sysdeps/unix/sysv/linux/check_native.c

   1 /* Determine whether interfaces use native transport.  Linux version.
   2    Copyright (C) 2007-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <errno.h>
  21 #include <ifaddrs.h>
  22 #include <stddef.h>
  23 #include <stdint.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include <time.h>
  27 #include <unistd.h>
  28 #include <net/if.h>
  29 #include <net/if_arp.h>
  30 #include <sys/ioctl.h>
  31
  32 #include <asm/types.h>
  33 #include <linux/netlink.h>
  34 #include <linux/rtnetlink.h>
  35
  36 #include <not-cancel.h>
  37
  38 #include "netlinkaccess.h"
  39
  40 void
  41 __check_native (uint32_t a1_index, int *a1_native,
  42                 uint32_t a2_index, int *a2_native)
  43 {
  44   int fd = __socket (PF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
  45
  46   struct sockaddr_nl nladdr;
  47   memset (&nladdr, '\0', sizeof (nladdr));
  48   nladdr.nl_family = AF_NETLINK;
  49
  50   socklen_t addr_len = sizeof (nladdr);
  51
  52   if (fd < 0)
  53     return;
  54
  55   /* Netlink requires that user buffer needs to be either 8kb or page size
  56      (whichever is bigger), however this has been changed over time and now
  57      8Kb is sufficient (check NLMSG_DEFAULT_SIZE on Linux
  58      linux/include/linux/netlink.h).  */
  59   const size_t buf_size = 8192;
  60   char *buf = malloc (buf_size);
  61
  62   if (buf == NULL)
  63     goto out;
  64
  65   if (__bind (fd, (struct sockaddr *) &nladdr, sizeof (nladdr)) != 0
  66       || __getsockname (fd, (struct sockaddr *) &nladdr, &addr_len) != 0)
  67     goto out;
  68
  69   pid_t pid = nladdr.nl_pid;
  70   struct req
  71   {
  72     struct nlmsghdr nlh;
  73     struct rtgenmsg g;
  74     /* struct rtgenmsg consists of a single byte.  This means there
  75        are three bytes of padding included in the REQ definition.
  76        We make them explicit here.  */
  77     char pad[3];
  78   } req;
  79
  80   req.nlh.nlmsg_len = sizeof (req);
  81   req.nlh.nlmsg_type = RTM_GETLINK;
  82   req.nlh.nlmsg_flags = NLM_F_ROOT | NLM_F_MATCH | NLM_F_REQUEST;
  83   req.nlh.nlmsg_pid = 0;
  84   req.nlh.nlmsg_seq = time_now ();
  85   req.g.rtgen_family = AF_UNSPEC;
  86
  87   assert (sizeof (req) - offsetof (struct req, pad) == 3);
  88   memset (req.pad, '\0', sizeof (req.pad));
  89
  90   memset (&nladdr, '\0', sizeof (nladdr));
  91   nladdr.nl_family = AF_NETLINK;
  92
  93   struct iovec iov = { buf, buf_size };
  94
  95   if (TEMP_FAILURE_RETRY (__sendto (fd, (void *) &req, sizeof (req), 0,
  96                                     (struct sockaddr *) &nladdr,
  97                                     sizeof (nladdr))) < 0)
  98     goto out;
  99
 100   bool done = false;
 101   do
 102     {
 103       struct msghdr msg =
 104         {
 105           .msg_name = (void *) &nladdr,
 106           .msg_namelen =  sizeof (nladdr),
 107           .msg_iov = &iov,
 108           .msg_iovlen = 1,
 109           .msg_control = NULL,
 110           .msg_controllen = 0,
 111           .msg_flags = 0
 112         };
 113
 114       ssize_t read_len = TEMP_FAILURE_RETRY (__recvmsg (fd, &msg, 0));
 115       __netlink_assert_response (fd, read_len);
 116       if (read_len < 0)
 117         goto out;
 118
 119       if (msg.msg_flags & MSG_TRUNC)
 120         goto out;
 121
 122       struct nlmsghdr *nlmh;
 123       for (nlmh = (struct nlmsghdr *) buf;
 124            NLMSG_OK (nlmh, (size_t) read_len);
 125            nlmh = (struct nlmsghdr *) NLMSG_NEXT (nlmh, read_len))
 126         {
 127           if (nladdr.nl_pid != 0 || (pid_t) nlmh->nlmsg_pid != pid
 128               || nlmh->nlmsg_seq != req.nlh.nlmsg_seq)
 129             continue;
 130
 131           if (nlmh->nlmsg_type == RTM_NEWLINK)
 132             {
 133               struct ifinfomsg *ifim = (struct ifinfomsg *) NLMSG_DATA (nlmh);
 134               int native = (ifim->ifi_type != ARPHRD_TUNNEL6
 135                             && ifim->ifi_type != ARPHRD_TUNNEL
 136                             && ifim->ifi_type != ARPHRD_SIT);
 137
 138               if (a1_index == ifim->ifi_index)
 139                 {
 140                   *a1_native = native;
 141                   a1_index = 0xffffffffu;
 142                 }
 143               if (a2_index == ifim->ifi_index)
 144                 {
 145                   *a2_native = native;
 146                   a2_index = 0xffffffffu;
 147                 }
 148
 149               if (a1_index == 0xffffffffu
 150                   && a2_index == 0xffffffffu)
 151                 goto out;
 152             }
 153           else if (nlmh->nlmsg_type == NLMSG_DONE)
 154             /* We found the end, leave the loop.  */
 155             done = true;
 156         }
 157     }
 158   while (! done);
 159
 160 out:
 161   __close_nocancel_nostatus (fd);
 162   free (buf);
 163 }