tap-fd-net-device-helper.cc

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/*
 * Copyright (c) 2012 INRIA, 2012 University of Washington
 *
 * SPDX-License-Identifier: GPL-2.0-only
 */
 
#include "tap-fd-net-device-helper.h"
 
#include "encode-decode.h"
 
#include "ns3/abort.h"
#include "ns3/config.h"
#include "ns3/fd-net-device.h"
#include "ns3/log.h"
#include "ns3/names.h"
#include "ns3/object-factory.h"
#include "ns3/packet.h"
#include "ns3/simulator.h"
#include "ns3/trace-helper.h"
 
#include <arpa/inet.h>
#include <errno.h>
#include <iomanip>
#include <iostream>
#include <limits>
#include <memory>
#include <net/ethernet.h>
#include <net/if.h>
#include <netinet/in.h>
#include <netpacket/packet.h>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/un.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>
 
namespace ns3
{
 
NS_LOG_COMPONENT_DEFINE("TapFdNetDeviceHelper");
 
#define TAP_MAGIC 95549
 
TapFdNetDeviceHelper::TapFdNetDeviceHelper()
{
    m_deviceName = "";
    m_modePi = false;
    m_tapIp4 = Ipv4Address::GetZero();
    m_tapMask4 = Ipv4Mask::GetZero();
    m_tapIp6 = Ipv6Address::GetZero();
    m_tapPrefix6 = 64;
    m_tapMac = Mac48Address::Allocate();
}
 
void
TapFdNetDeviceHelper::SetModePi(bool modePi)
{
    m_modePi = modePi;
}
 
void
TapFdNetDeviceHelper::SetTapIpv4Address(Ipv4Address address)
{
    m_tapIp4 = address;
}
 
void
TapFdNetDeviceHelper::SetTapIpv4Mask(Ipv4Mask mask)
{
    m_tapMask4 = mask;
}
 
void
TapFdNetDeviceHelper::SetTapIpv6Address(Ipv6Address address)
{
    m_tapIp6 = address;
}
 
void
TapFdNetDeviceHelper::SetTapIpv6Prefix(int prefix)
{
    m_tapPrefix6 = prefix;
}
 
void
TapFdNetDeviceHelper::SetTapMacAddress(Mac48Address mac)
{
    m_tapMac = mac;
}
 
Ptr<NetDevice>
TapFdNetDeviceHelper::InstallPriv(Ptr<Node> node) const
{
    Ptr<NetDevice> d = FdNetDeviceHelper::InstallPriv(node);
    Ptr<FdNetDevice> device = d->GetObject<FdNetDevice>();
 
    //
    // We need to explicitly set the encapsulation mode for the traffic
    // traversing the TAP device, so the FdNetDevice is able to know
    // how to treat the traffic in a way that in compatible with the
    // TAP device.
    //
    if (m_modePi)
    {
        device->SetEncapsulationMode(FdNetDevice::DIXPI);
    }
 
    SetFileDescriptor(device);
    return device;
}
 
void
TapFdNetDeviceHelper::SetFileDescriptor(Ptr<FdNetDevice> device) const
{
    NS_LOG_LOGIC("Creating TAP device");
 
    //
    // Call out to a separate process running as suid root in order to create a
    // TAP device.  We do this to avoid having the entire simulation running as root.
    //
    int fd = CreateFileDescriptor();
    device->SetFileDescriptor(fd);
}
 
int
TapFdNetDeviceHelper::CreateFileDescriptor() const
{
    NS_LOG_FUNCTION(this);
 
    //
    // We're going to fork and exec that program soon, but first we need to have
    // a socket to talk to it with.  So we create a local interprocess (Unix)
    // socket for that purpose.
    //
    int sock = socket(PF_UNIX, SOCK_DGRAM, 0);
    NS_ABORT_MSG_IF(
        sock == -1,
        "TapFdNetDeviceHelper::CreateFileDescriptor(): Unix socket creation error, errno = "
            << strerror(errno));
 
    //
    // Bind to that socket and let the kernel allocate an endpoint
    //
    struct sockaddr_un un;
    memset(&un, 0, sizeof(un));
    un.sun_family = AF_UNIX;
    int status = bind(sock, (struct sockaddr*)&un, sizeof(sa_family_t));
    NS_ABORT_MSG_IF(status == -1,
                    "TapFdNetDeviceHelper::CreateFileDescriptor(): Could not bind(): errno = "
                        << strerror(errno));
    NS_LOG_INFO("Created Unix socket");
    NS_LOG_INFO("sun_family = " << un.sun_family);
    NS_LOG_INFO("sun_path = " << un.sun_path);
 
    //
    // We have a socket here, but we want to get it there -- to the program we're
    // going to exec.  What we'll do is to do a getsockname and then encode the
    // resulting address information as a string, and then send the string to the
    // program as an argument.  So we need to get the sock name.
    //
    socklen_t len = sizeof(un);
    status = getsockname(sock, (struct sockaddr*)&un, &len);
    NS_ABORT_MSG_IF(
        status == -1,
        "TapFdNetDeviceHelper::CreateFileDescriptor(): Could not getsockname(): errno = "
            << strerror(errno));
 
    //
    // Now encode that socket name (family and path) as a string of hex digits
    //
    std::string path = BufferToString((uint8_t*)&un, len);
    NS_LOG_INFO("Encoded Unix socket as \"" << path << "\"");
 
    //
    // Fork and exec the process to create our socket.  If we're us (the parent)
    // we wait for the child (the creator) to complete and read the socket it
    // created and passed back using the ancillary data mechanism.
    //
    pid_t pid = ::fork();
    if (pid == 0)
    {
        NS_LOG_DEBUG("Child process");
 
        //
        // build a command line argument from the encoded endpoint string that
        // the socket creation process will use to figure out how to respond to
        // the (now) parent process.  We're going to have to give this program
        // quite a bit of information.
        //
        // -d<device-name> The name of the tap device we want to create;
        // -m<MAC-address> The MAC-48 address to assign to the new tap device;
        // -i<IPv4-address> The IP v4 address to assign to the new tap device;
        // -I<IPv6-address> The IP v6 address to assign to the new tap device;
        // -n<network-IPv4-mask> The network IPv4 mask to assign to the new tap device;
        // -N<network-IPv6-mask> The network IPv6 mask to assign to the new tap device;
        // -t Set the IFF_TAP flag
        // -h Set the IFF_NO_PI flag
        // -p<path> the path to the unix socket described above.
        //
        // Example tap-creator -dnewdev -i1.2.3.1 -m08:00:2e:00:01:23 -n255.255.255.0 -t -h -pblah
        //
 
        //
        // The device-name is something we may want the system to make up in
        // every case.  We also rely on it being configured via an Attribute
        // through the helper.  By default, it is set to the empty string
        // which tells the system to make up a device name such as "tap123".
        //
        std::ostringstream ossDeviceName;
        if (!m_deviceName.empty())
        {
            ossDeviceName << "-d" << m_deviceName;
        }
 
        std::ostringstream ossMac;
        ossMac << "-m" << m_tapMac;
 
        std::ostringstream ossIp4;
        if (m_tapIp4 != Ipv4Address::GetZero())
        {
            ossIp4 << "-i" << m_tapIp4;
        }
 
        std::ostringstream ossIp6;
        if (m_tapIp6 != Ipv6Address::GetZero())
        {
            ossIp6 << "-I" << m_tapIp6;
        }
 
        std::ostringstream ossNetmask4;
        if (m_tapMask4 != Ipv4Mask::GetZero())
        {
            ossNetmask4 << "-n" << m_tapMask4;
        }
 
        std::ostringstream ossPrefix6;
        ossPrefix6 << "-P" << m_tapPrefix6;
 
        std::ostringstream ossMode;
        ossMode << "-t";
 
        std::ostringstream ossPI;
        if (m_modePi)
        {
            ossPI << "-h";
        }
 
        std::ostringstream ossPath;
        ossPath << "-p" << path;
 
        //
        // Execute the socket creation process image.
        //
        status = ::execlp(TAP_DEV_CREATOR,
                          TAP_DEV_CREATOR,             // argv[0] (filename)
                          ossDeviceName.str().c_str(), // argv[1] (-d<device name>)
                          ossMac.str().c_str(),        // argv[2] (-m<MAC address>
                          ossIp4.str().c_str(),        // argv[3] (-i<IP v4 address>)
                          ossIp6.str().c_str(),        // argv[4] (-I<IP v6 address>)
                          ossNetmask4.str().c_str(),   // argv[5] (-n<IP v4 net mask>)
                          ossPrefix6.str().c_str(),    // argv[6] (-P<IP v6 prefix>)
                          ossMode.str().c_str(),       // argv[7] (-t <tap>)
                          ossPI.str().c_str(),         // argv[8] (-h <pi>)
                          ossPath.str().c_str(),       // argv[9] (-p<path>)
                          (char*)nullptr);
 
        //
        // If the execlp successfully completes, it never returns.  If it returns it failed or the
        // OS is broken.  In either case, we bail.
        //
        NS_FATAL_ERROR("TapFdNetDeviceHelper::CreateFileDescriptor(): Back from execlp(), status = "
                       << status << ", errno = " << ::strerror(errno));
    }
    else
    {
        NS_LOG_DEBUG("Parent process");
        //
        // We're the process running the emu net device.  We need to wait for the
        // socket creator process to finish its job.
        //
        int st;
        pid_t waited = waitpid(pid, &st, 0);
        NS_ABORT_MSG_IF(waited == -1,
                        "TapFdNetDeviceHelper::CreateFileDescriptor(): waitpid() fails, errno = "
                            << strerror(errno));
        NS_ASSERT_MSG(pid == waited, "TapFdNetDeviceHelper::CreateFileDescriptor(): pid mismatch");
 
        //
        // Check to see if the socket creator exited normally and then take a
        // look at the exit code.  If it bailed, so should we.  If it didn't
        // even exit normally, we bail too.
        //
        if (WIFEXITED(st))
        {
            int exitStatus = WEXITSTATUS(st);
            NS_ABORT_MSG_IF(exitStatus != 0,
                            "TapFdNetDeviceHelper::CreateFileDescriptor(): socket creator exited "
                            "normally with status "
                                << exitStatus);
        }
        else
        {
            NS_FATAL_ERROR(
                "TapFdNetDeviceHelper::CreateFileDescriptor(): socket creator exited abnormally");
        }
 
        //
        // At this point, the socket creator has run successfully and should
        // have created our tap device, initialized it with the information we
        // passed and sent it back to the socket address we provided.  A socket
        // (fd) we can use to talk to this tap device should be waiting on the
        // Unix socket we set up to receive information back from the creator
        // program.  We've got to do a bunch of grunt work to get at it, though.
        //
        // The struct iovec below is part of a scatter-gather list.  It describes a
        // buffer.  In this case, it describes a buffer (an integer) that will
        // get the data that comes back from the socket creator process.  It will
        // be a magic number that we use as a consistency/sanity check.
        //
        struct iovec iov;
        uint32_t magic;
        iov.iov_base = &magic;
        iov.iov_len = sizeof(magic);
 
        //
        // The CMSG macros you'll see below are used to create and access control
        // messages (which is another name for ancillary data).  The ancillary
        // data is made up of pairs of struct cmsghdr structures and associated
        // data arrays.
        //
        // First, we're going to allocate a buffer on the stack to receive our
        // data array (that contains the socket).  Sometimes you'll see this called
        // an "ancillary element" but the msghdr uses the control message termimology
        // so we call it "control."
        //
        constexpr size_t msg_size = sizeof(int);
        char control[CMSG_SPACE(msg_size)];
 
        //
        // There is a msghdr that is used to minimize the number of parameters
        // passed to recvmsg (which we will use to receive our ancillary data).
        // This structure uses terminology corresponding to control messages, so
        // you'll see msg_control, which is the pointer to the ancillary data and
        // controllen which is the size of the ancillary data array.
        //
        // So, initialize the message header that describes the ancillary/control
        // data we expect to receive and point it to buffer.
        //
        struct msghdr msg;
        msg.msg_name = nullptr;
        msg.msg_namelen = 0;
        msg.msg_iov = &iov;
        msg.msg_iovlen = 1;
        msg.msg_control = control;
        msg.msg_controllen = sizeof(control);
        msg.msg_flags = 0;
 
        //
        // Now we can actually receive the interesting bits from the tap
        // creator process.  Lots of pain to get four bytes.
        //
        ssize_t bytesRead = recvmsg(sock, &msg, 0);
        NS_ABORT_MSG_IF(
            bytesRead != sizeof(int),
            "TapFdNetDeviceHelper::CreateFileDescriptor(): Wrong byte count from socket creator");
 
        //
        // There may be a number of message headers/ancillary data arrays coming in.
        // Let's look for the one with a type SCM_RIGHTS which indicates it's the
        // one we're interested in.
        //
        struct cmsghdr* cmsg;
        for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != nullptr; cmsg = CMSG_NXTHDR(&msg, cmsg))
        {
            if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_RIGHTS)
            {
                //
                // This is the type of message we want.  Check to see if the magic
                // number is correct and then pull out the socket we care about if
                // it matches
                //
                if (magic == TAP_MAGIC)
                {
                    NS_LOG_INFO("Got SCM_RIGHTS with correct magic " << magic);
                    int* rawSocket = (int*)CMSG_DATA(cmsg);
                    NS_LOG_INFO("Got the socket from the socket creator = " << *rawSocket);
                    return *rawSocket;
                }
                else
                {
                    NS_LOG_INFO("Got SCM_RIGHTS, but with bad magic " << magic);
                }
            }
        }
        NS_FATAL_ERROR("Did not get the raw socket from the socket creator");
    }
    NS_FATAL_ERROR("Should be unreachable");
    return 0; // Silence compiler warning about lack of return value
}
 
} // namespace ns3