linux-kernel - Re: [PATCH] drm/mediatek: fix device use-after-free on unbind

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Message-ID: <4240cc29adb6707005cba18c956a70ab414edc07.camel@collabora.com>
Date: Wed, 22 Oct 2025 12:16:21 +0530
From: Ritesh Raj Sarraf <ritesh.sarraf@...labora.com>
To: Johan Hovold <johan@...nel.org>, Chun-Kuang Hu
 <chunkuang.hu@...nel.org>,  Philipp Zabel <p.zabel@...gutronix.de>
Cc: David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Matthias Brugger <matthias.bgg@...il.com>, AngeloGioacchino Del Regno
 <angelogioacchino.delregno@...labora.com>,  CK Hu <ck.hu@...iatek.com>, Ma
 Ke <make24@...as.ac.cn>, Sjoerd Simons <sjoerd@...labora.com>, 
	dri-devel@...ts.freedesktop.org, linux-mediatek@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] drm/mediatek: fix device use-after-free on unbind

On Mon, 2025-10-06 at 11:39 +0200, Johan Hovold wrote:
> A recent change fixed device reference leaks when looking up drm
> platform device driver data during bind() but failed to remove a
> partial
> fix which had been added by commit 80805b62ea5b ("drm/mediatek: Fix
> kobject put for component sub-drivers").
> 
> This results in a reference imbalance on component bind() failures
> and
> on unbind() which could lead to a user-after-free.
> 
> Make sure to only drop the references after retrieving the driver
> data
> by effectively reverting the previous partial fix.
> 
> Note that holding a reference to a device does not prevent its driver
> data from going away so there is no point in keeping the reference.
> 

We ran into the same issue in mesaci[1] and have test validated this
proposed fix. It was tested with Linux 6.17.3 + this fix.

[1] https://gitlab.freedesktop.org/RickXy/mesa/-/jobs/86389548


Tested-by: Ritesh Raj Sarraf <ritesh.sarraf@...labora.com>

> Fixes: 1f403699c40f ("drm/mediatek: Fix device/node reference count
> leaks in mtk_drm_get_all_drm_priv")
> Reported-by: Sjoerd Simons <sjoerd@...labora.com>
> Link:
> https://lore.kernel.org/r/20251003-mtk-drm-refcount-v1-1-3b3f2813b0db@collabora.com
> Cc: stable@...r.kernel.org
> Cc: Ma Ke <make24@...as.ac.cn>
> Cc: AngeloGioacchino Del Regno
> <angelogioacchino.delregno@...labora.com>
> Signed-off-by: Johan Hovold <johan@...nel.org>

-- 
Ritesh Raj Sarraf
Collabora