pimd/mtracebis_routeget.c

   1 /*
   2  * Multicast Traceroute for FRRouting
   3  * Copyright (C) 2018  Mladen Sablic
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful, but
  11  * WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; see the file COPYING; if not, write to the Free Software
  17  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
  18  */
  19
  20 #ifdef HAVE_CONFIG_H
  21 #include "config.h"
  22 #endif
  23
  24 #ifdef __linux__
  25
  26 #include <asm/types.h>
  27 #include <linux/netlink.h>
  28 #include <linux/rtnetlink.h>
  29 #include <sys/types.h>
  30 #include <stdio.h>
  31 #include <arpa/inet.h>
  32 #include <string.h>
  33
  34 #include "mtracebis_netlink.h"
  35 #include "mtracebis_routeget.h"
  36
  37 static int find_dst(struct nlmsghdr *n, struct in_addr *src, struct in_addr *gw)
  38 {
  39         struct rtmsg *r = NLMSG_DATA(n);
  40         int len = n->nlmsg_len;
  41         struct rtattr *tb[RTA_MAX + 1];
  42
  43         len -= NLMSG_LENGTH(sizeof(*r));
  44         if (len < 0) {
  45                 fprintf(stderr, "BUG: wrong nlmsg len %d\n", len);
  46                 return -1;
  47         }
  48
  49         parse_rtattr(tb, RTA_MAX, RTM_RTA(r), len);
  50         if (tb[RTA_PREFSRC])
  51                 src->s_addr = *(uint32_t *)RTA_DATA(tb[RTA_PREFSRC]);
  52         if (tb[RTA_GATEWAY])
  53                 gw->s_addr = *(uint32_t *)RTA_DATA(tb[RTA_GATEWAY]);
  54         if (tb[RTA_OIF])
  55                 return *(int *)RTA_DATA(tb[RTA_OIF]);
  56         return 0;
  57 }
  58
  59 int routeget(struct in_addr dst, struct in_addr *src, struct in_addr *gw)
  60 {
  61         struct {
  62                 struct nlmsghdr n;
  63                 struct rtmsg r;
  64                 char buf[1024];
  65         } req;
  66         int ret;
  67         struct rtnl_handle rth = {.fd = -1};
  68
  69         memset(&req, 0, sizeof(req));
  70
  71         req.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg));
  72         req.n.nlmsg_flags = NLM_F_REQUEST;
  73         req.n.nlmsg_type = RTM_GETROUTE;
  74         req.r.rtm_family = AF_INET;
  75         req.r.rtm_table = 0;
  76         req.r.rtm_protocol = 0;
  77         req.r.rtm_scope = 0;
  78         req.r.rtm_type = 0;
  79         req.r.rtm_src_len = 0;
  80         req.r.rtm_dst_len = 0;
  81         req.r.rtm_tos = 0;
  82
  83         addattr_l(&req.n, sizeof(req), RTA_DST, &dst.s_addr, 4);
  84         req.r.rtm_dst_len = 32;
  85
  86         ret = rtnl_open(&rth, 0);
  87
  88         if (ret < 0 || rth.fd <= 0)
  89                 return ret;
  90
  91         if (rtnl_talk(&rth, &req.n, 0, 0, &req.n, NULL, NULL) < 0) {
  92                 ret = -1;
  93                 goto close_rth;
  94         }
  95
  96         ret = find_dst(&req.n, src, gw);
  97 close_rth:
  98         rtnl_close(&rth);
  99         return ret;
 100 }
 101
 102 #endif /* __linux__ */