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Date:      Sun, 18 May 2008 20:56:01 +0100
From:      "Steven Hartland" <killing@multiplay.co.uk>
To:        <freebsd-hackers@freebsd.org>
Subject:   Using sendmsg for SCM_CREDS results in EINVAL on PF_INET socket
Message-ID:  <BCBAE9EA84D54762AD983B29B2752492@multiplay.co.uk>
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sendmsg is not documented as ever returning EINVAL but yet when
using the following code to send credentials to a remote host
results in EINVAL from sendmsg.

I suspect that SCM_CREDS is only valid for PF_LOCAL / PF_UNIX
sockets and not PF_INET sockets and hence the code in dbus
is actually invalid.

Can anyone confirm this is the case or not?

[code from dbus-sysdeps-unix.c]
write_credentials_byte (int             server_fd,
                        DBusError      *error)
{
  int bytes_written;
  char buf[1] = { '\0' };
#if defined(HAVE_CMSGCRED) 
  union {
      struct cmsghdr hdr;
      char cred[CMSG_SPACE (sizeof (struct cmsgcred))];
  } cmsg;
  struct iovec iov;
  struct msghdr msg;
  iov.iov_base = buf;
  iov.iov_len = 1;

  memset (&msg, 0, sizeof (msg));
  msg.msg_iov = &iov;
  msg.msg_iovlen = 1;

  msg.msg_control = (caddr_t) &cmsg;
  msg.msg_controllen = CMSG_SPACE (sizeof (struct cmsgcred));
  memset (&cmsg, 0, sizeof (cmsg));
  cmsg.hdr.cmsg_len = CMSG_LEN (sizeof (struct cmsgcred));
  cmsg.hdr.cmsg_level = SOL_SOCKET;
  cmsg.hdr.cmsg_type = SCM_CREDS;
#endif

  _DBUS_ASSERT_ERROR_IS_CLEAR (error);

 again:

#if defined(HAVE_CMSGCRED) 
  bytes_written = sendmsg (server_fd, &msg, 0);
#else
  bytes_written = write (server_fd, buf, 1);
#endif

  if (bytes_written < 0 && errno == EINTR)
    goto again;

  if (bytes_written < 0)
    {
      dbus_set_error (error, _dbus_error_from_errno (errno),
                      "Failed to write credentials byte: %s",
                     _dbus_strerror (errno));
      return FALSE;
    }
  else if (bytes_written == 0)
    {
      dbus_set_error (error, DBUS_ERROR_IO_ERROR,
                      "wrote zero bytes writing credentials byte");
      return FALSE;
    }
  else
    {
      _dbus_assert (bytes_written == 1);
      _dbus_verbose ("wrote credentials byte\n");
      return TRUE;
    }
}
[/code from dbus-sysdeps-unix.c]

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