Bluetooth: L2CAP: Fix null-ptr-deref in l2cap_sock_state_change_cb()

commit 2ff1a41 upstream.

Add the same NULL guard already present in
l2cap_sock_resume_cb() and l2cap_sock_ready_cb().

Fixes: 89bc500 ("Bluetooth: Add state tracking to struct l2cap_chan")
Cc: stable@kernel.org
Signed-off-by: Siwei Zhang <oss@fourdim.xyz>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: fourdim

net/bluetooth/l2cap_sock.c

@@ -1627,6 +1627,9 @@ static void l2cap_sock_state_change_cb(struct l2cap_chan *chan, int state,
 {
 	struct sock *sk = chan->data;
 
+	if (!sk)
+		return;
+
 	sk->sk_state = state;
 
 	if (err)