1 /* vi: set sw=4 ts=4: */
3 * RFC3927 ZeroConf IPv4 Link-Local addressing
4 * (see <http://www.zeroconf.org/>)
6 * Copyright (C) 2003 by Arthur van Hoff (avh@strangeberry.com)
7 * Copyright (C) 2004 by David Brownell
9 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
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.
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)
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 -l x.x.0.0 Use this range instead of 169.254"
34 //usage: "\n -v Verbose"
36 //usage: "\n$LOGGING=none Suppress logging"
37 //usage: "\n$LOGGING=syslog Log to syslog"
39 //usage: "\nWith no -q, runs continuously monitoring for ARP conflicts,"
40 //usage: "\nexits only on I/O errors (link down etc)"
43 #include "common_bufsiz.h"
44 #include <netinet/ether.h>
46 #include <net/if_arp.h>
47 #include <linux/sockios.h>
51 /* We don't need more than 32 bits of the counter */
52 #define MONOTONIC_US() ((unsigned)monotonic_us())
55 struct ether_header eth;
60 /* 0-1 seconds before sending 1st probe */
62 /* 1-2 seconds between probes */
65 PROBE_NUM = 3, /* total probes to send */
66 ANNOUNCE_INTERVAL = 2, /* 2 seconds between announces */
67 ANNOUNCE_NUM = 3, /* announces to send */
68 /* if probe/announce sees a conflict, multiply RANDOM(NUM_CONFLICT) by... */
69 CONFLICT_MULTIPLIER = 2,
70 /* if we monitor and see a conflict, how long is defend state? */
74 /* States during the configuration process. */
82 #define VDBG(...) do { } while (0)
90 struct sockaddr iface_sockaddr;
91 struct ether_addr our_ethaddr;
94 #define G (*(struct globals*)bb_common_bufsiz1)
95 #define INIT_G() do { setup_common_bufsiz(); } while (0)
99 * Pick a random link local IP address on 169.254/16, except that
100 * the first and last 256 addresses are reserved.
102 static uint32_t pick_nip(void)
107 tmp = rand() & IN_CLASSB_HOST;
108 } while (tmp > (IN_CLASSB_HOST - 0x0200));
109 return htonl((G.localnet_ip + 0x0100) + tmp);
112 static const char *nip_to_a(uint32_t nip)
116 return inet_ntoa(in);
120 * Broadcast an ARP packet.
122 static void send_arp_request(
123 /* int op, - always ARPOP_REQUEST */
124 /* const struct ether_addr *source_eth, - always &G.our_ethaddr */
126 const struct ether_addr *target_eth, uint32_t target_nip)
128 enum { op = ARPOP_REQUEST };
129 #define source_eth (&G.our_ethaddr)
132 memset(&p, 0, sizeof(p));
135 p.eth.ether_type = htons(ETHERTYPE_ARP);
136 memcpy(p.eth.ether_shost, source_eth, ETH_ALEN);
137 memset(p.eth.ether_dhost, 0xff, ETH_ALEN);
140 p.arp.arp_hrd = htons(ARPHRD_ETHER);
141 p.arp.arp_pro = htons(ETHERTYPE_IP);
142 p.arp.arp_hln = ETH_ALEN;
144 p.arp.arp_op = htons(op);
145 memcpy(&p.arp.arp_sha, source_eth, ETH_ALEN);
146 memcpy(&p.arp.arp_spa, &source_nip, 4);
147 memcpy(&p.arp.arp_tha, target_eth, ETH_ALEN);
148 memcpy(&p.arp.arp_tpa, &target_nip, 4);
151 // Even though sock_fd is already bound to G.iface_sockaddr, just send()
152 // won't work, because "socket is not connected"
153 // (and connect() won't fix that, "operation not supported").
154 // Thus we sendto() to G.iface_sockaddr. I wonder which sockaddr
155 // (from bind() or from sendto()?) kernel actually uses
156 // to determine iface to emit the packet from...
157 xsendto(sock_fd, &p, sizeof(p), &G.iface_sockaddr, sizeof(G.iface_sockaddr));
163 * argv[0]:intf argv[1]:script_name argv[2]:junk argv[3]:NULL
165 static int run(char *argv[3], const char *param, uint32_t nip)
168 const char *addr = addr; /* for gcc */
169 const char *fmt = "%s %s %s" + 3;
171 argv[2] = (char*)param;
173 VDBG("%s run %s %s\n", argv[0], argv[1], argv[2]);
176 addr = nip_to_a(nip);
180 bb_error_msg(fmt, argv[2], argv[0], addr);
182 status = spawn_and_wait(argv + 1);
184 bb_perror_msg("%s %s %s" + 3, argv[2], argv[0]);
188 bb_error_msg("script %s %s failed, exitcode=%d", argv[1], argv[2], status & 0xff);
193 * Return milliseconds of random delay, up to "secs" seconds.
195 static ALWAYS_INLINE unsigned random_delay_ms(unsigned secs)
197 return (unsigned)rand() % (secs * 1000);
203 int zcip_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
204 int zcip_main(int argc UNUSED_PARAM, char **argv)
207 const char *l_opt = "169.254.0.0";
212 // Ugly trick, but I want these zeroed in one go
214 const struct ether_addr null_ethaddr;
218 int timeout_ms; // must be signed
221 #define null_ethaddr (L.null_ethaddr)
223 #define chosen_nip (L.chosen_nip )
224 #define conflicts (L.conflicts )
225 #define timeout_ms (L.timeout_ms )
226 #define verbose (L.verbose )
228 memset(&L, 0, sizeof(L));
231 #define FOREGROUND (opts & 1)
232 #define QUIT (opts & 2)
233 // Parse commandline: prog [options] ifname script
234 // exactly 2 args; -v accumulates and implies -f
235 opt_complementary = "=2:vv:vf";
236 opts = getopt32(argv, "fqr:l:v", &r_opt, &l_opt, &verbose);
238 // on NOMMU reexec early (or else we will rerun things twice)
240 bb_daemonize_or_rexec(0 /*was: DAEMON_CHDIR_ROOT*/, argv);
242 // Open an ARP socket
243 // (need to do it before openlog to prevent openlog from taking
244 // fd 3 (sock_fd==3))
245 xmove_fd(xsocket(AF_PACKET, SOCK_PACKET, htons(ETH_P_ARP)), sock_fd);
247 // do it before all bb_xx_msg calls
248 openlog(applet_name, 0, LOG_DAEMON);
249 logmode |= LOGMODE_SYSLOG;
251 bb_logenv_override();
255 if (inet_aton(l_opt, &net) == 0
256 || (net.s_addr & htonl(IN_CLASSB_NET)) != net.s_addr
258 bb_error_msg_and_die("invalid network address");
260 G.localnet_ip = ntohl(net.s_addr);
262 if (opts & 4) { // -r n.n.n.n
264 if (inet_aton(r_opt, &ip) == 0
265 || (ntohl(ip.s_addr) & IN_CLASSB_NET) != G.localnet_ip
267 bb_error_msg_and_die("invalid link address");
269 chosen_nip = ip.s_addr;
273 /* Now: argv[0]:junk argv[1]:intf argv[2]:script argv[3]:NULL */
274 /* We need to make space for script argument: */
277 /* Now: argv[0]:intf argv[1]:script argv[2]:junk argv[3]:NULL */
278 #define argv_intf (argv[0])
280 xsetenv("interface", argv_intf);
282 // Initialize the interface (modprobe, ifup, etc)
283 if (run(argv, "init", 0))
286 // Initialize G.iface_sockaddr
287 // G.iface_sockaddr is: { u16 sa_family; u8 sa_data[14]; }
288 //memset(&G.iface_sockaddr, 0, sizeof(G.iface_sockaddr));
289 //TODO: are we leaving sa_family == 0 (AF_UNSPEC)?!
290 safe_strncpy(G.iface_sockaddr.sa_data, argv_intf, sizeof(G.iface_sockaddr.sa_data));
292 // Bind to the interface's ARP socket
293 xbind(sock_fd, &G.iface_sockaddr, sizeof(G.iface_sockaddr));
295 // Get the interface's ethernet address
296 //memset(&ifr, 0, sizeof(ifr));
297 strncpy_IFNAMSIZ(ifr.ifr_name, argv_intf);
298 xioctl(sock_fd, SIOCGIFHWADDR, &ifr);
299 memcpy(&G.our_ethaddr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
301 // Start with some stable ip address, either a function of
302 // the hardware address or else the last address we used.
303 // we are taking low-order four bytes, as top-order ones
304 // aren't random enough.
305 // NOTE: the sequence of addresses we try changes only
306 // depending on when we detect conflicts.
309 move_from_unaligned32(t, ((char *)&G.our_ethaddr + 2));
312 // FIXME cases to handle:
313 // - zcip already running!
314 // - link already has local address... just defend/update
316 // Daemonize now; don't delay system startup
319 bb_daemonize(0 /*was: DAEMON_CHDIR_ROOT*/);
321 bb_error_msg("start, interface %s", argv_intf);
324 // Run the dynamic address negotiation protocol,
325 // restarting after address conflicts:
326 // - start with some address we want to try
327 // - short random delay
328 // - arp probes to see if another host uses it
329 // 00:04:e2:64:23:c2 > ff:ff:ff:ff:ff:ff arp who-has 169.254.194.171 tell 0.0.0.0
330 // - arp announcements that we're claiming it
331 // 00:04:e2:64:23:c2 > ff:ff:ff:ff:ff:ff arp who-has 169.254.194.171 (00:04:e2:64:23:c2) tell 169.254.194.171
333 // - defend it, within limits
335 // - address is successfully obtained and -q was given:
336 // run "<script> config", then exit with exitcode 0
337 // - poll error (when does this happen?)
338 // - read error (when does this happen?)
339 // - sendto error (in send_arp_request()) (when does this happen?)
340 // - revents & POLLERR (link down). run "<script> deconfig" first
341 if (chosen_nip == 0) {
343 chosen_nip = pick_nip();
348 struct pollfd fds[1];
349 unsigned deadline_us = deadline_us;
355 fds[0].events = POLLIN;
358 // Poll, being ready to adjust current timeout
360 timeout_ms = random_delay_ms(PROBE_WAIT);
361 // FIXME setsockopt(sock_fd, SO_ATTACH_FILTER, ...) to
362 // make the kernel filter out all packets except
363 // ones we'd care about.
365 if (timeout_ms >= 0) {
366 // Set deadline_us to the point in time when we timeout
367 deadline_us = MONOTONIC_US() + timeout_ms * 1000;
370 VDBG("...wait %d %s nsent=%u\n",
371 timeout_ms, argv_intf, nsent);
373 n = safe_poll(fds, 1, timeout_ms);
375 //bb_perror_msg("poll"); - done in safe_poll
378 if (n == 0) { // timed out?
379 VDBG("state:%d\n", state);
382 // No conflicting ARP packets were seen:
383 // we can progress through the states
384 if (nsent < PROBE_NUM) {
386 VDBG("probe/%u %s@%s\n",
387 nsent, argv_intf, nip_to_a(chosen_nip));
388 timeout_ms = PROBE_MIN * 1000;
389 timeout_ms += random_delay_ms(PROBE_MAX - PROBE_MIN);
390 send_arp_request(0, &null_ethaddr, chosen_nip);
393 // Switch to announce state
398 // No conflicting ARP packets were seen:
399 // we can progress through the states
400 if (nsent < ANNOUNCE_NUM) {
403 VDBG("announce/%u %s@%s\n",
404 nsent, argv_intf, nip_to_a(chosen_nip));
405 timeout_ms = ANNOUNCE_INTERVAL * 1000;
406 send_arp_request(chosen_nip, &G.our_ethaddr, chosen_nip);
409 // Switch to monitor state
410 // FIXME update filters
411 run(argv, "config", chosen_nip);
412 // NOTE: all other exit paths should deconfig...
415 // fall through: switch to MONITOR
418 // case MONITOR: (shouldn't happen, MONITOR timeout is infinite)
419 // Defend period ended with no ARP replies - we won
420 timeout_ms = -1; // never timeout in monitor state
426 // Packet arrived, or link went down.
427 // We need to adjust the timeout in case we didn't receive
428 // a conflicting packet.
429 if (timeout_ms > 0) {
430 unsigned diff = deadline_us - MONOTONIC_US();
431 if ((int)(diff) < 0) {
432 // Current time is greater than the expected timeout time.
435 VDBG("adjusting timeout\n");
436 timeout_ms = (diff / 1000) | 1; // never 0
439 if ((fds[0].revents & POLLIN) == 0) {
440 if (fds[0].revents & POLLERR) {
441 // FIXME: links routinely go down;
442 // this shouldn't necessarily exit.
443 bb_error_msg("iface %s is down", argv_intf);
444 if (state >= MONITOR) {
445 // Only if we are in MONITOR or DEFEND
446 run(argv, "deconfig", chosen_nip);
454 if (safe_read(sock_fd, &p, sizeof(p)) < 0) {
455 bb_perror_msg_and_die(bb_msg_read_error);
458 if (p.eth.ether_type != htons(ETHERTYPE_ARP))
460 if (p.arp.arp_op != htons(ARPOP_REQUEST)
461 && p.arp.arp_op != htons(ARPOP_REPLY)
467 struct ether_addr *sha = (struct ether_addr *) p.arp.arp_sha;
468 struct ether_addr *tha = (struct ether_addr *) p.arp.arp_tha;
469 struct in_addr *spa = (struct in_addr *) p.arp.arp_spa;
470 struct in_addr *tpa = (struct in_addr *) p.arp.arp_tpa;
471 VDBG("source=%s %s\n", ether_ntoa(sha), inet_ntoa(*spa));
472 VDBG("target=%s %s\n", ether_ntoa(tha), inet_ntoa(*tpa));
476 if (memcmp(&p.arp.arp_sha, &G.our_ethaddr, ETH_ALEN) != 0) {
477 if (memcmp(p.arp.arp_spa, &chosen_nip, 4) == 0) {
478 // A probe or reply with source_ip == chosen ip
481 if (p.arp.arp_op == htons(ARPOP_REQUEST)
482 && memcmp(p.arp.arp_spa, &const_int_0, 4) == 0
483 && memcmp(p.arp.arp_tpa, &chosen_nip, 4) == 0
485 // A probe with source_ip == 0.0.0.0, target_ip == chosen ip:
486 // another host trying to claim this ip!
490 VDBG("state:%d ip_conflict:%d\n", state, ip_conflict);
494 // Either src or target IP conflict exists
495 if (state <= ANNOUNCE) {
498 timeout_ms = PROBE_MIN * 1000
499 + CONFLICT_MULTIPLIER * random_delay_ms(conflicts);
500 goto new_nip_and_PROBE;
503 // MONITOR or DEFEND: only src IP conflict is a problem
504 if (ip_conflict & 1) {
505 if (state == MONITOR) {
506 // Src IP conflict, defend with a single ARP probe
507 VDBG("monitor conflict - defending\n");
508 timeout_ms = DEFEND_INTERVAL * 1000;
510 send_arp_request(chosen_nip, &G.our_ethaddr, chosen_nip);
514 // Another src IP conflict, start over
515 VDBG("defend conflict - starting over\n");
516 run(argv, "deconfig", chosen_nip);
519 goto new_nip_and_PROBE;
521 // Note: if we only have a target IP conflict here (ip_conflict & 2),
522 // IOW: if we just saw this sort of ARP packet:
523 // aa:bb:cc:dd:ee:ff > xx:xx:xx:xx:xx:xx arp who-has <chosen_nip> tell 0.0.0.0
524 // we expect _kernel_ to respond to that, because <chosen_nip>
525 // is (expected to be) configured on this iface.