[PATCH RFC v2] Bluetooth: hci_sync: Fix tx_work queuing race during device close

["syzbot" <syzbot@kernel.org>]

During the shutdown process of a Bluetooth device in hci_dev_close_sync(),
tx_work can still be queued by concurrent transmission paths or raw HCI
socket operations after HCI_UP has been checked or while workqueues are
being flushed. This causes __queue_work() to trigger a warning when
attempting to queue work on a draining workqueue:

workqueue: cannot queue hci_tx_work on wq hci0
WARNING: kernel/workqueue.c:2306 at __queue_work+0xd4a/0x1090
Call Trace:
 <TASK>
 queue_work_on+0x106/0x1c0 kernel/workqueue.c:2452
 l2cap_chan_send+0x168a/0x22f0 net/bluetooth/l2cap_core.c:-1
 l2cap_sock_sendmsg+0x33a/0x4d0 net/bluetooth/l2cap_sock.c:1180
 ____sys_sendmsg+0x54e/0x850 net/socket.c:2684
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2738
 __sys_sendmmsg+0x273/0x4d0 net/socket.c:2827
 </TASK>

To fix this, replace flush_work() with disable_work_sync() and re-enable it
with enable_work() in hci_dev_close_sync() to establish a work exclusion
interval for hdev->tx_work while the device is closing. Additionally,
ensure raw HCI socket producers in hci_sock_sendmsg() are quiesced by
holding rcu_read_lock() while checking HCI_UP, paired with
synchronize_rcu() in hci_dev_close_sync() right after disabling tx_work.

Fixes: 76727c02c1e1 ("Bluetooth: Call drain_workqueue() before resetting state")
Assisted-by: Gemini:gemini-3.6-flash Gemini:gemini-3.1-pro-preview syzbot
Reported-by: syzbot+b6919040d9958e2fc1ae@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b6919040d9958e2fc1ae
Link: https://syzkaller.appspot.com/ai_job?id=bb132695-7f6d-4df7-8464-0dd1708b1661
To: <linux-bluetooth@vger.kernel.org>
To: "Luiz Augusto von Dentz" <luiz.dentz@gmail.com>
To: "Marcel Holtmann" <marcel@holtmann.org>
To: "Johan Hedberg" <johan.hedberg@intel.com>
Cc: <linux-kernel@vger.kernel.org>

---
v2:
- Replaced per-send HCI_UP checks in hci_core.c with disable_work_sync() and enable_work() on hdev->tx_work in hci_dev_close_sync() to establish a work exclusion interval during shutdown.
- Added rcu_read_lock() protection around the HCI_UP check in hci_sock_sendmsg() and synchronize_rcu() in hci_dev_close_sync() to quiesce raw HCI producers.

v1:
https://lore.kernel.org/all/2c2febf2-fc12-4407-9c81-d3d9713f09a4@mail.kernel.org/T/
---
diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
index 070ca388f..8345ebbbd 100644
--- a/net/bluetooth/hci_sock.c
+++ b/net/bluetooth/hci_sock.c
@@ -1850,9 +1850,10 @@ static int hci_sock_sendmsg(struct socket *sock, struct msghdr *msg,
 		goto drop;
 	}
 
+	rcu_read_lock();
 	if (!test_bit(HCI_UP, &hdev->flags)) {
 		err = -ENETDOWN;
-		goto drop;
+		goto drop_rcu;
 	}
 
 	hci_skb_pkt_type(skb) = skb->data[0];
@@ -1870,7 +1871,7 @@ static int hci_sock_sendmsg(struct socket *sock, struct msghdr *msg,
 		    hci_skb_pkt_type(skb) != HCI_ISODATA_PKT &&
 		    hci_skb_pkt_type(skb) != HCI_DRV_PKT) {
 			err = -EINVAL;
-			goto drop;
+			goto drop_rcu;
 		}
 
 		skb_queue_tail(&hdev->raw_q, skb);
@@ -1885,7 +1886,7 @@ static int hci_sock_sendmsg(struct socket *sock, struct msghdr *msg,
 				   &hci_sec_filter.ocf_mask[ogf])) &&
 		    !capable(CAP_NET_RAW)) {
 			err = -EPERM;
-			goto drop;
+			goto drop_rcu;
 		}
 
 		/* Since the opcode has already been extracted here, store
@@ -1908,14 +1909,14 @@ static int hci_sock_sendmsg(struct socket *sock, struct msghdr *msg,
 	} else {
 		if (!capable(CAP_NET_RAW)) {
 			err = -EPERM;
-			goto drop;
+			goto drop_rcu;
 		}
 
 		if (hci_skb_pkt_type(skb) != HCI_ACLDATA_PKT &&
 		    hci_skb_pkt_type(skb) != HCI_SCODATA_PKT &&
 		    hci_skb_pkt_type(skb) != HCI_ISODATA_PKT) {
 			err = -EINVAL;
-			goto drop;
+			goto drop_rcu;
 		}
 
 		skb_queue_tail(&hdev->raw_q, skb);
@@ -1923,14 +1924,16 @@ static int hci_sock_sendmsg(struct socket *sock, struct msghdr *msg,
 	}
 
 	err = len;
+	rcu_read_unlock();
+	goto done;
 
+drop_rcu:
+	rcu_read_unlock();
+drop:
+	kfree_skb(skb);
 done:
 	release_sock(sk);
 	return err;
-
-drop:
-	kfree_skb(skb);
-	goto done;
 }
 
 static int hci_sock_setsockopt_old(struct socket *sock, int level, int optname,
diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
index c8d14128c..bad83313b 100644
--- a/net/bluetooth/hci_sync.c
+++ b/net/bluetooth/hci_sync.c
@@ -5472,9 +5472,11 @@ int hci_dev_close_sync(struct hci_dev *hdev)
 	hci_leds_update_powered(hdev, false);
 
 	/* Flush RX and TX works */
-	flush_work(&hdev->tx_work);
+	disable_work_sync(&hdev->tx_work);
 	flush_work(&hdev->rx_work);
 
+	synchronize_rcu();
+
 	if (hdev->discov_timeout > 0) {
 		hdev->discov_timeout = 0;
 		hci_dev_clear_flag(hdev, HCI_DISCOVERABLE);
@@ -5576,6 +5578,8 @@ int hci_dev_close_sync(struct hci_dev *hdev)
 	bacpy(&hdev->random_addr, BDADDR_ANY);
 	hci_codec_list_clear(&hdev->local_codecs);
 
+	enable_work(&hdev->tx_work);
+
 	hci_dev_put(hdev);
 	return err;
 }


base-commit: 075b74841bd0065a3bda3440873c747938e69b68
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