drm/mst: Fix error handling during MST sideband message reception

commit 448421b5e93b9177c5698f0cf6f5e72d2995eeca upstream.

Handle any error due to partial reads, timeouts etc. to avoid parsing
uninitialized data subsequently. Also bail out if the parsing itself
fails.

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/20170719114330.26540-2-imre.deak@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index d3fc7e4e85b7413eb586256540467cbd25f6090d..025c406f2744da92e114a580dbc06b972197b0e2 100644 (file)
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2196,11 +2196,17 @@ static void drm_dp_get_one_sb_msg(struct drm_dp_mst_topology_mgr *mgr, bool up)
                ret = drm_dp_dpcd_read(mgr->aux, basereg + curreply,
                                    replyblock, len);
                if (ret != len) {
-                       DRM_DEBUG_KMS("failed to read a chunk\n");
+                       DRM_DEBUG_KMS("failed to read a chunk (len %d, ret %d)\n",
+                                     len, ret);
+                       return;
                }
+
                ret = drm_dp_sideband_msg_build(msg, replyblock, len, false);
-               if (ret == false)
+               if (!ret) {
                        DRM_DEBUG_KMS("failed to build sideband msg\n");
+                       return;
+               }
+
                curreply += len;
                replylen -= len;
        }