3.16.62-rc1 review patch. If anyone has any objections, please let me know.
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From: Emil Lundmark lndmrk@chromium.org
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.
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... Signed-off-by: Sean Paul seanpaul@chromium.org [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/gpu/drm/udl/udl_fb.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
--- a/drivers/gpu/drm/udl/udl_fb.c +++ b/drivers/gpu/drm/udl/udl_fb.c @@ -574,9 +574,11 @@ static void udl_fbdev_destroy(struct drm framebuffer_release(info); } drm_fb_helper_fini(&ufbdev->helper); - drm_framebuffer_unregister_private(&ufbdev->ufb.base); - drm_framebuffer_cleanup(&ufbdev->ufb.base); - drm_gem_object_unreference_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_unreference_unlocked(&ufbdev->ufb.obj->base); + } }
int udl_fbdev_init(struct drm_device *dev)