4.4-stable review patch. If anyone has any objections, please let me know.
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From: Stanislav Lisovskiy stanislav.lisovskiy@intel.com
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 lyude@redhat.com Signed-off-by: Stanislav Lisovskiy stanislav.lisovskiy@intel.com 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-stanisl... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/gpu/drm/drm_dp_mst_topology.c | 3 +++ 1 file changed, 3 insertions(+)
--- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -1225,6 +1225,9 @@ static struct drm_dp_mst_branch *drm_dp_ 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;