drm/mst: Avoid dereferencing a NULL mstb in drm_dp_mst_handle_up_req()

BugLink: http://bugs.launchpad.net/bugs/1707233
commit 7f8b3987da54cb4d41ad2545cd4d7958b9a36bdf upstream.

In case of an unknown broadcast message is sent mstb will remain unset,
so check for this.

Cc: Dave Airlie <airlied@redhat.com>
Cc: Lyude <lyude@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Lyude <lyude@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20170719114330.26540-3-imre.deak@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 3a93c98ddd84cf115d77a3eae69f60a665093cc7..1fc68dfb113d66bd9b7c9a68a39e6b7b6d545889 100644 (file)
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2333,7 +2333,9 @@ static int drm_dp_mst_handle_up_req(struct drm_dp_mst_topology_mgr *mgr)
                        DRM_DEBUG_KMS("Got RSN: pn: %d avail_pbn %d\n", msg.u.resource_stat.port_number, msg.u.resource_stat.available_pbn);
                }
 
-               drm_dp_put_mst_branch_device(mstb);
+               if (mstb)
+                       drm_dp_put_mst_branch_device(mstb);
+
                memset(&mgr->up_req_recv, 0, sizeof(struct drm_dp_sideband_msg_rx));
        }
        return ret;