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Message-ID: <tencent_554425A5BAF0BB7633499ED51B7D4BEF1B08@qq.com>
From: Edward Adam Davis <eadavis@qq.com>
To: syzbot+b7f6f8c9303466e16c8a@syzkaller.appspotmail.com
Cc: linux-kernel@vger.kernel.org,
	syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [bluetooth?] general protection fault in l2cap_sock_recv_cb
Date: Tue, 11 Jun 2024 14:35:55 +0800
In-Reply-To: <000000000000b0906d061a468b93@google.com>
References: <000000000000b0906d061a468b93@google.com>
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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..a9edcf9152c3 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1413,6 +1413,9 @@ static int l2cap_sock_release(struct socket *sock)
 	l2cap_chan_hold(chan);
 	l2cap_chan_lock(chan);
 
+	printk("chan %p data: %p, sk: %p, %s\n", chan, chan->data, sk, __func__);
+	if (refcount_read(&sk->sk_refcnt))
+		chan->data = NULL;
 	sock_orphan(sk);
 	l2cap_sock_kill(sk);
 
@@ -1481,12 +1484,23 @@ 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;
 
+	printk("chan %p data: %p, is :%d, %s\n", chan, chan->data, IS_ERR_OR_NULL(sk), __func__);
+	if (IS_ERR_OR_NULL(sk) || sock_flag(sk, SOCK_DEAD)) {
+		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 +1549,8 @@ 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;
 }