linux-kernel - RE: [PATCH][next] drm/i915/hdcp: Fix null pointer dereference of connector->encoder

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Date:   Fri, 26 Feb 2021 05:01:06 +0000
From:   "Gupta, Anshuman" <anshuman.gupta@...el.com>
To:     Colin King <colin.king@...onical.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        "Vivi, Rodrigo" <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "C, Ramalingam" <ramalingam.c@...el.com>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
CC:     "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH][next] drm/i915/hdcp: Fix null pointer dereference of
 connector->encoder



> -----Original Message-----
> From: Colin King <colin.king@...onical.com>
> Sent: Wednesday, February 24, 2021 12:49 AM
> To: Jani Nikula <jani.nikula@...ux.intel.com>; Joonas Lahtinen
> <joonas.lahtinen@...ux.intel.com>; Vivi, Rodrigo <rodrigo.vivi@...el.com>;
> David Airlie <airlied@...ux.ie>; Daniel Vetter <daniel@...ll.ch>; C, Ramalingam
> <ramalingam.c@...el.com>; Gupta, Anshuman <anshuman.gupta@...el.com>;
> intel-gfx@...ts.freedesktop.org; dri-devel@...ts.freedesktop.org
> Cc: kernel-janitors@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: [PATCH][next] drm/i915/hdcp: Fix null pointer dereference of
> connector->encoder
> 
> From: Colin Ian King <colin.king@...onical.com>
> 
> The recent commit 6c63e6e14da7 ("drm/i915/hdcp: No HDCP when encoder is't
> initialized") added a null pointer check on connector->encoder hence implying
> that it could potentially be null.  This means that the initialization of dig_port via
> the call intel_attached_dig_port may cause a null pointer dereference on
> connector->encoder. Fix this by only assigning dig_port after a null check has
> been performed on connector->encoder.
> 
> Addresses-Coverity: ("Dereference before null check")
> Fixes: 36e5e7042b20 ("drm/i915: Don't fully disable HDCP on a port if multiple
> pipes are using it")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
Looks good to me.
Reviewed-by: Anshuman Gupta <anshuman.gupta@...el.com>
> ---
>  drivers/gpu/drm/i915/display/intel_hdcp.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_hdcp.c
> b/drivers/gpu/drm/i915/display/intel_hdcp.c
> index ae1371c36a32..7525ea31766c 100644
> --- a/drivers/gpu/drm/i915/display/intel_hdcp.c
> +++ b/drivers/gpu/drm/i915/display/intel_hdcp.c
> @@ -2260,7 +2260,7 @@ int intel_hdcp_enable(struct intel_connector
> *connector,
>  		      const struct intel_crtc_state *pipe_config, u8 content_type)
> {
>  	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
> -	struct intel_digital_port *dig_port =
> intel_attached_dig_port(connector);
> +	struct intel_digital_port *dig_port;
>  	struct intel_hdcp *hdcp = &connector->hdcp;
>  	unsigned long check_link_interval = DRM_HDCP_CHECK_PERIOD_MS;
>  	int ret = -EINVAL;
> @@ -2274,6 +2274,7 @@ int intel_hdcp_enable(struct intel_connector
> *connector,
>  		return -ENODEV;
>  	}
> 
> +	dig_port = intel_attached_dig_port(connector);
>  	mutex_lock(&hdcp->mutex);
>  	mutex_lock(&dig_port->hdcp_mutex);
>  	drm_WARN_ON(&dev_priv->drm,
> --
> 2.30.0