[Mesa-dev] [PATCH] egl/drm: ensure the backing gbm is set before using it

[Emil Velikov]

On Fri, 5 Jul 2019 at 22:58, Eric Engestrom <eric.engestrom at intel.com> wrote:
>
> On Friday, 2019-07-05 11:21:41 +0100, Emil Velikov wrote:
> > From: Emil Velikov <emil.velikov at collabora.com>
> >
> > Currently, if we error out before gbm_dri is set (say due to a different
> > name of the backing GBM implementation, or otherwise) the tear down will
> > trigger a NULL ptr deref and crash out.
> >
> > Move the gbm_dri initialization as early as possible. To be on the extra
> > safe side add a NULL check in the teardown.
> >
> > Reported-by: Christian Gmeiner <christian.gmeiner at gmail.com>
> > Cc: Christian Gmeiner <christian.gmeiner at gmail.com>
> > Cc: Eric Engestrom <eric.engestrom at intel.com>
> > Cc: mesa-stable at lists.freedesktop.org
> > Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
> > ---
> > Supersedes https://gitlab.freedesktop.org/mesa/mesa/merge_requests/1182
> > ---
> >  src/egl/drivers/dri2/platform_drm.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/src/egl/drivers/dri2/platform_drm.c b/src/egl/drivers/dri2/platform_drm.c
> > index a811834114d..3e2124ad39c 100644
> > --- a/src/egl/drivers/dri2/platform_drm.c
> > +++ b/src/egl/drivers/dri2/platform_drm.c
> > @@ -704,6 +704,7 @@ dri2_initialize_drm(_EGLDisplay *disp)
> >           goto cleanup;
> >        }
> >     }
> > +   dri2_dpy->gbm_dri = gbm_dri_device(gbm);
> >
> >     if (strcmp(gbm_device_get_backend_name(gbm), "drm") != 0) {
> >        err = "DRI2: gbm device using incorrect/incompatible backend";
> > @@ -718,7 +719,6 @@ dri2_initialize_drm(_EGLDisplay *disp)
> >
> >     disp->Device = dev;
> >
> > -   dri2_dpy->gbm_dri = gbm_dri_device(gbm);
> >     dri2_dpy->driver_name = strdup(dri2_dpy->gbm_dri->driver_name);
> >
> >     dri2_dpy->dri_screen = dri2_dpy->gbm_dri->screen;
> > @@ -777,6 +777,6 @@ cleanup:
> >  void
> >  dri2_teardown_drm(struct dri2_egl_display *dri2_dpy)
> >  {
> > -   if (dri2_dpy->own_device)
> > +   if (dri2_dpy->own_device && dri2_dpy->gbm_dri)
>
> This would only be reachable by eglTerminate()ing an uninitialised
> display, which is explicitly invalid anyway.
>
> I think you can drop this check.
>
> The gbm_dri_device(gbm) move above is:
> Reviewed-by: Eric Engestrom <eric.engestrom at intel.com>
>
Dropped the check in dri2_teardown_drm() and pushed to master.

Thank you
Emil