[PATCH] drm/mst: Fix possible NULL pointer dereference in drm_dp_mst_process_up_req()

[Lyude Paul]

Reviewed-by: Lyude Paul <lyude at redhat.com>

I'll go ahead and push this now, thanks!

On Wed, 2020-01-29 at 15:24 -0800, José Roberto de Souza wrote:
> According to DP specification, DP_SINK_EVENT_NOTIFY is also a
> broadcast message but as this function only handles
> DP_CONNECTION_STATUS_NOTIFY I will only make the static
> analyzer that caught this issue happy by not calling
> drm_dp_get_mst_branch_device_by_guid() with a NULL guid, causing
> drm_dp_mst_process_up_req() to return in the "if (!mstb)" right
> bellow.
> 
> Fixes: 9408cc94eb04 ("drm/dp_mst: Handle UP requests asynchronously")
> Cc: Lyude Paul <lyude at redhat.com>
> Cc: Sean Paul <sean at poorly.run>
> Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 23cf46bfef74..a811247cecfe 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -3829,7 +3829,8 @@ drm_dp_mst_process_up_req(struct
> drm_dp_mst_topology_mgr *mgr,
>  		else if (msg->req_type == DP_RESOURCE_STATUS_NOTIFY)
>  			guid = msg->u.resource_stat.guid;
>  
> -		mstb = drm_dp_get_mst_branch_device_by_guid(mgr, guid);
> +		if (guid)
> +			mstb = drm_dp_get_mst_branch_device_by_guid(mgr,
> guid);
>  	} else {
>  		mstb = drm_dp_get_mst_branch_device(mgr, hdr->lct, hdr->rad);
>  	}
-- 
Cheers,
	Lyude Paul