linux-kernel - Re: [BUG] Buffer Overflow in drivers/video/fbmem.c

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Date:	Thu, 26 Sep 2013 14:14:36 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	徐永健 <xuyongjiande@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [BUG] Buffer Overflow in drivers/video/fbmem.c

On Mon, 23 Sep 2013 19:32:04 +0800 _________ <xuyongjiande@...il.com> wrote:

> Hi,
> Buffer overflow found in drivers/video/fbmem.c.
> [Version]:Newest
> 
> [Detail]:
> 1592 static int do_register_framebuffer(struct fb_info *fb_info)
> 1593 {
> 1594 |   int i;
> 1595 |   struct fb_event event;
> 1596 |   struct fb_videomode mode;
> ........
> 1607 |   num_registered_fb++;
> 1608 |   for (i = 0 ; i < FB_MAX; i++)    //******* i could be FB_MAX
> after loop *********/
> 1609 |   |   if (!registered_fb[i])
> 1610 |   |   |   break;
> ........
> 
> 1646 |   fb_var_to_videomode(&mode, &fb_info->var);
> 1647 |   fb_add_videomode(&mode, &fb_info->modelist);
> 1648 |   registered_fb[i] = fb_info;          // ****** Here will be a
> off-by-one overflow  *******/

I don't think so.  This test:

	if (num_registered_fb == FB_MAX)
		return -ENXIO;

guarantees that there is at least one empty entry in registered_fb[],
so `i' will never reach FB_MAX.


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