From: Stanislav Lisovskiy Date: Fri, 9 Nov 2018 09:00:12 +0000 (+0200) Subject: drm/dp_mst: Check if primary mstb is null X-Git-Tag: v4.18.20~20 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4a7daecdaab98554a1cc51ae57f51636434e4f0c;p=thirdparty%2Fkernel%2Fstable.git drm/dp_mst: Check if primary mstb is null commit 23d8003907d094f77cf959228e2248d6db819fa7 upstream. Unfortunately drm_dp_get_mst_branch_device which is called from both drm_dp_mst_handle_down_rep and drm_dp_mst_handle_up_rep seem to rely on that mgr->mst_primary is not NULL, which seem to be wrong as it can be cleared with simultaneous mode set, if probing fails or in other case. mgr->lock mutex doesn't protect against that as it might just get assigned to NULL right before, not simultaneously. There are currently bugs 107738, 108616 bugs which crash in drm_dp_get_mst_branch_device, caused by this issue. v2: Refactored the code, as it was nicely noticed. Fixed Bugzilla bug numbers(second was 108616, but not 108816) and added links. [changed title and added stable cc] Signed-off-by: Lyude Paul Signed-off-by: Stanislav Lisovskiy Cc: stable@vger.kernel.org Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108616 Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107738 Link: https://patchwork.freedesktop.org/patch/msgid/20181109090012.24438-1-stanislav.lisovskiy@intel.com Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index 658830620ca36..9c166621e920b 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -1274,6 +1274,9 @@ static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_ mutex_lock(&mgr->lock); mstb = mgr->mst_primary; + if (!mstb) + goto out; + for (i = 0; i < lct - 1; i++) { int shift = (i % 2) ? 0 : 4; int port_num = (rad[i / 2] >> shift) & 0xf;