Bluetooth: Only mark socket zapped after unlocking

Since l2cap_sock_teardown_cb doesn't acquire the channel lock before
setting the socket as zapped, it could potentially race with
l2cap_sock_release which frees the socket. Thus, wait until the cleanup
is complete before marking the socket as zapped.

This race was reproduced on a JBL GO speaker after the remote device
rejected L2CAP connection due to resource unavailability.

Here is a dmesg log with debug logs from a repro of this bug:
[ 3465.424086] Bluetooth: hci_core.c:hci_acldata_packet() hci0 len 16 handle 0x0003 flags 0x0002
[ 3465.424090] Bluetooth: hci_conn.c:hci_conn_enter_active_mode() hcon 00000000cfedd07d mode 0
[ 3465.424094] Bluetooth: l2cap_core.c:l2cap_recv_acldata() conn 000000007eae8952 len 16 flags 0x2
[ 3465.424098] Bluetooth: l2cap_core.c:l2cap_recv_frame() len 12, cid 0x0001
[ 3465.424102] Bluetooth: l2cap_core.c:l2cap_raw_recv() conn 000000007eae8952
[ 3465.424175] Bluetooth: l2cap_core.c:l2cap_sig_channel() code 0x03 len 8 id 0x0c
[ 3465.424180] Bluetooth: l2cap_core.c:l2cap_connect_create_rsp() dcid 0x0045 scid 0x0000 result 0x02 status 0x00
[ 3465.424189] Bluetooth: l2cap_core.c:l2cap_chan_put() chan 000000006acf9bff orig refcnt 4
[ 3465.424196] Bluetooth: l2cap_core.c:l2cap_chan_del() chan 000000006acf9bff, conn 000000007eae8952, err 111, state BT_CONNECT
[ 3465.424203] Bluetooth: l2cap_sock.c:l2cap_sock_teardown_cb() chan 000000006acf9bff state BT_CONNECT
[ 3465.424221] Bluetooth: l2cap_core.c:l2cap_chan_put() chan 000000006acf9bff orig refcnt 3
[ 3465.424226] Bluetooth: hci_core.h:hci_conn_drop() hcon 00000000cfedd07d orig refcnt 6
[ 3465.424234] BUG: spinlock bad magic on CPU#2, kworker/u17:0/159
[ 3465.425626] Bluetooth: hci_sock.c:hci_sock_sendmsg() sock 000000002bb0cb64 sk 00000000a7964053
[ 3465.430330]  lock: 0xffffff804410aac0, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
[ 3465.430332] Causing a watchdog bite!

Signed-off-by: Abhishek Pandit-Subedi <[email protected]>
Reported-by: Balakrishna Godavarthi <[email protected]>
Reviewed-by: Manish Mandlik <[email protected]>
Signed-off-by: Marcel Holtmann <[email protected]>

Author: apandit

net/bluetooth/l2cap_sock.c

@@ -1521,8 +1521,6 @@ static void l2cap_sock_teardown_cb(struct l2cap_chan *chan, int err)
 
 	parent = bt_sk(sk)->parent;
 
-	sock_set_flag(sk, SOCK_ZAPPED);
-
 	switch (chan->state) {
 	case BT_OPEN:
 	case BT_BOUND:
@@ -1549,8 +1547,11 @@ static void l2cap_sock_teardown_cb(struct l2cap_chan *chan, int err)
 
 		break;
 	}
-
 	release_sock(sk);
+
+	/* Only zap after cleanup to avoid use after free race */
+	sock_set_flag(sk, SOCK_ZAPPED);
+
 }
 
 static void l2cap_sock_state_change_cb(struct l2cap_chan *chan, int state,