2010-11-21 17:40:20

by Vasily Kulikov

Subject: [PATCH] video: arcfb: fix buffer overflow

(count + p) is not checked for integer overflow. If p < fbmemlength
and count == (size_t)(1 - p) (very big unsigned integer) then
count + p == 1 < fbmemlength and copy_to_user(base_addr+p, buf, count)
overflows base_addr.

Signed-off-by: Vasiliy Kulikov <[email protected]>
---
Compile tested only.

drivers/video/arcfb.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/video/arcfb.c b/drivers/video/arcfb.c
index 3ec4923..67a4cd4 100644
--- a/drivers/video/arcfb.c
+++ b/drivers/video/arcfb.c
@@ -454,7 +454,7 @@ static ssize_t arcfb_write(struct fb_info *info, const char __user *buf,
xres = info->var.xres;
fbmemlength = (xres * info->var.yres)/8;

- if (p > fbmemlength)
+ if (p > fbmemlength || (p + count < p))
return -ENOSPC;

err = 0;
--
1.7.0.4

2010-11-24 06:26:47

by Paul Mundt

Subject: Re: [PATCH] video: arcfb: fix buffer overflow

On Sun, Nov 21, 2010 at 08:40:01PM +0300, Vasiliy Kulikov wrote:
> (count + p) is not checked for integer overflow. If p < fbmemlength
> and count == (size_t)(1 - p) (very big unsigned integer) then
> count + p == 1 < fbmemlength and copy_to_user(base_addr+p, buf, count)
> overflows base_addr.
>
> Signed-off-by: Vasiliy Kulikov <[email protected]>

Applied, thanks.

2010-11-24 06:49:15

by Dan Carpenter

Subject: Re: [PATCH] video: arcfb: fix buffer overflow

On Wed, Nov 24, 2010 at 03:25:58PM +0900, Paul Mundt wrote:
> On Sun, Nov 21, 2010 at 08:40:01PM +0300, Vasiliy Kulikov wrote:
> > (count + p) is not checked for integer overflow. If p < fbmemlength
> > and count == (size_t)(1 - p) (very big unsigned integer) then
> > count + p == 1 < fbmemlength and copy_to_user(base_addr+p, buf, count)
> > overflows base_addr.
> >
> > Signed-off-by: Vasiliy Kulikov <[email protected]>
>
> Applied, thanks.

The patch is harmless, but the integer overflow would actually be caught
in rw_verify_area().

regards,
dan carpenter

2010-11-24 07:00:10

by Paul Mundt

Subject: Re: [PATCH] video: arcfb: fix buffer overflow

On Wed, Nov 24, 2010 at 09:46:49AM +0300, Dan Carpenter wrote:
> On Wed, Nov 24, 2010 at 03:25:58PM +0900, Paul Mundt wrote:
> > On Sun, Nov 21, 2010 at 08:40:01PM +0300, Vasiliy Kulikov wrote:
> > > (count + p) is not checked for integer overflow. If p < fbmemlength
> > > and count == (size_t)(1 - p) (very big unsigned integer) then
> > > count + p == 1 < fbmemlength and copy_to_user(base_addr+p, buf, count)
> > > overflows base_addr.
> > >
> > > Signed-off-by: Vasiliy Kulikov <[email protected]>
> >
> > Applied, thanks.
>
> The patch is harmless, but the integer overflow would actually be caught
> in rw_verify_area().
>
Ah, so it is, I'll drop it then, thanks.