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 * ZCIP just manages the 169.254.*.* addresses. That network is not
13 * routed at the IP level, though various proxies or bridges can
14 * certainly be used. Its naming is built over multicast DNS.
15 */
16 //config:config ZCIP
17 //config: bool "zcip (8.4 kb)"
18 //config: default y
19 //config: select FEATURE_SYSLOG
20 //config: help
21 //config: ZCIP provides ZeroConf IPv4 address selection, according to RFC 3927.
22 //config: It's a daemon that allocates and defends a dynamically assigned
23 //config: address on the 169.254/16 network, requiring no system administrator.
24 //config:
25 //config: See http://www.zeroconf.org for further details, and "zcip.script"
26 //config: in the busybox examples.
27
28 //applet:IF_ZCIP(APPLET(zcip, BB_DIR_SBIN, BB_SUID_DROP))
29
30 //kbuild:lib-$(CONFIG_ZCIP) += zcip.o
31
32 //#define DEBUG
33
34 // TODO:
35 // - more real-world usage/testing, especially daemon mode
36 // - kernel packet filters to reduce scheduling noise
37 // - avoid silent script failures, especially under load...
38 // - link status monitoring (restart on link-up; stop on link-down)
39
40 //usage:#define zcip_trivial_usage
41 //usage: "[OPTIONS] IFACE SCRIPT"
42 //usage:#define zcip_full_usage "\n\n"
43 //usage: "Manage a ZeroConf IPv4 link-local address\n"
44 //usage: "\n -f Run in foreground"
45 //usage: "\n -q Quit after obtaining address"
46 //usage: "\n -r 169.254.x.x Request this address first"
47 //usage: "\n -l x.x.0.0 Use this range instead of 169.254"
48 //usage: "\n -v Verbose"
49 //usage: "\n"
50 //usage: "\n$LOGGING=none Suppress logging"
51 //usage: "\n$LOGGING=syslog Log to syslog"
52 //usage: "\n"
53 //usage: "\nWith no -q, runs continuously monitoring for ARP conflicts,"
54 //usage: "\nexits only on I/O errors (link down etc)"
55
56 #include "libbb.h"
57 #include "common_bufsiz.h"
58 #include <netinet/ether.h>
59 #include <net/if.h>
60 #include <net/if_arp.h>
61 #include <linux/sockios.h>
62
63 #include <syslog.h>
64
65 /* We don't need more than 32 bits of the counter */
66 #define MONOTONIC_US() ((unsigned)monotonic_us())
67
68 struct arp_packet {
69 struct ether_header eth;
70 struct ether_arp arp;
71 } PACKED;
72
73 enum {
74 /* 0-1 seconds before sending 1st probe */
75 PROBE_WAIT = 1,
76 /* 1-2 seconds between probes */
77 PROBE_MIN = 1,
78 PROBE_MAX = 2,
79 PROBE_NUM = 3, /* total probes to send */
80 ANNOUNCE_INTERVAL = 2, /* 2 seconds between announces */
81 ANNOUNCE_NUM = 3, /* announces to send */
82 /* if probe/announce sees a conflict, multiply RANDOM(NUM_CONFLICT) by... */
83 CONFLICT_MULTIPLIER = 2,
84 /* if we monitor and see a conflict, how long is defend state? */
85 DEFEND_INTERVAL = 10,
86 };
87
88 /* States during the configuration process. */
89 enum {
90 PROBE = 0,
91 ANNOUNCE,
92 MONITOR,
93 DEFEND
94 };
95
96 #define VDBG(...) do { } while (0)
97
98
99 enum {
100 sock_fd = 3
101 };
102
103 struct globals {
104 struct sockaddr iface_sockaddr;
105 struct ether_addr our_ethaddr;
106 uint32_t localnet_ip;
107 } FIX_ALIASING;
108 #define G (*(struct globals*)bb_common_bufsiz1)
109 #define INIT_G() do { setup_common_bufsiz(); } while (0)
110
111
112 /**
113 * Pick a random link local IP address on 169.254/16, except that
114 * the first and last 256 addresses are reserved.
115 */
pick_nip(void)116 static uint32_t pick_nip(void)
117 {
118 unsigned tmp;
119
120 do {
121 tmp = rand() & IN_CLASSB_HOST;
122 } while (tmp > (IN_CLASSB_HOST - 0x0200));
123 return htonl((G.localnet_ip + 0x0100) + tmp);
124 }
125
nip_to_a(uint32_t nip)126 static const char *nip_to_a(uint32_t nip)
127 {
128 struct in_addr in;
129 in.s_addr = nip;
130 return inet_ntoa(in);
131 }
132
133 /**
134 * Broadcast an ARP packet.
135 */
send_arp_request(uint32_t source_nip,const struct ether_addr * target_eth,uint32_t target_nip)136 static void send_arp_request(
137 /* int op, - always ARPOP_REQUEST */
138 /* const struct ether_addr *source_eth, - always &G.our_ethaddr */
139 uint32_t source_nip,
140 const struct ether_addr *target_eth, uint32_t target_nip)
141 {
142 enum { op = ARPOP_REQUEST };
143 #define source_eth (&G.our_ethaddr)
144
145 struct arp_packet p;
146 memset(&p, 0, sizeof(p));
147
148 // ether header
149 p.eth.ether_type = htons(ETHERTYPE_ARP);
150 memcpy(p.eth.ether_shost, source_eth, ETH_ALEN);
151 memset(p.eth.ether_dhost, 0xff, ETH_ALEN);
152
153 // arp request
154 p.arp.arp_hrd = htons(ARPHRD_ETHER);
155 p.arp.arp_pro = htons(ETHERTYPE_IP);
156 p.arp.arp_hln = ETH_ALEN;
157 p.arp.arp_pln = 4;
158 p.arp.arp_op = htons(op);
159 memcpy(&p.arp.arp_sha, source_eth, ETH_ALEN);
160 memcpy(&p.arp.arp_spa, &source_nip, 4);
161 memcpy(&p.arp.arp_tha, target_eth, ETH_ALEN);
162 memcpy(&p.arp.arp_tpa, &target_nip, 4);
163
164 // send it
165 // Even though sock_fd is already bound to G.iface_sockaddr, just send()
166 // won't work, because "socket is not connected"
167 // (and connect() won't fix that, "operation not supported").
168 // Thus we sendto() to G.iface_sockaddr. I wonder which sockaddr
169 // (from bind() or from sendto()?) kernel actually uses
170 // to determine iface to emit the packet from...
171 xsendto(sock_fd, &p, sizeof(p), &G.iface_sockaddr, sizeof(G.iface_sockaddr));
172 #undef source_eth
173 }
174
175 /**
176 * Run a script.
177 * argv[0]:intf argv[1]:script_name argv[2]:junk argv[3]:NULL
178 */
run(char * argv[3],const char * param,uint32_t nip)179 static int run(char *argv[3], const char *param, uint32_t nip)
180 {
181 int status;
182 const char *addr = addr; /* for gcc */
183 const char *fmt = "%s %s %s" + 3;
184 char *env_ip = env_ip;
185
186 argv[2] = (char*)param;
187
188 VDBG("%s run %s %s\n", argv[0], argv[1], argv[2]);
189
190 if (nip != 0) {
191 addr = nip_to_a(nip);
192 /* Must not use setenv() repeatedly, it leaks memory. Use putenv() */
193 env_ip = xasprintf("ip=%s", addr);
194 putenv(env_ip);
195 fmt -= 3;
196 }
197 bb_info_msg(fmt, argv[2], argv[0], addr);
198 status = spawn_and_wait(argv + 1);
199 if (nip != 0)
200 bb_unsetenv_and_free(env_ip);
201
202 if (status < 0) {
203 bb_perror_msg("%s %s %s" + 3, argv[2], argv[0]);
204 return -errno;
205 }
206 if (status != 0)
207 bb_error_msg("script %s %s failed, exitcode=%d", argv[1], argv[2], status & 0xff);
208 return status;
209 }
210
211 /**
212 * Return milliseconds of random delay, up to "secs" seconds.
213 */
random_delay_ms(unsigned secs)214 static ALWAYS_INLINE unsigned random_delay_ms(unsigned secs)
215 {
216 return (unsigned)rand() % (secs * 1000);
217 }
218
219 /**
220 * main program
221 */
222 int zcip_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
zcip_main(int argc UNUSED_PARAM,char ** argv)223 int zcip_main(int argc UNUSED_PARAM, char **argv)
224 {
225 char *r_opt;
226 const char *l_opt = "169.254.0.0";
227 int state;
228 int nsent;
229 unsigned opts;
230
231 // Ugly trick, but I want these zeroed in one go
232 struct {
233 const struct ether_addr null_ethaddr;
234 struct ifreq ifr;
235 uint32_t chosen_nip;
236 int conflicts;
237 int timeout_ms; // must be signed
238 int verbose;
239 } L;
240 #define null_ethaddr (L.null_ethaddr)
241 #define ifr (L.ifr )
242 #define chosen_nip (L.chosen_nip )
243 #define conflicts (L.conflicts )
244 #define timeout_ms (L.timeout_ms )
245 #define verbose (L.verbose )
246
247 memset(&L, 0, sizeof(L));
248 INIT_G();
249
250 #define FOREGROUND (opts & 1)
251 #define QUIT (opts & 2)
252 // Parse commandline: prog [options] ifname script
253 // exactly 2 args; -v accumulates and implies -f
254 opts = getopt32(argv, "^" "fqr:l:v" "\0" "=2:vv:vf",
255 &r_opt, &l_opt, &verbose
256 );
257 #if !BB_MMU
258 // on NOMMU reexec early (or else we will rerun things twice)
259 if (!FOREGROUND)
260 bb_daemonize_or_rexec(0 /*was: DAEMON_CHDIR_ROOT*/, argv);
261 #endif
262 // Open an ARP socket
263 // (need to do it before openlog to prevent openlog from taking
264 // fd 3 (sock_fd==3))
265 xmove_fd(xsocket(AF_PACKET, SOCK_PACKET, htons(ETH_P_ARP)), sock_fd);
266 if (!FOREGROUND) {
267 // do it before all bb_xx_msg calls
268 openlog(applet_name, 0, LOG_DAEMON);
269 logmode |= LOGMODE_SYSLOG;
270 }
271 bb_logenv_override();
272
273 { // -l n.n.n.n
274 struct in_addr net;
275 if (inet_aton(l_opt, &net) == 0
276 || (net.s_addr & htonl(IN_CLASSB_NET)) != net.s_addr
277 ) {
278 bb_simple_error_msg_and_die("invalid network address");
279 }
280 G.localnet_ip = ntohl(net.s_addr);
281 }
282 if (opts & 4) { // -r n.n.n.n
283 struct in_addr ip;
284 if (inet_aton(r_opt, &ip) == 0
285 || (ntohl(ip.s_addr) & IN_CLASSB_NET) != G.localnet_ip
286 ) {
287 bb_simple_error_msg_and_die("invalid link address");
288 }
289 chosen_nip = ip.s_addr;
290 }
291 argv += optind - 1;
292
293 /* Now: argv[0]:junk argv[1]:intf argv[2]:script argv[3]:NULL */
294 /* We need to make space for script argument: */
295 argv[0] = argv[1];
296 argv[1] = argv[2];
297 /* Now: argv[0]:intf argv[1]:script argv[2]:junk argv[3]:NULL */
298 #define argv_intf (argv[0])
299
300 xsetenv("interface", argv_intf);
301
302 // Initialize the interface (modprobe, ifup, etc)
303 if (run(argv, "init", 0))
304 return EXIT_FAILURE;
305
306 // Initialize G.iface_sockaddr
307 // G.iface_sockaddr is: { u16 sa_family; u8 sa_data[14]; }
308 //memset(&G.iface_sockaddr, 0, sizeof(G.iface_sockaddr));
309 //TODO: are we leaving sa_family == 0 (AF_UNSPEC)?!
310 safe_strncpy(G.iface_sockaddr.sa_data, argv_intf, sizeof(G.iface_sockaddr.sa_data));
311
312 // Bind to the interface's ARP socket
313 xbind(sock_fd, &G.iface_sockaddr, sizeof(G.iface_sockaddr));
314
315 // Get the interface's ethernet address
316 //memset(&ifr, 0, sizeof(ifr));
317 strncpy_IFNAMSIZ(ifr.ifr_name, argv_intf);
318 xioctl(sock_fd, SIOCGIFHWADDR, &ifr);
319 memcpy(&G.our_ethaddr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
320
321 // Start with some stable ip address, either a function of
322 // the hardware address or else the last address we used.
323 // we are taking low-order four bytes, as top-order ones
324 // aren't random enough.
325 // NOTE: the sequence of addresses we try changes only
326 // depending on when we detect conflicts.
327 {
328 uint32_t t;
329 move_from_unaligned32(t, ((char *)&G.our_ethaddr + 2));
330 srand(t);
331 }
332 // FIXME cases to handle:
333 // - zcip already running!
334 // - link already has local address... just defend/update
335
336 // Daemonize now; don't delay system startup
337 if (!FOREGROUND) {
338 #if BB_MMU
339 bb_daemonize(0 /*was: DAEMON_CHDIR_ROOT*/);
340 #endif
341 bb_info_msg("start, interface %s", argv_intf);
342 }
343
344 // Run the dynamic address negotiation protocol,
345 // restarting after address conflicts:
346 // - start with some address we want to try
347 // - short random delay
348 // - arp probes to see if another host uses it
349 // 00:04:e2:64:23:c2 > ff:ff:ff:ff:ff:ff arp who-has 169.254.194.171 tell 0.0.0.0
350 // - arp announcements that we're claiming it
351 // 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
352 // - use it
353 // - defend it, within limits
354 // exit if:
355 // - address is successfully obtained and -q was given:
356 // run "<script> config", then exit with exitcode 0
357 // - poll error (when does this happen?)
358 // - read error (when does this happen?)
359 // - sendto error (in send_arp_request()) (when does this happen?)
360 // - revents & POLLERR (link down). run "<script> deconfig" first
361 if (chosen_nip == 0) {
362 new_nip_and_PROBE:
363 chosen_nip = pick_nip();
364 }
365 nsent = 0;
366 state = PROBE;
367 while (1) {
368 struct pollfd fds[1];
369 unsigned deadline_us = deadline_us;
370 struct arp_packet p;
371 int ip_conflict;
372 int n;
373
374 fds[0].fd = sock_fd;
375 fds[0].events = POLLIN;
376 fds[0].revents = 0;
377
378 // Poll, being ready to adjust current timeout
379 if (!timeout_ms) {
380 timeout_ms = random_delay_ms(PROBE_WAIT);
381 // FIXME setsockopt(sock_fd, SO_ATTACH_FILTER, ...) to
382 // make the kernel filter out all packets except
383 // ones we'd care about.
384 }
385 if (timeout_ms >= 0) {
386 // Set deadline_us to the point in time when we timeout
387 deadline_us = MONOTONIC_US() + timeout_ms * 1000;
388 }
389
390 VDBG("...wait %d %s nsent=%u\n",
391 timeout_ms, argv_intf, nsent);
392
393 n = safe_poll(fds, 1, timeout_ms);
394 if (n < 0) {
395 //bb_perror_msg("poll"); - done in safe_poll
396 return EXIT_FAILURE;
397 }
398 if (n == 0) { // timed out?
399 VDBG("state:%d\n", state);
400 switch (state) {
401 case PROBE:
402 // No conflicting ARP packets were seen:
403 // we can progress through the states
404 if (nsent < PROBE_NUM) {
405 nsent++;
406 VDBG("probe/%u %s@%s\n",
407 nsent, argv_intf, nip_to_a(chosen_nip));
408 timeout_ms = PROBE_MIN * 1000;
409 timeout_ms += random_delay_ms(PROBE_MAX - PROBE_MIN);
410 send_arp_request(0, &null_ethaddr, chosen_nip);
411 continue;
412 }
413 // Switch to announce state
414 nsent = 0;
415 state = ANNOUNCE;
416 goto send_announce;
417 case ANNOUNCE:
418 // No conflicting ARP packets were seen:
419 // we can progress through the states
420 if (nsent < ANNOUNCE_NUM) {
421 send_announce:
422 nsent++;
423 VDBG("announce/%u %s@%s\n",
424 nsent, argv_intf, nip_to_a(chosen_nip));
425 timeout_ms = ANNOUNCE_INTERVAL * 1000;
426 send_arp_request(chosen_nip, &G.our_ethaddr, chosen_nip);
427 continue;
428 }
429 // Switch to monitor state
430 // FIXME update filters
431 run(argv, "config", chosen_nip);
432 // NOTE: all other exit paths should deconfig...
433 if (QUIT)
434 return EXIT_SUCCESS;
435 // fall through: switch to MONITOR
436 default:
437 // case DEFEND:
438 // case MONITOR: (shouldn't happen, MONITOR timeout is infinite)
439 // Defend period ended with no ARP replies - we won
440 timeout_ms = -1; // never timeout in monitor state
441 state = MONITOR;
442 continue;
443 }
444 }
445
446 // Packet arrived, or link went down.
447 // We need to adjust the timeout in case we didn't receive
448 // a conflicting packet.
449 if (timeout_ms > 0) {
450 unsigned diff = deadline_us - MONOTONIC_US();
451 if ((int)(diff) < 0) {
452 // Current time is greater than the expected timeout time.
453 diff = 0;
454 }
455 VDBG("adjusting timeout\n");
456 timeout_ms = (diff / 1000) | 1; // never 0
457 }
458
459 if ((fds[0].revents & POLLIN) == 0) {
460 if (fds[0].revents & POLLERR) {
461 // FIXME: links routinely go down;
462 // this shouldn't necessarily exit.
463 bb_error_msg("iface %s is down", argv_intf);
464 if (state >= MONITOR) {
465 // Only if we are in MONITOR or DEFEND
466 run(argv, "deconfig", chosen_nip);
467 }
468 return EXIT_FAILURE;
469 }
470 continue;
471 }
472
473 // Read ARP packet
474 if (safe_read(sock_fd, &p, sizeof(p)) < 0) {
475 bb_simple_perror_msg_and_die(bb_msg_read_error);
476 }
477
478 if (p.eth.ether_type != htons(ETHERTYPE_ARP))
479 continue;
480 if (p.arp.arp_op != htons(ARPOP_REQUEST)
481 && p.arp.arp_op != htons(ARPOP_REPLY)
482 ) {
483 continue;
484 }
485 #ifdef DEBUG
486 {
487 struct ether_addr *sha = (struct ether_addr *) p.arp.arp_sha;
488 struct ether_addr *tha = (struct ether_addr *) p.arp.arp_tha;
489 struct in_addr *spa = (struct in_addr *) p.arp.arp_spa;
490 struct in_addr *tpa = (struct in_addr *) p.arp.arp_tpa;
491 VDBG("source=%s %s\n", ether_ntoa(sha), inet_ntoa(*spa));
492 VDBG("target=%s %s\n", ether_ntoa(tha), inet_ntoa(*tpa));
493 }
494 #endif
495 ip_conflict = 0;
496 if (memcmp(&p.arp.arp_sha, &G.our_ethaddr, ETH_ALEN) != 0) {
497 if (memcmp(p.arp.arp_spa, &chosen_nip, 4) == 0) {
498 // A probe or reply with source_ip == chosen ip
499 ip_conflict = 1;
500 }
501 if (p.arp.arp_op == htons(ARPOP_REQUEST)
502 && memcmp(p.arp.arp_spa, &const_int_0, 4) == 0
503 && memcmp(p.arp.arp_tpa, &chosen_nip, 4) == 0
504 ) {
505 // A probe with source_ip == 0.0.0.0, target_ip == chosen ip:
506 // another host trying to claim this ip!
507 ip_conflict |= 2;
508 }
509 }
510 VDBG("state:%d ip_conflict:%d\n", state, ip_conflict);
511 if (!ip_conflict)
512 continue;
513
514 // Either src or target IP conflict exists
515 if (state <= ANNOUNCE) {
516 // PROBE or ANNOUNCE
517 conflicts++;
518 timeout_ms = PROBE_MIN * 1000
519 + CONFLICT_MULTIPLIER * random_delay_ms(conflicts);
520 goto new_nip_and_PROBE;
521 }
522
523 // MONITOR or DEFEND: only src IP conflict is a problem
524 if (ip_conflict & 1) {
525 if (state == MONITOR) {
526 // Src IP conflict, defend with a single ARP probe
527 VDBG("monitor conflict - defending\n");
528 timeout_ms = DEFEND_INTERVAL * 1000;
529 state = DEFEND;
530 send_arp_request(chosen_nip, &G.our_ethaddr, chosen_nip);
531 continue;
532 }
533 // state == DEFEND
534 // Another src IP conflict, start over
535 VDBG("defend conflict - starting over\n");
536 run(argv, "deconfig", chosen_nip);
537 conflicts = 0;
538 timeout_ms = 0;
539 goto new_nip_and_PROBE;
540 }
541 // Note: if we only have a target IP conflict here (ip_conflict & 2),
542 // IOW: if we just saw this sort of ARP packet:
543 // aa:bb:cc:dd:ee:ff > xx:xx:xx:xx:xx:xx arp who-has <chosen_nip> tell 0.0.0.0
544 // we expect _kernel_ to respond to that, because <chosen_nip>
545 // is (expected to be) configured on this iface.
546 } // while (1)
547 #undef argv_intf
548 }
549