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

[Siarhei Siamashka]

On Mon, 21 Sep 2015 16:43:46 -0400
Søren Sandmann <soren.sandmann at gmail.com> wrote:

> Regardless of who ends up listed as the patch author, this is
> 
> Reviewed-by: soren.sandmann at gmail.com
> 
> Søren

Thanks! Is your Reviewed-by still valid after adding an extra
"width <= 0" check to the patch?

Best regards,
Siarhei Siamashka

> 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.