Bluetooth: rfcomm: Fix null-ptr-deref in rfcomm_check_security

JIRA: https://issues.redhat.com/browse/RHEL-30099

JIRA: https://issues.redhat.com/browse/RHEL-27921

CVE: CVE-2024-22099

commit 2535b848fa0f42ddff3e5255cf5e742c9b77bb26
Author: Yuxuan Hu <20373622@buaa.edu.cn>
Date:   Wed Jan 3 17:10:43 2024 +0800

    Bluetooth: rfcomm: Fix null-ptr-deref in rfcomm_check_security

    During our fuzz testing of the connection and disconnection process at the
    RFCOMM layer, we discovered this bug. By comparing the packets from a
    normal connection and disconnection process with the testcase that
    triggered a KASAN report. We analyzed the cause of this bug as follows:

    1. In the packets captured during a normal connection, the host sends a
    `Read Encryption Key Size` type of `HCI_CMD` packet
    (Command Opcode: 0x1408) to the controller to inquire the length of
    encryption key.After receiving this packet, the controller immediately
    replies with a Command Completepacket (Event Code: 0x0e) to return the
    Encryption Key Size.

    2. In our fuzz test case, the timing of the controller's response to this
    packet was delayed to an unexpected point: after the RFCOMM and L2CAP
    layers had disconnected but before the HCI layer had disconnected.

    3. After receiving the Encryption Key Size Response at the time described
    in point 2, the host still called the rfcomm_check_security function.
    However, by this time `struct l2cap_conn *conn = l2cap_pi(sk)->chan->conn;`
    had already been released, and when the function executed
    `return hci_conn_security(conn->hcon, d->sec_level, auth_type, d->out);`,
    specifically when accessing `conn->hcon`, a null-ptr-deref error occurred.

    To fix this bug, check if `sk->sk_state` is BT_CLOSED before calling
    rfcomm_recv_frame in rfcomm_process_rx.

    Signed-off-by: Yuxuan Hu <20373622@buaa.edu.cn>
    Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

Signed-off-by: David Marlin <dmarlin@redhat.com>

net/bluetooth/rfcomm/core.c

@@ -1941,7 +1941,7 @@ static struct rfcomm_session *rfcomm_process_rx(struct rfcomm_session *s)
 	/* Get data directly from socket receive queue without copying it. */
 	while ((skb = skb_dequeue(&sk->sk_receive_queue))) {
 		skb_orphan(skb);
-		if (!skb_linearize(skb)) {
+		if (!skb_linearize(skb) && sk->sk_state != BT_CLOSED) {
 			s = rfcomm_recv_frame(s, skb);
 			if (!s)
 				break;