drm/dp_mst: Fix resetting msg rx state after topology removal

commit a6fa67d26de385c3c7a23c1e109a0e23bfda4ec7 upstream.

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
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241203160223.2926014-2-imre.deak@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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 e68dd0306490..bcf3a33123be 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 @@ out_fail:
 }
 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)
@@ -4172,6 +4176,17 @@ out:
 	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.
@@ -4206,6 +4221,8 @@ 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 f6a1cbb0f600..a80ba457a858 100644
--- a/include/drm/display/drm_dp_mst_helper.h
+++ b/include/drm/display/drm_dp_mst_helper.h
@@ -700,6 +700,13 @@ 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
 	 * read/write from the atomic commit (not check) context.