src/bfd.c

   1 #include <syslog.h>
   2 #include <signal.h>
   3 #include <stddef.h>
   4 #include <stdlib.h>
   5 #include <netinet/ip6.h>
   6 #include <netinet/icmp6.h>
   7
   8 #include <sys/socket.h>
   9 #include <net/if.h>
  10 #include <net/ethernet.h>
  11 #include <netpacket/packet.h>
  12 #include <linux/rtnetlink.h>
  13 #include <linux/filter.h>
  14
  15 #include <fcntl.h>
  16 #include <unistd.h>
  17
  18 #include "odhcp6c.h"
  19
  20 static int sock = -1, rtnl = -1;
  21 static int if_index = -1;
  22 static int bfd_failed = 0, bfd_limit = 0, bfd_interval = 0;
  23 static bool bfd_armed = false;
  24
  25
  26 static void bfd_send(int signal __attribute__((unused)))
  27 {
  28         struct {
  29                 struct ip6_hdr ip6;
  30                 struct icmp6_hdr icmp6;
  31         } ping;
  32         memset(&ping, 0, sizeof(ping));
  33
  34         ping.ip6.ip6_vfc = 6 << 4;
  35         ping.ip6.ip6_plen = htons(8);
  36         ping.ip6.ip6_nxt = IPPROTO_ICMPV6;
  37         ping.ip6.ip6_hlim = 255;
  38
  39         ping.icmp6.icmp6_type = ICMP6_ECHO_REQUEST;
  40         ping.icmp6.icmp6_data32[0] = htonl(0xbfd0bfd);
  41
  42         size_t pdlen, rtlen;
  43         struct odhcp6c_entry *pd = odhcp6c_get_state(STATE_IA_PD, &pdlen), *cpd = NULL;
  44         struct odhcp6c_entry *rt = odhcp6c_get_state(STATE_RA_ROUTE, &rtlen), *crt = NULL;
  45         bool crt_found = false;
  46
  47         alarm(bfd_interval);
  48
  49         if (bfd_armed) {
  50                 if (++bfd_failed > bfd_limit) {
  51                         raise(SIGUSR2);
  52                         return;
  53                 }
  54         }
  55
  56         // Detect PD-Prefix
  57         for (size_t i = 0; i < pdlen / sizeof(*pd); ++i)
  58                 if (!cpd || ((cpd->target.s6_addr[0] & 7) == 0xfc) > ((pd[i].target.s6_addr[0] & 7) == 0xfc)
  59                                 || cpd->preferred < pd[i].preferred)
  60                         cpd = &pd[i];
  61
  62         // Detect default router
  63         for (size_t i = 0; i < rtlen / sizeof(*rt); ++i)
  64                 if (IN6_IS_ADDR_UNSPECIFIED(&rt[i].target) && (!crt || crt->priority > rt[i].priority))
  65                         crt = &rt[i];
  66
  67         struct sockaddr_ll dest = {
  68                 .sll_family = AF_PACKET,
  69                 .sll_protocol = htons(ETH_P_IPV6),
  70                 .sll_ifindex = if_index,
  71                 .sll_halen = ETH_ALEN,
  72         };
  73
  74         if (crt) {
  75                 struct {
  76                         struct nlmsghdr hdr;
  77                         struct ndmsg ndm;
  78                 } req = {
  79                         .hdr = {sizeof(req), RTM_GETNEIGH, NLM_F_REQUEST | NLM_F_DUMP, 1, 0},
  80                         .ndm = {.ndm_family = AF_INET6, .ndm_ifindex = if_index}
  81                 };
  82                 send(rtnl, &req, sizeof(req), 0);
  83
  84                 uint8_t buf[8192];
  85                 struct nlmsghdr *nhm;
  86                 do {
  87                         ssize_t read = recv(rtnl, buf, sizeof(buf), 0);
  88                         nhm = (struct nlmsghdr*)buf;
  89                         if (read < 0 || !NLMSG_OK(nhm, (size_t)read))
  90                                 continue;
  91
  92                         for (; read > 0 && NLMSG_OK(nhm, (size_t)read); nhm = NLMSG_NEXT(nhm, read)) {
  93                                 ssize_t attrlen = NLMSG_PAYLOAD(nhm, sizeof(struct ndmsg));
  94                                 if (nhm->nlmsg_type != RTM_NEWNEIGH || attrlen <= 0) {
  95                                         nhm = NULL;
  96                                         break;
  97                                 }
  98
  99                                 // Already have our MAC
 100                                 if (crt_found)
 101                                         continue;
 102
 103                                 struct ndmsg *ndm = NLMSG_DATA(nhm);
 104                                 for (struct rtattr *rta = (struct rtattr*)&ndm[1];
 105                                                 attrlen > 0 && RTA_OK(rta, (size_t)attrlen);
 106                                                 rta = RTA_NEXT(rta, attrlen)) {
 107                                         if (rta->rta_type == NDA_DST) {
 108                                                 crt_found = IN6_ARE_ADDR_EQUAL(RTA_DATA(rta), &crt->router);
 109                                         } else if (rta->rta_type == NDA_LLADDR) {
 110                                                 memcpy(dest.sll_addr, RTA_DATA(rta), ETH_ALEN);
 111                                         }
 112                                 }
 113                         }
 114                 } while (nhm);
 115         }
 116
 117         if (!crt_found || !cpd)
 118                 return;
 119
 120         ping.ip6.ip6_src = cpd->target;
 121         ping.ip6.ip6_dst = cpd->target;
 122
 123 /*
 124         uint16_t sum = cksum(&ping.ip6.ip6_src, sizeof(ping.ip6.ip6_src), 0);
 125         sum = cksum(&ping.ip6.ip6_dst, sizeof(ping.ip6.ip6_dst), ~sum);
 126         sum = cksum(&ping.ip6.ip6_plen, sizeof(ping.ip6.ip6_plen), ~sum);
 127
 128         uint8_t next[4] = {0, 0, 0, ping.ip6.ip6_nxt};
 129         sum = cksum(next, sizeof(next), ~sum);
 130
 131         ping.icmp6.icmp6_cksum = cksum(&ping.icmp6, sizeof(ping.icmp6), ~sum);
 132 */
 133
 134         struct sock_filter bpf[] = {
 135                 BPF_STMT(BPF_LD | BPF_W | BPF_ABS, offsetof(struct ip6_hdr, ip6_plen)),
 136                 BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 8 << 16 | IPPROTO_ICMPV6 << 8 | 254, 0, 13),
 137                 BPF_STMT(BPF_LD | BPF_W | BPF_ABS, offsetof(struct ip6_hdr, ip6_dst)),
 138                 BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, ntohl(ping.ip6.ip6_dst.s6_addr32[0]), 0, 11),
 139                 BPF_STMT(BPF_LD | BPF_W | BPF_ABS, offsetof(struct ip6_hdr, ip6_dst) + 4),
 140                 BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, ntohl(ping.ip6.ip6_dst.s6_addr32[1]), 0, 9),
 141                 BPF_STMT(BPF_LD | BPF_W | BPF_ABS, offsetof(struct ip6_hdr, ip6_dst) + 8),
 142                 BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, ntohl(ping.ip6.ip6_dst.s6_addr32[2]), 0, 7),
 143                 BPF_STMT(BPF_LD | BPF_W | BPF_ABS, offsetof(struct ip6_hdr, ip6_dst) + 12),
 144                 BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, ntohl(ping.ip6.ip6_dst.s6_addr32[3]), 0, 5),
 145                 BPF_STMT(BPF_LD | BPF_W | BPF_ABS, sizeof(struct ip6_hdr) +
 146                                 offsetof(struct icmp6_hdr, icmp6_type)),
 147                 BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, ICMP6_ECHO_REQUEST << 24, 0, 3),
 148                 BPF_STMT(BPF_LD | BPF_W | BPF_ABS, sizeof(struct ip6_hdr) +
 149                                 offsetof(struct icmp6_hdr, icmp6_data32)),
 150                 BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, ntohl(ping.icmp6.icmp6_data32[0]), 0, 1),
 151                 BPF_STMT(BPF_RET | BPF_K, 0xffffffff),
 152                 BPF_STMT(BPF_RET | BPF_K, 0),
 153         };
 154         struct sock_fprog bpf_prog = {sizeof(bpf) / sizeof(*bpf), bpf};
 155
 156
 157         if (sock < 0) {
 158                 sock = socket(AF_PACKET, SOCK_DGRAM | SOCK_CLOEXEC, htons(ETH_P_IPV6));
 159                 bind(sock, (struct sockaddr*)&dest, sizeof(dest));
 160
 161                 fcntl(sock, F_SETOWN, getpid());
 162                 fcntl(sock, F_SETFL, fcntl(sock, F_GETFL) | O_ASYNC);
 163         }
 164
 165         setsockopt(sock, SOL_SOCKET, SO_DETACH_FILTER, &bpf_prog, sizeof(bpf_prog));
 166         if (setsockopt(sock, SOL_SOCKET, SO_ATTACH_FILTER, &bpf_prog, sizeof(bpf_prog))) {
 167                 close(sock);
 168                 sock = -1;
 169                 return;
 170         }
 171
 172         uint8_t dummy[8];
 173         while (recv(sock, dummy, sizeof(dummy), MSG_DONTWAIT | MSG_TRUNC) > 0);
 174
 175         sendto(sock, &ping, sizeof(ping), MSG_DONTWAIT,
 176                         (struct sockaddr*)&dest, sizeof(dest));
 177 }
 178
 179
 180 void bfd_receive(void)
 181 {
 182         uint8_t dummy[8];
 183         while (recv(sock, dummy, sizeof(dummy), MSG_DONTWAIT | MSG_TRUNC) > 0) {
 184                 bfd_failed = 0;
 185                 bfd_armed = true;
 186         }
 187 }
 188
 189
 190 int bfd_start(const char *ifname, int limit, int interval)
 191 {
 192         if_index = if_nametoindex(ifname);
 193         bfd_armed = false;
 194         bfd_failed = 0;
 195         bfd_limit = limit;
 196         bfd_interval = interval;
 197
 198         if (limit < 1 || interval < 1)
 199                 return 0;
 200
 201         rtnl = socket(AF_NETLINK, SOCK_DGRAM | SOCK_CLOEXEC, NETLINK_ROUTE);
 202         struct sockaddr_nl rtnl_kernel = { .nl_family = AF_NETLINK };
 203         connect(rtnl, (const struct sockaddr*)&rtnl_kernel, sizeof(rtnl_kernel));
 204
 205         signal(SIGALRM, bfd_send);
 206         alarm(5);
 207         return 0;
 208 }
 209
 210
 211 void bfd_stop(void)
 212 {
 213         alarm(0);
 214         close(sock);
 215         close(rtnl);
 216
 217         sock = -1;
 218         rtnl = -1;
 219 }
 220
 221 /*
 222
 223 uint16_t cksum(const uint16_t *addr, size_t count, uint16_t start)
 224 {
 225         uint32_t sum = start;
 226
 227         while (count > 1) {
 228                 sum += *addr++;
 229                 count -= 2;
 230         }
 231
 232         while (sum >> 16)
 233                 sum = (sum & 0xffff) + (sum >> 16);
 234
 235         return ~sum;
 236 }
 237
 238 */