linux-kernel - Re: [syzbot] [bluetooth?] general protection fault in l2cap_sock_recv

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Date: Fri, 21 Jun 2024 22:56:26 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+b7f6f8c9303466e16c8a@...kaller.appspotmail.com
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bluetooth?] general protection fault in l2cap_sock_recv_cb

please test null ptr defref in l2cap_sock_recv_cb

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

diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index 6db60946c627..c0fe74a6b45e 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -47,6 +47,7 @@ static void l2cap_sock_init(struct sock *sk, struct sock *parent);
 static struct sock *l2cap_sock_alloc(struct net *net, struct socket *sock,
 				     int proto, gfp_t prio, int kern);
 static void l2cap_sock_cleanup_listen(struct sock *parent);
+static DEFINE_MUTEX(chan_data_lock);
 
 bool l2cap_is_socket(struct socket *sock)
 {
@@ -1239,6 +1240,9 @@ static void l2cap_sock_kill(struct sock *sk)
 
 	BT_DBG("sk %p state %s", sk, state_to_string(sk->sk_state));
 
+	mutex_lock(&chan_data_lock);
+	l2cap_pi(sk)->chan->data = NULL;
+	mutex_unlock(&chan_data_lock);
 	/* Kill poor orphan */
 
 	l2cap_chan_put(l2cap_pi(sk)->chan);
@@ -1481,10 +1485,18 @@ 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;
 
+	mutex_lock(&chan_data_lock);
+	sk = chan->data;
+	if (!sk) {
+		mutex_unlock(&chan_data_lock);
+		return -ENXIO;
+	}
+
+	pi = l2cap_pi(sk);
 	lock_sock(sk);
 
 	if (chan->mode == L2CAP_MODE_ERTM && !list_empty(&pi->rx_busy)) {
@@ -1535,6 +1547,7 @@ static int l2cap_sock_recv_cb(struct l2cap_chan *chan, struct sk_buff *skb)
 
 done:
 	release_sock(sk);
+	mutex_unlock(&chan_data_lock);
 
 	return err;
 }