linux-kernel - Re: drm_mode_create_dumb

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Message-ID: <CANq1E4S97B_RA+WQbsHe8JQsVnqTS3g6=uR3EQFN9n9bptFV2w@mail.gmail.com>
Date:	Sun, 24 Aug 2014 19:18:11 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	Tommi Rantala <tt.rantala@...il.com>
Cc:	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	trinity@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	David Airlie <airlied@...ux.ie>, Dave Jones <davej@...hat.com>
Subject: Re: drm_mode_create_dumb_ioctl: divide error

Hi

On Sun, Aug 24, 2014 at 7:12 PM, Tommi Rantala <tt.rantala@...il.com> wrote:
> (gdb) info locals
> cpp = 0
> stride = 0
> size = <optimized out>
>
> (gdb) print /x *(struct drm_mode_create_dumb *)data
> $13 = {
>   height = 0xffffffff,
>   width = 0xffffffff,
>   bpp = 0xffffffff,
>   flags = 0xffffffff,
>   handle = 0xffffffff,
>   pitch = 0xffffffff,
>   size = 0xffffffffffffffff
> }

Thanks a lot for digging into this. Looks like DIV_ROUND_UP() can
overflow... *check*
Yes, it's defined as:
        #define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))

Kinda unexpected that a function called "DIV" can overflow, but makes
sense here. Obvious fix is to test "cpp" for zero. I will send it to
dri-devel.

Thanks!
David
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