Bluetooth: fix dangling sco_conn and use-after-free in sco_sock_timeout

Connecting the same socket twice consecutively in sco_sock_connect()
could lead to a race condition where two sco_conn objects are created
but only one is associated with the socket. If the socket is closed
before the SCO connection is established, the timer associated with the
dangling sco_conn object won't be canceled. As the sock object is being
freed, the use-after-free problem happens when the timer callback
function sco_sock_timeout() accesses the socket. Here's the call trace:

dump_stack+0x107/0x163
? refcount_inc+0x1c/
print_address_description.constprop.0+0x1c/0x47e
? refcount_inc+0x1c/0x7b
kasan_report+0x13a/0x173
? refcount_inc+0x1c/0x7b
check_memory_region+0x132/0x139
refcount_inc+0x1c/0x7b
sco_sock_timeout+0xb2/0x1ba
process_one_work+0x739/0xbd1
? cancel_delayed_work+0x13f/0x13f
? __raw_spin_lock_init+0xf0/0xf0
? to_kthread+0x59/0x85
worker_thread+0x593/0x70e
kthread+0x346/0x35a
? drain_workqueue+0x31a/0x31a
? kthread_bind+0x4b/0x4b
ret_from_fork+0x1f/0x30

Link: https://syzkaller.appspot.com/bug?extid=2bef95d3ab4daa10155b
Reported-by: syzbot+2bef95d3ab4daa10155b@syzkaller.appspotmail.com
Fixes: e1dee2c1 ("Bluetooth: fix repeated calls to sco_sock_kill")
Signed-off-by: Ying Hsu <yinghsu@chromium.org>
Reviewed-by: Joseph Hwang <josephsih@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/sco.c

@@ -574,19 +574,24 @@ static int sco_sock_connect(struct socket *sock, struct sockaddr *addr, int alen
 	    addr->sa_family != AF_BLUETOOTH)
 		return -EINVAL;
 
-	if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND)
-		return -EBADFD;
+	lock_sock(sk);
+	if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND) {
+		err = -EBADFD;
+		goto done;
+	}
 
-	if (sk->sk_type != SOCK_SEQPACKET)
-		return -EINVAL;
+	if (sk->sk_type != SOCK_SEQPACKET) {
+		err = -EINVAL;
+		goto done;
+	}
 
 	hdev = hci_get_route(&sa->sco_bdaddr, &sco_pi(sk)->src, BDADDR_BREDR);
-	if (!hdev)
-		return -EHOSTUNREACH;
+	if (!hdev) {
+		err = -EHOSTUNREACH;
+		goto done;
+	}
 	hci_dev_lock(hdev);
 
-	lock_sock(sk);
-
 	/* Set destination address and psm */
 	bacpy(&sco_pi(sk)->dst, &sa->sco_bdaddr);