linux-kernel - Re: [PATCH v4 05/45] drm/connector: Check drm_connector

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Date:   Tue, 28 Nov 2023 14:29:40 +0100
From:   Maxime Ripard <mripard@...nel.org>
To:     Jani Nikula <jani.nikula@...ux.intel.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Emma Anholt <emma@...olt.net>,
        Jonathan Corbet <corbet@....net>,
        Sandy Huang <hjc@...k-chips.com>,
        Heiko Stübner <heiko@...ech.de>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH v4 05/45] drm/connector: Check drm_connector_init
 pointers arguments

Hi Jani,

On Tue, Nov 28, 2023 at 02:54:02PM +0200, Jani Nikula wrote:
> On Tue, 28 Nov 2023, Maxime Ripard <mripard@...nel.org> wrote:
> > All the drm_connector_init variants take at least a pointer to the
> > device, connector and hooks implementation.
> >
> > However, none of them check their value before dereferencing those
> > pointers which can lead to a NULL-pointer dereference if the author
> > isn't careful.
> 
> Arguably oopsing on the spot is preferrable when this can't be caused by
> user input. It's always a mistake that should be caught early during
> development.
> 
> Not everyone checks the return value of drm_connector_init and friends,
> so those cases will lead to more mysterious bugs later. And probably
> oopses as well.

So maybe we can do both then, with something like

if (WARN_ON(!dev))
   return -EINVAL

if (drm_WARN_ON(dev, !connector || !funcs))
   return -EINVAL;

I'd still like to check for this, so we can have proper testing, and we
already check for those pointers in some places (like funcs in
drm_connector_init), so if we don't cover everything we're inconsistent.

Maxime

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