linux-kernel - Re: [PATCH] drm/bridge: it6505: Fix potential NULL dereference

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Date: Sun, 9 Jun 2024 22:38:39 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Allen Chen <allen.chen@....com.tw>, 
	Andrzej Hajda <andrzej.hajda@...el.com>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Robert Foss <rfoss@...nel.org>, Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
	Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Daniel Vetter <daniel@...ll.ch>, Hermes Wu <hermes.wu@....com.tw>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: it6505: Fix potential NULL dereference

On Sat, Jun 08, 2024 at 05:21:08PM +0300, Dan Carpenter wrote:
> Smatch complains correctly that the NULL checking isn't consistent:
> 
>     drivers/gpu/drm/bridge/ite-it6505.c:2583 it6505_poweron()
>     error: we previously assumed 'pdata->pwr18' could be null
>     (see line 2569)
> 
> Add a NULL check to prevent a NULL dereference on the error path.
> 
> Fixes: b5c84a9edcd4 ("drm/bridge: add it6505 driver")
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> ---
>  drivers/gpu/drm/bridge/ite-it6505.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/ite-it6505.c b/drivers/gpu/drm/bridge/ite-it6505.c
> index 3f68c82888c2..4f01fadaec0f 100644
> --- a/drivers/gpu/drm/bridge/ite-it6505.c
> +++ b/drivers/gpu/drm/bridge/ite-it6505.c
> @@ -2580,7 +2580,8 @@ static int it6505_poweron(struct it6505 *it6505)
>  		usleep_range(1000, 2000);
>  		err = regulator_enable(pdata->ovdd);
>  		if (err) {
> -			regulator_disable(pdata->pwr18);
> +			if (pdata->pwr18)
> +				regulator_disable(pdata->pwr18);

Wait... I wat too quick to R-B it. The driver uses devm_regulator_get(),
which always returns non-NULL result. So all `if (pdata->pwr18)` and
`if (pdata->ovdd)` checks in the driver are useless. Could you please
send a patch, removing them?

>  			return err;
>  		}
>  	}
> -- 
> 2.43.0
> 

-- 
With best wishes
Dmitry