pimd/mtracebis_routeget.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Multicast Traceroute for FRRouting
   4  * Copyright (C) 2018  Mladen Sablic
   5  */
   6
   7 #ifdef HAVE_CONFIG_H
   8 #include "config.h"
   9 #endif
  10
  11 #ifdef __linux__
  12
  13 #include <asm/types.h>
  14 #include <linux/netlink.h>
  15 #include <linux/rtnetlink.h>
  16 #include <sys/types.h>
  17 #include <stdio.h>
  18 #include <arpa/inet.h>
  19 #include <string.h>
  20
  21 #include "mtracebis_netlink.h"
  22 #include "mtracebis_routeget.h"
  23
  24 static int find_dst(struct nlmsghdr *n, struct in_addr *src, struct in_addr *gw)
  25 {
  26         struct rtmsg *r = NLMSG_DATA(n);
  27         int len = n->nlmsg_len;
  28         struct rtattr *tb[RTA_MAX + 1];
  29
  30         len -= NLMSG_LENGTH(sizeof(*r));
  31         if (len < 0) {
  32                 fprintf(stderr, "BUG: wrong nlmsg len %d\n", len);
  33                 return -1;
  34         }
  35
  36         parse_rtattr(tb, RTA_MAX, RTM_RTA(r), len);
  37         if (tb[RTA_PREFSRC])
  38                 src->s_addr = *(uint32_t *)RTA_DATA(tb[RTA_PREFSRC]);
  39         if (tb[RTA_GATEWAY])
  40                 gw->s_addr = *(uint32_t *)RTA_DATA(tb[RTA_GATEWAY]);
  41         if (tb[RTA_OIF])
  42                 return *(int *)RTA_DATA(tb[RTA_OIF]);
  43         return 0;
  44 }
  45
  46 int routeget(struct in_addr dst, struct in_addr *src, struct in_addr *gw)
  47 {
  48         struct {
  49                 struct nlmsghdr n;
  50                 struct rtmsg r;
  51                 char buf[1024];
  52         } req;
  53         int ret;
  54         struct rtnl_handle rth = {.fd = -1};
  55
  56         memset(&req, 0, sizeof(req));
  57
  58         req.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg));
  59         req.n.nlmsg_flags = NLM_F_REQUEST;
  60         req.n.nlmsg_type = RTM_GETROUTE;
  61         req.r.rtm_family = AF_INET;
  62         req.r.rtm_table = 0;
  63         req.r.rtm_protocol = 0;
  64         req.r.rtm_scope = 0;
  65         req.r.rtm_type = 0;
  66         req.r.rtm_src_len = 0;
  67         req.r.rtm_dst_len = 0;
  68         req.r.rtm_tos = 0;
  69
  70         addattr_l(&req.n, sizeof(req), RTA_DST, &dst.s_addr, 4);
  71         req.r.rtm_dst_len = 32;
  72
  73         ret = rtnl_open(&rth, 0);
  74
  75         if (ret < 0 || rth.fd <= 0)
  76                 return ret;
  77
  78         if (rtnl_talk(&rth, &req.n, 0, 0, &req.n, NULL, NULL) < 0) {
  79                 ret = -1;
  80                 goto close_rth;
  81         }
  82
  83         ret = find_dst(&req.n, src, gw);
  84 close_rth:
  85         rtnl_close(&rth);
  86         return ret;
  87 }
  88
  89 #endif /* __linux__ */