linux-kernel - Re: [PATCH] drm/tegra: Handle EDID allocation failures in tegra_output_connector_get

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Message-ID: <874j07xuqs.fsf@intel.com>
Date: Wed, 05 Mar 2025 19:17:15 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Wentao Liang <vulab@...as.ac.cn>, thierry.reding@...il.com,
 mperttunen@...dia.com, airlied@...il.com, simona@...ll.ch,
 jonathanh@...dia.com
Cc: dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
 linux-kernel@...r.kernel.org, Wentao Liang <vulab@...as.ac.cn>,
 stable@...r.kernel.org
Subject: Re: [PATCH] drm/tegra: Handle EDID allocation failures in
 tegra_output_connector_get_modes()

On Wed, 05 Mar 2025, Wentao Liang <vulab@...as.ac.cn> wrote:
> The return values of `drm_edid_dup()` and `drm_edid_read_ddc()` must
> be checked in `tegra_output_connector_get_modes()` to prevent NULL
> pointer dereferences. If either function fails, the function should
> immediately return 0, indicating that no display modes can be retrieved.

No. It works as designed, and drm_edid_connector_update() and
cec_notifier_set_phys_addr() *must* be called with NULL drm_edid in case
of failure.

> A proper implementation can be found in `vidi_get_modes()`, where the
> return values are carefully validated, and the function returns 0 upon
> failure.

That case is slightly different, as it doesn't actually access the
display at that point, but it wouldn't be wrong to skip the early
!drm_edid check there too.

> Fixes: 98365ca74cbf ("drm/tegra: convert to struct drm_edid")

When you claim to fix a commit, it's encouraged to Cc: the author and
possibly reviewers of said commit.


BR,
Jani.


> Cc: stable@...r.kernel.org # 6.12+
> Signed-off-by: Wentao Liang <vulab@...as.ac.cn>
> ---
>  drivers/gpu/drm/tegra/output.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/tegra/output.c b/drivers/gpu/drm/tegra/output.c
> index 49e4f63a5550..360c4f83a4f8 100644
> --- a/drivers/gpu/drm/tegra/output.c
> +++ b/drivers/gpu/drm/tegra/output.c
> @@ -39,6 +39,9 @@ int tegra_output_connector_get_modes(struct drm_connector *connector)
>  	else if (output->ddc)
>  		drm_edid = drm_edid_read_ddc(connector, output->ddc);
>  
> +	if (!drm_edid)
> +		return 0;
> +
>  	drm_edid_connector_update(connector, drm_edid);
>  	cec_notifier_set_phys_addr(output->cec,
>  				   connector->display_info.source_physical_address);

-- 
Jani Nikula, Intel