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// Copyright 2017 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//! Runs hardware devices in child processes.
use libc::pid_t;
use std::{self, fmt, io};
use std::os::unix::io::{AsRawFd, RawFd};
use std::os::unix::net::UnixDatagram;
use std::process;
use std::time::Duration;
use byteorder::{NativeEndian, ByteOrder};
use BusDevice;
use io_jail::{self, Minijail};
/// Errors for proxy devices.
#[derive(Debug)]
pub enum Error {
ForkingJail(io_jail::Error),
Io(io::Error),
}
pub type Result<T> = std::result::Result<T, Error>;
impl fmt::Display for Error {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
match self {
&Error::ForkingJail(_) => write!(f, "Failed to fork jail process"),
&Error::Io(ref e) => write!(f, "IO error configuring proxy device {}.", e),
}
}
}
const SOCKET_TIMEOUT_MS: u64 = 2000;
const MSG_SIZE: usize = 24;
enum Command {
Read = 0,
Write = 1,
Shutdown = 2,
}
fn child_proc(sock: UnixDatagram, device: &mut BusDevice) {
let mut running = true;
while running {
let mut buf = [0; MSG_SIZE];
match handle_eintr!(sock.recv(&mut buf)) {
Ok(c) if c != buf.len() => {
error!("child device process incorrect recv size: got {}, expected {}",
c,
buf.len());
break;
}
Err(e) => {
error!("child device process failed recv: {}", e);
break;
}
_ => {}
}
let cmd = NativeEndian::read_u32(&buf[0..]);
let len = NativeEndian::read_u32(&buf[4..]) as usize;
let offset = NativeEndian::read_u64(&buf[8..]);
let res = if cmd == Command::Read as u32 {
device.read(offset, &mut buf[16..16 + len]);
handle_eintr!(sock.send(&buf))
} else if cmd == Command::Write as u32 {
device.write(offset, &buf[16..16 + len]);
handle_eintr!(sock.send(&buf))
} else if cmd == Command::Shutdown as u32 {
running = false;
handle_eintr!(sock.send(&buf))
} else {
error!("child device process unknown command: {}", cmd);
break;
};
if let Err(e) = res {
error!("error: child device process failed send: {}", e);
break;
}
}
}
/// Wraps an inner `BusDevice` that is run inside a child process via fork.
///
/// Because forks are very unfriendly to destructors and all memory mappings and file descriptors
/// are inherited, this should be used as early as possible in the main process.
pub struct ProxyDevice {
sock: UnixDatagram,
pid: pid_t,
}
impl ProxyDevice {
/// Takes the given device and isolates it into another process via fork before returning.
///
/// The forked process will automatically be terminated when this is dropped, so be sure to keep
/// a reference.
///
/// # Arguments
/// * `device` - The device to isolate to another process.
/// * `keep_fds` - File descriptors that will be kept open in the child
pub fn new<D: BusDevice>(mut device: D, jail: &Minijail, mut keep_fds: Vec<RawFd>)
-> Result<ProxyDevice>
{
let (child_sock, parent_sock) = UnixDatagram::pair().map_err(Error::Io)?;
keep_fds.push(child_sock.as_raw_fd());
// Forking here is safe as long as the program is still single threaded.
let pid = unsafe {
match jail.fork(Some(&keep_fds)).map_err(Error::ForkingJail)? {
0 => {
child_proc(child_sock, &mut device);
// ! Never returns
process::exit(0);
},
p => p,
}
};
parent_sock
.set_write_timeout(Some(Duration::from_millis(SOCKET_TIMEOUT_MS)))
.map_err(Error::Io)?;
parent_sock
.set_read_timeout(Some(Duration::from_millis(SOCKET_TIMEOUT_MS)))
.map_err(Error::Io)?;
Ok(ProxyDevice {
sock: parent_sock,
pid: pid,
})
}
pub fn pid(&self) -> pid_t {
self.pid
}
fn send_cmd(&self, cmd: Command, offset: u64, len: u32, data: &[u8]) -> Result<()> {
let mut buf = [0; MSG_SIZE];
NativeEndian::write_u32(&mut buf[0..], cmd as u32);
NativeEndian::write_u32(&mut buf[4..], len);
NativeEndian::write_u64(&mut buf[8..], offset);
buf[16..16 + data.len()].clone_from_slice(data);
handle_eintr!(self.sock.send(&buf)).map(|_| ()).map_err(Error::Io)
}
fn recv_resp(&self, data: &mut [u8]) -> Result<()> {
let mut buf = [0; MSG_SIZE];
handle_eintr!(self.sock.recv(&mut buf)).map_err(Error::Io)?;
let len = data.len();
data.clone_from_slice(&buf[16..16 + len]);
Ok(())
}
fn wait(&self) -> Result<()> {
let mut buf = [0; MSG_SIZE];
handle_eintr!(self.sock.recv(&mut buf)).map(|_| ()).map_err(Error::Io)
}
}
impl BusDevice for ProxyDevice {
fn read(&mut self, offset: u64, data: &mut [u8]) {
let res = self.send_cmd(Command::Read, offset, data.len() as u32, &[])
.and_then(|_| self.recv_resp(data));
if let Err(e) = res {
error!("failed read from child device process: {}", e);
}
}
fn write(&mut self, offset: u64, data: &[u8]) {
let res = self.send_cmd(Command::Write, offset, data.len() as u32, data)
.and_then(|_| self.wait());
if let Err(e) = res {
error!("failed write to child device process: {}", e);
}
}
}
impl Drop for ProxyDevice {
fn drop(&mut self) {
let res = self.send_cmd(Command::Shutdown, 0, 0, &[]);
if let Err(e) = res {
error!("failed to shutdown child device process: {}", e);
}
}
}
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