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Date: Mon, 8 Jun 2015 10:31:25 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20150608093125.GF30104@stefanha-thinkpad.redhat.com>
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Subject: Re: [Qemu-devel] segfault in memcmp
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To: perrier vincent <clownix@clownix.net>
Cc: qemu-devel@nongnu.org, Gerd Hoffmann <kraxel@redhat.com>


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On Fri, Jun 05, 2015 at 05:19:53PM -0500, perrier vincent wrote:
> Using a very old guest (lenny) with spice and vga=3Dcirrus, I have
> a segfault:
>=20
> FILE:      ui/spice-display.c
> FUNCTION:  qemu_spice_create_update
> LINE:      if (memcmp(guest + yoff + xoff,
>                        mirror + yoff + xoff,
>                        bw * bpp) =3D=3D 0)
>=20
> The address of mirror + yoff + xoff is out of boundaries.
>=20
> I use the following to avoid the crash:
>=20
> ...
>   img_get_stride =3D pixman_image_get_stride(ssd->mirror);
>   img_height =3D pixman_image_get_height(ssd->mirror);
>   img_max =3D img_height * img_get_stride;
> ...
>   if (yoff > img_max)
>     {
>     if (dirty_top[blk] =3D=3D -1)
>       dirty_top[blk] =3D y;
>     }
>   else if (memcmp(guest + yoff + xoff,
>                   mirror + yoff + xoff,
>                   bw * bpp) =3D=3D 0)
>     {
> ...

Thanks for the report.  I have CCed Gerd Hoffmann who maintains the
graphics subsystem.

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