linux-kernel - Re: [Security] [PATCH] drivers/video/sis/sis_main.c: prevent reading uninitialized stack memory

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Date:	Thu, 16 Sep 2010 14:06:44 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dan Rosenberg <drosenberg@...curity.com>
Cc:	thomas@...ischhofer.net, security@...nel.org,
	linux-kernel@...r.kernel.org, stable@...nel.org
Subject: Re: [Security] [PATCH] drivers/video/sis/sis_main.c: prevent
 reading uninitialized stack memory

On Wed, 15 Sep 2010 17:43:53 -0400
Dan Rosenberg <drosenberg@...curity.com> wrote:

> The FBIOGET_VBLANK device ioctl allows unprivileged users to read 16
> bytes of uninitialized stack memory, because the "reserved" member of
> the fb_vblank struct declared on the stack is not altered or zeroed
> before being copied back to the user.  This patch takes care of it.
> 
> Signed-off-by: Dan Rosenberg <dan.j.rosenberg@...il.com>
> 
> --- linux-2.6.35.4.orig/drivers/video/sis/sis_main.c	2010-08-26 19:47:12.000000000 -0400
> +++ linux-2.6.35.4/drivers/video/sis/sis_main.c	2010-09-15 11:52:41.437375730 -0400
> @@ -1701,6 +1701,9 @@ static int	sisfb_ioctl(struct fb_info *i
>  		break;
>  
>  	   case FBIOGET_VBLANK:
> +
> +		memset(&sisvbblank, 0, sizeof(struct fb_vblank));

grumble.  Every one of these patches I need to go in and check that the
types are correct.  In this case, that sisvbblank really does have the
type `struct fb_vblank'.

If the code had done

		memset(&sisvbblank, 0, sizeof(sisvbblank));

then I wouldn't need to do that.

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