[PATCH v6] Bluetooth: hci_conn: hold a reference for LE connection timeout

[PATCH v6] Bluetooth: hci_conn: hold a reference for LE connection timeout

[Chengfeng Ye]

le_conn_timeout is embedded in struct hci_conn, but queued timeout work
does not hold a connection reference. hci_conn_del() uses
cancel_delayed_work() because synchronous cancellation would deadlock when
le_conn_timeout() itself calls hci_conn_del() while holding hdev->lock.

This leaves the following interleaving possible:

  CPU 0                               CPU 1
  le_conn_timeout()
                                      hci_conn_del()
                                        cancel_delayed_work() = false
                                        hci_conn_cleanup()
                                          put_device()
                                            kfree(conn)
  hci_conn_failed(conn, ...)

The callback then dereferences the released connection. KASAN reported:

  BUG: KASAN: slab-use-after-free in hci_conn_failed+0x232/0x250
  Read of size 8 at addr ffff8881180e8e20 by task kworker/u33:1/111
  Workqueue: hci0 le_conn_timeout
  Call Trace:
   hci_conn_failed+0x232/0x250
   le_conn_timeout+0x23e/0x2c0
   process_one_work+0x61b/0xf50
   worker_thread+0x45b/0xd10

  Allocated by task 115:
   __hci_conn_add+0x1758/0x1b90
   hci_connect_le+0x523/0x780
   l2cap_chan_connect+0xfca/0x1bd0
   l2cap_sock_connect+0x310/0x530

  Freed by task 110:
   kfree+0x149/0x330
   device_release+0xc8/0x240
   kobject_put+0x14d/0x280
   hci_conn_del+0x561/0xe70
   hci_abort_conn_sync+0x3e3/0x800

Take a connection reference before queueing le_conn_timeout. Drop it when
queueing fails or cancellation removes a pending instance. An executing
callback defers its put to the system workqueue. The final reference can
release the controller and destroy hdev->workqueue. Flush the previous
deferred put before reusing its embedded work item.

Keep the timeout on hdev->workqueue so it remains ordered with received HCI
events. It can also enqueue chained controller work while that workqueue is
being drained. Under hdev->lock, act only while the connection is still
registered and in BT_CONNECT.

Release hdev->lock around the existing timeout flush in a failed connection
completion. Revalidate the connection after reacquiring it. This allows the
timeout's locked state check to finish without deadlocking its flusher.

Fixes: 980ffc0a2cec ("Bluetooth: Fix LE connection timeout deadlock")
Cc: stable@vger.kernel.org
Assisted-by: GPT-6-Astra
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
---
Changes in v6:
- Replace v5's command-sync wait and advertising-state changes with a
  lifetime-only fix after validation found regressions in those paths.
- Hold a connection reference for queued timeout work and defer the final
  put to the system workqueue, avoiding destruction of hdev->workqueue from
  one of its own workers.
- Keep the timeout ordered with received HCI events on hdev->workqueue.
  Serialize its state check with hdev->lock and revalidate the connection
  after flushing the timeout without that lock.
- Validate the lifetime and ordering cases with focused tests, the normal
  Bluetooth test suites, a full kernel build and Sashiko with zero findings.

Link: https://lore.kernel.org/all/20260824134149.212607-1-nicoyip.dev@gmail.com/ [v5]
Link: https://lore.kernel.org/all/20260821172441.3020751-1-nicoyip.dev@gmail.com/ [v4]
Link: https://lore.kernel.org/all/20260821164512.2842464-1-nicoyip.dev@gmail.com/ [v3]
Link: https://lore.kernel.org/all/20260801145430.3560911-1-nicoyip.dev@gmail.com/ [v2]
Link: https://lore.kernel.org/all/20260730104103.2080325-1-nicoyip.dev@gmail.com/ [v1]

 include/net/bluetooth/hci_core.h |  3 ++
 net/bluetooth/hci_conn.c         | 51 ++++++++++++++++++++++++++------
 net/bluetooth/hci_event.c        | 10 ++-----
 net/bluetooth/hci_sync.c         |  6 ++++
 4 files changed, 54 insertions(+), 16 deletions(-)

diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
index 788d6600f500..f1e85bfe6366 100644
--- a/include/net/bluetooth/hci_core.h
+++ b/include/net/bluetooth/hci_core.h
@@ -773,6 +773,7 @@ struct hci_conn {
 	struct delayed_work auto_accept_work;
 	struct delayed_work idle_work;
 	struct delayed_work le_conn_timeout;
+	struct work_struct le_conn_timeout_put;
 
 	struct device	dev;
 	struct dentry	*debugfs;
@@ -1641,6 +1642,8 @@ struct hci_conn *hci_conn_add(struct hci_dev *hdev, int type, bdaddr_t *dst,
 struct hci_conn *hci_conn_add_unset(struct hci_dev *hdev, int type,
 				    bdaddr_t *dst, u8 dst_type, u8 role);
 void hci_conn_del(struct hci_conn *conn);
+void hci_conn_queue_le_timeout(struct hci_conn *conn);
+void hci_conn_cancel_le_timeout(struct hci_conn *conn);
 void hci_conn_hash_flush(struct hci_dev *hdev);
 
 struct hci_chan *hci_chan_create(struct hci_conn *conn);
diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 96195d2fd10f..78c6e0bfa184 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -714,6 +714,14 @@ static void le_disable_advertising(struct hci_dev *hdev)
 	}
 }
 
+static void le_conn_timeout_put(struct work_struct *work)
+{
+	struct hci_conn *conn = container_of(work, struct hci_conn,
+					     le_conn_timeout_put);
+
+	hci_conn_put(conn);
+}
+
 static void le_conn_timeout(struct work_struct *work)
 {
 	struct hci_conn *conn = container_of(work, struct hci_conn,
@@ -722,21 +730,45 @@ static void le_conn_timeout(struct work_struct *work)
 
 	BT_DBG("");
 
+	/* A queued instance owns one reference. Wait for an earlier instance
+	 * to release its reference before reusing the put work.
+	 */
+	flush_work(&conn->le_conn_timeout_put);
+
 	/* We could end up here due to having done directed advertising,
 	 * so clean up the state if necessary. This should however only
 	 * happen with broken hardware or if low duty cycle was used
 	 * (which doesn't have a timeout of its own).
 	 */
-	if (conn->role == HCI_ROLE_SLAVE) {
-		/* Disable LE Advertising */
-		le_disable_advertising(hdev);
-		hci_dev_lock(hdev);
-		hci_conn_failed(conn, HCI_ERROR_ADVERTISING_TIMEOUT);
-		hci_dev_unlock(hdev);
-		return;
+	hci_dev_lock(hdev);
+	if (hci_conn_valid(hdev, conn) && conn->state == BT_CONNECT) {
+		if (conn->role == HCI_ROLE_SLAVE) {
+			/* Disable LE Advertising */
+			le_disable_advertising(hdev);
+			hci_conn_failed(conn, HCI_ERROR_ADVERTISING_TIMEOUT);
+		} else {
+			hci_abort_conn(conn, HCI_ERROR_REMOTE_USER_TERM);
+		}
 	}
+	hci_dev_unlock(hdev);
+
+	/* The final put can release hdev and destroy its workqueue. */
+	schedule_work(&conn->le_conn_timeout_put);
+}
 
-	hci_abort_conn(conn, HCI_ERROR_REMOTE_USER_TERM);
+void hci_conn_queue_le_timeout(struct hci_conn *conn)
+{
+	/* Keep the connection alive until the work runs or is canceled. */
+	hci_conn_get(conn);
+	if (!queue_delayed_work(conn->hdev->workqueue,
+				&conn->le_conn_timeout, conn->conn_timeout))
+		hci_conn_put(conn);
+}
+
+void hci_conn_cancel_le_timeout(struct hci_conn *conn)
+{
+	if (cancel_delayed_work(&conn->le_conn_timeout))
+		hci_conn_put(conn);
 }
 
 struct iso_list_data {
@@ -1145,6 +1177,7 @@ static struct hci_conn *__hci_conn_add(struct hci_dev *hdev, int type,
 	INIT_DELAYED_WORK(&conn->auto_accept_work, hci_conn_auto_accept);
 	INIT_DELAYED_WORK(&conn->idle_work, hci_conn_idle);
 	INIT_DELAYED_WORK(&conn->le_conn_timeout, le_conn_timeout);
+	INIT_WORK(&conn->le_conn_timeout_put, le_conn_timeout_put);
 
 	spin_lock_init(&conn->proto_lock);
 
@@ -1292,7 +1325,7 @@ void hci_conn_del(struct hci_conn *conn)
 			hdev->acl_cnt += conn->sent;
 		break;
 	case LE_LINK:
-		cancel_delayed_work(&conn->le_conn_timeout);
+		hci_conn_cancel_le_timeout(conn);
 
 		if (hdev->le_pkts) {
 			if (!hci_conn_num(hdev, LE_LINK) ||
diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index 5ac2357e92c9..d34c70f51ae7 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -1593,9 +1593,7 @@ static u8 hci_cc_le_set_adv_enable(struct hci_dev *hdev, void *data,
 
 		conn = hci_lookup_le_connect(hdev);
 		if (conn)
-			queue_delayed_work(hdev->workqueue,
-					   &conn->le_conn_timeout,
-					   conn->conn_timeout);
+			hci_conn_queue_le_timeout(conn);
 	} else {
 		hci_dev_clear_flag(hdev, HCI_LE_ADV);
 	}
@@ -1641,9 +1639,7 @@ static u8 hci_cc_le_set_ext_adv_enable(struct hci_dev *hdev, void *data,
 
 		conn = hci_lookup_le_connect(hdev);
 		if (conn)
-			queue_delayed_work(hdev->workqueue,
-					   &conn->le_conn_timeout,
-					   conn->conn_timeout);
+			hci_conn_queue_le_timeout(conn);
 	} else {
 		if (cp->num_of_sets) {
 			if (adv)
@@ -5801,7 +5797,7 @@ static void le_conn_complete_evt(struct hci_dev *hdev, u8 status,
 			}
 		}
 	} else {
-		cancel_delayed_work(&conn->le_conn_timeout);
+		hci_conn_cancel_le_timeout(conn);
 	}
 
 	/* The HCI_LE_Connection_Complete event is only sent once per connection.
diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
index 00be55cf60ac..6c4f93f55a4d 100644
--- a/net/bluetooth/hci_sync.c
+++ b/net/bluetooth/hci_sync.c
@@ -7308,7 +7308,13 @@ static void create_le_conn_complete(struct hci_dev *hdev, void *data, int err)
 		goto unlock;
 
 	/* Flush to make sure we send create conn cancel command if needed */
+	hci_dev_unlock(hdev);
 	flush_delayed_work(&conn->le_conn_timeout);
+	hci_dev_lock(hdev);
+
+	if (!hci_conn_valid(hdev, conn) || conn->state != BT_CONNECT)
+		goto unlock;
+
 	hci_conn_failed(conn, bt_status(err));
 
 unlock:
-- 
2.43.0

RE: [v6] Bluetooth: hci_conn: hold a reference for LE connection timeout

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 2159 bytes --]

This is automated email and please do not reply to this email!

Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/series/1178509/

---Test result---

Test Summary:
CheckPatch                    PASS      1.43 seconds
VerifyFixes                   PASS      0.09 seconds
VerifySignedoff               PASS      0.09 seconds
GitLint                       PASS      0.26 seconds
SubjectPrefix                 PASS      0.08 seconds
BuildKernel                   PASS      29.69 seconds
CheckAllWarning               PASS      33.33 seconds
CheckSparse                   WARNING   36.32 seconds
BuildKernel32                 PASS      29.54 seconds
CheckKernelLLVM               PASS      35.12 seconds
TestRunnerSetup               PASS      798.47 seconds
TestRunner_l2cap-tester       PASS      12.55 seconds
TestRunner_iso-tester         PASS      14.67 seconds
TestRunner_bnep-tester        PASS      3.07 seconds
TestRunner_mgmt-tester        PASS      61.41 seconds
TestRunner_rfcomm-tester      PASS      4.48 seconds
TestRunner_sco-tester         PASS      5.60 seconds
TestRunner_ioctl-tester       PASS      4.66 seconds
TestRunner_mesh-tester        FAIL      7.81 seconds
TestRunner_smp-tester         PASS      4.29 seconds
TestRunner_userchan-tester    PASS      3.16 seconds
TestRunner_6lowpan-tester     PASS      4.42 seconds
IncrementalBuild              PASS      27.99 seconds

Details
##############################
Test: CheckSparse - WARNING
Desc: Run sparse tool with linux kernel
Output:
net/bluetooth/hci_event.c: note: in included file (through include/net/bluetooth/hci_core.h):
##############################
Test: TestRunner_mesh-tester - FAIL
Desc: Run mesh-tester with test-runner
Output:
Total: 10, Passed: 8 (80.0%), Failed: 2, Not Run: 0

Failed Test Cases
Mesh - Send cancel - 1                               Timed out    2.396 seconds
Mesh - Send cancel - 2                               Timed out    1.999 seconds


https://github.com/bluez/bluetooth-next/pull/853

---
Regards,
Linux Bluetooth