linux-kernel - Re: [PATCH] drm/mediatek: Fix potential NULL dereference in mtk_crtc

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Message-ID: <CAAOTY_8kG67ns8OokhzujmH7UNM-O+4Aa=GruO_spLOALMeARA@mail.gmail.com>
Date: Wed, 23 Oct 2024 22:13:10 +0800
From: Chun-Kuang Hu <chunkuang.hu@...nel.org>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Chun-Kuang Hu <chunkuang.hu@...nel.org>, Philipp Zabel <p.zabel@...gutronix.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, dri-devel@...ts.freedesktop.org, 
	linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, kernel-janitors@...r.kernel.org, 
	Jason-JH Lin (林睿祥) <Jason-JH.Lin@...iatek.com>
Subject: Re: [PATCH] drm/mediatek: Fix potential NULL dereference in mtk_crtc_destroy()

Hi, Dan:

Dan Carpenter <dan.carpenter@...aro.org> 於 2024年9月12日 週四 下午4:45寫道：
>
> In mtk_crtc_create(), if the call to mbox_request_channel() fails then we
> set the "mtk_crtc->cmdq_client.chan" pointer to NULL.  In that situation,
> we do not call cmdq_pkt_create().
>
> During the cleanup, we need to check if the "mtk_crtc->cmdq_client.chan"
> is NULL first before calling cmdq_pkt_destroy().  Calling
> cmdq_pkt_destroy() is unnecessary if we didn't call cmdq_pkt_create() and
> it will result in a NULL pointer dereference.

Applied to mediatek-drm-fixes [1], thanks.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/chunkuang.hu/linux.git/log/?h=mediatek-drm-fixes

Regards,
Chun-Kuang.

>
> Fixes: 7627122fd1c0 ("drm/mediatek: Add cmdq_handle in mtk_crtc")
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> ---
>  drivers/gpu/drm/mediatek/mtk_crtc.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/mediatek/mtk_crtc.c b/drivers/gpu/drm/mediatek/mtk_crtc.c
> index 175b00e5a253..c15013792583 100644
> --- a/drivers/gpu/drm/mediatek/mtk_crtc.c
> +++ b/drivers/gpu/drm/mediatek/mtk_crtc.c
> @@ -127,9 +127,8 @@ static void mtk_crtc_destroy(struct drm_crtc *crtc)
>
>         mtk_mutex_put(mtk_crtc->mutex);
>  #if IS_REACHABLE(CONFIG_MTK_CMDQ)
> -       cmdq_pkt_destroy(&mtk_crtc->cmdq_client, &mtk_crtc->cmdq_handle);
> -
>         if (mtk_crtc->cmdq_client.chan) {
> +               cmdq_pkt_destroy(&mtk_crtc->cmdq_client, &mtk_crtc->cmdq_handle);
>                 mbox_free_channel(mtk_crtc->cmdq_client.chan);
>                 mtk_crtc->cmdq_client.chan = NULL;
>         }
> --
> 2.45.2
>