networking/zcip.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * RFC3927 ZeroConf IPv4 Link-Local addressing
   4  * (see <http://www.zeroconf.org/>)
   5  *
   6  * Copyright (C) 2003 by Arthur van Hoff (avh@strangeberry.com)
   7  * Copyright (C) 2004 by David Brownell
   8  *
   9  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  10  */
  11
  12 /*
  13  * ZCIP just manages the 169.254.*.* addresses.  That network is not
  14  * routed at the IP level, though various proxies or bridges can
  15  * certainly be used.  Its naming is built over multicast DNS.
  16  */
  17
  18 //#define DEBUG
  19
  20 // TODO:
  21 // - more real-world usage/testing, especially daemon mode
  22 // - kernel packet filters to reduce scheduling noise
  23 // - avoid silent script failures, especially under load...
  24 // - link status monitoring (restart on link-up; stop on link-down)
  25
  26 //usage:#define zcip_trivial_usage
  27 //usage:       "[OPTIONS] IFACE SCRIPT"
  28 //usage:#define zcip_full_usage "\n\n"
  29 //usage:       "Manage a ZeroConf IPv4 link-local address\n"
  30 //usage:     "\n        -f              Run in foreground"
  31 //usage:     "\n        -q              Quit after obtaining address"
  32 //usage:     "\n        -r 169.254.x.x  Request this address first"
  33 //usage:     "\n        -v              Verbose"
  34 //usage:     "\n"
  35 //usage:     "\nWith no -q, runs continuously monitoring for ARP conflicts,"
  36 //usage:     "\nexits only on I/O errors (link down etc)"
  37
  38 #include "libbb.h"
  39 #include <netinet/ether.h>
  40 #include <net/if.h>
  41 #include <net/if_arp.h>
  42 #include <linux/sockios.h>
  43
  44 #include <syslog.h>
  45
  46 /* We don't need more than 32 bits of the counter */
  47 #define MONOTONIC_US() ((unsigned)monotonic_us())
  48
  49 struct arp_packet {
  50         struct ether_header eth;
  51         struct ether_arp arp;
  52 } PACKED;
  53
  54 enum {
  55 /* 169.254.0.0 */
  56         LINKLOCAL_ADDR = 0xa9fe0000,
  57
  58 /* protocol timeout parameters, specified in seconds */
  59         PROBE_WAIT = 1,
  60         PROBE_MIN = 1,
  61         PROBE_MAX = 2,
  62         PROBE_NUM = 3,
  63         MAX_CONFLICTS = 10,
  64         RATE_LIMIT_INTERVAL = 60,
  65         ANNOUNCE_WAIT = 2,
  66         ANNOUNCE_NUM = 2,
  67         ANNOUNCE_INTERVAL = 2,
  68         DEFEND_INTERVAL = 10
  69 };
  70
  71 /* States during the configuration process. */
  72 enum {
  73         PROBE = 0,
  74         RATE_LIMIT_PROBE,
  75         ANNOUNCE,
  76         MONITOR,
  77         DEFEND
  78 };
  79
  80 #define VDBG(...) do { } while (0)
  81
  82
  83 enum {
  84         sock_fd = 3
  85 };
  86
  87 struct globals {
  88         struct sockaddr saddr;
  89         struct ether_addr eth_addr;
  90 } FIX_ALIASING;
  91 #define G (*(struct globals*)&bb_common_bufsiz1)
  92 #define saddr    (G.saddr   )
  93 #define eth_addr (G.eth_addr)
  94 #define INIT_G() do { } while (0)
  95
  96
  97 /**
  98  * Pick a random link local IP address on 169.254/16, except that
  99  * the first and last 256 addresses are reserved.
 100  */
 101 static uint32_t pick(void)
 102 {
 103         unsigned tmp;
 104
 105         do {
 106                 tmp = rand() & IN_CLASSB_HOST;
 107         } while (tmp > (IN_CLASSB_HOST - 0x0200));
 108         return htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
 109 }
 110
 111 /**
 112  * Broadcast an ARP packet.
 113  */
 114 static void arp(
 115         /* int op, - always ARPOP_REQUEST */
 116         /* const struct ether_addr *source_eth, - always &eth_addr */
 117                                         struct in_addr source_ip,
 118         const struct ether_addr *target_eth, struct in_addr target_ip)
 119 {
 120         enum { op = ARPOP_REQUEST };
 121 #define source_eth (&eth_addr)
 122
 123         struct arp_packet p;
 124         memset(&p, 0, sizeof(p));
 125
 126         // ether header
 127         p.eth.ether_type = htons(ETHERTYPE_ARP);
 128         memcpy(p.eth.ether_shost, source_eth, ETH_ALEN);
 129         memset(p.eth.ether_dhost, 0xff, ETH_ALEN);
 130
 131         // arp request
 132         p.arp.arp_hrd = htons(ARPHRD_ETHER);
 133         p.arp.arp_pro = htons(ETHERTYPE_IP);
 134         p.arp.arp_hln = ETH_ALEN;
 135         p.arp.arp_pln = 4;
 136         p.arp.arp_op = htons(op);
 137         memcpy(&p.arp.arp_sha, source_eth, ETH_ALEN);
 138         memcpy(&p.arp.arp_spa, &source_ip, sizeof(p.arp.arp_spa));
 139         memcpy(&p.arp.arp_tha, target_eth, ETH_ALEN);
 140         memcpy(&p.arp.arp_tpa, &target_ip, sizeof(p.arp.arp_tpa));
 141
 142         // send it
 143         // Even though sock_fd is already bound to saddr, just send()
 144         // won't work, because "socket is not connected"
 145         // (and connect() won't fix that, "operation not supported").
 146         // Thus we sendto() to saddr. I wonder which sockaddr
 147         // (from bind() or from sendto()?) kernel actually uses
 148         // to determine iface to emit the packet from...
 149         xsendto(sock_fd, &p, sizeof(p), &saddr, sizeof(saddr));
 150 #undef source_eth
 151 }
 152
 153 /**
 154  * Run a script.
 155  * argv[0]:intf argv[1]:script_name argv[2]:junk argv[3]:NULL
 156  */
 157 static int run(char *argv[3], const char *param, struct in_addr *ip)
 158 {
 159         int status;
 160         char *addr = addr; /* for gcc */
 161         const char *fmt = "%s %s %s" + 3;
 162
 163         argv[2] = (char*)param;
 164
 165         VDBG("%s run %s %s\n", argv[0], argv[1], argv[2]);
 166
 167         if (ip) {
 168                 addr = inet_ntoa(*ip);
 169                 xsetenv("ip", addr);
 170                 fmt -= 3;
 171         }
 172         bb_info_msg(fmt, argv[2], argv[0], addr);
 173
 174         status = spawn_and_wait(argv + 1);
 175         if (status < 0) {
 176                 bb_perror_msg("%s %s %s" + 3, argv[2], argv[0]);
 177                 return -errno;
 178         }
 179         if (status != 0)
 180                 bb_error_msg("script %s %s failed, exitcode=%d", argv[1], argv[2], status & 0xff);
 181         return status;
 182 }
 183
 184 /**
 185  * Return milliseconds of random delay, up to "secs" seconds.
 186  */
 187 static ALWAYS_INLINE unsigned random_delay_ms(unsigned secs)
 188 {
 189         return rand() % (secs * 1000);
 190 }
 191
 192 /**
 193  * main program
 194  */
 195 int zcip_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 196 int zcip_main(int argc UNUSED_PARAM, char **argv)
 197 {
 198         int state;
 199         char *r_opt;
 200         unsigned opts;
 201
 202         // ugly trick, but I want these zeroed in one go
 203         struct {
 204                 const struct in_addr null_ip;
 205                 const struct ether_addr null_addr;
 206                 struct in_addr ip;
 207                 struct ifreq ifr;
 208                 int timeout_ms; /* must be signed */
 209                 unsigned conflicts;
 210                 unsigned nprobes;
 211                 unsigned nclaims;
 212                 int ready;
 213                 int verbose;
 214         } L;
 215 #define null_ip    (L.null_ip   )
 216 #define null_addr  (L.null_addr )
 217 #define ip         (L.ip        )
 218 #define ifr        (L.ifr       )
 219 #define timeout_ms (L.timeout_ms)
 220 #define conflicts  (L.conflicts )
 221 #define nprobes    (L.nprobes   )
 222 #define nclaims    (L.nclaims   )
 223 #define ready      (L.ready     )
 224 #define verbose    (L.verbose   )
 225
 226         memset(&L, 0, sizeof(L));
 227         INIT_G();
 228
 229 #define FOREGROUND (opts & 1)
 230 #define QUIT       (opts & 2)
 231         // parse commandline: prog [options] ifname script
 232         // exactly 2 args; -v accumulates and implies -f
 233         opt_complementary = "=2:vv:vf";
 234         opts = getopt32(argv, "fqr:v", &r_opt, &verbose);
 235 #if !BB_MMU
 236         // on NOMMU reexec early (or else we will rerun things twice)
 237         if (!FOREGROUND)
 238                 bb_daemonize_or_rexec(0 /*was: DAEMON_CHDIR_ROOT*/, argv);
 239 #endif
 240         // open an ARP socket
 241         // (need to do it before openlog to prevent openlog from taking
 242         // fd 3 (sock_fd==3))
 243         xmove_fd(xsocket(AF_PACKET, SOCK_PACKET, htons(ETH_P_ARP)), sock_fd);
 244         if (!FOREGROUND) {
 245                 // do it before all bb_xx_msg calls
 246                 openlog(applet_name, 0, LOG_DAEMON);
 247                 logmode |= LOGMODE_SYSLOG;
 248         }
 249         if (opts & 4) { // -r n.n.n.n
 250                 if (inet_aton(r_opt, &ip) == 0
 251                  || (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR
 252                 ) {
 253                         bb_error_msg_and_die("invalid link address");
 254                 }
 255         }
 256         argv += optind - 1;
 257
 258         /* Now: argv[0]:junk argv[1]:intf argv[2]:script argv[3]:NULL */
 259         /* We need to make space for script argument: */
 260         argv[0] = argv[1];
 261         argv[1] = argv[2];
 262         /* Now: argv[0]:intf argv[1]:script argv[2]:junk argv[3]:NULL */
 263 #define argv_intf (argv[0])
 264
 265         xsetenv("interface", argv_intf);
 266
 267         // initialize the interface (modprobe, ifup, etc)
 268         if (run(argv, "init", NULL))
 269                 return EXIT_FAILURE;
 270
 271         // initialize saddr
 272         // saddr is: { u16 sa_family; u8 sa_data[14]; }
 273         //memset(&saddr, 0, sizeof(saddr));
 274         //TODO: are we leaving sa_family == 0 (AF_UNSPEC)?!
 275         safe_strncpy(saddr.sa_data, argv_intf, sizeof(saddr.sa_data));
 276
 277         // bind to the interface's ARP socket
 278         xbind(sock_fd, &saddr, sizeof(saddr));
 279
 280         // get the interface's ethernet address
 281         //memset(&ifr, 0, sizeof(ifr));
 282         strncpy_IFNAMSIZ(ifr.ifr_name, argv_intf);
 283         xioctl(sock_fd, SIOCGIFHWADDR, &ifr);
 284         memcpy(&eth_addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
 285
 286         // start with some stable ip address, either a function of
 287         // the hardware address or else the last address we used.
 288         // we are taking low-order four bytes, as top-order ones
 289         // aren't random enough.
 290         // NOTE: the sequence of addresses we try changes only
 291         // depending on when we detect conflicts.
 292         {
 293                 uint32_t t;
 294                 move_from_unaligned32(t, ((char *)&eth_addr + 2));
 295                 srand(t);
 296         }
 297         if (ip.s_addr == 0)
 298                 ip.s_addr = pick();
 299
 300         // FIXME cases to handle:
 301         //  - zcip already running!
 302         //  - link already has local address... just defend/update
 303
 304         // daemonize now; don't delay system startup
 305         if (!FOREGROUND) {
 306 #if BB_MMU
 307                 bb_daemonize(0 /*was: DAEMON_CHDIR_ROOT*/);
 308 #endif
 309                 bb_info_msg("start, interface %s", argv_intf);
 310         }
 311
 312         // run the dynamic address negotiation protocol,
 313         // restarting after address conflicts:
 314         //  - start with some address we want to try
 315         //  - short random delay
 316         //  - arp probes to see if another host uses it
 317         //  - arp announcements that we're claiming it
 318         //  - use it
 319         //  - defend it, within limits
 320         // exit if:
 321         // - address is successfully obtained and -q was given:
 322         //   run "<script> config", then exit with exitcode 0
 323         // - poll error (when does this happen?)
 324         // - read error (when does this happen?)
 325         // - sendto error (in arp()) (when does this happen?)
 326         // - revents & POLLERR (link down). run "<script> deconfig" first
 327         state = PROBE;
 328         while (1) {
 329                 struct pollfd fds[1];
 330                 unsigned deadline_us;
 331                 struct arp_packet p;
 332                 int source_ip_conflict;
 333                 int target_ip_conflict;
 334
 335                 fds[0].fd = sock_fd;
 336                 fds[0].events = POLLIN;
 337                 fds[0].revents = 0;
 338
 339                 // poll, being ready to adjust current timeout
 340                 if (!timeout_ms) {
 341                         timeout_ms = random_delay_ms(PROBE_WAIT);
 342                         // FIXME setsockopt(sock_fd, SO_ATTACH_FILTER, ...) to
 343                         // make the kernel filter out all packets except
 344                         // ones we'd care about.
 345                 }
 346                 // set deadline_us to the point in time when we timeout
 347                 deadline_us = MONOTONIC_US() + timeout_ms * 1000;
 348
 349                 VDBG("...wait %d %s nprobes=%u, nclaims=%u\n",
 350                                 timeout_ms, argv_intf, nprobes, nclaims);
 351
 352                 switch (safe_poll(fds, 1, timeout_ms)) {
 353
 354                 default:
 355                         //bb_perror_msg("poll"); - done in safe_poll
 356                         return EXIT_FAILURE;
 357
 358                 // timeout
 359                 case 0:
 360                         VDBG("state = %d\n", state);
 361                         switch (state) {
 362                         case PROBE:
 363                                 // timeouts in the PROBE state mean no conflicting ARP packets
 364                                 // have been received, so we can progress through the states
 365                                 if (nprobes < PROBE_NUM) {
 366                                         nprobes++;
 367                                         VDBG("probe/%u %s@%s\n",
 368                                                         nprobes, argv_intf, inet_ntoa(ip));
 369                                         arp(/* ARPOP_REQUEST, */
 370                                                         /* &eth_addr, */ null_ip,
 371                                                         &null_addr, ip);
 372                                         timeout_ms = PROBE_MIN * 1000;
 373                                         timeout_ms += random_delay_ms(PROBE_MAX - PROBE_MIN);
 374                                 }
 375                                 else {
 376                                         // Switch to announce state.
 377                                         state = ANNOUNCE;
 378                                         nclaims = 0;
 379                                         VDBG("announce/%u %s@%s\n",
 380                                                         nclaims, argv_intf, inet_ntoa(ip));
 381                                         arp(/* ARPOP_REQUEST, */
 382                                                         /* &eth_addr, */ ip,
 383                                                         &eth_addr, ip);
 384                                         timeout_ms = ANNOUNCE_INTERVAL * 1000;
 385                                 }
 386                                 break;
 387                         case RATE_LIMIT_PROBE:
 388                                 // timeouts in the RATE_LIMIT_PROBE state mean no conflicting ARP packets
 389                                 // have been received, so we can move immediately to the announce state
 390                                 state = ANNOUNCE;
 391                                 nclaims = 0;
 392                                 VDBG("announce/%u %s@%s\n",
 393                                                 nclaims, argv_intf, inet_ntoa(ip));
 394                                 arp(/* ARPOP_REQUEST, */
 395                                                 /* &eth_addr, */ ip,
 396                                                 &eth_addr, ip);
 397                                 timeout_ms = ANNOUNCE_INTERVAL * 1000;
 398                                 break;
 399                         case ANNOUNCE:
 400                                 // timeouts in the ANNOUNCE state mean no conflicting ARP packets
 401                                 // have been received, so we can progress through the states
 402                                 if (nclaims < ANNOUNCE_NUM) {
 403                                         nclaims++;
 404                                         VDBG("announce/%u %s@%s\n",
 405                                                         nclaims, argv_intf, inet_ntoa(ip));
 406                                         arp(/* ARPOP_REQUEST, */
 407                                                         /* &eth_addr, */ ip,
 408                                                         &eth_addr, ip);
 409                                         timeout_ms = ANNOUNCE_INTERVAL * 1000;
 410                                 }
 411                                 else {
 412                                         // Switch to monitor state.
 413                                         state = MONITOR;
 414                                         // link is ok to use earlier
 415                                         // FIXME update filters
 416                                         run(argv, "config", &ip);
 417                                         ready = 1;
 418                                         conflicts = 0;
 419                                         timeout_ms = -1; // Never timeout in the monitor state.
 420
 421                                         // NOTE: all other exit paths
 422                                         // should deconfig ...
 423                                         if (QUIT)
 424                                                 return EXIT_SUCCESS;
 425                                 }
 426                                 break;
 427                         case DEFEND:
 428                                 // We won!  No ARP replies, so just go back to monitor.
 429                                 state = MONITOR;
 430                                 timeout_ms = -1;
 431                                 conflicts = 0;
 432                                 break;
 433                         default:
 434                                 // Invalid, should never happen.  Restart the whole protocol.
 435                                 state = PROBE;
 436                                 ip.s_addr = pick();
 437                                 timeout_ms = 0;
 438                                 nprobes = 0;
 439                                 nclaims = 0;
 440                                 break;
 441                         } // switch (state)
 442                         break; // case 0 (timeout)
 443
 444                 // packets arriving, or link went down
 445                 case 1:
 446                         // We need to adjust the timeout in case we didn't receive
 447                         // a conflicting packet.
 448                         if (timeout_ms > 0) {
 449                                 unsigned diff = deadline_us - MONOTONIC_US();
 450                                 if ((int)(diff) < 0) {
 451                                         // Current time is greater than the expected timeout time.
 452                                         // Should never happen.
 453                                         VDBG("missed an expected timeout\n");
 454                                         timeout_ms = 0;
 455                                 } else {
 456                                         VDBG("adjusting timeout\n");
 457                                         timeout_ms = (diff / 1000) | 1; /* never 0 */
 458                                 }
 459                         }
 460
 461                         if ((fds[0].revents & POLLIN) == 0) {
 462                                 if (fds[0].revents & POLLERR) {
 463                                         // FIXME: links routinely go down;
 464                                         // this shouldn't necessarily exit.
 465                                         bb_error_msg("iface %s is down", argv_intf);
 466                                         if (ready) {
 467                                                 run(argv, "deconfig", &ip);
 468                                         }
 469                                         return EXIT_FAILURE;
 470                                 }
 471                                 continue;
 472                         }
 473
 474                         // read ARP packet
 475                         if (safe_read(sock_fd, &p, sizeof(p)) < 0) {
 476                                 bb_perror_msg_and_die(bb_msg_read_error);
 477                         }
 478                         if (p.eth.ether_type != htons(ETHERTYPE_ARP))
 479                                 continue;
 480 #ifdef DEBUG
 481                         {
 482                                 struct ether_addr *sha = (struct ether_addr *) p.arp.arp_sha;
 483                                 struct ether_addr *tha = (struct ether_addr *) p.arp.arp_tha;
 484                                 struct in_addr *spa = (struct in_addr *) p.arp.arp_spa;
 485                                 struct in_addr *tpa = (struct in_addr *) p.arp.arp_tpa;
 486                                 VDBG("%s recv arp type=%d, op=%d,\n",
 487                                         argv_intf, ntohs(p.eth.ether_type),
 488                                         ntohs(p.arp.arp_op));
 489                                 VDBG("\tsource=%s %s\n",
 490                                         ether_ntoa(sha),
 491                                         inet_ntoa(*spa));
 492                                 VDBG("\ttarget=%s %s\n",
 493                                         ether_ntoa(tha),
 494                                         inet_ntoa(*tpa));
 495                         }
 496 #endif
 497                         if (p.arp.arp_op != htons(ARPOP_REQUEST)
 498                          && p.arp.arp_op != htons(ARPOP_REPLY))
 499                                 continue;
 500
 501                         source_ip_conflict = 0;
 502                         target_ip_conflict = 0;
 503
 504                         if (memcmp(p.arp.arp_spa, &ip.s_addr, sizeof(struct in_addr)) == 0
 505                          && memcmp(&p.arp.arp_sha, &eth_addr, ETH_ALEN) != 0
 506                         ) {
 507                                 source_ip_conflict = 1;
 508                         }
 509                         if (p.arp.arp_op == htons(ARPOP_REQUEST)
 510                          && memcmp(p.arp.arp_tpa, &ip.s_addr, sizeof(struct in_addr)) == 0
 511                          && memcmp(&p.arp.arp_tha, &eth_addr, ETH_ALEN) != 0
 512                         ) {
 513                                 target_ip_conflict = 1;
 514                         }
 515
 516                         VDBG("state = %d, source ip conflict = %d, target ip conflict = %d\n",
 517                                 state, source_ip_conflict, target_ip_conflict);
 518                         switch (state) {
 519                         case PROBE:
 520                         case ANNOUNCE:
 521                                 // When probing or announcing, check for source IP conflicts
 522                                 // and other hosts doing ARP probes (target IP conflicts).
 523                                 if (source_ip_conflict || target_ip_conflict) {
 524                                         conflicts++;
 525                                         if (conflicts >= MAX_CONFLICTS) {
 526                                                 VDBG("%s ratelimit\n", argv_intf);
 527                                                 timeout_ms = RATE_LIMIT_INTERVAL * 1000;
 528                                                 state = RATE_LIMIT_PROBE;
 529                                         }
 530
 531                                         // restart the whole protocol
 532                                         ip.s_addr = pick();
 533                                         timeout_ms = 0;
 534                                         nprobes = 0;
 535                                         nclaims = 0;
 536                                 }
 537                                 break;
 538                         case MONITOR:
 539                                 // If a conflict, we try to defend with a single ARP probe.
 540                                 if (source_ip_conflict) {
 541                                         VDBG("monitor conflict -- defending\n");
 542                                         state = DEFEND;
 543                                         timeout_ms = DEFEND_INTERVAL * 1000;
 544                                         arp(/* ARPOP_REQUEST, */
 545                                                 /* &eth_addr, */ ip,
 546                                                 &eth_addr, ip);
 547                                 }
 548                                 break;
 549                         case DEFEND:
 550                                 // Well, we tried.  Start over (on conflict).
 551                                 if (source_ip_conflict) {
 552                                         state = PROBE;
 553                                         VDBG("defend conflict -- starting over\n");
 554                                         ready = 0;
 555                                         run(argv, "deconfig", &ip);
 556
 557                                         // restart the whole protocol
 558                                         ip.s_addr = pick();
 559                                         timeout_ms = 0;
 560                                         nprobes = 0;
 561                                         nclaims = 0;
 562                                 }
 563                                 break;
 564                         default:
 565                                 // Invalid, should never happen.  Restart the whole protocol.
 566                                 VDBG("invalid state -- starting over\n");
 567                                 state = PROBE;
 568                                 ip.s_addr = pick();
 569                                 timeout_ms = 0;
 570                                 nprobes = 0;
 571                                 nclaims = 0;
 572                                 break;
 573                         } // switch state
 574                         break; // case 1 (packets arriving)
 575                 } // switch poll
 576         } // while (1)
 577 #undef argv_intf
 578 }