[PATCH v2 2/3] drm/mst: Avoid dereferencing a NULL mstb in drm_dp_mst_handle_up_req()

[Imre Deak]

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

Cc: Dave Airlie <airlied at redhat.com>
Cc: Lyude <lyude at redhat.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Imre Deak <imre.deak at intel.com>
Reviewed-by: Lyude <lyude at redhat.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index c6ae3e68918f..78e9a7d58794 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2328,7 +2328,9 @@ 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;
-- 
2.13.2