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