[PATCH] using an interface without IP address

Chris Hanson <[email protected]> Wed, 25 Feb 2004 00:41:22 -0500

Newsgroups	gmane.comp.security.libnet
Message-ID	<[email protected]>

   Date: Thu, 29 Jan 2004 06:21:25 +0100
   From: =?iso-8859-1?Q?Fr=E9d=E9ric_Raynal?= <[email protected]>

   Currently, I still havent found the ioct() giving me all the devices,
   even those that are down (I even sent a mail to net-linux to get the
   solution but got no answer).  So, results bellow are "normal"

Hi, I'm helping out Domenico by co-maintaining libnet for Debian.

I have some experience with this, having had to solve this problem for
another program.  AFAIK, the only way to get all the interfaces is to
read and parse "/proc/net/dev".

I've attached some code that does this.  This code is a fragment from
my program.  I'm going to try to integrate this into libnet 1.1.1, and
if that works I'll send you a patch.

foo.c (text/x-csrc, 3.1 KB)

/* Use /proc/net/dev if available, since that will give us a list of
   all of the interfaces.  Otherwise use SIOCGIFCONF, which will at
   least give us the interfaces that are up.  */

static struct ifreq *
get_interface_list (unsigned int * n_ifcs_return)
{
  struct ifreq * ifcs = (proc_interface_list (n_ifcs_return));
  return
    ((ifcs == 0)
     ? (conf_interface_list (n_ifcs_return))
     : ifcs);
}

static struct ifreq *
conf_interface_list (unsigned int * n_ifcs_return)
{
  struct ifconf ifc;
  unsigned int n_ifcs = 4;
  unsigned int n_bytes = ((sizeof (struct ifreq)) * n_ifcs);

  (ifc . ifc_len) = n_bytes;
  (ifc . ifc_req) = (xmalloc (n_bytes));
  while (1)
    {
      if ((ioctl (kernel_connection, SIOCGIFCONF, (&ifc))) < 0)
	{
	  log_perror ("SIOCGIFCONF");
	  free (ifc . ifc_req);
	  return (0);
	}
      if ((ifc . ifc_len) < n_bytes)
	break;
      n_ifcs *= 2;
      n_bytes = ((sizeof (struct ifreq)) * n_ifcs);
      (ifc . ifc_req) = (xrealloc ((ifc . ifc_req), n_bytes));
    }

  (*n_ifcs_return) = ((ifc . ifc_len) / (sizeof (struct ifreq)));
  return (ifc . ifc_req);
}

static struct ifreq *
proc_interface_list (unsigned int * n_ifcs_return)
{
  FILE * s = (fopen ("/proc/net/dev", "r"));
  if (s == 0)
    {
      log_perror ("Unable to open /proc/net/dev");
      return (0);
    }
  discard_line (s);
  discard_line (s);
  {
    unsigned int i = 0;
    unsigned int n = 4;
    struct ifreq * ifcs = (xmalloc ((sizeof (struct ifreq)) * n));
    struct ifreq ifc;
    while (proc_interface_name (s, (&ifc)))
      {
	if (i == n)
	  {
	    n *= 2;
	    ifcs = (xrealloc (ifcs, ((sizeof (struct ifreq)) * n)));
	  }
	(ifcs[i++]) = ifc;
      }
    fclose (s);
    (*n_ifcs_return) = i;
    return (ifcs);
  }
}

static void
discard_line (FILE * s)
{
  while (1)
    {
      int c = (getc (s));
      if ((c == EOF) || (c == '\n'))
	break;
    }
}

#define PIN_GETC(c, s)							\
{									\
  c = (getc (s));							\
  if (c == EOF)								\
    return (0);								\
  if (c == '\0')							\
    {									\
      discard_line (s);							\
      goto restart;							\
    }									\
}

#define PIN_ACCUM(c)							\
{									\
  if (i < n)								\
    (name[i++]) = (c);							\
  else									\
    {									\
      discard_line (s);							\
      goto restart;							\
    }									\
}

static int
proc_interface_name (FILE * s, struct ifreq * ifc)
{
  char * name = (ifc -> ifr_name);
  unsigned int n = (sizeof (ifc -> ifr_name));
  unsigned int i;
  int c;

 restart:
  do
    {
      PIN_GETC (c, s);
    }
  while (isspace (c));
  i = 0;
  while (1)
    {
      PIN_ACCUM (c);
      PIN_GETC (c, s);
      if (isspace (c))
	{
	  if (c != '\n')
	    discard_line (s);
	  break;
	}
      if (c == ':')
	{
	  if (i < n)
	    /* Might be part of an alias; check.  */
	    {
	      unsigned int saved_i = i;
	      while (1)
		{
		  PIN_ACCUM (c);
		  PIN_GETC (c, s);
		  if (!isdigit (c))
		    {
		      if (c != ':')
			/* Not an alias; first colon was name terminator.  */
			i = saved_i;
		      if (c != '\n')
			discard_line (s);
		      break;
		    }
		}
	    }
	  break;
	}
    }
  if (i < n)
    (name[i]) = '\0';
  return (1);
}