drm: udl: Destroy framebuffer only if it was initialized

commit fcb74da1eb8edd3a4ef9b9724f88ed709d684227 upstream.

This fixes a NULL pointer dereference that can happen if the UDL
driver is unloaded before the framebuffer is initialized. This can
happen e.g. if the USB device is unplugged right after it was plugged
in.

As explained by Stéphane Marchesin:

It happens when fbdev is disabled (which is the case for Chrome OS).
Even though intialization of the fbdev part is optional (it's done in
udlfb_create which is the callback for fb_probe()), the teardown isn't
optional (udl_driver_unload -> udl_fbdev_cleanup ->
udl_fbdev_destroy).

Note that udl_fbdev_cleanup *tries* to be conditional (you can see it
does if (!udl->fbdev)) but that doesn't work, because udl->fbdev is
always set during udl_fbdev_init.

Cc: stable@vger.kernel.org
Suggested-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Emil Lundmark <lndmrk@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180528142711.142466-1-lndmrk@chromium.org
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/udl/udl_fb.c b/drivers/gpu/drm/udl/udl_fb.c
index 8746eeeec44d9801d08e2917eb5fb8be9f43b392..491f1892b50e7995de815f44909f9cca6ebd07cd 100644 (file)
--- a/drivers/gpu/drm/udl/udl_fb.c
+++ b/drivers/gpu/drm/udl/udl_fb.c
@@ -432,9 +432,11 @@ static void udl_fbdev_destroy(struct drm_device *dev,
 {
        drm_fb_helper_unregister_fbi(&ufbdev->helper);
        drm_fb_helper_fini(&ufbdev->helper);
-       drm_framebuffer_unregister_private(&ufbdev->ufb.base);
-       drm_framebuffer_cleanup(&ufbdev->ufb.base);
-       drm_gem_object_put_unlocked(&ufbdev->ufb.obj->base);
+       if (ufbdev->ufb.obj) {
+               drm_framebuffer_unregister_private(&ufbdev->ufb.base);
+               drm_framebuffer_cleanup(&ufbdev->ufb.base);
+               drm_gem_object_put_unlocked(&ufbdev->ufb.obj->base);
+       }
 }
 
 int udl_fbdev_init(struct drm_device *dev)