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

[Emil Velikov]

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)
       gbm_device_destroy(&dri2_dpy->gbm_dri->base);
 }
-- 
2.21.0