[PATCH v5] Bluetooth: l2cap: defer conn param update to avoid conn->lock/hdev->lock inversion
From: Mikhail Gavrilov
Date: Tue Apr 14 2026 - 17:53:18 EST
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@xxxxxxxxx>
Reviewed-by: Paul Menzel <pmenzel@xxxxxxxxxxxxx>
---
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