glibc/sysdeps/unix/sysv/linux/check_native.c

/* Determine whether interfaces use native transport.  Linux version.
   Copyright (C) 2007 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <assert.h>
#include <errno.h>
#include <ifaddrs.h>
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <sys/ioctl.h>

#include <linux/netlink.h>
#include <linux/rtnetlink.h>

#include <not-cancel.h>


void
__check_native (uint32_t a1_index, int *a1_native,
		uint32_t a2_index, int *a2_native)
{
  int fd = __socket (PF_NETLINK, SOCK_RAW, NETLINK_ROUTE);

  struct sockaddr_nl nladdr;
  memset (&nladdr, '\0', sizeof (nladdr));
  nladdr.nl_family = AF_NETLINK;

  socklen_t addr_len = sizeof (nladdr);

  if (fd < 0
      || __bind (fd, (struct sockaddr *) &nladdr, sizeof (nladdr)) != 0
      || __getsockname (fd, (struct sockaddr *) &nladdr, &addr_len) != 0)
    return;

  pid_t pid = nladdr.nl_pid;
  struct req
  {
    struct nlmsghdr nlh;
    struct rtgenmsg g;
    /* struct rtgenmsg consists of a single byte.  This means there
       are three bytes of padding included in the REQ definition.
       We make them explicit here.  */
    char pad[3];
  } req;

  req.nlh.nlmsg_len = sizeof (req);
  req.nlh.nlmsg_type = RTM_GETLINK;
  req.nlh.nlmsg_flags = NLM_F_ROOT | NLM_F_MATCH | NLM_F_REQUEST;
  req.nlh.nlmsg_pid = 0;
  req.nlh.nlmsg_seq = time (NULL);
  req.g.rtgen_family = AF_UNSPEC;

  assert (sizeof (req) - offsetof (struct req, pad) == 3);
  memset (req.pad, '\0', sizeof (req.pad));

  memset (&nladdr, '\0', sizeof (nladdr));
  nladdr.nl_family = AF_NETLINK;

#ifdef PAGE_SIZE
  /* Help the compiler optimize out the malloc call if PAGE_SIZE
     is constant and smaller or equal to PTHREAD_STACK_MIN/4.  */
  const size_t buf_size = PAGE_SIZE;
#else
  const size_t buf_size = __getpagesize ();
#endif
  bool use_malloc = false;
  char *buf;

  if (__libc_use_alloca (buf_size))
    buf = alloca (buf_size);
  else
    {
      buf = malloc (buf_size);
      if (buf != NULL)
	use_malloc = true;
      else
	goto out_fail;
    }

  struct iovec iov = { buf, buf_size };

  if (TEMP_FAILURE_RETRY (__sendto (fd, (void *) &req, sizeof (req), 0,
				    (struct sockaddr *) &nladdr,
				    sizeof (nladdr))) < 0)
    goto out_fail;

  bool done = false;
  int v4fd = -1;
  do
    {
      struct msghdr msg =
	{
	  (void *) &nladdr, sizeof (nladdr),
	  &iov, 1,
	  NULL, 0,
	  0
	};

      ssize_t read_len = TEMP_FAILURE_RETRY (__recvmsg (fd, &msg, 0));
      if (read_len < 0)
	goto out_fail;

      if (msg.msg_flags & MSG_TRUNC)
	goto out_fail;

      struct nlmsghdr *nlmh;
      for (nlmh = (struct nlmsghdr *) buf;
	   NLMSG_OK (nlmh, (size_t) read_len);
	   nlmh = (struct nlmsghdr *) NLMSG_NEXT (nlmh, read_len))
	{
	  if (nladdr.nl_pid != 0 || (pid_t) nlmh->nlmsg_pid != pid
	      || nlmh->nlmsg_seq != req.nlh.nlmsg_seq)
	    continue;

	  if (nlmh->nlmsg_type == RTM_NEWLINK)
	    {
	      /* A RTM_NEWLINK message can have IFLA_STATS data. We need to
		 know the size before creating the list to allocate enough
		 memory.  */
	      struct ifinfomsg *ifim = (struct ifinfomsg *) NLMSG_DATA (nlmh);
	      struct rtattr *rta = IFLA_RTA (ifim);
	      size_t rtasize = IFLA_PAYLOAD (nlmh);
	      int index = ifim->ifi_index;

	      if (a1_index == index || a2_index == index)
		while (RTA_OK (rta, rtasize))
		  {
		    char *rta_data = RTA_DATA (rta);
		    size_t rta_payload = RTA_PAYLOAD (rta);

		    if (rta->rta_type == IFLA_IFNAME)
		      {
			struct ifreq ifr;
			*((char *) mempcpy (ifr.ifr_name, rta_data,
					    rta_payload))= '\0';

			if (v4fd == -1)
			  {
			    v4fd = __socket (AF_INET, SOCK_DGRAM, 0);
			    if (v4fd == -1)
			      return;
			  }

			if (__ioctl (v4fd, SIOCGIFHWADDR, &ifr) >= 0)
			  {
			    int native
			      = (ifr.ifr_hwaddr.sa_family != ARPHRD_TUNNEL6
				 && ifr.ifr_hwaddr.sa_family != ARPHRD_TUNNEL
				 && ifr.ifr_hwaddr.sa_family != ARPHRD_SIT);

			    if (a1_index == index)
			      {
				*a1_native = native;
				a1_index = 0xffffffffu;
			      }
			    if (a2_index == index)
			      {
				*a2_native = native;
				a2_index = 0xffffffffu;
			      }

			    if (a1_index == 0xffffffffu
				&& a2_index == 0xffffffffu)
			      goto out;
			  }
			break;
		      }

		    rta = RTA_NEXT (rta, rtasize);
		  }
	    }
	  else if (nlmh->nlmsg_type == NLMSG_DONE)
	    /* We found the end, leave the loop.  */
	    done = true;
	}
    }
  while (! done);

 out:
  close_not_cancel_no_status (fd);
  if (v4fd != -1)
    close_not_cancel_no_status (v4fd);

  return;

out_fail:
  if (use_malloc)
    free (buf);
}