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

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Date: Sat, 15 Jun 2024 09:25:12 +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..d6c2394f0235 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1241,6 +1241,7 @@ static void l2cap_sock_kill(struct sock *sk)
 
 	/* Kill poor orphan */
 
+	l2cap_pi(sk)->chan->data = NULL;
 	l2cap_chan_put(l2cap_pi(sk)->chan);
 	sock_set_flag(sk, SOCK_DEAD);
 	sock_put(sk);
@@ -1413,6 +1414,7 @@ static int l2cap_sock_release(struct socket *sock)
 	l2cap_chan_hold(chan);
 	l2cap_chan_lock(chan);
 
+	printk("err: %d, sk refcnt: %u, %s\n", err, refcount_read(&sk->sk_refcnt), __func__);
 	sock_orphan(sk);
 	l2cap_sock_kill(sk);
 
@@ -1481,12 +1483,23 @@ 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;
 
-	lock_sock(sk);
+	l2cap_chan_hold(chan);
+	l2cap_chan_lock(chan);
+	sk = chan->data;
+
+	if (!sk) {
+		printk("%s\n", __func__);
+		l2cap_chan_unlock(chan);
+		l2cap_chan_put(chan);
+		return -ENXIO;
+	}
 
+	pi = l2cap_pi(sk);
+	lock_sock(sk);
 	if (chan->mode == L2CAP_MODE_ERTM && !list_empty(&pi->rx_busy)) {
 		err = -ENOMEM;
 		goto done;
@@ -1535,6 +1548,8 @@ static int l2cap_sock_recv_cb(struct l2cap_chan *chan, struct sk_buff *skb)
 
 done:
 	release_sock(sk);
+	l2cap_chan_unlock(chan);
+	l2cap_chan_put(chan);
 
 	return err;
 }