[Pixman] [PATCH] Fix arithmetic overflow in pointer arithmetic in ‘general_composite_rect’

[Søren Sandmann]

Regardless of who ends up listed as the patch author, this is

Reviewed-by: soren.sandmann at gmail.com

Søren
On Sep 21, 2015 3:07 PM, "Siarhei Siamashka" <siarhei.siamashka at gmail.com>
wrote:

> On Mon, 21 Sep 2015 17:10:36 +0200
> ludo at gnu.org (Ludovic Courtès) wrote:
>
> > Hello,
> >
> > The patch below intends to fix an arithmetic overflow occurring in a
> > pointer arithmetic context in ‘general_composite_rect’, as explained at:
> >
> >   https://bugs.freedesktop.org/show_bug.cgi?id=92027#c6
>
> Sorry, I forgot to mention
>     http://cgit.freedesktop.org/pixman/tree/README?id=pixman-0.33.2#n46
>
> We would also need a commit message for the patch. So it normally
> should be created with "git format-patch" command and sent to the
> mailing list using "git send-email".
>
> > The bug can most likely lead to a crash.
>
> Yes, I can confirm that the bug is reproducible on my x86-64 system:
>
>     export CFLAGS="-O2 -m32" && ./autogen.sh
>     ./configure --disable-libpng --disable-gtk && make
>     setarch i686 -R test/stress-test
>
> > In a preliminary review, Siarhei Siamashka notes that ‘width + 1’ is
> > insufficient to take 16-byte alignment constraints into account.
> > Indeed, AFAICS, it is sufficient when Bpp == 16 but probably not when
> > Bpp == 4.
> >
> > Siarhei also suggests that more rewriting in needed in that part of the
> > code, but I’ll leave that to you.  ;-)
>
> Basically, I would probably do it in the following way:
>
>
> diff --git a/pixman/pixman-general.c b/pixman/pixman-general.c
> index 7cdea29..5ffa063 100644
> --- a/pixman/pixman-general.c
> +++ b/pixman/pixman-general.c
> @@ -155,23 +155,21 @@ general_composite_rect  (pixman_implementation_t
> *imp, #define
> ALIGN(addr)                                                     \
> ((uint8_t *)((((uintptr_t)(addr)) + 15) & (~15)))
> -    src_buffer = ALIGN (scanline_buffer);
> -    mask_buffer = ALIGN (src_buffer + width * Bpp);
> -    dest_buffer = ALIGN (mask_buffer + width * Bpp);
> +    if (_pixman_multiply_overflows_int (width, Bpp * 3))
> +       return;
>
> -    if (ALIGN (dest_buffer + width * Bpp) >
> -           scanline_buffer + sizeof (stack_scanline_buffer))
> +    if (width * Bpp * 3 > sizeof (stack_scanline_buffer) - 32 * 3)
>      {
>         scanline_buffer = pixman_malloc_ab_plus_c (width, Bpp * 3, 32
> * 3);
>         if (!scanline_buffer)
>             return;
> -
> -       src_buffer = ALIGN (scanline_buffer);
> -       mask_buffer = ALIGN (src_buffer + width * Bpp);
> -       dest_buffer = ALIGN (mask_buffer + width * Bpp);
>      }
>
> +    src_buffer = ALIGN (scanline_buffer);
> +    mask_buffer = ALIGN (src_buffer + width * Bpp);
> +    dest_buffer = ALIGN (mask_buffer + width * Bpp);
> +
>      if (width_flag == ITER_WIDE)
>      {
>         /* To make sure there aren't any NANs in the buffers */
>
>
>
> This bug is your find and you should get credit for it :-)
> Please let me know if you:
> 1. are going to send an updated patch yourself.
> 2. want me to do this on your behalf (listing you as the patch author).
> 3. want me to submit a patch myself (listing you as the bug reporter).
>
>
> Also this is an important bugfix for a non-obvious problem, which can
> be really a PITA to debug. I would nominate it for a pixman-0.32.8
> bugfix release.
>
> --
> Best regards,
> Siarhei Siamashka
> _______________________________________________
> Pixman mailing list
> Pixman at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/pixman
>
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