Bluetooth: L2CAP: Fix deadlock

This fixes the following deadlock introduced by 39a92a55be13
("bluetooth/l2cap: sync sock recv cb and release")

============================================
WARNING: possible recursive locking detected
6.10.0-rc3-g4029dba6b6f1 #6823 Not tainted
--------------------------------------------
kworker/u5:0/35 is trying to acquire lock:
ffff888002ec2510 (&chan->lock#2/1){+.+.}-{3:3}, at:
l2cap_sock_recv_cb+0x44/0x1e0

but task is already holding lock:
ffff888002ec2510 (&chan->lock#2/1){+.+.}-{3:3}, at:
l2cap_get_chan_by_scid+0xaf/0xd0

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&chan->lock#2/1);
  lock(&chan->lock#2/1);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by kworker/u5:0/35:
 #0: ffff888002b8a940 ((wq_completion)hci0#2){+.+.}-{0:0}, at:
process_one_work+0x750/0x930
 #1: ffff888002c67dd0 ((work_completion)(&hdev->rx_work)){+.+.}-{0:0},
at: process_one_work+0x44e/0x930
 #2: ffff888002ec2510 (&chan->lock#2/1){+.+.}-{3:3}, at:
l2cap_get_chan_by_scid+0xaf/0xd0

To fix the original problem this introduces l2cap_chan_lock at
l2cap_conless_channel to ensure that l2cap_sock_recv_cb is called with
chan->lock held.

Fixes: 89e856e124 ("bluetooth/l2cap: sync sock recv cb and release")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

include/net/bluetooth/hci_sync.h

@@ -38,6 +38,8 @@ int __hci_cmd_sync_status(struct hci_dev *hdev, u16 opcode, u32 plen,
 int __hci_cmd_sync_status_sk(struct hci_dev *hdev, u16 opcode, u32 plen,
 			     const void *param, u8 event, u32 timeout,
 			     struct sock *sk);
+int hci_cmd_sync_status(struct hci_dev *hdev, u16 opcode, u32 plen,
+			const void *param, u32 timeout);
 
 void hci_cmd_sync_init(struct hci_dev *hdev);
 void hci_cmd_sync_clear(struct hci_dev *hdev);

net/bluetooth/hci_core.c

@@ -63,50 +63,6 @@ DEFINE_MUTEX(hci_cb_list_lock);
 /* HCI ID Numbering */
 static DEFINE_IDA(hci_index_ida);
 
-static int hci_scan_req(struct hci_request *req, unsigned long opt)
-{
-	__u8 scan = opt;
-
-	BT_DBG("%s %x", req->hdev->name, scan);
-
-	/* Inquiry and Page scans */
-	hci_req_add(req, HCI_OP_WRITE_SCAN_ENABLE, 1, &scan);
-	return 0;
-}
-
-static int hci_auth_req(struct hci_request *req, unsigned long opt)
-{
-	__u8 auth = opt;
-
-	BT_DBG("%s %x", req->hdev->name, auth);
-
-	/* Authentication */
-	hci_req_add(req, HCI_OP_WRITE_AUTH_ENABLE, 1, &auth);
-	return 0;
-}
-
-static int hci_encrypt_req(struct hci_request *req, unsigned long opt)
-{
-	__u8 encrypt = opt;
-
-	BT_DBG("%s %x", req->hdev->name, encrypt);
-
-	/* Encryption */
-	hci_req_add(req, HCI_OP_WRITE_ENCRYPT_MODE, 1, &encrypt);
-	return 0;
-}
-
-static int hci_linkpol_req(struct hci_request *req, unsigned long opt)
-{
-	__le16 policy = cpu_to_le16(opt);
-
-	BT_DBG("%s %x", req->hdev->name, policy);
-
-	/* Default link policy */
-	hci_req_add(req, HCI_OP_WRITE_DEF_LINK_POLICY, 2, &policy);
-	return 0;
-}
-
 /* Get HCI device by index.
  * Device is held on return. */
 struct hci_dev *hci_dev_get(int index)
@@ -735,6 +691,7 @@ int hci_dev_cmd(unsigned int cmd, void __user *arg)
 {
 	struct hci_dev *hdev;
 	struct hci_dev_req dr;
+	__le16 policy;
 	int err = 0;
 
 	if (copy_from_user(&dr, arg, sizeof(dr)))
@@ -761,8 +718,8 @@ int hci_dev_cmd(unsigned int cmd, void __user *arg)
 
 	switch (cmd) {
 	case HCISETAUTH:
-		err = hci_req_sync(hdev, hci_auth_req, dr.dev_opt,
+		err = __hci_cmd_sync_status(hdev, HCI_OP_WRITE_AUTH_ENABLE,
-				   HCI_INIT_TIMEOUT, NULL);
+					    1, &dr.dev_opt, HCI_CMD_TIMEOUT);
 		break;
 
 	case HCISETENCRYPT:
@@ -773,19 +730,23 @@ int hci_dev_cmd(unsigned int cmd, void __user *arg)
 
 		if (!test_bit(HCI_AUTH, &hdev->flags)) {
 			/* Auth must be enabled first */
-			err = hci_req_sync(hdev, hci_auth_req, dr.dev_opt,
+			err = __hci_cmd_sync_status(hdev,
-					   HCI_INIT_TIMEOUT, NULL);
+						    HCI_OP_WRITE_AUTH_ENABLE,
+						    1, &dr.dev_opt,
+						    HCI_CMD_TIMEOUT);
 			if (err)
 				break;
 		}
 
-		err = hci_req_sync(hdev, hci_encrypt_req, dr.dev_opt,
+		err = __hci_cmd_sync_status(hdev, HCI_OP_WRITE_ENCRYPT_MODE,
-				   HCI_INIT_TIMEOUT, NULL);
+					    1, &dr.dev_opt,
+					    HCI_CMD_TIMEOUT);
 		break;
 
 	case HCISETSCAN:
-		err = hci_req_sync(hdev, hci_scan_req, dr.dev_opt,
+		err = __hci_cmd_sync_status(hdev, HCI_OP_WRITE_SCAN_ENABLE,
-				   HCI_INIT_TIMEOUT, NULL);
+					    1, &dr.dev_opt,
+					    HCI_CMD_TIMEOUT);
 
 		/* Ensure that the connectable and discoverable states
 		 * get correctly modified as this was a non-mgmt change.
@@ -795,8 +756,11 @@ int hci_dev_cmd(unsigned int cmd, void __user *arg)
 		break;
 
 	case HCISETLINKPOL:
-		err = hci_req_sync(hdev, hci_linkpol_req, dr.dev_opt,
+		policy = cpu_to_le16(dr.dev_opt);
-				   HCI_INIT_TIMEOUT, NULL);
+
+		err = __hci_cmd_sync_status(hdev, HCI_OP_WRITE_DEF_LINK_POLICY,
+					    2, &policy,
+					    HCI_CMD_TIMEOUT);
 		break;
 
 	case HCISETLINKMODE:

net/bluetooth/hci_sync.c

@@ -280,6 +280,19 @@ int __hci_cmd_sync_status(struct hci_dev *hdev, u16 opcode, u32 plen,
 }
 EXPORT_SYMBOL(__hci_cmd_sync_status);
 
+int hci_cmd_sync_status(struct hci_dev *hdev, u16 opcode, u32 plen,
+			const void *param, u32 timeout)
+{
+	int err;
+
+	hci_req_sync_lock(hdev);
+	err = __hci_cmd_sync_status(hdev, opcode, plen, param, timeout);
+	hci_req_sync_unlock(hdev);
+
+	return err;
+}
+EXPORT_SYMBOL(hci_cmd_sync_status);
+
 static void hci_cmd_sync_work(struct work_struct *work)
 {
 	struct hci_dev *hdev = container_of(work, struct hci_dev, cmd_sync_work);

net/bluetooth/l2cap_core.c

@@ -6761,6 +6761,8 @@ static void l2cap_conless_channel(struct l2cap_conn *conn, __le16 psm,
 
 	BT_DBG("chan %p, len %d", chan, skb->len);
 
+	l2cap_chan_lock(chan);
+
 	if (chan->state != BT_BOUND && chan->state != BT_CONNECTED)
 		goto drop;
 
@@ -6777,6 +6779,7 @@ static void l2cap_conless_channel(struct l2cap_conn *conn, __le16 psm,
 	}
 
 drop:
+	l2cap_chan_unlock(chan);
 	l2cap_chan_put(chan);
 free_skb:
 	kfree_skb(skb);

net/bluetooth/l2cap_sock.c

@@ -1489,18 +1489,9 @@ static int l2cap_sock_recv_cb(struct l2cap_chan *chan, struct sk_buff *skb)
 	struct l2cap_pinfo *pi;
 	int err;
 
-	/* To avoid race with sock_release, a chan lock needs to be added here
-	 * to synchronize the sock.
-	 */
-	l2cap_chan_hold(chan);
-	l2cap_chan_lock(chan);
 	sk = chan->data;
-
+	if (!sk)
-	if (!sk) {
-		l2cap_chan_unlock(chan);
-		l2cap_chan_put(chan);
 		return -ENXIO;
-	}
 
 	pi = l2cap_pi(sk);
 	lock_sock(sk);
@@ -1552,8 +1543,6 @@ static int l2cap_sock_recv_cb(struct l2cap_chan *chan, struct sk_buff *skb)
 
 done:
 	release_sock(sk);
-	l2cap_chan_unlock(chan);
-	l2cap_chan_put(chan);
 
 	return err;
 }