CVE-2024-26903

In the Linux kernel, the following vulnerability has been resolved:
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.