linux-kernel - Re: [PATCH] drm/i915/dp: prevent potential div-by-zero

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Date:   Fri, 5 May 2023 10:29:20 -0400
From:   Rodrigo Vivi <rodrigo.vivi@...nel.org>
To:     Nikita Zhandarovich <n.zhandarovich@...tech.ru>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>,
        Ankit Nautiyal <ankit.k.nautiyal@...el.com>,
        Manasi Navare <manasi.d.navare@...el.com>,
        Stanislav Lisovskiy <stanislav.lisovskiy@...el.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org
Subject: Re: [PATCH] drm/i915/dp: prevent potential div-by-zero

On Tue, Apr 18, 2023 at 07:04:30AM -0700, Nikita Zhandarovich wrote:
> drm_dp_dsc_sink_max_slice_count() may return 0 if something goes
> wrong on the part of the DSC sink and its DPCD register. This null
> value may be later used as a divisor in intel_dsc_compute_params(),
> which will lead to an error.
> In the unlikely event that this issue occurs, fix it by testing the
> return value of drm_dp_dsc_sink_max_slice_count() against zero.
> 
> Found by Linux Verification Center (linuxtesting.org) with static
> analysis tool SVACE.
> 
> Fixes: a4a157777c80 ("drm/i915/dp: Compute DSC pipe config in atomic check")
> Signed-off-by: Nikita Zhandarovich <n.zhandarovich@...tech.ru>

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@...el.com>

and pushed.

Thanks for the patch and sorry for the delay.

> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 62cbab7402e9..c1825f8f885c 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1533,6 +1533,11 @@ int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
>  		pipe_config->dsc.slice_count =
>  			drm_dp_dsc_sink_max_slice_count(intel_dp->dsc_dpcd,
>  							true);
> +		if (!pipe_config->dsc.slice_count) {
> +			drm_dbg_kms(&dev_priv->drm, "Unsupported Slice Count %d\n",
> +				    pipe_config->dsc.slice_count);
> +			return -EINVAL;
> +		}
>  	} else {
>  		u16 dsc_max_output_bpp = 0;
>  		u8 dsc_dp_slice_count;
> -- 
> 2.25.1
>