src/ra.c

   1 #include <fcntl.h>
   2 #include <stdio.h>
   3 #include <signal.h>
   4 #include <string.h>
   5 #include <stddef.h>
   6 #include <stdbool.h>
   7 #include <unistd.h>
   8
   9 #include <net/if.h>
  10 #include <sys/socket.h>
  11 #include <netinet/in.h>
  12 #include <netinet/icmp6.h>
  13
  14 #include <linux/rtnetlink.h>
  15
  16
  17 #include "odhcp6c.h"
  18 #include "ra.h"
  19
  20
  21 static int sock = -1, rtnl_sock = -1;
  22 static unsigned if_index = 0;
  23 static char if_name[IF_NAMESIZE] = {0};
  24 static volatile int rs_attempt = 0;
  25 static struct in6_addr lladdr = IN6ADDR_ANY_INIT;
  26
  27 static void ra_send_rs(int signal __attribute__((unused)));
  28
  29 int ra_init(const char *ifname)
  30 {
  31         sock = socket(AF_INET6, SOCK_RAW | SOCK_CLOEXEC, IPPROTO_ICMPV6);
  32         if_index = if_nametoindex(ifname);
  33         strncpy(if_name, ifname, sizeof(if_name) - 1);
  34
  35         // Filter ICMPv6 package types
  36         struct icmp6_filter filt;
  37         ICMP6_FILTER_SETBLOCKALL(&filt);
  38         ICMP6_FILTER_SETPASS(ND_ROUTER_ADVERT, &filt);
  39         setsockopt(sock, IPPROTO_ICMPV6, ICMP6_FILTER, &filt, sizeof(filt));
  40
  41         // Bind to all-nodes
  42         struct ipv6_mreq an = {ALL_IPV6_NODES, if_index};
  43         setsockopt(sock, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &an, sizeof(an));
  44
  45         // Let the kernel compute our checksums
  46         int val = 2;
  47         setsockopt(sock, IPPROTO_RAW, IPV6_CHECKSUM, &val, sizeof(val));
  48
  49         // This is required by RFC 4861
  50         val = 255;
  51         setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &val, sizeof(val));
  52
  53         // Bind to one device
  54         setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, ifname, strlen(ifname));
  55
  56         // Add async-mode
  57         const pid_t ourpid = getpid();
  58         fcntl(sock, F_SETOWN, ourpid);
  59         fcntl(sock, F_SETFL, fcntl(sock, F_GETFL) | O_ASYNC);
  60
  61         // Get LL-addr
  62         FILE *fp = fopen("/proc/net/if_inet6", "r");
  63         if (fp) {
  64                 char addrbuf[33], ifbuf[16];
  65                 while (fscanf(fp, "%32s %*x %*x %*x %*x %15s", addrbuf, ifbuf) == 2) {
  66                         if (!strcmp(ifbuf, if_name)) {
  67                                 script_unhexlify((uint8_t*)&lladdr, sizeof(lladdr), addrbuf);
  68                                 break;
  69                         }
  70                 }
  71                 fclose(fp);
  72         }
  73
  74         // Open rtnetlink socket
  75         rtnl_sock = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
  76         struct sockaddr_nl rtnl_kernel = { .nl_family = AF_NETLINK };
  77         if (connect(rtnl_sock, (struct sockaddr*)&rtnl_kernel, sizeof(rtnl_kernel)))
  78                 return -1;
  79         uint32_t group = RTNLGRP_IPV6_IFADDR;
  80         setsockopt(rtnl_sock, SOL_NETLINK, NETLINK_ADD_MEMBERSHIP, &group, sizeof(group));
  81
  82         // Add async-mode
  83         fcntl(rtnl_sock, F_SETOWN, ourpid);
  84         fcntl(rtnl_sock, F_SETFL, fcntl(rtnl_sock, F_GETFL) | O_ASYNC);
  85
  86         // Send RS
  87         signal(SIGALRM, ra_send_rs);
  88         ra_send_rs(SIGALRM);
  89
  90         return 0;
  91 }
  92
  93
  94 static void ra_send_rs(int signal __attribute__((unused)))
  95 {
  96         const struct icmp6_hdr rs = {ND_ROUTER_SOLICIT, 0, 0, {{0}}};
  97         const struct sockaddr_in6 dest = {AF_INET6, 0, 0, ALL_IPV6_ROUTERS, if_index};
  98         sendto(sock, &rs, sizeof(rs), MSG_DONTWAIT, (struct sockaddr*)&dest, sizeof(dest));
  99
 100         if (++rs_attempt <= 3)
 101                 alarm(4);
 102 }
 103
 104
 105 static int16_t pref_to_priority(uint8_t flags)
 106 {
 107         flags = (flags >> 3) & 0x03;
 108         return (flags == 0x0) ? 1024 : (flags == 0x1) ? 512 :
 109                         (flags == 0x3) ? 2048 : -1;
 110 }
 111
 112
 113 static void update_proc(const char *sect, const char *opt, uint32_t value)
 114 {
 115         char buf[64];
 116         snprintf(buf, sizeof(buf), "/proc/sys/net/ipv6/%s/%s/%s", sect, if_name, opt);
 117
 118         int fd = open(buf, O_WRONLY);
 119         write(fd, buf, snprintf(buf, sizeof(buf), "%u", value));
 120         close(fd);
 121 }
 122
 123
 124 static bool ra_deduplicate(const struct in6_addr *any, uint8_t length)
 125 {
 126   struct odhcp6c_entry entry = {IN6ADDR_ANY_INIT, length, 0, *any, 0, 0, 0};
 127         struct odhcp6c_entry *x = odhcp6c_find_entry(STATE_RA_PREFIX, &entry);
 128         if (x && IN6_ARE_ADDR_EQUAL(&x->target, any)) {
 129                 odhcp6c_random(&x->target.s6_addr32[2], 2 * sizeof(uint32_t));
 130         } else if (odhcp6c_find_entry(STATE_IA_NA, &entry)) {
 131                 dhcpv6_request(DHCPV6_MSG_DECLINE);
 132                 raise(SIGUSR2);
 133         }
 134
 135         return !!x;
 136 }
 137
 138
 139 bool ra_rtnl_process(void)
 140 {
 141         bool found = false;
 142         uint8_t buf[8192];
 143         while (true) {
 144                 ssize_t len = recv(rtnl_sock, buf, sizeof(buf), MSG_DONTWAIT);
 145                 if (len < 0)
 146                         break;
 147
 148                 for (struct nlmsghdr *nh = (struct nlmsghdr*)buf; NLMSG_OK(nh, (size_t)len);
 149                                         nh = NLMSG_NEXT(nh, len)) {
 150                         struct ifaddrmsg *ifa = NLMSG_DATA(nh);
 151                         struct in6_addr *addr = NULL;
 152                         if (NLMSG_PAYLOAD(nh, 0) < sizeof(*ifa) || ifa->ifa_index != if_index ||
 153                                         (nh->nlmsg_type == RTM_NEWADDR && !(ifa->ifa_flags & IFA_F_DADFAILED)) ||
 154                                         (nh->nlmsg_type == RTM_DELADDR && !(ifa->ifa_flags & IFA_F_TENTATIVE)))
 155                                 continue;
 156
 157                         ssize_t alen = NLMSG_PAYLOAD(nh, sizeof(*ifa));
 158                         for (struct rtattr *rta = (struct rtattr*)&ifa[1]; RTA_OK(rta, alen);
 159                                         rta = RTA_NEXT(rta, alen))
 160                                 if (rta->rta_type == IFA_ADDRESS && RTA_PAYLOAD(rta) >= sizeof(*addr))
 161                                         addr = RTA_DATA(rta);
 162
 163                         if (addr)
 164                                 found |= ra_deduplicate(addr, ifa->ifa_prefixlen);
 165                 }
 166         }
 167         return found;
 168 }
 169
 170
 171 bool ra_process(void)
 172 {
 173         bool found = false;
 174         uint8_t buf[1500];
 175         struct nd_router_advert *adv = (struct nd_router_advert*)buf;
 176         struct odhcp6c_entry entry = {IN6ADDR_ANY_INIT, 0, 0, IN6ADDR_ANY_INIT, 0, 0, 0};
 177         const struct in6_addr any = IN6ADDR_ANY_INIT;
 178         odhcp6c_expire();
 179
 180         while (true) {
 181                 struct sockaddr_in6 from;
 182                 socklen_t from_len = sizeof(from);
 183                 ssize_t len = recvfrom(sock, buf, sizeof(buf), MSG_DONTWAIT, &from, &from_len);
 184                 if (len < 0)
 185                         break;
 186                 else if (len < (ssize_t)sizeof(*adv))
 187                         continue;
 188
 189                 // Stop sending solicits
 190                 if (rs_attempt > 0) {
 191                         alarm(0);
 192                         rs_attempt = 0;
 193                 }
 194
 195                 found = true;
 196                 uint32_t router_valid = ntohs(adv->nd_ra_router_lifetime);
 197
 198                 // Parse default route
 199                 entry.router = from.sin6_addr;
 200                 entry.priority = pref_to_priority(adv->nd_ra_flags_reserved);
 201                 if (entry.priority < 0)
 202                         entry.priority = pref_to_priority(0);
 203                 entry.valid = router_valid;
 204                 entry.preferred = entry.valid;
 205                 odhcp6c_update_entry(STATE_RA_ROUTE, &entry);
 206
 207                 // Parse ND parameters
 208                 if (adv->nd_ra_reachable)
 209                         update_proc("neigh", "base_reachable_time_ms", ntohl(adv->nd_ra_reachable));
 210
 211                 if (adv->nd_ra_retransmit)
 212                         update_proc("neigh", "retrans_time_ms", ntohl(adv->nd_ra_retransmit));
 213
 214
 215                 // Evaluate options
 216                 struct icmpv6_opt *opt;
 217                 icmpv6_for_each_option(opt, &adv[1], &buf[len]) {
 218                         if (opt->type == ND_OPT_MTU) {
 219                                 update_proc("conf", "mtu", ntohl(*((uint32_t*)&opt->data[2])));
 220                         } else if (opt->type == ND_OPT_ROUTE_INFORMATION && opt->len <= 3) {
 221                                 entry.router = from.sin6_addr;
 222                                 entry.target = any;
 223                                 entry.priority = pref_to_priority(opt->data[1]);
 224                                 entry.length = opt->data[0];
 225                                 entry.valid = ntohl(*((uint32_t*)&opt->data[2]));
 226                                 memcpy(&entry.target, &opt->data[6], (opt->len - 1) * 8);
 227
 228                                 if (entry.length > 128 || IN6_IS_ADDR_LINKLOCAL(&entry.target)
 229                                                 || IN6_IS_ADDR_LOOPBACK(&entry.target)
 230                                                 || IN6_IS_ADDR_MULTICAST(&entry.target))
 231                                         continue;
 232
 233                                 if (entry.priority > 0)
 234                                         odhcp6c_update_entry(STATE_RA_ROUTE, &entry);
 235                         } else if (opt->type == ND_OPT_PREFIX_INFORMATION && opt->len == 4) {
 236                                 struct nd_opt_prefix_info *pinfo = (struct nd_opt_prefix_info*)opt;
 237                                 entry.router = any;
 238                                 entry.target = pinfo->nd_opt_pi_prefix;
 239                                 entry.priority = 256;
 240                                 entry.length = pinfo->nd_opt_pi_prefix_len;
 241                                 entry.valid = ntohl(pinfo->nd_opt_pi_valid_time);
 242                                 entry.preferred = ntohl(pinfo->nd_opt_pi_preferred_time);
 243
 244                                 if (entry.length > 128 || IN6_IS_ADDR_LINKLOCAL(&entry.target)
 245                                                 || IN6_IS_ADDR_LOOPBACK(&entry.target)
 246                                                 || IN6_IS_ADDR_MULTICAST(&entry.target)
 247                                                 || entry.valid < entry.preferred)
 248                                         continue;
 249
 250                                 if (pinfo->nd_opt_pi_flags_reserved & ND_OPT_PI_FLAG_ONLINK)
 251                                         odhcp6c_update_entry_safe(STATE_RA_ROUTE, &entry, 7200);
 252
 253                                 if (!(pinfo->nd_opt_pi_flags_reserved & ND_OPT_PI_FLAG_AUTO) ||
 254                                                 pinfo->nd_opt_pi_prefix_len != 64)
 255                                         continue;
 256
 257                                 entry.target.s6_addr32[2] = lladdr.s6_addr32[2];
 258                                 entry.target.s6_addr32[3] = lladdr.s6_addr32[3];
 259
 260                                 odhcp6c_update_entry_safe(STATE_RA_PREFIX, &entry, 7200);
 261                         } else if (opt->type == ND_OPT_RECURSIVE_DNS && opt->len > 2) {
 262                                 entry.router = from.sin6_addr;
 263                                 entry.priority = 0;
 264                                 entry.length = 128;
 265                                 entry.valid = ntohl(*((uint32_t*)&opt->data[2]));
 266                                 entry.preferred = 0;
 267
 268                                 for (ssize_t i = 0; i < (opt->len - 1) / 2; ++i) {
 269                                         memcpy(&entry.target, &opt->data[6 + i * sizeof(entry.target)],
 270                                                         sizeof(entry.target));
 271                                         odhcp6c_update_entry(STATE_RA_DNS, &entry);
 272                                 }
 273                         }
 274                 }
 275
 276                 size_t ra_dns_len;
 277                 struct odhcp6c_entry *entry = odhcp6c_get_state(STATE_RA_DNS, &ra_dns_len);
 278                 for (size_t i = 0; i < ra_dns_len / sizeof(*entry); ++i)
 279                         if (IN6_ARE_ADDR_EQUAL(&entry[i].router, &from.sin6_addr) &&
 280                                         entry[i].valid > router_valid)
 281                                 entry[i].valid = router_valid;
 282         }
 283
 284         odhcp6c_expire();
 285         return found;
 286 }