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Subject: [PATCH] Bluetooth: L2CAP: reject accept queue add unless BT_LISTEN
Author: pav@iki.fi

New items should not be added to parent socket accept queue after last
l2cap_sock_cleanup_listen() has run in l2cap_sock_teardown_cb() and
state set to BT_CLOSED, as that can result to UAF on dereferencing the
dangling parent reference.

Add check for sk_state == BT_LISTEN after acquiring sk lock in
l2cap_sock_new_connection_cb() to avoid this.

Add lock_sock() around sk_state changes where it was missing.

That this can trigger appears to be possible since l2cap_chan::state is
not consistently guarded by a lock, so data races on it can exist in
checking parent pchan->state == BT_LISTEN in l2cap_core.

Fixes: 2ff1a41a912d ("Bluetooth: L2CAP: Fix null-ptr-deref in l2cap_sock_state_change_cb()")
Reported-by: syzbot+9265e754091c2d27ea29@syzkaller.appspotmail.com
---

#syz test

 net/bluetooth/l2cap_sock.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index 735167f73f31..8c2ac8b911e0 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1568,6 +1568,11 @@ static int l2cap_sock_new_connection_cb(struct l2cap_chan *chan,
 
 	lock_sock(parent);
 
+	if (parent->sk_state != BT_LISTEN) {
+		release_sock(parent);
+		return -EINVAL;
+	}
+
 	/* Check for backlog size */
 	if (sk_acceptq_is_full(parent)) {
 		BT_DBG("backlog full %d", parent->sk_ack_backlog);
@@ -1731,10 +1736,14 @@ static void l2cap_sock_state_change_cb(struct l2cap_chan *chan, int state,
 	if (!sk)
 		return;
 
+	lock_sock(sk);
+
 	sk->sk_state = state;
 
 	if (err)
 		sk->sk_err = err;
+
+	release_sock(sk);
 }
 
 static struct sk_buff *l2cap_sock_alloc_skb_cb(struct l2cap_chan *chan,
@@ -1810,6 +1819,8 @@ static void l2cap_sock_resume_cb(struct l2cap_chan *chan)
 	if (!sk)
 		return;
 
+	lock_sock(sk);
+
 	if (test_and_clear_bit(FLAG_PENDING_SECURITY, &chan->flags)) {
 		sk->sk_state = BT_CONNECTED;
 		chan->state = BT_CONNECTED;
@@ -1817,6 +1828,8 @@ static void l2cap_sock_resume_cb(struct l2cap_chan *chan)
 
 	clear_bit(BT_SK_SUSPEND, &bt_sk(sk)->flags);
 	sk->sk_state_change(sk);
+
+	release_sock(sk);
 }
 
 static void l2cap_sock_set_shutdown_cb(struct l2cap_chan *chan)
-- 
2.55.0