linux-kernel - Re: [PATCH] drm/meson: add check to prevent dereference of NULL

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Message-ID: <CAFBinCATiUnR=P9VRBxWeQhf49k6PVxK+nU95G7w94f-mR2HWQ@mail.gmail.com>
Date: Sat, 10 Aug 2024 11:09:40 +0200
From: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To: Anastasia Belova <abelova@...ralinux.ru>
Cc: Neil Armstrong <neil.armstrong@...aro.org>, 
	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>, 
	Kevin Hilman <khilman@...libre.com>, Jerome Brunet <jbrunet@...libre.com>, 
	dri-devel@...ts.freedesktop.org, linux-amlogic@...ts.infradead.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	lvc-project@...uxtesting.org
Subject: Re: [PATCH] drm/meson: add check to prevent dereference of NULL

Hello Anastasia,

Thank you for working on this!

On Fri, Aug 9, 2024 at 2:48 PM Anastasia Belova <abelova@...ralinux.ru> wrote:
[...]
> @@ -373,9 +373,11 @@ static int meson_drv_bind_master(struct device *dev, bool has_components)
>  free_drm:
>         drm_dev_put(drm);
>
> -       meson_encoder_dsi_remove(priv);
> -       meson_encoder_hdmi_remove(priv);
> -       meson_encoder_cvbs_remove(priv);
> +       if (priv) {
> +               meson_encoder_dsi_remove(priv);
> +               meson_encoder_hdmi_remove(priv);
> +               meson_encoder_cvbs_remove(priv);
> +       }
This is the straight-forward approach.

There's been conversions from non-devm_ functions to their devm_*
counterparts in the past in various subsystems.
I just found that there's a devm_drm_dev_alloc() which seems to be
calling drm_dev_put() automatically - but I have never used it myself
before.
As an alternative to your suggested approach: could you please look
into whether devm_drm_dev_alloc() is a suitable replacement (if not:
just explain why - then this patch is good to be merged)?


Thank you!
Martin