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// Copyright 2024 The ChromiumOS Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
use std::fs::File;
use std::io::Error as IOError;
use std::io::ErrorKind;
use std::io::Write;
use std::sync::Arc;
use base::debug;
use base::error;
use base::warn;
use base::AsRawDescriptor;
use base::EventType;
use base::RawDescriptor;
use sync::Mutex;
use zerocopy::FromBytes;
use zerocopy::FromZeroes;
use crate::usb::backend::fido_backend::constants;
use crate::usb::backend::fido_backend::error::Error;
use crate::usb::backend::fido_backend::error::Result;
use crate::usb::backend::fido_backend::fido_guest::FidoGuestKey;
use crate::usb::backend::fido_backend::fido_transaction::TransactionManager;
use crate::usb::backend::fido_backend::hid_utils::verify_is_fido_device;
use crate::usb::backend::fido_backend::poll_thread::PollTimer;
use crate::utils::EventLoop;
#[derive(FromZeroes, FromBytes, Debug)]
#[repr(C)]
pub struct InitPacket {
cid: u32,
cmd: u8,
bcnth: u8,
bcntl: u8,
data: [u8; constants::PACKET_INIT_DATA_SIZE],
}
impl InitPacket {
pub fn extract_cid(bytes: [u8; constants::U2FHID_PACKET_SIZE]) -> Result<u32> {
// cid is the first 4 bytes so we don't need to worry about anything else in the bytes
// buffer, we can just read from prefix.
FromBytes::read_from_prefix(&bytes[..]).ok_or_else(|| Error::CannotExtractCidFromBytes)
}
fn is_valid(bytes: [u8; constants::U2FHID_PACKET_SIZE]) -> bool {
(bytes[4] & constants::PACKET_INIT_VALID_CMD) != 0
}
pub fn from_bytes(bytes: [u8; constants::U2FHID_PACKET_SIZE]) -> Result<InitPacket> {
if !InitPacket::is_valid(bytes) {
return Err(Error::InvalidInitPacket);
}
InitPacket::read_from(&bytes[..]).ok_or_else(|| Error::CannotConvertInitPacketFromBytes)
}
pub fn bcnt(&self) -> u16 {
(self.bcnth as u16) << 8 | (self.bcntl as u16)
}
}
/// A virtual representation of a FidoDevice emulated on the Host.
pub struct FidoDevice {
/// Guest representation of the virtual security key device
pub guest_key: Arc<Mutex<FidoGuestKey>>,
/// The `TransactionManager` which handles starting and stopping u2f transactions
pub transaction_manager: Arc<Mutex<TransactionManager>>,
/// Marks whether the current device is active in a transaction. If it is not active, the fd
/// polling event loop does not handle the device fd monitoring.
pub is_active: bool,
/// Marks whether the device has been lost. In case the FD stops being responsive we signal
/// that the device is lost and any further transaction will return a failure.
pub is_device_lost: bool,
/// Backend provider event loop to attach/detach the monitored fd.
event_loop: Arc<EventLoop>,
/// Timer to poll for active USB transfers
pub transfer_timer: PollTimer,
/// fd of the actual hidraw device
pub fd: Arc<Mutex<File>>,
}
impl AsRawDescriptor for FidoDevice {
fn as_raw_descriptor(&self) -> RawDescriptor {
self.fd.lock().as_raw_descriptor()
}
}
impl FidoDevice {
pub fn new(hidraw: File, event_loop: Arc<EventLoop>) -> Result<FidoDevice> {
verify_is_fido_device(&hidraw)?;
let timer = PollTimer::new(
"USB transfer timer".to_string(),
std::time::Duration::from_millis(constants::USB_POLL_RATE_MILLIS),
)?;
Ok(FidoDevice {
guest_key: Arc::new(Mutex::new(FidoGuestKey::new()?)),
transaction_manager: Arc::new(Mutex::new(TransactionManager::new()?)),
is_active: false,
is_device_lost: false,
event_loop,
transfer_timer: timer,
fd: Arc::new(Mutex::new(hidraw)),
})
}
/// Sets the device active state. If the device becomes active, it toggles polling on the file
/// descriptor for the host hid device. If the devices becomes inactive, it stops polling.
/// In case of error, it's not possible to recover so we just log the warning and continue.
pub fn set_active(&mut self, active: bool) {
if self.is_active && !active {
if let Err(e) = self.event_loop.pause_event_for_descriptor(self) {
error!("Could not deactivate polling of host device: {}", e);
}
} else if !self.is_active && active {
if let Err(e) = self
.event_loop
.resume_event_for_descriptor(self, EventType::Read)
{
error!(
"Could not resume polling of host device, transactions will be lost: {}",
e
);
}
}
self.is_active = active;
}
/// Starts a new transaction from a given init packet.
pub fn start_transaction(&mut self, packet: &InitPacket) -> Result<()> {
let nonce = if packet.cid == constants::BROADCAST_CID {
packet.data[..constants::NONCE_SIZE]
.try_into()
.map_err(|_| Error::InvalidNonceSize)?
} else {
constants::EMPTY_NONCE
};
// Start a transaction and the expiration timer if necessary
if self
.transaction_manager
.lock()
.start_transaction(packet.cid, nonce)
{
// Enable the timer that polls for transactions to expire
self.transaction_manager.lock().transaction_timer.arm()?;
}
// Transition the low level device to active for a response from the host
self.set_active(true);
Ok(())
}
/// Receives a low-level request from the host device. It means we read data from the actual
/// key on the host.
pub fn recv_from_host(&mut self, packet: [u8; constants::U2FHID_PACKET_SIZE]) -> Result<()> {
let cid = InitPacket::extract_cid(packet)?;
let transaction_opt = if cid == constants::BROADCAST_CID {
match InitPacket::from_bytes(packet) {
Ok(packet) => {
// This is a special case, in case of an error message we return to the
// latest broadcast transaction without nonce checking.
if packet.cmd == constants::U2FHID_ERROR_CMD {
self.transaction_manager.lock().get_transaction(cid)
// Otherwise we verify that the nonce matches the right transaction.
} else {
let nonce = packet.data[..constants::NONCE_SIZE]
.try_into()
.map_err(|_| Error::InvalidNonceSize)?;
self.transaction_manager
.lock()
.get_transaction_from_nonce(nonce)
}
}
_ => {
// Drop init transaction with bad init packet
return Ok(());
}
}
} else {
self.transaction_manager.lock().get_transaction(cid)
};
let transaction = match transaction_opt {
Some(t) => t,
None => {
debug!("Ignoring non-started transaction");
return Ok(());
}
};
match InitPacket::from_bytes(packet) {
Ok(packet) => {
if packet.cid == constants::BROADCAST_CID {
let nonce = &packet.data[..constants::NONCE_SIZE];
if transaction.nonce != nonce {
// In case of an error command we can let it through, otherwise we drop the
// response.
if packet.cmd != constants::U2FHID_ERROR_CMD {
warn!(
"u2f: received a broadcast transaction with mismatched nonce.\
Ignoring transaction."
);
return Ok(());
}
}
}
self.transaction_manager.lock().update_transaction(
cid,
packet.bcnt(),
constants::PACKET_INIT_DATA_SIZE as u16,
);
}
// It's not an init packet, it means it's a continuation packet
Err(Error::InvalidInitPacket) => {
self.transaction_manager.lock().update_transaction(
cid,
transaction.resp_bcnt,
transaction.resp_size + constants::PACKET_CONT_DATA_SIZE as u16,
);
}
Err(e) => {
error!(
"u2f: received an invalid transaction state: {:?}. Ignoring transaction.",
e
);
return Ok(());
}
}
// Fetch the transaction again to check if we are done processing it or if we should wait
// for more continuation packets.
let transaction = match self.transaction_manager.lock().get_transaction(cid) {
Some(t) => t,
None => {
error!(
"We lost a transaction on the way. This is a bug. (cid: {})",
cid
);
return Ok(());
}
};
// Check for the end of the transaction
if transaction.resp_size >= transaction.resp_bcnt {
if self
.transaction_manager
.lock()
.close_transaction(transaction.cid)
{
// Resets the device as inactive, since we're not waiting for more data to come
// from the host.
self.set_active(false);
}
}
let mut guest_key = self.guest_key.lock();
if guest_key.pending_in_packets.is_empty() {
// We start polling waiting to send the data back to the guest.
if let Err(e) = guest_key.timer.arm() {
error!(
"Unable to start U2F guest key timer. U2F packets may be lost. {}",
e
);
}
}
guest_key.pending_in_packets.push_back(packet);
Ok(())
}
/// Receives a request from the guest device to write into the actual device on the host.
pub fn recv_from_guest(
&mut self,
packet: [u8; constants::U2FHID_PACKET_SIZE],
) -> Result<usize> {
// The first byte in the host packet request is the HID report request ID as required by
// the Linux kernel. The real request data starts from the second byte, so we need to
// allocate one extra byte in our write buffer.
// See: https://docs.kernel.org/hid/hidraw.html#write
let mut host_packet = vec![0; constants::U2FHID_PACKET_SIZE + 1];
match InitPacket::from_bytes(packet) {
Ok(init_packet) => {
self.start_transaction(&init_packet)?;
}
Err(Error::InvalidInitPacket) => {
// It's not an init packet, so we don't start a transaction.
}
Err(e) => {
warn!("Received malformed or invalid u2f-hid init packet, request will be dropped");
return Err(e);
}
}
host_packet[1..].copy_from_slice(&packet);
let written = self
.fd
.lock()
.write(&host_packet)
.map_err(Error::WriteHidrawDevice)?;
if written != host_packet.len() {
return Err(Error::WriteHidrawDevice(IOError::new(
ErrorKind::Other,
"Wrote too few bytes to hidraw device.",
)));
}
// we subtract 1 because we added 1 extra byte to the host packet
Ok(host_packet.len() - 1)
}
}