[PATCH 4.4 075/100] drm: NULL pointer dereference [null-pointer-deref] (CWE 476) problem

[Greg Kroah-Hartman]

From: Joe Moriarty <joe.moriarty@xxxxxxxxxx>

commit 22a07038c0eaf4d1315a493ce66dcd255accba19 upstream.

The Parfait (version 2.1.0) static code analysis tool found the
following NULL pointer derefernce problem.

- drivers/gpu/drm/drm_dp_mst_topology.c
The call to drm_dp_calculate_rad() in function drm_dp_port_setup_pdt()
could result in a NULL pointer being returned to port->mstb due to a
failure to allocate memory for port->mstb.

Signed-off-by: Joe Moriarty <joe.moriarty@xxxxxxxxxx>
Reviewed-by: Steven Sistare <steven.sistare@xxxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20180212195144.98323-3-joe.moriarty@xxxxxxxxxx
Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/drm_dp_mst_topology.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1036,10 +1036,12 @@ static bool drm_dp_port_setup_pdt(struct
 		lct = drm_dp_calculate_rad(port, rad);
 
 		port->mstb = drm_dp_add_mst_branch_device(lct, rad);
-		port->mstb->mgr = port->mgr;
-		port->mstb->port_parent = port;
+		if (port->mstb) {
+			port->mstb->mgr = port->mgr;
+			port->mstb->port_parent = port;
 
-		send_link = true;
+			send_link = true;
+		}
 		break;
 	}
 	return send_link;