Bluetooth: MGMT: validate LTK enc_size on load

Load Long Term Keys stores the user-provided enc_size and later uses
it to size fixed-size stack operations when replying to LE LTK
requests. An enc_size larger than the 16-byte key buffer can therefore
overflow the reply stack buffer.

Reject oversized enc_size values while validating the management LTK
record so invalid keys never reach the stored key state.

Fixes: 346af67 ("Bluetooth: Add MGMT handlers for dealing with SMP LTK's")
Reported-by: Keenan Dong <keenanat2000@gmail.com>
Signed-off-by: Keenan Dong <keenanat2000@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

Author: Niebelungen-D

net/bluetooth/mgmt.c

@@ -7248,6 +7248,9 @@ static bool ltk_is_valid(struct mgmt_ltk_info *key)
 	if (key->initiator != 0x00 && key->initiator != 0x01)
 		return false;
 
+	if (key->enc_size > sizeof(key->val))
+		return false;
+
 	switch (key->addr.type) {
 	case BDADDR_LE_PUBLIC:
 		return true;