinet_sysctl_register(stru
> >   		return;
> >   	memcpy(t, &devinet_sysctl, sizeof(*t));
> >   	for (i = 0; i < ARRAY_SIZE(t->devinet_vars) - 1; i++) {
> >  -		t->devinet_vars[i].data += (char *)p - (char *)&ipv4_devconf;
> >  +		t->devinet_vars[i].data += (int)((char *)p - (char *)&ipv4_devconf);
> 
> Confused.  These appear to be equivalent (on 32-bit CPUs, anyway).

Indeed, please describe the exact failure case when posting
such patches.

Re: PATCH: Fix poor pointer math in devinet_sysctl_register

[Mikael Pettersson]

Jordan Crouse writes:
 > This patch fixes pointer math that under certain circumstances, results
 > in really bad pointers. This was encountered on a system compiled for i486, so
 > other compilers may differ, but I don't think it hurts anyone.
 > 
 > Signed-off-by: Jordan Crouse <jordan.crouse@amd.com>
 > ---
 > 
 >  net/ipv4/devinet.c |    2 +-
 >  1 files changed, 1 insertions(+), 1 deletions(-)
 > 
 > diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
 > index 4ec4b2c..7585fce 100644
 > --- a/net/ipv4/devinet.c
 > +++ b/net/ipv4/devinet.c
 > @@ -1454,7 +1454,7 @@ static void devinet_sysctl_register(stru
 >  		return;
 >  	memcpy(t, &devinet_sysctl, sizeof(*t));
 >  	for (i = 0; i < ARRAY_SIZE(t->devinet_vars) - 1; i++) {
 > -		t->devinet_vars[i].data += (char *)p - (char *)&ipv4_devconf;
 > +		t->devinet_vars[i].data += (int)((char *)p - (char *)&ipv4_devconf);
 >  		t->devinet_vars[i].de = NULL;
 >  	}

This is the same code which broke due to a known gcc-4.0.0 bug:
<http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21173>. If you're
indeed using gcc-4.0.0, then it's time to upgrade.

/Mikael

Re: PATCH: Fix poor pointer math in devinet_sysctl_register

[Jordan Crouse]

> This is the same code which broke due to a known gcc-4.0.0 bug:
> <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21173>. If you're
> indeed using gcc-4.0.0, then it's time to upgrade.
> 
Indeed, I am using 4.0.0, so may indeed be it.  I'll upgrade and take
another shot at it.

Thanks,

Jordan

-- 
Jordan Crouse
Senior Linux Engineer
AMD - Personal Connectivity Solutions Group
<www.amd.com/embeddedprocessors>