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SubjectRe: [PATCH v2] drm: udl: Destroy framebuffer only if it was initialized
On Mon, May 28, 2018 at 04:27:11PM +0200, Emil Lundmark wrote:
> 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>
> Signed-off-by: Emil Lundmark <lndmrk@chromium.org>

You lost the r-b from Sean when resending, I'll leave that to Sean to
readd when he merges. Anyway, lgtm now with the more detailed explanation.

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
> Changes in v2:
> - Updated commit message with explanation from Stéphane Marchesin
>
> drivers/gpu/drm/udl/udl_fb.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/udl/udl_fb.c b/drivers/gpu/drm/udl/udl_fb.c
> index 2ebdc6d5a76e..5754e37f741b 100644
> --- a/drivers/gpu/drm/udl/udl_fb.c
> +++ b/drivers/gpu/drm/udl/udl_fb.c
> @@ -426,9 +426,11 @@ 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)
> --
> 2.17.0.921.gf22659ad46-goog
>

--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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