fix #>&- syntax for closing fds
[oweals/busybox.git] / 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 the GPL v2 or later, see the file LICENSE in this tarball.
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 #include <netinet/ether.h>
27 #include <net/ethernet.h>
28 #include <net/if.h>
29 #include <net/if_arp.h>
30 #include <linux/if_packet.h>
31 #include <linux/sockios.h>
32
33 #include "libbb.h"
34 #include <syslog.h>
35
36 /* We don't need more than 32 bits of the counter */
37 #define MONOTONIC_US() ((unsigned)monotonic_us())
38
39 struct arp_packet {
40         struct ether_header eth;
41         struct ether_arp arp;
42 } PACKED;
43
44 enum {
45 /* 169.254.0.0 */
46         LINKLOCAL_ADDR = 0xa9fe0000,
47
48 /* protocol timeout parameters, specified in seconds */
49         PROBE_WAIT = 1,
50         PROBE_MIN = 1,
51         PROBE_MAX = 2,
52         PROBE_NUM = 3,
53         MAX_CONFLICTS = 10,
54         RATE_LIMIT_INTERVAL = 60,
55         ANNOUNCE_WAIT = 2,
56         ANNOUNCE_NUM = 2,
57         ANNOUNCE_INTERVAL = 2,
58         DEFEND_INTERVAL = 10
59 };
60
61 /* States during the configuration process. */
62 enum {
63         PROBE = 0,
64         RATE_LIMIT_PROBE,
65         ANNOUNCE,
66         MONITOR,
67         DEFEND
68 };
69
70 #define VDBG(...) do { } while (0)
71
72
73 enum {
74         sock_fd = 3
75 };
76
77 struct globals {
78         struct sockaddr saddr;
79         struct ether_addr eth_addr;
80 };
81 #define G (*(struct globals*)&bb_common_bufsiz1)
82 #define saddr    (G.saddr   )
83 #define eth_addr (G.eth_addr)
84
85
86 /**
87  * Pick a random link local IP address on 169.254/16, except that
88  * the first and last 256 addresses are reserved.
89  */
90 static uint32_t pick(void)
91 {
92         unsigned tmp;
93
94         do {
95                 tmp = rand() & IN_CLASSB_HOST;
96         } while (tmp > (IN_CLASSB_HOST - 0x0200));
97         return htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
98 }
99
100 /**
101  * Broadcast an ARP packet.
102  */
103 static void arp(
104         /* int op, - always ARPOP_REQUEST */
105         /* const struct ether_addr *source_eth, - always &eth_addr */
106                                         struct in_addr source_ip,
107         const struct ether_addr *target_eth, struct in_addr target_ip)
108 {
109         enum { op = ARPOP_REQUEST };
110 #define source_eth (&eth_addr)
111
112         struct arp_packet p;
113         memset(&p, 0, sizeof(p));
114
115         // ether header
116         p.eth.ether_type = htons(ETHERTYPE_ARP);
117         memcpy(p.eth.ether_shost, source_eth, ETH_ALEN);
118         memset(p.eth.ether_dhost, 0xff, ETH_ALEN);
119
120         // arp request
121         p.arp.arp_hrd = htons(ARPHRD_ETHER);
122         p.arp.arp_pro = htons(ETHERTYPE_IP);
123         p.arp.arp_hln = ETH_ALEN;
124         p.arp.arp_pln = 4;
125         p.arp.arp_op = htons(op);
126         memcpy(&p.arp.arp_sha, source_eth, ETH_ALEN);
127         memcpy(&p.arp.arp_spa, &source_ip, sizeof(p.arp.arp_spa));
128         memcpy(&p.arp.arp_tha, target_eth, ETH_ALEN);
129         memcpy(&p.arp.arp_tpa, &target_ip, sizeof(p.arp.arp_tpa));
130
131         // send it
132         // Even though sock_fd is already bound to saddr, just send()
133         // won't work, because "socket is not connected"
134         // (and connect() won't fix that, "operation not supported").
135         // Thus we sendto() to saddr. I wonder which sockaddr
136         // (from bind() or from sendto()?) kernel actually uses
137         // to determine iface to emit the packet from...
138         xsendto(sock_fd, &p, sizeof(p), &saddr, sizeof(saddr));
139 #undef source_eth
140 }
141
142 /**
143  * Run a script.
144  * argv[0]:intf argv[1]:script_name argv[2]:junk argv[3]:NULL
145  */
146 static int run(char *argv[3], const char *param, struct in_addr *ip)
147 {
148         int status;
149         char *addr = addr; /* for gcc */
150         const char *fmt = "%s %s %s" + 3;
151
152         argv[2] = (char*)param;
153
154         VDBG("%s run %s %s\n", argv[0], argv[1], argv[2]);
155
156         if (ip) {
157                 addr = inet_ntoa(*ip);
158                 xsetenv("ip", addr);
159                 fmt -= 3;
160         }
161         bb_info_msg(fmt, argv[2], argv[0], addr);
162
163         status = wait4pid(spawn(argv + 1));
164         if (status < 0) {
165                 bb_perror_msg("%s %s %s" + 3, argv[2], argv[0]);
166                 return -errno;
167         }
168         if (status != 0)
169                 bb_error_msg("script %s %s failed, exitcode=%d", argv[1], argv[2], status);
170         return status;
171 }
172
173 /**
174  * Return milliseconds of random delay, up to "secs" seconds.
175  */
176 static ALWAYS_INLINE unsigned random_delay_ms(unsigned secs)
177 {
178         return rand() % (secs * 1000);
179 }
180
181 /**
182  * main program
183  */
184 int zcip_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
185 int zcip_main(int argc, char **argv)
186 {
187         int state;
188         char *r_opt;
189         unsigned opts;
190
191         // ugly trick, but I want these zeroed in one go
192         struct {
193                 const struct in_addr null_ip;
194                 const struct ether_addr null_addr;
195                 struct in_addr ip;
196                 struct ifreq ifr;
197                 int timeout_ms; /* must be signed */
198                 unsigned conflicts;
199                 unsigned nprobes;
200                 unsigned nclaims;
201                 int ready;
202                 int verbose;
203         } L;
204 #define null_ip    (L.null_ip   )
205 #define null_addr  (L.null_addr )
206 #define ip         (L.ip        )
207 #define ifr        (L.ifr       )
208 #define timeout_ms (L.timeout_ms)
209 #define conflicts  (L.conflicts )
210 #define nprobes    (L.nprobes   )
211 #define nclaims    (L.nclaims   )
212 #define ready      (L.ready     )
213 #define verbose    (L.verbose   )
214
215         memset(&L, 0, sizeof(L));
216
217 #define FOREGROUND (opts & 1)
218 #define QUIT       (opts & 2)
219         // parse commandline: prog [options] ifname script
220         // exactly 2 args; -v accumulates and implies -f
221         opt_complementary = "=2:vv:vf";
222         opts = getopt32(argv, "fqr:v", &r_opt, &verbose);
223 #if !BB_MMU
224         // on NOMMU reexec early (or else we will rerun things twice)
225         if (!FOREGROUND)
226                 bb_daemonize_or_rexec(0 /*was: DAEMON_CHDIR_ROOT*/, argv);
227 #endif
228         // open an ARP socket
229         // (need to do it before openlog to prevent openlog from taking
230         // fd 3 (sock_fd==3))
231         xmove_fd(xsocket(AF_PACKET, SOCK_PACKET, htons(ETH_P_ARP)), sock_fd);
232         if (!FOREGROUND) {
233                 // do it before all bb_xx_msg calls
234                 openlog(applet_name, 0, LOG_DAEMON);
235                 logmode |= LOGMODE_SYSLOG;
236         }
237         if (opts & 4) { // -r n.n.n.n
238                 if (inet_aton(r_opt, &ip) == 0
239                  || (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR
240                 ) {
241                         bb_error_msg_and_die("invalid link address");
242                 }
243         }
244         argc -= optind;
245         argv += optind - 1;
246
247         /* Now: argv[0]:junk argv[1]:intf argv[2]:script argv[3]:NULL */
248         /* We need to make space for script argument: */
249         argv[0] = argv[1];
250         argv[1] = argv[2];
251         /* Now: argv[0]:intf argv[1]:script argv[2]:junk argv[3]:NULL */
252 #define argv_intf (argv[0])
253
254         xsetenv("interface", argv_intf);
255
256         // initialize the interface (modprobe, ifup, etc)
257         if (run(argv, "init", NULL))
258                 return EXIT_FAILURE;
259
260         // initialize saddr
261         // saddr is: { u16 sa_family; u8 sa_data[14]; }
262         //memset(&saddr, 0, sizeof(saddr));
263         //TODO: are we leaving sa_family == 0 (AF_UNSPEC)?!
264         safe_strncpy(saddr.sa_data, argv_intf, sizeof(saddr.sa_data));
265
266         // bind to the interface's ARP socket
267         xbind(sock_fd, &saddr, sizeof(saddr));
268
269         // get the interface's ethernet address
270         //memset(&ifr, 0, sizeof(ifr));
271         strncpy_IFNAMSIZ(ifr.ifr_name, argv_intf);
272         xioctl(sock_fd, SIOCGIFHWADDR, &ifr);
273         memcpy(&eth_addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
274
275         // start with some stable ip address, either a function of
276         // the hardware address or else the last address we used.
277         // we are taking low-order four bytes, as top-order ones
278         // aren't random enough.
279         // NOTE: the sequence of addresses we try changes only
280         // depending on when we detect conflicts.
281         {
282                 uint32_t t;
283                 move_from_unaligned32(t, ((char *)&eth_addr + 2));
284                 srand(t);
285         }
286         if (ip.s_addr == 0)
287                 ip.s_addr = pick();
288
289         // FIXME cases to handle:
290         //  - zcip already running!
291         //  - link already has local address... just defend/update
292
293         // daemonize now; don't delay system startup
294         if (!FOREGROUND) {
295 #if BB_MMU
296                 bb_daemonize(0 /*was: DAEMON_CHDIR_ROOT*/);
297 #endif
298                 bb_info_msg("start, interface %s", argv_intf);
299         }
300
301         // run the dynamic address negotiation protocol,
302         // restarting after address conflicts:
303         //  - start with some address we want to try
304         //  - short random delay
305         //  - arp probes to see if another host uses it
306         //  - arp announcements that we're claiming it
307         //  - use it
308         //  - defend it, within limits
309         // exit if:
310         // - address is successfully obtained and -q was given:
311         //   run "<script> config", then exit with exitcode 0
312         // - poll error (when does this happen?)
313         // - read error (when does this happen?)
314         // - sendto error (in arp()) (when does this happen?)
315         // - revents & POLLERR (link down). run "<script> deconfig" first
316         state = PROBE;
317         while (1) {
318                 struct pollfd fds[1];
319                 unsigned deadline_us;
320                 struct arp_packet p;
321                 int source_ip_conflict;
322                 int target_ip_conflict;
323
324                 fds[0].fd = sock_fd;
325                 fds[0].events = POLLIN;
326                 fds[0].revents = 0;
327
328                 // poll, being ready to adjust current timeout
329                 if (!timeout_ms) {
330                         timeout_ms = random_delay_ms(PROBE_WAIT);
331                         // FIXME setsockopt(sock_fd, SO_ATTACH_FILTER, ...) to
332                         // make the kernel filter out all packets except
333                         // ones we'd care about.
334                 }
335                 // set deadline_us to the point in time when we timeout
336                 deadline_us = MONOTONIC_US() + timeout_ms * 1000;
337
338                 VDBG("...wait %d %s nprobes=%u, nclaims=%u\n",
339                                 timeout_ms, argv_intf, nprobes, nclaims);
340
341                 switch (safe_poll(fds, 1, timeout_ms)) {
342
343                 default:
344                         //bb_perror_msg("poll"); - done in safe_poll
345                         return EXIT_FAILURE;
346
347                 // timeout
348                 case 0:
349                         VDBG("state = %d\n", state);
350                         switch (state) {
351                         case PROBE:
352                                 // timeouts in the PROBE state mean no conflicting ARP packets
353                                 // have been received, so we can progress through the states
354                                 if (nprobes < PROBE_NUM) {
355                                         nprobes++;
356                                         VDBG("probe/%u %s@%s\n",
357                                                         nprobes, argv_intf, inet_ntoa(ip));
358                                         arp(/* ARPOP_REQUEST, */
359                                                         /* &eth_addr, */ null_ip,
360                                                         &null_addr, ip);
361                                         timeout_ms = PROBE_MIN * 1000;
362                                         timeout_ms += random_delay_ms(PROBE_MAX - PROBE_MIN);
363                                 }
364                                 else {
365                                         // Switch to announce state.
366                                         state = ANNOUNCE;
367                                         nclaims = 0;
368                                         VDBG("announce/%u %s@%s\n",
369                                                         nclaims, argv_intf, inet_ntoa(ip));
370                                         arp(/* ARPOP_REQUEST, */
371                                                         /* &eth_addr, */ ip,
372                                                         &eth_addr, ip);
373                                         timeout_ms = ANNOUNCE_INTERVAL * 1000;
374                                 }
375                                 break;
376                         case RATE_LIMIT_PROBE:
377                                 // timeouts in the RATE_LIMIT_PROBE state mean no conflicting ARP packets
378                                 // have been received, so we can move immediately to the announce state
379                                 state = ANNOUNCE;
380                                 nclaims = 0;
381                                 VDBG("announce/%u %s@%s\n",
382                                                 nclaims, argv_intf, inet_ntoa(ip));
383                                 arp(/* ARPOP_REQUEST, */
384                                                 /* &eth_addr, */ ip,
385                                                 &eth_addr, ip);
386                                 timeout_ms = ANNOUNCE_INTERVAL * 1000;
387                                 break;
388                         case ANNOUNCE:
389                                 // timeouts in the ANNOUNCE state mean no conflicting ARP packets
390                                 // have been received, so we can progress through the states
391                                 if (nclaims < ANNOUNCE_NUM) {
392                                         nclaims++;
393                                         VDBG("announce/%u %s@%s\n",
394                                                         nclaims, argv_intf, inet_ntoa(ip));
395                                         arp(/* ARPOP_REQUEST, */
396                                                         /* &eth_addr, */ ip,
397                                                         &eth_addr, ip);
398                                         timeout_ms = ANNOUNCE_INTERVAL * 1000;
399                                 }
400                                 else {
401                                         // Switch to monitor state.
402                                         state = MONITOR;
403                                         // link is ok to use earlier
404                                         // FIXME update filters
405                                         run(argv, "config", &ip);
406                                         ready = 1;
407                                         conflicts = 0;
408                                         timeout_ms = -1; // Never timeout in the monitor state.
409
410                                         // NOTE: all other exit paths
411                                         // should deconfig ...
412                                         if (QUIT)
413                                                 return EXIT_SUCCESS;
414                                 }
415                                 break;
416                         case DEFEND:
417                                 // We won!  No ARP replies, so just go back to monitor.
418                                 state = MONITOR;
419                                 timeout_ms = -1;
420                                 conflicts = 0;
421                                 break;
422                         default:
423                                 // Invalid, should never happen.  Restart the whole protocol.
424                                 state = PROBE;
425                                 ip.s_addr = pick();
426                                 timeout_ms = 0;
427                                 nprobes = 0;
428                                 nclaims = 0;
429                                 break;
430                         } // switch (state)
431                         break; // case 0 (timeout)
432
433                 // packets arriving, or link went down
434                 case 1:
435                         // We need to adjust the timeout in case we didn't receive
436                         // a conflicting packet.
437                         if (timeout_ms > 0) {
438                                 unsigned diff = deadline_us - MONOTONIC_US();
439                                 if ((int)(diff) < 0) {
440                                         // Current time is greater than the expected timeout time.
441                                         // Should never happen.
442                                         VDBG("missed an expected timeout\n");
443                                         timeout_ms = 0;
444                                 } else {
445                                         VDBG("adjusting timeout\n");
446                                         timeout_ms = (diff / 1000) | 1; /* never 0 */
447                                 }
448                         }
449
450                         if ((fds[0].revents & POLLIN) == 0) {
451                                 if (fds[0].revents & POLLERR) {
452                                         // FIXME: links routinely go down;
453                                         // this shouldn't necessarily exit.
454                                         bb_error_msg("iface %s is down", argv_intf);
455                                         if (ready) {
456                                                 run(argv, "deconfig", &ip);
457                                         }
458                                         return EXIT_FAILURE;
459                                 }
460                                 continue;
461                         }
462
463                         // read ARP packet
464                         if (safe_read(sock_fd, &p, sizeof(p)) < 0) {
465                                 bb_perror_msg_and_die(bb_msg_read_error);
466                         }
467                         if (p.eth.ether_type != htons(ETHERTYPE_ARP))
468                                 continue;
469 #ifdef DEBUG
470                         {
471                                 struct ether_addr *sha = (struct ether_addr *) p.arp.arp_sha;
472                                 struct ether_addr *tha = (struct ether_addr *) p.arp.arp_tha;
473                                 struct in_addr *spa = (struct in_addr *) p.arp.arp_spa;
474                                 struct in_addr *tpa = (struct in_addr *) p.arp.arp_tpa;
475                                 VDBG("%s recv arp type=%d, op=%d,\n",
476                                         argv_intf, ntohs(p.eth.ether_type),
477                                         ntohs(p.arp.arp_op));
478                                 VDBG("\tsource=%s %s\n",
479                                         ether_ntoa(sha),
480                                         inet_ntoa(*spa));
481                                 VDBG("\ttarget=%s %s\n",
482                                         ether_ntoa(tha),
483                                         inet_ntoa(*tpa));
484                         }
485 #endif
486                         if (p.arp.arp_op != htons(ARPOP_REQUEST)
487                          && p.arp.arp_op != htons(ARPOP_REPLY))
488                                 continue;
489
490                         source_ip_conflict = 0;
491                         target_ip_conflict = 0;
492
493                         if (memcmp(p.arp.arp_spa, &ip.s_addr, sizeof(struct in_addr)) == 0
494                          && memcmp(&p.arp.arp_sha, &eth_addr, ETH_ALEN) != 0
495                         ) {
496                                 source_ip_conflict = 1;
497                         }
498                         if (p.arp.arp_op == htons(ARPOP_REQUEST)
499                          && memcmp(p.arp.arp_tpa, &ip.s_addr, sizeof(struct in_addr)) == 0
500                          && memcmp(&p.arp.arp_tha, &eth_addr, ETH_ALEN) != 0
501                         ) {
502                                 target_ip_conflict = 1;
503                         }
504
505                         VDBG("state = %d, source ip conflict = %d, target ip conflict = %d\n",
506                                 state, source_ip_conflict, target_ip_conflict);
507                         switch (state) {
508                         case PROBE:
509                         case ANNOUNCE:
510                                 // When probing or announcing, check for source IP conflicts
511                                 // and other hosts doing ARP probes (target IP conflicts).
512                                 if (source_ip_conflict || target_ip_conflict) {
513                                         conflicts++;
514                                         if (conflicts >= MAX_CONFLICTS) {
515                                                 VDBG("%s ratelimit\n", argv_intf);
516                                                 timeout_ms = RATE_LIMIT_INTERVAL * 1000;
517                                                 state = RATE_LIMIT_PROBE;
518                                         }
519
520                                         // restart the whole protocol
521                                         ip.s_addr = pick();
522                                         timeout_ms = 0;
523                                         nprobes = 0;
524                                         nclaims = 0;
525                                 }
526                                 break;
527                         case MONITOR:
528                                 // If a conflict, we try to defend with a single ARP probe.
529                                 if (source_ip_conflict) {
530                                         VDBG("monitor conflict -- defending\n");
531                                         state = DEFEND;
532                                         timeout_ms = DEFEND_INTERVAL * 1000;
533                                         arp(/* ARPOP_REQUEST, */
534                                                 /* &eth_addr, */ ip,
535                                                 &eth_addr, ip);
536                                 }
537                                 break;
538                         case DEFEND:
539                                 // Well, we tried.  Start over (on conflict).
540                                 if (source_ip_conflict) {
541                                         state = PROBE;
542                                         VDBG("defend conflict -- starting over\n");
543                                         ready = 0;
544                                         run(argv, "deconfig", &ip);
545
546                                         // restart the whole protocol
547                                         ip.s_addr = pick();
548                                         timeout_ms = 0;
549                                         nprobes = 0;
550                                         nclaims = 0;
551                                 }
552                                 break;
553                         default:
554                                 // Invalid, should never happen.  Restart the whole protocol.
555                                 VDBG("invalid state -- starting over\n");
556                                 state = PROBE;
557                                 ip.s_addr = pick();
558                                 timeout_ms = 0;
559                                 nprobes = 0;
560                                 nclaims = 0;
561                                 break;
562                         } // switch state
563                         break; // case 1 (packets arriving)
564                 } // switch poll
565         } // while (1)
566 #undef argv_intf
567 }