Re: [syzbot] [bluetooth?] general protection fault in l2cap_sock_recv_cb

[Hillf Danton <hdanton@sina.com>]

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  cc8ed4d0a848

--- x/net/bluetooth/l2cap_core.c
+++ y/net/bluetooth/l2cap_core.c
@@ -6756,6 +6756,7 @@ static void l2cap_conless_channel(struct
 {
 	struct hci_conn *hcon = conn->hcon;
 	struct l2cap_chan *chan;
+	int rc;
 
 	if (hcon->type != ACL_LINK)
 		goto free_skb;
@@ -6767,6 +6768,8 @@ static void l2cap_conless_channel(struct
 
 	BT_DBG("chan %p, len %d", chan, skb->len);
 
+	l2cap_chan_lock(chan);
+
 	if (chan->state != BT_BOUND && chan->state != BT_CONNECTED)
 		goto drop;
 
@@ -6777,15 +6780,15 @@ static void l2cap_conless_channel(struct
 	bacpy(&bt_cb(skb)->l2cap.bdaddr, &hcon->dst);
 	bt_cb(skb)->l2cap.psm = psm;
 
-	if (!chan->ops->recv(chan, skb)) {
-		l2cap_chan_put(chan);
-		return;
-	}
+	rc = chan->ops->recv(chan, skb);
 
 drop:
+	l2cap_chan_unlock(chan);
 	l2cap_chan_put(chan);
+	if (rc) {
 free_skb:
-	kfree_skb(skb);
+		kfree_skb(skb);
+	}
 }
 
 static void l2cap_recv_frame(struct l2cap_conn *conn, struct sk_buff *skb)
--- x/net/bluetooth/l2cap_sock.c
+++ y/net/bluetooth/l2cap_sock.c
@@ -1237,6 +1237,7 @@ static void l2cap_sock_kill(struct sock
 	if (!sock_flag(sk, SOCK_ZAPPED) || sk->sk_socket)
 		return;
 
+	l2cap_pi(sk)->chan->data = NULL;
 	BT_DBG("sk %p state %s", sk, state_to_string(sk->sk_state));
 
 	/* Kill poor orphan */
@@ -1481,11 +1482,16 @@ static struct l2cap_chan *l2cap_sock_new
 
 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;
--