In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: rfcomm: Fix null-ptr-deref in rfcommchecksecurity
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:
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.
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.
After receiving the Encryption Key Size Response at the time described
in point 2, the host still called the rfcommchecksecurity 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 BTCLOSED before calling
rfcommrecvframe in rfcommprocess_rx.