Re: [Intel-gfx] [PATCH] drm/i915/debugfs: HDCP capability enc NULL check

["Nautiyal, Ankit K" <ankit.k.nautiyal@intel.com>]

On 1/29/2021 1:30 PM, Anshuman Gupta wrote:
> DP-MST connector encoder initializes at modeset
> Adding a connector->encoder NULL check in order to
> avoid any NULL pointer dereference.
> intel_hdcp_enable() already handle this but debugfs
> can also invoke the intel_{hdcp,hdcp2_capable}.
> Handling it gracefully.
>
> Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
> ---
>   drivers/gpu/drm/i915/display/intel_hdcp.c | 14 ++++++++++++--
>   1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_hdcp.c b/drivers/gpu/drm/i915/display/intel_hdcp.c
> index ae1371c36a32..58af323d189a 100644
> --- a/drivers/gpu/drm/i915/display/intel_hdcp.c
> +++ b/drivers/gpu/drm/i915/display/intel_hdcp.c
> @@ -135,11 +135,16 @@ int intel_hdcp_read_valid_bksv(struct intel_digital_port *dig_port,
>   /* Is HDCP1.4 capable on Platform and Sink */
>   bool intel_hdcp_capable(struct intel_connector *connector)
>   {
> -	struct intel_digital_port *dig_port = intel_attached_dig_port(connector);
> +	struct intel_digital_port *dig_port;
>   	const struct intel_hdcp_shim *shim = connector->hdcp.shim;
>   	bool capable = false;
>   	u8 bksv[5];
>   
> +	if (!connector->encoder)
> +		return -ENODEV;
> +

For connector->encoder check, I feel the correct place should be in 
function:
enc_to_dig_port(), where we should return if encoder is NULL in 
display_types.h
Currently we assume encoder is not NULL and try to check encoder->type, 
which might break in case of MST.
With that change, we can simply check NULL check for 'dig_port', as 
intel_attached_dig_port(connector) might still return NULL.

Regards,
Ankit

> +	dig_port = intel_attached_dig_port(connector);
> +
>   	if (!shim)
>   		return capable;
>   
> @@ -156,11 +161,16 @@ bool intel_hdcp_capable(struct intel_connector *connector)
>   /* Is HDCP2.2 capable on Platform and Sink */
>   bool intel_hdcp2_capable(struct intel_connector *connector)
>   {
> -	struct intel_digital_port *dig_port = intel_attached_dig_port(connector);
> +	struct intel_digital_port *dig_port;
>   	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
>   	struct intel_hdcp *hdcp = &connector->hdcp;
>   	bool capable = false;
>   
> +	if (!connector->encoder)
> +		return -ENODEV;
> +
> +	dig_port = intel_attached_dig_port(connector);
> +
>   	/* I915 support for HDCP2.2 */
>   	if (!hdcp->hdcp2_supported)
>   		return false;
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