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

BugLink: http://bugs.launchpad.net/bugs/1707233
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>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index fba529061c3f6b90d45d82c32718d77e8eb3b65a..3a93c98ddd84cf115d77a3eae69f60a665093cc7 100644 (file)
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2205,11 +2205,17 @@ 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;
        }