tor/src/lib/net/socketpair.c

/* Copyright (c) 2003-2004, Roger Dingledine
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
 * Copyright (c) 2007-2018, The Tor Project, Inc. */

#include "lib/net/socketpair.h"
#include "lib/net/inaddr_st.h"
#include "lib/arch/bytes.h"

#include <errno.h>
#include <string.h>

#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_NETINET_IN_H
#include <netinet/in.h>
#endif

#ifdef _WIN32
#include <winsock2.h>
#include <windows.h>
#define socket_errno() (WSAGetLastError())
#define SOCKET_EPROTONOSUPPORT WSAEPROTONOSUPPORT
#else
#define closesocket(x) close(x)
#define socket_errno() (errno)
#define SOCKET_EPROTONOSUPPORT EPROTONOSUPPORT
#endif

#ifdef NEED_ERSATZ_SOCKETPAIR

// Avoid warning about call to memcmp.
#define raw_memcmp memcmp

static tor_socket_t
get_local_listener(int family, int type)
{
  struct sockaddr_in sin;
  struct sockaddr_in6 sin6;
  struct sockaddr *sa;
  int len;

  memset(&sin, 0, sizeof(sin));
  memset(&sin6, 0, sizeof(sin6));

  tor_socket_t sock = TOR_INVALID_SOCKET;
  sock = socket(family, type, 0);
  if (!SOCKET_OK(sock)) {
    return TOR_INVALID_SOCKET;
  }

  if (family == AF_INET) {
    sa = (struct sockaddr *) &sin;
    sin.sin_family = AF_INET;
    sin.sin_addr.s_addr = tor_htonl(0x7f000001);
    len = sizeof(sin);
  } else {
    sa = (struct sockaddr *) &sin6;
    sin6.sin6_family = AF_INET;
    sin6.sin6_addr.s6_addr[15] = 1;
    len = sizeof(sin6);
  }

  if (bind(sock, sa, len) == -1)
    goto err;
  if (listen(sock, 1) == -1)
    goto err;

  return sock;
 err:
  closesocket(sock);
  return TOR_INVALID_SOCKET;
}

static int
sockaddr_eq(struct sockaddr *sa1, struct sockaddr *sa2)
{
  if (sa1->sa_family != sa2->sa_family)
    return 0;

  if (sa1->sa_family == AF_INET6) {
    struct sockaddr_in6 *sin6_1 = (struct sockaddr_in6 *) sa1;
    struct sockaddr_in6 *sin6_2 = (struct sockaddr_in6 *) sa2;
    return sin6_1->sin6_port == sin6_2->sin6_port &&
      0==raw_memcmp(sin6_1->sin6_addr.s6_addr, sin6_2->sin6_addr.s6_addr, 16);
  } else if (sa1->sa_family == AF_INET) {
    struct sockaddr_in *sin_1 = (struct sockaddr_in *) sa1;
    struct sockaddr_in *sin_2 = (struct sockaddr_in *) sa2;
    return sin_1->sin_port == sin_2->sin_port &&
      sin_1->sin_addr.s_addr == sin_2->sin_addr.s_addr;
  } else {
    return 0;
  }
}

/**
 * Helper used to implement socketpair on systems that lack it, by
 * making a direct connection to localhost.
 */
int
tor_ersatz_socketpair(int family, int type, int protocol, tor_socket_t fd[2])
{
    /* This socketpair does not work when localhost is down. So
     * it's really not the same thing at all. But it's close enough
     * for now, and really, when localhost is down sometimes, we
     * have other problems too.
     */
    tor_socket_t listener = TOR_INVALID_SOCKET;
    tor_socket_t connector = TOR_INVALID_SOCKET;
    tor_socket_t acceptor = TOR_INVALID_SOCKET;
    struct sockaddr_storage accepted_addr_ss;
    struct sockaddr_storage connect_addr_ss;
    struct sockaddr *connect_addr = (struct sockaddr *) &connect_addr_ss;
    struct sockaddr *accepted_addr = (struct sockaddr *) &accepted_addr_ss;
    socklen_t size;
    int saved_errno = -1;
    int ersatz_domain = AF_INET;
    socklen_t addrlen = sizeof(struct sockaddr_in);

    memset(&accepted_addr_ss, 0, sizeof(accepted_addr_ss));
    memset(&connect_addr_ss, 0, sizeof(connect_addr_ss));

    if (protocol
#ifdef AF_UNIX
        || family != AF_UNIX
#endif
        ) {
#ifdef _WIN32
      return -WSAEAFNOSUPPORT;
#else
      return -EAFNOSUPPORT;
#endif
    }
    if (!fd) {
      return -EINVAL;
    }

    listener = get_local_listener(ersatz_domain, type);
    if (!SOCKET_OK(listener)) {
      int first_errno = socket_errno();
      if (first_errno == SOCKET_EPROTONOSUPPORT) {
        /* Assume we're on an IPv6-only system */
        ersatz_domain = AF_INET6;
        addrlen = sizeof(struct sockaddr_in6);
        listener = get_local_listener(ersatz_domain, type);
      }
      if (!SOCKET_OK(listener)) {
        /* Keep the previous behaviour, which was to return the IPv4 error.
         * (This may be less informative on IPv6-only systems.)
         * XX/teor - is there a better way to decide which errno to return?
         * (I doubt we care much either way, once there is an error.)
         */
        return -first_errno;
      }
    }

    connector = socket(ersatz_domain, type, 0);
    if (!SOCKET_OK(connector))
      goto tidy_up_and_fail;
    /* We want to find out the port number to connect to.  */
    size = sizeof(connect_addr_ss);
    if (getsockname(listener, connect_addr, &size) == -1)
      goto tidy_up_and_fail;
    if (size != addrlen)
      goto abort_tidy_up_and_fail;
    if (connect(connector, connect_addr, size) == -1)
      goto tidy_up_and_fail;

    size = sizeof(accepted_addr_ss);
    acceptor = accept(listener, accepted_addr, &size);
    if (!SOCKET_OK(acceptor))
      goto tidy_up_and_fail;
    if (size != addrlen)
      goto abort_tidy_up_and_fail;
    /* Now check we are talking to ourself by matching port and host on the
       two sockets.  */
    if (getsockname(connector, connect_addr, &size) == -1)
      goto tidy_up_and_fail;
    /* Set *_tor_addr and *_port to the address and port that was used */
    if (!sockaddr_eq(accepted_addr, connect_addr))
      goto abort_tidy_up_and_fail;
    closesocket(listener);
    fd[0] = connector;
    fd[1] = acceptor;
    return 0;

  abort_tidy_up_and_fail:
#ifdef _WIN32
    saved_errno = WSAECONNABORTED;
#else
    saved_errno = ECONNABORTED; /* I hope this is portable and appropriate.  */
#endif
  tidy_up_and_fail:
    if (saved_errno < 0)
      saved_errno = errno;
    if (SOCKET_OK(listener))
      closesocket(listener);
    if (SOCKET_OK(connector))
      closesocket(connector);
    if (SOCKET_OK(acceptor))
      closesocket(acceptor);
    return -saved_errno;
}

#endif /* defined(NEED_ERSATZ_SOCKETPAIR) */