utun.hpp

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//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012- OpenVPN Inc.
//
//    SPDX-License-Identifier: MPL-2.0 OR AGPL-3.0-only WITH openvpn3-openssl-exception
//
//
 
// Thanks to Jonathan Levin for proof-of-concept utun code for Mac OS X.
// http://newosxbook.com/src.jl?tree=listings&file=17-15-utun.c
 
// Open a utun device on Mac OS X.
 
#ifndef OPENVPN_TUN_MAC_UTUN_H
#define OPENVPN_TUN_MAC_UTUN_H
 
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/sys_domain.h>
#include <sys/kern_control.h>
#include <net/if_utun.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>
#include <stdlib.h>
 
#include <string>
 
#include <openvpn/common/size.hpp>
#include <openvpn/common/exception.hpp>
#include <openvpn/common/to_string.hpp>
#include <openvpn/common/scoped_fd.hpp>
 
namespace openvpn::TunMac::UTun {
OPENVPN_EXCEPTION(utun_error);
 
// Open specific utun device unit and return fd.
// If the unit number is already in use, return -1.
// Throw exceptions for all other errors.
// Return the iface name in name.
inline int utun_open(std::string &name, const int unit)
{
    struct sockaddr_ctl sc;
    struct ctl_info ctlInfo;
 
    memset(&ctlInfo, 0, sizeof(ctlInfo));
    if (strlcpy(ctlInfo.ctl_name, UTUN_CONTROL_NAME, sizeof(ctlInfo.ctl_name))
        >= sizeof(ctlInfo.ctl_name))
        throw utun_error("UTUN_CONTROL_NAME too long");
 
    ScopedFD fd(socket(PF_SYSTEM, SOCK_DGRAM, SYSPROTO_CONTROL));
    if (!fd.defined())
        throw utun_error("socket(SYSPROTO_CONTROL)");
 
    if (ioctl(fd(), CTLIOCGINFO, &ctlInfo) == -1)
        throw utun_error("ioctl(CTLIOCGINFO)");
 
    sc.sc_id = ctlInfo.ctl_id;
    sc.sc_len = sizeof(sc);
    sc.sc_family = AF_SYSTEM;
    sc.ss_sysaddr = AF_SYS_CONTROL;
    sc.sc_unit = unit + 1;
    std::memset(sc.sc_reserved, 0, sizeof(sc.sc_reserved));
 
    // If the connect is successful, a utunX device will be created, where X
    // is our unit number - 1.
    if (connect(fd(), (struct sockaddr *)&sc, sizeof(sc)) == -1)
        return -1;
 
    // Get iface name of newly created utun dev.
    char utunname[20];
    socklen_t utunname_len = sizeof(utunname);
    if (getsockopt(fd(), SYSPROTO_CONTROL, UTUN_OPT_IFNAME, utunname, &utunname_len))
        throw utun_error("getsockopt(SYSPROTO_CONTROL)");
    name = utunname;
 
    return fd.release();
}
 
// Try to open an available utun device unit.
// Return the iface name in name.
inline int utun_open(std::string &name)
{
    for (int unit = 0; unit < 256; ++unit)
    {
        const int fd = utun_open(name, unit);
        if (fd >= 0)
            return fd;
    }
    throw utun_error("cannot open available utun device");
}
} // namespace openvpn::TunMac::UTun
 
#endif