linux-kernel - Re: [PATCH] drivers/video/via/ioctl.c: prevent reading uninitialized stack memory

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Date:	Thu, 16 Sep 2010 00:42:12 +0200
From:	Florian Tobias Schandinat <FlorianSchandinat@....de>
To:	Dan Rosenberg <drosenberg@...curity.com>
CC:	JosephChan@....com.tw, linux-fbdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, security@...nel.org,
	stable@...nel.org
Subject: Re: [PATCH] drivers/video/via/ioctl.c: prevent reading uninitialized
 stack memory

Hi,

Dan Rosenberg schrieb:
> The VIAFB_GET_INFO device ioctl allows unprivileged users to read 1968
> bytes of uninitialized stack memory, because the "reserved" member of
> the viafb_ioctl_info struct declared on the stack is not altered or
> zeroed before being copied back to the user.  This patch takes care of
> it.

I am wondering about the number of bytes as sizeof(struct viafb_ioctl_info) = 
256 so it should be a bit less. But that's just nitpicking, the issue is 
certainly real. Your patch does the right thing but there is a bug in it:

> Signed-off-by: Dan Rosenberg <dan.j.rosenberg@...il.com>
> 
> --- linux-2.6.35.4.orig/drivers/video/via/ioctl.c	2010-08-26 19:47:12.000000000 -0400
> +++ linux-2.6.35.4/drivers/video/via/ioctl.c	2010-09-15 11:53:29.997375748 -0400
> @@ -25,6 +25,8 @@ int viafb_ioctl_get_viafb_info(u_long ar
>  {
>  	struct viafb_ioctl_info viainfo;
>  
> +	memset(&viainfo, 0, sizeof(struct viafb_ioctl));

Shouldn't it be sizeof(struct viafb_ioctl_info) or sizeof(viainfo) ?
At least here it does not even compile otherwise....


Thanks,

Florian Tobias Schandinat
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