networking/zcip.c

   1 /*
   2  * RFC3927 ZeroConf IPv4 Link-Local addressing
   3  * (see <http://www.zeroconf.org/>)
   4  *
   5  * Copyright (C) 2003 by Arthur van Hoff (avh@strangeberry.com)
   6  * Copyright (C) 2004 by David Brownell
   7  *
   8  * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
   9  */
  10
  11 /*
  12  * This can build as part of BusyBox or by itself:
  13  *
  14  *      $(CROSS_COMPILE)cc -Os -Wall -DNO_BUSYBOX -DDEBUG -o zcip zcip.c
  15  *
  16  * ZCIP just manages the 169.254.*.* addresses.  That network is not
  17  * routed at the IP level, though various proxies or bridges can
  18  * certainly be used.  Its naming is built over multicast DNS.
  19  */
  20
  21 // #define      DEBUG
  22
  23 // TODO:
  24 // - more real-world usage/testing, especially daemon mode
  25 // - kernel packet filters to reduce scheduling noise
  26 // - avoid silent script failures, especially under load...
  27 // - link status monitoring (restart on link-up; stop on link-down)
  28
  29 #include <errno.h>
  30 #include <stdlib.h>
  31 #include <stdio.h>
  32 #include <string.h>
  33 #include <syslog.h>
  34 #include <poll.h>
  35 #include <time.h>
  36 #include <unistd.h>
  37
  38 #include <sys/ioctl.h>
  39 #include <sys/types.h>
  40 #include <sys/wait.h>
  41 #include <sys/socket.h>
  42
  43 #include <arpa/inet.h>
  44 #include <netinet/in.h>
  45 #include <netinet/ether.h>
  46 #include <net/ethernet.h>
  47 #include <net/if.h>
  48 #include <net/if_arp.h>
  49
  50 #include <linux/if_packet.h>
  51 #include <linux/sockios.h>
  52
  53
  54 struct arp_packet {
  55         struct ether_header hdr;
  56         // FIXME this part is netinet/if_ether.h "struct ether_arp"
  57         struct arphdr arp;
  58         struct ether_addr source_addr;
  59         struct in_addr source_ip;
  60         struct ether_addr target_addr;
  61         struct in_addr target_ip;
  62 } ATTRIBUTE_PACKED;
  63
  64 enum {
  65 /* 169.254.0.0 */
  66         LINKLOCAL_ADDR = 0xa9fe0000,
  67
  68 /* protocol timeout parameters, specified in seconds */
  69         PROBE_WAIT = 1,
  70         PROBE_MIN = 1,
  71         PROBE_MAX = 2,
  72         PROBE_NUM = 3,
  73         MAX_CONFLICTS = 10,
  74         RATE_LIMIT_INTERVAL = 60,
  75         ANNOUNCE_WAIT = 2,
  76         ANNOUNCE_NUM = 2,
  77         ANNOUNCE_INTERVAL = 2,
  78         DEFEND_INTERVAL = 10
  79 };
  80
  81 static const unsigned char ZCIP_VERSION[] = "0.75 (18 April 2005)";
  82 static char *prog;
  83
  84 static const struct in_addr null_ip = { 0 };
  85 static const struct ether_addr null_addr = { {0, 0, 0, 0, 0, 0} };
  86
  87 static int verbose = 0;
  88
  89 #ifdef DEBUG
  90
  91 #define DBG(fmt,args...) \
  92         fprintf(stderr, "%s: " fmt , prog , ## args)
  93 #define VDBG(fmt,args...) do { \
  94         if (verbose) fprintf(stderr, "%s: " fmt , prog ,## args); \
  95         } while (0)
  96 #else
  97
  98 #define DBG(fmt,args...) \
  99         do { } while (0)
 100 #define VDBG    DBG
 101 #endif                          /* DEBUG */
 102
 103 /**
 104  * Pick a random link local IP address on 169.254/16, except that
 105  * the first and last 256 addresses are reserved.
 106  */
 107 static void
 108 pick(struct in_addr *ip)
 109 {
 110         unsigned        tmp;
 111
 112         /* use cheaper math than lrand48() mod N */
 113         do {
 114                 tmp = (lrand48() >> 16) & IN_CLASSB_HOST;
 115         } while (tmp > (IN_CLASSB_HOST - 0x0200));
 116         ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
 117 }
 118
 119 /**
 120  * Broadcast an ARP packet.
 121  */
 122 static int
 123 arp(int fd, struct sockaddr *saddr, int op,
 124         const struct ether_addr *source_addr, struct in_addr source_ip,
 125         const struct ether_addr *target_addr, struct in_addr target_ip)
 126 {
 127         struct arp_packet p;
 128
 129         // ether header
 130         p.hdr.ether_type = htons(ETHERTYPE_ARP);
 131         memcpy(p.hdr.ether_shost, source_addr, ETH_ALEN);
 132         memset(p.hdr.ether_dhost, 0xff, ETH_ALEN);
 133
 134         // arp request
 135         p.arp.ar_hrd = htons(ARPHRD_ETHER);
 136         p.arp.ar_pro = htons(ETHERTYPE_IP);
 137         p.arp.ar_hln = ETH_ALEN;
 138         p.arp.ar_pln = 4;
 139         p.arp.ar_op = htons(op);
 140         memcpy(&p.source_addr, source_addr, ETH_ALEN);
 141         memcpy(&p.source_ip, &source_ip, sizeof (p.source_ip));
 142         memcpy(&p.target_addr, target_addr, ETH_ALEN);
 143         memcpy(&p.target_ip, &target_ip, sizeof (p.target_ip));
 144
 145         // send it
 146         if (sendto(fd, &p, sizeof (p), 0, saddr, sizeof (*saddr)) < 0) {
 147                 perror("sendto");
 148                 return -errno;
 149         }
 150         return 0;
 151 }
 152
 153 /**
 154  * Run a script.
 155  */
 156 static int
 157 run(char *script, char *arg, char *intf, struct in_addr *ip)
 158 {
 159         int pid, status;
 160         char *why;
 161
 162         if (script != NULL) {
 163                 VDBG("%s run %s %s\n", intf, script, arg);
 164                 if (ip != NULL) {
 165                         char *addr = inet_ntoa(*ip);
 166                         setenv("ip", addr, 1);
 167                         syslog(LOG_INFO, "%s %s %s", arg, intf, addr);
 168                 }
 169
 170                 pid = vfork();
 171                 if (pid < 0) {                  // error
 172                         why = "vfork";
 173                         goto bad;
 174                 } else if (pid == 0) {          // child
 175                         execl(script, script, arg, NULL);
 176                         perror("execl");
 177                         _exit(EXIT_FAILURE);
 178                 }
 179
 180                 if (waitpid(pid, &status, 0) <= 0) {
 181                         why = "waitpid";
 182                         goto bad;
 183                 }
 184                 if (WEXITSTATUS(status) != 0) {
 185                         fprintf(stderr, "%s: script %s failed, exit=%d\n",
 186                                         prog, script, WEXITSTATUS(status));
 187                         return -errno;
 188                 }
 189         }
 190         return 0;
 191 bad:
 192         status = -errno;
 193         syslog(LOG_ERR, "%s %s, %s error: %s",
 194                 arg, intf, why, strerror(errno));
 195         return status;
 196 }
 197
 198 #ifndef NO_BUSYBOX
 199 #include "busybox.h"
 200 #endif
 201
 202 /**
 203  * Print usage information.
 204  */
 205 static void ATTRIBUTE_NORETURN
 206 zcip_usage(const char *msg)
 207 {
 208         fprintf(stderr, "%s: %s\n", prog, msg);
 209 #ifdef  NO_BUSYBOX
 210         fprintf(stderr, "Usage: %s [OPTIONS] ifname script\n"
 211                         "\t-f              foreground mode (implied by -v)\n"
 212                         "\t-q              quit after address (no daemon)\n"
 213                         "\t-r 169.254.x.x  request this address first\n"
 214                         "\t-v              verbose; show version\n",
 215                         prog);
 216         exit(0);
 217 #else
 218         bb_show_usage();
 219 #endif
 220 }
 221
 222 /**
 223  * Return milliseconds of random delay, up to "secs" seconds.
 224  */
 225 static inline unsigned
 226 ms_rdelay(unsigned secs)
 227 {
 228         return lrand48() % (secs * 1000);
 229 }
 230
 231 /**
 232  * main program
 233  */
 234
 235 #ifdef  NO_BUSYBOX
 236 int
 237 main(int argc, char *argv[])
 238         __attribute__ ((weak, alias ("zcip_main")));
 239 #endif
 240
 241 int zcip_main(int argc, char *argv[])
 242 {
 243         char *intf = NULL;
 244         char *script = NULL;
 245         int quit = 0;
 246         int foreground = 0;
 247
 248         char *why;
 249         struct sockaddr saddr;
 250         struct ether_addr addr;
 251         struct in_addr ip = { 0 };
 252         int fd;
 253         int ready = 0;
 254         suseconds_t timeout = 0;        // milliseconds
 255         time_t defend = 0;
 256         unsigned conflicts = 0;
 257         unsigned nprobes = 0;
 258         unsigned nclaims = 0;
 259         int t;
 260
 261         // parse commandline: prog [options] ifname script
 262         prog = argv[0];
 263         while ((t = getopt(argc, argv, "fqr:v")) != EOF) {
 264                 switch (t) {
 265                 case 'f':
 266                         foreground = 1;
 267                         continue;
 268                 case 'q':
 269                         quit = 1;
 270                         continue;
 271                 case 'r':
 272                         if (inet_aton(optarg, &ip) == 0
 273                                         || (ntohl(ip.s_addr) & IN_CLASSB_NET)
 274                                                 != LINKLOCAL_ADDR) {
 275                                 zcip_usage("invalid link address");
 276                         }
 277                         continue;
 278                 case 'v':
 279                         if (!verbose)
 280                                 printf("%s: version %s\n", prog, ZCIP_VERSION);
 281                         verbose++;
 282                         foreground = 1;
 283                         continue;
 284                 default:
 285                         zcip_usage("bad option");
 286                 }
 287         }
 288         if (optind < argc - 1) {
 289                 intf = argv[optind++];
 290                 setenv("interface", intf, 1);
 291                 script = argv[optind++];
 292         }
 293         if (optind != argc || !intf)
 294                 zcip_usage("wrong number of arguments");
 295         openlog(prog, 0, LOG_DAEMON);
 296
 297         // initialize the interface (modprobe, ifup, etc)
 298         if (run(script, "init", intf, NULL) < 0)
 299                 return EXIT_FAILURE;
 300
 301         // initialize saddr
 302         memset(&saddr, 0, sizeof (saddr));
 303         strncpy(saddr.sa_data, intf, sizeof (saddr.sa_data));
 304
 305         // open an ARP socket
 306         if ((fd = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP))) < 0) {
 307                 why = "open";
 308 fail:
 309                 foreground = 1;
 310                 goto bad;
 311         }
 312         // bind to the interface's ARP socket
 313         if (bind(fd, &saddr, sizeof (saddr)) < 0) {
 314                 why = "bind";
 315                 goto fail;
 316         } else {
 317                 struct ifreq ifr;
 318                 unsigned short seed[3];
 319
 320                 // get the interface's ethernet address
 321                 memset(&ifr, 0, sizeof (ifr));
 322                 strncpy(ifr.ifr_name, intf, sizeof (ifr.ifr_name));
 323                 if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0) {
 324                         why = "get ethernet address";
 325                         goto fail;
 326                 }
 327                 memcpy(&addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
 328
 329                 // start with some stable ip address, either a function of
 330                 // the hardware address or else the last address we used.
 331                 // NOTE: the sequence of addresses we try changes only
 332                 // depending on when we detect conflicts.
 333                 memcpy(seed, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
 334                 seed48(seed);
 335                 if (ip.s_addr == 0)
 336                         pick(&ip);
 337         }
 338
 339         // FIXME cases to handle:
 340         //  - zcip already running!
 341         //  - link already has local address... just defend/update
 342
 343         // daemonize now; don't delay system startup
 344         if (!foreground) {
 345                 if (daemon(0, verbose) < 0) {
 346                         why = "daemon";
 347                         goto bad;
 348                 }
 349                 syslog(LOG_INFO, "start, interface %s", intf);
 350         }
 351
 352         // run the dynamic address negotiation protocol,
 353         // restarting after address conflicts:
 354         //  - start with some address we want to try
 355         //  - short random delay
 356         //  - arp probes to see if another host else uses it
 357         //  - arp announcements that we're claiming it
 358         //  - use it
 359         //  - defend it, within limits
 360         while (1) {
 361                 struct pollfd fds[1];
 362                 struct timeval tv1;
 363                 struct arp_packet p;
 364
 365                 fds[0].fd = fd;
 366                 fds[0].events = POLLIN;
 367                 fds[0].revents = 0;
 368
 369                 // poll, being ready to adjust current timeout
 370                 if (timeout > 0) {
 371                         gettimeofday(&tv1, NULL);
 372                         tv1.tv_usec += (timeout % 1000) * 1000;
 373                         while (tv1.tv_usec > 1000000) {
 374                                 tv1.tv_usec -= 1000000;
 375                                 tv1.tv_sec++;
 376                         }
 377                         tv1.tv_sec += timeout / 1000;
 378                 } else if (timeout == 0) {
 379                         timeout = ms_rdelay(PROBE_WAIT);
 380                         // FIXME setsockopt(fd, SO_ATTACH_FILTER, ...) to
 381                         // make the kernel filter out all packets except
 382                         // ones we'd care about.
 383                 }
 384                 VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n",
 385                                 timeout, intf, nprobes, nclaims);
 386                 switch (poll(fds, 1, timeout)) {
 387
 388                 // timeouts trigger protocol transitions
 389                 case 0:
 390                         // probes
 391                         if (nprobes < PROBE_NUM) {
 392                                 nprobes++;
 393                                 VDBG("probe/%d %s@%s\n",
 394                                                 nprobes, intf, inet_ntoa(ip));
 395                                 (void)arp(fd, &saddr, ARPOP_REQUEST,
 396                                                 &addr, null_ip,
 397                                                 &null_addr, ip);
 398                                 if (nprobes < PROBE_NUM) {
 399                                         timeout = PROBE_MIN * 1000;
 400                                         timeout += ms_rdelay(PROBE_MAX
 401                                                         - PROBE_MIN);
 402                                 } else
 403                                         timeout = ANNOUNCE_WAIT * 1000;
 404                         }
 405                         // then announcements
 406                         else if (nclaims < ANNOUNCE_NUM) {
 407                                 nclaims++;
 408                                 VDBG("announce/%d %s@%s\n",
 409                                                 nclaims, intf, inet_ntoa(ip));
 410                                 (void)arp(fd, &saddr, ARPOP_REQUEST,
 411                                                 &addr, ip,
 412                                                 &addr, ip);
 413                                 if (nclaims < ANNOUNCE_NUM) {
 414                                         timeout = ANNOUNCE_INTERVAL * 1000;
 415                                 } else {
 416                                         // link is ok to use earlier
 417                                         run(script, "config", intf, &ip);
 418                                         ready = 1;
 419                                         conflicts = 0;
 420                                         timeout = -1;
 421
 422                                         // NOTE:  all other exit paths
 423                                         // should deconfig ...
 424                                         if (quit)
 425                                                 return EXIT_SUCCESS;
 426                                         // FIXME update filters
 427                                 }
 428                         }
 429                         break;
 430
 431                 // packets arriving
 432                 case 1:
 433                         // maybe adjust timeout
 434                         if (timeout > 0) {
 435                                 struct timeval tv2;
 436
 437                                 gettimeofday(&tv2, NULL);
 438                                 if (timercmp(&tv1, &tv2, <)) {
 439                                         timeout = 0;
 440                                 } else {
 441                                         timersub(&tv1, &tv2, &tv1);
 442                                         timeout = 1000 * tv1.tv_sec
 443                                                         + tv1.tv_usec / 1000;
 444                                 }
 445                         }
 446                         if ((fds[0].revents & POLLIN) == 0) {
 447                                 if (fds[0].revents & POLLERR) {
 448                                         // FIXME: links routinely go down;
 449                                         // this shouldn't necessarily exit.
 450                                         fprintf(stderr, "%s %s: poll error\n",
 451                                                         prog, intf);
 452                                         if (ready) {
 453                                                 run(script, "deconfig",
 454                                                                 intf, &ip);
 455                                         }
 456                                         return EXIT_FAILURE;
 457                                 }
 458                                 continue;
 459                         }
 460                         // read ARP packet
 461                         if (recv(fd, &p, sizeof (p), 0) < 0) {
 462                                 why = "recv";
 463                                 goto bad;
 464                         }
 465                         if (p.hdr.ether_type != htons(ETHERTYPE_ARP))
 466                                 continue;
 467
 468                         VDBG("%s recv arp type=%d, op=%d,\n",
 469                                         intf, ntohs(p.hdr.ether_type),
 470                                         ntohs(p.arp.ar_op));
 471                         VDBG("\tsource=%s %s\n",
 472                                         ether_ntoa(&p.source_addr),
 473                                         inet_ntoa(p.source_ip));
 474                         VDBG("\ttarget=%s %s\n",
 475                                         ether_ntoa(&p.target_addr),
 476                                         inet_ntoa(p.target_ip));
 477                         if (p.arp.ar_op != htons(ARPOP_REQUEST)
 478                                         && p.arp.ar_op != htons(ARPOP_REPLY))
 479                                 continue;
 480
 481                         // some cases are always conflicts
 482                         if ((p.source_ip.s_addr == ip.s_addr)
 483                                         && (memcmp(&addr, &p.source_addr,
 484                                                         ETH_ALEN) != 0)) {
 485 collision:
 486                                 VDBG("%s ARP conflict from %s\n", intf,
 487                                                 ether_ntoa(&p.source_addr));
 488                                 if (ready) {
 489                                         time_t now = time(0);
 490
 491                                         if ((defend + DEFEND_INTERVAL)
 492                                                         < now) {
 493                                                 defend = now;
 494                                                 (void)arp(fd, &saddr,
 495                                                                 ARPOP_REQUEST,
 496                                                                 &addr, ip,
 497                                                                 &addr, ip);
 498                                                 VDBG("%s defend\n", intf);
 499                                                 timeout = -1;
 500                                                 continue;
 501                                         }
 502                                         defend = now;
 503                                         ready = 0;
 504                                         run(script, "deconfig", intf, &ip);
 505                                         // FIXME rm filters: setsockopt(fd,
 506                                         // SO_DETACH_FILTER, ...)
 507                                 }
 508                                 conflicts++;
 509                                 if (conflicts >= MAX_CONFLICTS) {
 510                                         VDBG("%s ratelimit\n", intf);
 511                                         sleep(RATE_LIMIT_INTERVAL);
 512                                 }
 513                                 // restart the whole protocol
 514                                 pick(&ip);
 515                                 timeout = 0;
 516                                 nprobes = 0;
 517                                 nclaims = 0;
 518                         }
 519                         // two hosts probing one address is a collision too
 520                         else if (p.target_ip.s_addr == ip.s_addr
 521                                         && nclaims == 0
 522                                         && p.arp.ar_op == htons(ARPOP_REQUEST)
 523                                         && memcmp(&addr, &p.target_addr,
 524                                                         ETH_ALEN) != 0) {
 525                                 goto collision;
 526                         }
 527                         break;
 528
 529                 default:
 530                         why = "poll";
 531                         goto bad;
 532                 }
 533         }
 534 bad:
 535         if (foreground)
 536                 perror(why);
 537         else
 538                 syslog(LOG_ERR, "%s %s, %s error: %s",
 539                         prog, intf, why, strerror(errno));
 540         return EXIT_FAILURE;
 541 }