drm/amdgpu: avoid a possible array overflow

BugLink: http://bugs.launchpad.net/bugs/1621113

commit e1718d97 upstream.

When looking up the connector type make sure the index
is valid.  Avoids a later crash if we read past the end
of the array.

Workaround for bug:
https://bugs.freedesktop.org/show_bug.cgi?id=97460Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c

@@ -331,6 +331,12 @@ bool amdgpu_atombios_get_connector_info_from_object_table(struct amdgpu_device *
 			    (le16_to_cpu(path->usConnObjectId) &
 			     OBJECT_TYPE_MASK) >> OBJECT_TYPE_SHIFT;
 
+			if (con_obj_id >= ARRAY_SIZE(object_connector_convert)) {
+				DRM_ERROR("invalid con_obj_id %d for device tag 0x%04x\n",
+					  con_obj_id, le16_to_cpu(path->usDeviceTag));
+				continue;
+			}
+
 			connector_type =
 				object_connector_convert[con_obj_id];
 			connector_object_id = con_obj_id;