[PATCH] Bluetooth: SCO: fix sco_conn related locking and validity issues

[Pauli Virtanen <pav@xxxxxx>]

Operations that check/update sk_state and access conn should hold
lock_sock, otherwise they can race.

The order of taking locks is hci_dev_lock > lock_sock > sco_conn_lock,
which is how it is in connect/disconnect_cfm -> sco_conn_del ->
sco_chan_del.

Fix locking in sco_connect to take lock_sock around updating sk_state
and conn.

sco_conn_del must not occur during sco_connect, as it frees the
sco_conn. Hold hdev->lock longer to prevent that.

sco_conn_add shall return sco_conn with valid hcon. Make it so also when
reusing an old SCO connection waiting for disconnect timeout (see
__sco_sock_close where conn->hcon is set to NULL).

This should not reintroduce the issue fixed in the earlier
commit 9a8ec9e8ebb5 ("Bluetooth: SCO: Fix possible circular locking
dependency on sco_connect_cfm"), the relevant fix of releasing lock_sock
in sco_sock_connect before acquiring hdev->lock is retained.

These changes mirror similar fixes earlier in ISO sockets.

Fixes: 9a8ec9e8ebb5 ("Bluetooth: SCO: Fix possible circular locking dependency on sco_connect_cfm")
Signed-off-by: Pauli Virtanen <pav@xxxxxx>
---

Notes:
    Possibly related:
    
    https://lore.kernel.org/linux-bluetooth/00000000000036b9590600095d33@xxxxxxxxxx/
    https://lore.kernel.org/linux-bluetooth/HwByr9Ffw_HVVE5pnMu6CTIrQjKwBJpJcSskM0xOP0S-4XiIdmGFTLYAcgKJsOkrxt62je88hFJ1vkHzYtCgwsEATe0KFq3E4YX8LeN5Fdo=@protonmail.com/

 net/bluetooth/sco.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
index bbf7072f5e80..ec6dce488a40 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c
@@ -126,8 +126,11 @@ static struct sco_conn *sco_conn_add(struct hci_conn *hcon)
 	struct hci_dev *hdev = hcon->hdev;
 	struct sco_conn *conn = hcon->sco_data;
 
-	if (conn)
+	if (conn) {
+		if (!conn->hcon)
+			conn->hcon = hcon;
 		return conn;
+	}
 
 	conn = kzalloc(sizeof(struct sco_conn), GFP_KERNEL);
 	if (!conn)
@@ -268,21 +271,21 @@ static int sco_connect(struct sock *sk)
 		goto unlock;
 	}
 
-	hci_dev_unlock(hdev);
-	hci_dev_put(hdev);
-
 	conn = sco_conn_add(hcon);
 	if (!conn) {
 		hci_conn_drop(hcon);
-		return -ENOMEM;
+		err = -ENOMEM;
+		goto unlock;
 	}
 
-	err = sco_chan_add(conn, sk, NULL);
-	if (err)
-		return err;
-
 	lock_sock(sk);
 
+	err = sco_chan_add(conn, sk, NULL);
+	if (err) {
+		release_sock(sk);
+		goto unlock;
+	}
+
 	/* Update source addr of the socket */
 	bacpy(&sco_pi(sk)->src, &hcon->src);
 
@@ -296,8 +299,6 @@ static int sco_connect(struct sock *sk)
 
 	release_sock(sk);
 
-	return err;
-
 unlock:
 	hci_dev_unlock(hdev);
 	hci_dev_put(hdev);
-- 
2.41.0