[PATCH V3] Bluetooth/l2cap: sync sock recv cb and release

[Edward Adam Davis <eadavis@xxxxxx>]

The problem occurs between the system call to close the sock and hci_rx_work,
where the former releases the sock and the latter accesses it without lock protection.

           CPU0                       CPU1
           ----                       ----
           sock_close                 hci_rx_work
	   l2cap_sock_release         hci_acldata_packet
	   l2cap_sock_kill            l2cap_recv_frame
	   sk_free                    l2cap_conless_channel
	                              l2cap_sock_recv_cb

If hci_rx_work processes the data that needs to be received before the sock is
closed, then everything is normal; Otherwise, the work thread may access the
released sock when receiving data.

Add a chan lock in the l2cap_conless_channel of the sock to achieve sync
between the sock release and recv cb.

Sock is dead, so set chan data to NULL, avoid others use invalid sock pointer.

Reported-by: syzbot+b7f6f8c9303466e16c8a@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
---
 net/bluetooth/l2cap_core.c |  3 +++
 net/bluetooth/l2cap_sock.c | 13 +++++++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index aed025734d04..35a9534eb62d 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -6771,10 +6771,13 @@ static void l2cap_conless_channel(struct l2cap_conn *conn, __le16 psm,
 	bacpy(&bt_cb(skb)->l2cap.bdaddr, &hcon->dst);
 	bt_cb(skb)->l2cap.psm = psm;
 
+	l2cap_chan_lock(chan);
 	if (!chan->ops->recv(chan, skb)) {
+		l2cap_chan_unlock(chan);
 		l2cap_chan_put(chan);
 		return;
 	}
+	l2cap_chan_unlock(chan);
 
 drop:
 	l2cap_chan_put(chan);
diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index 6db60946c627..25091fb992a7 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1239,6 +1239,10 @@ static void l2cap_sock_kill(struct sock *sk)
 
 	BT_DBG("sk %p state %s", sk, state_to_string(sk->sk_state));
 
+	/* Sock is dead, so set chan data to NULL, avoid other task use invalid
+	 * sock pointer.
+	 */
+	l2cap_pi(sk)->chan->data = NULL;
 	/* Kill poor orphan */
 
 	l2cap_chan_put(l2cap_pi(sk)->chan);
@@ -1481,11 +1485,16 @@ static struct l2cap_chan *l2cap_sock_new_connection_cb(struct l2cap_chan *chan)
 
 static int l2cap_sock_recv_cb(struct l2cap_chan *chan, struct sk_buff *skb)
 {
-	struct sock *sk = chan->data;
-	struct l2cap_pinfo *pi = l2cap_pi(sk);
+	struct sock *sk;
+	struct l2cap_pinfo *pi;
 	int err;
 
+	if (!chan->data)
+		return -ENXIO;
+
+	sk = chan->data;
 	lock_sock(sk);
+	pi = l2cap_pi(sk);
 
 	if (chan->mode == L2CAP_MODE_ERTM && !list_empty(&pi->rx_busy)) {
 		err = -ENOMEM;
-- 
2.43.0