[PATCH 3/3] drm: 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>
Signed-off-by: Imre Deak <imre.deak at intel.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 12c0ab3..412b9ca 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2334,7 +2334,9 @@ 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;
-- 
2.5.0