If the MST topology is removed during the reception of an MST down reply or MST up request sideband message, the drm_dp_mst_topology_mgr::up_req_recv/down_rep_recv states could be reset from one thread via drm_dp_mst_topology_mgr_set_mst(false), racing with the reading/parsing of the message from another thread via drm_dp_mst_handle_down_rep() or drm_dp_mst_handle_up_req(). The race is possible since the reader/parser doesn't hold any lock while accessing the reception state. This in turn can lead to a memory corruption in the reader/parser as described by commit bd2fccac61b4 ("drm/dp_mst: Fix MST sideband message body length check").

Fix the above by resetting the message reception state if needed before reading/parsing a message. Another solution would be to hold the drm_dp_mst_topology_mgr::lock for the whole duration of the message reception/parsing in drm_dp_mst_handle_down_rep() and drm_dp_mst_handle_up_req(), however this would require a bigger change. Since the fix is also needed for stable, opting for the simpler solution in this patch.

Cc: Lyude Paul lyude@redhat.com Cc: stable@vger.kernel.org Fixes: 1d082618bbf3 ("drm/display/dp_mst: Fix down/up message handling after sink disconnect") Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13056 Signed-off-by: Imre Deak imre.deak@intel.com --- drivers/gpu/drm/display/drm_dp_mst_topology.c | 21 +++++++++++++++++-- include/drm/display/drm_dp_mst_helper.h | 7 +++++++ 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c index e6ee180815b20..1475aa95ab6b2 100644 --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c @@ -3700,8 +3700,7 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms ret = 0; mgr->payload_id_table_cleared = false;

- memset(&mgr->down_rep_recv, 0, sizeof(mgr->down_rep_recv)); - memset(&mgr->up_req_recv, 0, sizeof(mgr->up_req_recv)); + mgr->reset_rx_state = true; }

out_unlock: @@ -3859,6 +3858,11 @@ int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr, } EXPORT_SYMBOL(drm_dp_mst_topology_mgr_resume);

+static void reset_msg_rx_state(struct drm_dp_sideband_msg_rx *msg) +{ + memset(msg, 0, sizeof(*msg)); +} + static bool drm_dp_get_one_sb_msg(struct drm_dp_mst_topology_mgr *mgr, bool up, struct drm_dp_mst_branch **mstb) @@ -4141,6 +4145,17 @@ static int drm_dp_mst_handle_up_req(struct drm_dp_mst_topology_mgr *mgr) return 0; }

+static void update_msg_rx_state(struct drm_dp_mst_topology_mgr *mgr) +{ + mutex_lock(&mgr->lock); + if (mgr->reset_rx_state) { + mgr->reset_rx_state = false; + reset_msg_rx_state(&mgr->down_rep_recv); + reset_msg_rx_state(&mgr->up_req_recv); + } + mutex_unlock(&mgr->lock); +} + /** * drm_dp_mst_hpd_irq_handle_event() - MST hotplug IRQ handle MST event * @mgr: manager to notify irq for. @@ -4175,6 +4190,8 @@ int drm_dp_mst_hpd_irq_handle_event(struct drm_dp_mst_topology_mgr *mgr, const u *handled = true; }

+ update_msg_rx_state(mgr); + if (esi[1] & DP_DOWN_REP_MSG_RDY) { ret = drm_dp_mst_handle_down_rep(mgr); *handled = true; diff --git a/include/drm/display/drm_dp_mst_helper.h b/include/drm/display/drm_dp_mst_helper.h index f6a1cbb0f600f..a80ba457a858f 100644 --- a/include/drm/display/drm_dp_mst_helper.h +++ b/include/drm/display/drm_dp_mst_helper.h @@ -699,6 +699,13 @@ struct drm_dp_mst_topology_mgr { */ bool payload_id_table_cleared : 1;

+ /** + * @reset_rx_state: The down request's reply and up request message + * receiver state must be reset, after the topology manager got + * removed. Protected by @lock. + */ + bool reset_rx_state : 1; + /** * @payload_count: The number of currently active payloads in hardware. This value is only * intended to be used internally by MST helpers for payload tracking, and is only safe to