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References: <20190118122020.27596-1-kraxel@redhat.com> <20190118122020.27596-24-kraxel@redhat.com>
 <20190118154944.GH3271@phenom.ffwll.local> <20190118163233.GM20097@intel.com>
In-Reply-To: <20190118163233.GM20097@intel.com>
From:   Daniel Vetter <daniel@ffwll.ch>
Date:   Fri, 18 Jan 2019 18:15:44 +0100
Message-ID: <CAKMK7uF0e+cTXv-TyRDrqFUSKQCtnB99V3jRtrLbmPcptkEs+Q@mail.gmail.com>
Subject: Re: [PATCH v3 23/23] drm/qxl: add overflow checks to qxl_mode_dumb_create()
To:     =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= <ville.syrjala@linux.intel.com>
Cc:     Gerd Hoffmann <kraxel@redhat.com>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Dave Airlie <airlied@redhat.com>,
        David Airlie <airlied@linux.ie>,
        "open list:DRM DRIVER FOR QXL VIRTUAL GPU" 
        <virtualization@lists.linux-foundation.org>,
        "open list:DRM DRIVER FOR QXL VIRTUAL GPU" 
        <spice-devel@lists.freedesktop.org>,
        open list <linux-kernel@vger.kernel.org>
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On Fri, Jan 18, 2019 at 5:32 PM Ville Syrj=C3=A4l=C3=A4
<ville.syrjala@linux.intel.com> wrote:
>
> On Fri, Jan 18, 2019 at 04:49:44PM +0100, Daniel Vetter wrote:
> > On Fri, Jan 18, 2019 at 01:20:20PM +0100, Gerd Hoffmann wrote:
> > > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> >
> > We already do all reasonable overflow checks in drm_mode_create_dumb().=
 If
> > you don't trust them I think would be better time spent typing an igt t=
o
> > test this than adding redundant check in all drivers.
> >
> > You're also missing one check for bpp underflows :-)
>
> BTW I just noticed that we don't seem to validating
> create_dumb->flags at all. Someone should probably add some
> checks for that, or mark it as deprecated in case we already
> lost the battle with userspace stack garbage.

Given that every kms client/compositor under the sun uses this (or
well, all the generic ones at least) I think we can safely assume to
have lost that battle :-/
-Daniel

>
> > -Daniel
> >
> > > ---
> > >  drivers/gpu/drm/qxl/qxl_dumb.c | 10 ++++++----
> > >  1 file changed, 6 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/qxl/qxl_dumb.c b/drivers/gpu/drm/qxl/qxl=
_dumb.c
> > > index 272d19b677..bed6d06ee4 100644
> > > --- a/drivers/gpu/drm/qxl/qxl_dumb.c
> > > +++ b/drivers/gpu/drm/qxl/qxl_dumb.c
> > > @@ -37,11 +37,13 @@ int qxl_mode_dumb_create(struct drm_file *file_pr=
iv,
> > >     uint32_t handle;
> > >     int r;
> > >     struct qxl_surface surf;
> > > -   uint32_t pitch, format;
> > > +   uint32_t pitch, size, format;
> > >
> > > -   pitch =3D args->width * ((args->bpp + 1) / 8);
> > > -   args->size =3D pitch * args->height;
> > > -   args->size =3D ALIGN(args->size, PAGE_SIZE);
> > > +   if (check_mul_overflow(args->width, ((args->bpp + 1) / 8), &pitch=
))
> > > +           return -EINVAL;
> > > +   if (check_mul_overflow(pitch, args->height, &size))
> > > +           return -EINVAL;
> > > +   args->size =3D ALIGN(size, PAGE_SIZE);
> > >
> > >     switch (args->bpp) {
> > >     case 16:
> > > --
> > > 2.9.3
> > >
> >
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
> --
> Ville Syrj=C3=A4l=C3=A4
> Intel
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel


--=20
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch