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

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>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20170719114330.26540-2-imre.deak@intel.com

1 files changed, 8 insertions, 2 deletions

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index bfd237c15e76..ce0e58442939 100644
--- 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;
         }