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From: Daniel Vetter <daniel@ffwll.ch>
To: Emil Lundmark <lndmrk@chromium.org>
Cc: dri-devel@lists.freedesktop.org,
	"Dave Airlie" <airlied@redhat.com>,
	"Sean Paul" <seanpaul@chromium.org>,
	linux-kernel@vger.kernel.org, "Daniel Vetter" <daniel@ffwll.ch>,
	"Stéphane Marchesin" <stephane.marchesin@gmail.com>
Subject: Re: [PATCH v2] drm: udl: Destroy framebuffer only if it was initialized
Date: Tue, 29 May 2018 08:46:16 +0200	[thread overview]
Message-ID: <20180529064616.GS3438@phenom.ffwll.local> (raw)
In-Reply-To: <20180528142711.142466-1-lndmrk@chromium.org>

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

  reply	other threads:[~2018-05-29  6:46 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-20 11:50 [PATCH] " Emil Lundmark
2018-04-20 13:55 ` Sean Paul
2018-04-24 13:04   ` Daniel Vetter
2018-04-25 22:56     ` Stéphane Marchesin
2018-04-26  9:50       ` Daniel Vetter
2018-05-28 14:27 ` [PATCH v2] " Emil Lundmark
2018-05-29  6:46   ` Daniel Vetter [this message]
2018-09-10 14:23   ` Sean Paul

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