linux-kernel - Re: [PATCH] drm/tegra: fix a possible null pointer dereference

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Message-Id: <D1NWF7ESKQ0X.25OZ9MTC2DSBS@gmail.com>
Date: Fri, 31 May 2024 16:27:34 +0200
From: "Thierry Reding" <thierry.reding@...il.com>
To: "Huai-Yuan Liu" <qq810974084@...il.com>, <mperttunen@...dia.com>,
 <airlied@...il.com>, <daniel@...ll.ch>, <jonathanh@...dia.com>
Cc: <dri-devel@...ts.freedesktop.org>, <linux-tegra@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <baijiaju1990@...il.com>
Subject: Re: [PATCH] drm/tegra: fix a possible null pointer dereference

On Fri May 31, 2024 at 3:56 PM CEST, Huai-Yuan Liu wrote:
> In malidp_tegra_crtc_reset, new memory is allocated with kzalloc, but 
> no check is performed. Before calling __drm_atomic_helper_crtc_reset, 
> mw_state should be checked to prevent possible null pointer dereferene.

Please check that all these variable name references actually are valid.

Also, "dereference".

> Fixes: b7e0b04ae450 ("drm/tegra: Convert to using __drm_atomic_helper_crtc_reset() for reset.")
> Signed-off-by: Huai-Yuan Liu <qq810974084@...il.com>
> ---
>  drivers/gpu/drm/tegra/dc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
> index be61c9d1a4f0..7648e129c212 100644
> --- a/drivers/gpu/drm/tegra/dc.c
> +++ b/drivers/gpu/drm/tegra/dc.c
> @@ -1388,7 +1388,8 @@ static void tegra_crtc_reset(struct drm_crtc *crtc)
>  	if (crtc->state)
>  		tegra_crtc_atomic_destroy_state(crtc, crtc->state);
>  
> -	__drm_atomic_helper_crtc_reset(crtc, &state->base);
> +	if (state)
> +		__drm_atomic_helper_crtc_reset(crtc, &state->base);

Looking at how other drivers do this, they call

	__drm_atomic_helper_crtc_reset(crtc, NULL);

if they fail to allocate a new state. Any reason why we wouldn't want to
do the same thing here?

Thierry

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