All of lore.kernel.org
 help / color / mirror / Atom feed
* [PATCH v5] Bluetooth: l2cap: defer conn param update to avoid conn->lock/hdev->lock inversion
@ 2026-04-14 21:52 Mikhail Gavrilov
  2026-04-14 22:35 ` [v5] " bluez.test.bot
  2026-05-05 10:39 ` [PATCH v5] " Mikhail Gavrilov
  0 siblings, 2 replies; 4+ messages in thread
From: Mikhail Gavrilov @ 2026-04-14 21:52 UTC (permalink / raw)
  To: luiz.dentz, marcel
  Cc: pav, pmenzel, linux-bluetooth, linux-kernel, Mikhail Gavrilov

When a BLE peripheral sends an L2CAP Connection Parameter Update Request
the processing path is:

  process_pending_rx()          [takes conn->lock]
    l2cap_le_sig_channel()
      l2cap_conn_param_update_req()
        hci_le_conn_update()    [takes hdev->lock]

Meanwhile other code paths take the locks in the opposite order:

  l2cap_chan_connect()          [takes hdev->lock]
    ...
      mutex_lock(&conn->lock)

  l2cap_conn_ready()            [hdev->lock via hci_cb_list_lock]
    ...
      mutex_lock(&conn->lock)

This is a classic AB/BA deadlock which lockdep reports as a circular
locking dependency when connecting a BLE MIDI keyboard (Carry-On FC-49).

Fix this by making hci_le_conn_update() defer the HCI command through
hci_cmd_sync_queue() so it no longer needs to take hdev->lock in the
caller context.  The sync callback uses __hci_cmd_sync_status_sk() to
wait for the HCI_EV_LE_CONN_UPDATE_COMPLETE event, then updates the
stored connection parameters (hci_conn_params) and notifies userspace
(mgmt_new_conn_param) only after the controller has confirmed the update.

A reference on hci_conn is held via hci_conn_get()/hci_conn_put() for
the lifetime of the queued work to prevent use-after-free, and
hci_conn_valid() is checked before proceeding in case the connection was
removed while the work was pending.  The hci_dev_lock is held across
hci_conn_valid() and all conn field accesses to prevent a concurrent
disconnect from invalidating the connection mid-use.

Fixes: f044eb0524a0 ("Bluetooth: Store latency and supervision timeout in connection params")
Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
---

Changes in v5 (Pauli Virtanen, Luiz Augusto von Dentz):
- Keep hci_dev_lock held across hci_conn_valid() and all conn field reads
  (including conn->handle) to close the race window noted by Pauli
- Use conn->conn_timeout instead of HCI_CMD_TIMEOUT for the sync wait,
  matching hci_le_create_conn_sync() pattern
 
Changes in v4 (Luiz Augusto von Dentz, Sashiko/Gemini AI review):
- Use hci_conn_get()/hci_conn_put() to hold a reference while work is queued
- Use __hci_cmd_sync_status_sk() to wait for HCI_EV_LE_CONN_UPDATE_COMPLETE,
  then do params update + mgmt notification in the sync callback
- Use kzalloc_obj() per checkpatch recommendation
 
Changes in v3 (Luiz Augusto von Dentz):
- Move hci_cmd_sync_queue into hci_le_conn_update itself instead of open-coding
  the deferral in l2cap_core.c
- Move conn_params update and mgmt_new_conn_param into
  hci_le_conn_update_complete_evt, using hci_sent_cmd_data to retrieve
  the originally requested parameters
 
Changes in v2 (Paul Menzel, Sashiko/Gemini AI review):
- Allocate before sending ACCEPTED response to avoid state mismatch on OOM
- Verify connection handle and address in sync callback against reuse race
- Expand commit message with implementation details

 include/net/bluetooth/hci_core.h |   2 +-
 net/bluetooth/hci_conn.c         | 105 +++++++++++++++++++++++++------
 net/bluetooth/l2cap_core.c       |  12 +---
 3 files changed, 89 insertions(+), 30 deletions(-)

diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
index a7bffb908c1e..aa600fbf9a53 100644
--- a/include/net/bluetooth/hci_core.h
+++ b/include/net/bluetooth/hci_core.h
@@ -2495,7 +2495,7 @@ void mgmt_adv_monitor_device_lost(struct hci_dev *hdev, u16 handle,
 				  bdaddr_t *bdaddr, u8 addr_type);
 
 int hci_abort_conn(struct hci_conn *conn, u8 reason);
-u8 hci_le_conn_update(struct hci_conn *conn, u16 min, u16 max, u16 latency,
+void hci_le_conn_update(struct hci_conn *conn, u16 min, u16 max, u16 latency,
 		      u16 to_multiplier);
 void hci_le_start_enc(struct hci_conn *conn, __le16 ediv, __le64 rand,
 		      __u8 ltk[16], __u8 key_size);
diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 11d3ad8d2551..fea0764b8ba3 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -480,40 +480,107 @@ bool hci_setup_sync(struct hci_conn *conn, __u16 handle)
 	return hci_setup_sync_conn(conn, handle);
 }
 
-u8 hci_le_conn_update(struct hci_conn *conn, u16 min, u16 max, u16 latency,
-		      u16 to_multiplier)
+struct le_conn_update_data {
+	struct hci_conn *conn;
+	u16	min;
+	u16	max;
+	u16	latency;
+	u16	to_multiplier;
+};
+
+static int le_conn_update_sync(struct hci_dev *hdev, void *data)
 {
-	struct hci_dev *hdev = conn->hdev;
+	struct le_conn_update_data *d = data;
+	struct hci_conn *conn = d->conn;
 	struct hci_conn_params *params;
 	struct hci_cp_le_conn_update cp;
+	u16 timeout;
+	u8 store_hint;
+	int err;
 
+	/* Verify connection is still alive and read conn fields under
+	 * the same lock to prevent a concurrent disconnect from freeing
+	 * or reusing the connection while we build the HCI command.
+	 */
 	hci_dev_lock(hdev);
 
-	params = hci_conn_params_lookup(hdev, &conn->dst, conn->dst_type);
-	if (params) {
-		params->conn_min_interval = min;
-		params->conn_max_interval = max;
-		params->conn_latency = latency;
-		params->supervision_timeout = to_multiplier;
+	if (!hci_conn_valid(hdev, conn)) {
+		hci_dev_unlock(hdev);
+		return -ECANCELED;
 	}
 
-	hci_dev_unlock(hdev);
-
 	memset(&cp, 0, sizeof(cp));
 	cp.handle		= cpu_to_le16(conn->handle);
-	cp.conn_interval_min	= cpu_to_le16(min);
-	cp.conn_interval_max	= cpu_to_le16(max);
-	cp.conn_latency		= cpu_to_le16(latency);
-	cp.supervision_timeout	= cpu_to_le16(to_multiplier);
+	cp.conn_interval_min	= cpu_to_le16(d->min);
+	cp.conn_interval_max	= cpu_to_le16(d->max);
+	cp.conn_latency		= cpu_to_le16(d->latency);
+	cp.supervision_timeout	= cpu_to_le16(d->to_multiplier);
 	cp.min_ce_len		= cpu_to_le16(0x0000);
 	cp.max_ce_len		= cpu_to_le16(0x0000);
+	timeout			= conn->conn_timeout;
+
+	hci_dev_unlock(hdev);
+
+	err = __hci_cmd_sync_status_sk(hdev, HCI_OP_LE_CONN_UPDATE,
+				       sizeof(cp), &cp,
+				       HCI_EV_LE_CONN_UPDATE_COMPLETE,
+				       timeout, NULL);
+	if (err)
+		return err;
+
+	/* Update stored connection parameters after the controller has
+	 * confirmed the update via the LE Connection Update Complete event.
+	 */
+	hci_dev_lock(hdev);
+
+	params = hci_conn_params_lookup(hdev, &conn->dst, conn->dst_type);
+	if (params) {
+		params->conn_min_interval = d->min;
+		params->conn_max_interval = d->max;
+		params->conn_latency = d->latency;
+		params->supervision_timeout = d->to_multiplier;
+		store_hint = 0x01;
+	} else {
+		store_hint = 0x00;
+	}
 
-	hci_send_cmd(hdev, HCI_OP_LE_CONN_UPDATE, sizeof(cp), &cp);
+	hci_dev_unlock(hdev);
 
-	if (params)
-		return 0x01;
+	mgmt_new_conn_param(hdev, &conn->dst, conn->dst_type, store_hint,
+			    d->min, d->max, d->latency, d->to_multiplier);
 
-	return 0x00;
+	return 0;
+}
+
+static void le_conn_update_complete(struct hci_dev *hdev, void *data, int err)
+{
+	struct le_conn_update_data *d = data;
+
+	hci_conn_put(d->conn);
+	kfree(d);
+}
+
+void hci_le_conn_update(struct hci_conn *conn, u16 min, u16 max, u16 latency,
+			u16 to_multiplier)
+{
+	struct le_conn_update_data *d;
+
+	d = kzalloc_obj(*d);
+	if (!d)
+		return;
+
+	hci_conn_get(conn);
+	d->conn = conn;
+	d->min = min;
+	d->max = max;
+	d->latency = latency;
+	d->to_multiplier = to_multiplier;
+
+	if (hci_cmd_sync_queue(conn->hdev, le_conn_update_sync, d,
+			       le_conn_update_complete) < 0) {
+		hci_conn_put(conn);
+		kfree(d);
+	}
 }
 
 void hci_le_start_enc(struct hci_conn *conn, __le16 ediv, __le64 rand,
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 95c65fece39b..aac2db1d6fbb 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4706,16 +4706,8 @@ static inline int l2cap_conn_param_update_req(struct l2cap_conn *conn,
 	l2cap_send_cmd(conn, cmd->ident, L2CAP_CONN_PARAM_UPDATE_RSP,
 		       sizeof(rsp), &rsp);
 
-	if (!err) {
-		u8 store_hint;
-
-		store_hint = hci_le_conn_update(hcon, min, max, latency,
-						to_multiplier);
-		mgmt_new_conn_param(hcon->hdev, &hcon->dst, hcon->dst_type,
-				    store_hint, min, max, latency,
-				    to_multiplier);
-
-	}
+	if (!err)
+		hci_le_conn_update(hcon, min, max, latency, to_multiplier);
 
 	return 0;
 }
-- 
2.53.0


^ permalink raw reply related	[flat|nested] 4+ messages in thread
end of thread, other threads:[~2026-05-05 14:08 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-04-14 21:52 [PATCH v5] Bluetooth: l2cap: defer conn param update to avoid conn->lock/hdev->lock inversion Mikhail Gavrilov
2026-04-14 22:35 ` [v5] " bluez.test.bot
2026-05-05 10:39 ` [PATCH v5] " Mikhail Gavrilov
2026-05-05 14:08   ` Luiz Augusto von Dentz

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.