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

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

[Colin King]

From: Colin Ian King <colin.king@canonical.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@canonical.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

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

[Gupta, Anshuman]

> -----Original Message-----
> From: Colin King <colin.king@canonical.com>
> Sent: Wednesday, February 24, 2021 12:49 AM
> To: Jani Nikula <jani.nikula@linux.intel.com>; Joonas Lahtinen
> <joonas.lahtinen@linux.intel.com>; Vivi, Rodrigo <rodrigo.vivi@intel.com>;
> David Airlie <airlied@linux.ie>; Daniel Vetter <daniel@ffwll.ch>; C, Ramalingam
> <ramalingam.c@intel.com>; Gupta, Anshuman <anshuman.gupta@intel.com>;
> intel-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org
> Cc: kernel-janitors@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: [PATCH][next] drm/i915/hdcp: Fix null pointer dereference of
> connector->encoder
> 
> From: Colin Ian King <colin.king@canonical.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@canonical.com>
Looks good to me.
Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.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

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