path: root/net_util/src/lib.rs

// 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.

extern crate libc;
extern crate net_sys;
extern crate sys_util;

use std::fmt::Debug;
use std::fs::File;
use std::io::{Read, Write, Result as IoResult, Error as IoError, ErrorKind};
use std::mem;
use std::net;
use std::os::raw::*;
use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};

use sys_util::Pollable;
use sys_util::{ioctl_with_val, ioctl_with_ref, ioctl_with_mut_ref};

#[derive(Debug)]
pub enum Error {
    /// Failed to create a socket.
    CreateSocket(IoError),
    /// Couldn't open /dev/net/tun.
    OpenTun(IoError),
    /// Unable to create tap interface.
    CreateTap(IoError),
    /// ioctl failed.
    IoctlError(IoError),
}
pub type Result<T> = std::result::Result<T, Error>;

/// Create a sockaddr_in from an IPv4 address, and expose it as
/// an opaque sockaddr suitable for usage by socket ioctls.
fn create_sockaddr(ip_addr: net::Ipv4Addr) -> net_sys::sockaddr {
    // IPv4 addresses big-endian (network order), but Ipv4Addr will give us
    // a view of those bytes directly so we can avoid any endian trickiness.
    let addr_in = net_sys::sockaddr_in {
        sin_family: net_sys::AF_INET as u16,
        sin_port: 0,
        sin_addr: unsafe { mem::transmute(ip_addr.octets()) },
        __pad: [0; 8usize],
    };

    unsafe { mem::transmute(addr_in) }
}

fn create_socket() -> Result<net::UdpSocket> {
    // This is safe since we check the return value.
    let sock = unsafe { libc::socket(libc::AF_INET, libc::SOCK_DGRAM, 0) };
    if sock < 0 {
        return Err(Error::CreateSocket(IoError::last_os_error()));
    }

    // This is safe; nothing else will use or hold onto the raw sock fd.
    Ok(unsafe { net::UdpSocket::from_raw_fd(sock) })
}

/// Handle for a network tap interface.
///
/// For now, this simply wraps the file descriptor for the tap device so methods
/// can run ioctls on the interface. The tap interface fd will be closed when
/// Tap goes out of scope, and the kernel will clean up the interface
/// automatically.
#[derive(Debug)]
pub struct Tap {
    tap_file: File,
    if_name: [u8; 16usize],
}

impl Tap {
    /// Create a new tap interface.
    pub fn new() -> Result<Tap> {
        // Open calls are safe because we give a constant nul-terminated
        // string and verify the result.
        let fd = unsafe {
            libc::open(b"/dev/net/tun\0".as_ptr() as *const c_char,
                       libc::O_RDWR | libc::O_NONBLOCK | libc::O_CLOEXEC)
        };
        if fd < 0 {
            return Err(Error::OpenTun(IoError::last_os_error()));
        }

        // We just checked that the fd is valid.
        let tuntap = unsafe { File::from_raw_fd(fd) };

        const TUNTAP_DEV_FORMAT: &'static [u8; 8usize] = b"vmtap%d\0";

        // This is pretty messy because of the unions used by ifreq. Since we
        // don't call as_mut on the same union field more than once, this block
        // is safe.
        let mut ifreq: net_sys::ifreq = Default::default();
        unsafe {
            let ifrn_name = ifreq.ifr_ifrn.ifrn_name.as_mut();
            let ifru_flags = ifreq.ifr_ifru.ifru_flags.as_mut();
            let mut name_slice = &mut ifrn_name[..TUNTAP_DEV_FORMAT.len()];
            name_slice.copy_from_slice(TUNTAP_DEV_FORMAT);
            *ifru_flags = (net_sys::IFF_TAP | net_sys::IFF_NO_PI | net_sys::IFF_VNET_HDR) as
                          c_short;
        }

        // ioctl is safe since we call it with a valid tap fd and check the return
        // value.
        let ret = unsafe { ioctl_with_mut_ref(&tuntap, net_sys::TUNSETIFF(), &mut ifreq) };

        if ret < 0 {
            let error = IoError::last_os_error();

            // In a non-root, test environment, we won't have permission to call this; allow
            if !(cfg!(test) && error.kind() == ErrorKind::PermissionDenied) {
                return Err(Error::CreateTap(error));
            }
        }

        // Safe since only the name is accessed, and it's cloned out.
        Ok(Tap {
               tap_file: tuntap,
               if_name: unsafe { ifreq.ifr_ifrn.ifrn_name.as_ref().clone() },
           })
    }

    /// Set the host-side IP address for the tap interface.
    pub fn set_ip_addr(&self, ip_addr: net::Ipv4Addr) -> Result<()> {
        let sock = create_socket()?;
        let addr = create_sockaddr(ip_addr);

        let mut ifreq = self.get_ifreq();

        // We only access one field of the ifru union, hence this is safe.
        unsafe {
            let ifru_addr = ifreq.ifr_ifru.ifru_addr.as_mut();
            *ifru_addr = addr;
        }

        // ioctl is safe. Called with a valid sock fd, and we check the return.
        let ret =
            unsafe { ioctl_with_ref(&sock, net_sys::sockios::SIOCSIFADDR as c_ulong, &ifreq) };
        if ret < 0 {
            return Err(Error::IoctlError(IoError::last_os_error()));
        }

        Ok(())
    }

    /// Set the netmask for the subnet that the tap interface will exist on.
    pub fn set_netmask(&self, netmask: net::Ipv4Addr) -> Result<()> {
        let sock = create_socket()?;
        let addr = create_sockaddr(netmask);

        let mut ifreq = self.get_ifreq();

        // We only access one field of the ifru union, hence this is safe.
        unsafe {
            let ifru_addr = ifreq.ifr_ifru.ifru_addr.as_mut();
            *ifru_addr = addr;
        }

        // ioctl is safe. Called with a valid sock fd, and we check the return.
        let ret =
            unsafe { ioctl_with_ref(&sock, net_sys::sockios::SIOCSIFNETMASK as c_ulong, &ifreq) };
        if ret < 0 {
            return Err(Error::IoctlError(IoError::last_os_error()));
        }

        Ok(())
    }

    /// Set the offload flags for the tap interface.
    pub fn set_offload(&self, flags: c_uint) -> Result<()> {
        // ioctl is safe. Called with a valid tap fd, and we check the return.
        let ret =
            unsafe { ioctl_with_val(&self.tap_file, net_sys::TUNSETOFFLOAD(), flags as c_ulong) };
        if ret < 0 {
            return Err(Error::IoctlError(IoError::last_os_error()));
        }

        Ok(())
    }

    /// Enable the tap interface.
    pub fn enable(&self) -> Result<()> {
        let sock = create_socket()?;

        let mut ifreq = self.get_ifreq();

        // We only access one field of the ifru union, hence this is safe.
        unsafe {
            let ifru_flags = ifreq.ifr_ifru.ifru_flags.as_mut();
            *ifru_flags = (net_sys::net_device_flags_IFF_UP |
                           net_sys::net_device_flags_IFF_RUNNING) as i16;
        }

        // ioctl is safe. Called with a valid sock fd, and we check the return.
        let ret =
            unsafe { ioctl_with_ref(&sock, net_sys::sockios::SIOCSIFFLAGS as c_ulong, &ifreq) };
        if ret < 0 {
            return Err(Error::IoctlError(IoError::last_os_error()));
        }

        Ok(())
    }

    /// Set the size of the vnet hdr.
    pub fn set_vnet_hdr_size(&self, size: c_int) -> Result<()> {
        // ioctl is safe. Called with a valid tap fd, and we check the return.
        let ret = unsafe { ioctl_with_ref(&self.tap_file, net_sys::TUNSETVNETHDRSZ(), &size) };
        if ret < 0 {
            return Err(Error::IoctlError(IoError::last_os_error()));
        }

        Ok(())
    }

    fn get_ifreq(&self) -> net_sys::ifreq {
        let mut ifreq: net_sys::ifreq = Default::default();

        // This sets the name of the interface, which is the only entry
        // in a single-field union.
        unsafe {
            let ifrn_name = ifreq.ifr_ifrn.ifrn_name.as_mut();
            ifrn_name.clone_from_slice(&self.if_name);
        }

        ifreq
    }
}

impl Read for Tap {
    fn read(&mut self, buf: &mut [u8]) -> IoResult<usize> {
        self.tap_file.read(buf)
    }
}

impl Write for Tap {
    fn write(&mut self, buf: &[u8]) -> IoResult<usize> {
        self.tap_file.write(&buf)
    }

    fn flush(&mut self) -> IoResult<()> {
        Ok(())
    }
}

impl AsRawFd for Tap {
    fn as_raw_fd(&self) -> RawFd {
        self.tap_file.as_raw_fd()
    }
}

// Safe since the tap fd's lifetime lasts as long as this trait object, and the
// tap fd is pollable.
unsafe impl Pollable for Tap {
    fn pollable_fd(&self) -> RawFd {
        self.tap_file.as_raw_fd()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn tap_create() {
        Tap::new().unwrap();
    }

    #[test]
    fn tap_configure() {
        let tap = Tap::new().unwrap();
        let ip_addr: net::Ipv4Addr = "100.115.92.5".parse().unwrap();
        let netmask: net::Ipv4Addr = "255.255.255.252".parse().unwrap();

        let ret = tap.set_ip_addr(ip_addr);
        assert_ok_or_perm_denied(ret);
        let ret = tap.set_netmask(netmask);
        assert_ok_or_perm_denied(ret);
    }

    /// This test will only work if the test is run with root permissions and, unlike other tests
    /// in this file, do not return PermissionDenied. They fail because the TAP FD is not
    /// initialized (as opposed to permission denial). Run this with "cargo test -- --ignored".
    #[test]
    #[ignore]
    fn root_only_tests() {
        // This line will fail to provide an initialized FD if the test is not run as root.
        let tap = Tap::new().unwrap();
        tap.set_vnet_hdr_size(16).unwrap();
        tap.set_offload(0).unwrap();
    }

    #[test]
    fn tap_enable() {
        let tap = Tap::new().unwrap();

        let ret = tap.enable();
        assert_ok_or_perm_denied(ret);
    }

    #[test]
    fn tap_get_ifreq() {
        let tap = Tap::new().unwrap();
        let ret = tap.get_ifreq();
        assert_eq!("__BindgenUnionField", format!("{:?}", ret.ifr_ifrn.ifrn_name));
    }

    fn assert_ok_or_perm_denied<T>(res: Result<T>) {
        match res {
            // We won't have permission in test environments; allow that
            Ok(_t) => {},
            Err(Error::IoctlError(ref ioe)) if ioe.kind() == ErrorKind::PermissionDenied => {},
            Err(e) => panic!("Unexpected Error:\n{:?}", e),
        }
    }
}