/* vi: set sw=4 ts=4: */ /* * RFC3927 ZeroConf IPv4 Link-Local addressing * (see <http://www.zeroconf.org/>) * * Copyright (C) 2003 by Arthur van Hoff (avh@strangeberry.com) * Copyright (C) 2004 by David Brownell * * Licensed under GPLv2 or later, see file LICENSE in this source tree. */ /* * ZCIP just manages the 169.254.*.* addresses. That network is not * routed at the IP level, though various proxies or bridges can * certainly be used. Its naming is built over multicast DNS. */ //#define DEBUG // TODO: // - more real-world usage/testing, especially daemon mode // - kernel packet filters to reduce scheduling noise // - avoid silent script failures, especially under load... // - link status monitoring (restart on link-up; stop on link-down) #include <netinet/ether.h> #include <net/ethernet.h> #include <net/if.h> #include <net/if_arp.h> #include <linux/if_packet.h> #include <linux/sockios.h> #include "libbb.h" #include <syslog.h> /* We don't need more than 32 bits of the counter */ #define MONOTONIC_US() ((unsigned)monotonic_us()) struct arp_packet { struct ether_header eth; struct ether_arp arp; } PACKED; enum { /* 169.254.0.0 */ LINKLOCAL_ADDR = 0xa9fe0000, /* protocol timeout parameters, specified in seconds */ PROBE_WAIT = 1, PROBE_MIN = 1, PROBE_MAX = 2, PROBE_NUM = 3, MAX_CONFLICTS = 10, RATE_LIMIT_INTERVAL = 60, ANNOUNCE_WAIT = 2, ANNOUNCE_NUM = 2, ANNOUNCE_INTERVAL = 2, DEFEND_INTERVAL = 10 }; /* States during the configuration process. */ enum { PROBE = 0, RATE_LIMIT_PROBE, ANNOUNCE, MONITOR, DEFEND }; #define VDBG(...) do { } while (0) enum { sock_fd = 3 }; struct globals { struct sockaddr saddr; struct ether_addr eth_addr; } FIX_ALIASING; #define G (*(struct globals*)&bb_common_bufsiz1) #define saddr (G.saddr ) #define eth_addr (G.eth_addr) /** * Pick a random link local IP address on 169.254/16, except that * the first and last 256 addresses are reserved. */ static uint32_t pick(void) { unsigned tmp; do { tmp = rand() & IN_CLASSB_HOST; } while (tmp > (IN_CLASSB_HOST - 0x0200)); return htonl((LINKLOCAL_ADDR + 0x0100) + tmp); } /** * Broadcast an ARP packet. */ static void arp( /* int op, - always ARPOP_REQUEST */ /* const struct ether_addr *source_eth, - always ð_addr */ struct in_addr source_ip, const struct ether_addr *target_eth, struct in_addr target_ip) { enum { op = ARPOP_REQUEST }; #define source_eth (ð_addr) struct arp_packet p; memset(&p, 0, sizeof(p)); // ether header p.eth.ether_type = htons(ETHERTYPE_ARP); memcpy(p.eth.ether_shost, source_eth, ETH_ALEN); memset(p.eth.ether_dhost, 0xff, ETH_ALEN); // arp request p.arp.arp_hrd = htons(ARPHRD_ETHER); p.arp.arp_pro = htons(ETHERTYPE_IP); p.arp.arp_hln = ETH_ALEN; p.arp.arp_pln = 4; p.arp.arp_op = htons(op); memcpy(&p.arp.arp_sha, source_eth, ETH_ALEN); memcpy(&p.arp.arp_spa, &source_ip, sizeof(p.arp.arp_spa)); memcpy(&p.arp.arp_tha, target_eth, ETH_ALEN); memcpy(&p.arp.arp_tpa, &target_ip, sizeof(p.arp.arp_tpa)); // send it // Even though sock_fd is already bound to saddr, just send() // won't work, because "socket is not connected" // (and connect() won't fix that, "operation not supported"). // Thus we sendto() to saddr. I wonder which sockaddr // (from bind() or from sendto()?) kernel actually uses // to determine iface to emit the packet from... xsendto(sock_fd, &p, sizeof(p), &saddr, sizeof(saddr)); #undef source_eth } /** * Run a script. * argv[0]:intf argv[1]:script_name argv[2]:junk argv[3]:NULL */ static int run(char *argv[3], const char *param, struct in_addr *ip) { int status; char *addr = addr; /* for gcc */ const char *fmt = "%s %s %s" + 3; argv[2] = (char*)param; VDBG("%s run %s %s\n", argv[0], argv[1], argv[2]); if (ip) { addr = inet_ntoa(*ip); xsetenv("ip", addr); fmt -= 3; } bb_info_msg(fmt, argv[2], argv[0], addr); status = spawn_and_wait(argv + 1); if (status < 0) { bb_perror_msg("%s %s %s" + 3, argv[2], argv[0]); return -errno; } if (status != 0) bb_error_msg("script %s %s failed, exitcode=%d", argv[1], argv[2], status & 0xff); return status; } /** * Return milliseconds of random delay, up to "secs" seconds. */ static ALWAYS_INLINE unsigned random_delay_ms(unsigned secs) { return rand() % (secs * 1000); } /** * main program */ int zcip_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; int zcip_main(int argc UNUSED_PARAM, char **argv) { int state; char *r_opt; unsigned opts; // ugly trick, but I want these zeroed in one go struct { const struct in_addr null_ip; const struct ether_addr null_addr; struct in_addr ip; struct ifreq ifr; int timeout_ms; /* must be signed */ unsigned conflicts; unsigned nprobes; unsigned nclaims; int ready; int verbose; } L; #define null_ip (L.null_ip ) #define null_addr (L.null_addr ) #define ip (L.ip ) #define ifr (L.ifr ) #define timeout_ms (L.timeout_ms) #define conflicts (L.conflicts ) #define nprobes (L.nprobes ) #define nclaims (L.nclaims ) #define ready (L.ready ) #define verbose (L.verbose ) memset(&L, 0, sizeof(L)); #define FOREGROUND (opts & 1) #define QUIT (opts & 2) // parse commandline: prog [options] ifname script // exactly 2 args; -v accumulates and implies -f opt_complementary = "=2:vv:vf"; opts = getopt32(argv, "fqr:v", &r_opt, &verbose); #if !BB_MMU // on NOMMU reexec early (or else we will rerun things twice) if (!FOREGROUND) bb_daemonize_or_rexec(0 /*was: DAEMON_CHDIR_ROOT*/, argv); #endif // open an ARP socket // (need to do it before openlog to prevent openlog from taking // fd 3 (sock_fd==3)) xmove_fd(xsocket(AF_PACKET, SOCK_PACKET, htons(ETH_P_ARP)), sock_fd); if (!FOREGROUND) { // do it before all bb_xx_msg calls openlog(applet_name, 0, LOG_DAEMON); logmode |= LOGMODE_SYSLOG; } if (opts & 4) { // -r n.n.n.n if (inet_aton(r_opt, &ip) == 0 || (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR ) { bb_error_msg_and_die("invalid link address"); } } argv += optind - 1; /* Now: argv[0]:junk argv[1]:intf argv[2]:script argv[3]:NULL */ /* We need to make space for script argument: */ argv[0] = argv[1]; argv[1] = argv[2]; /* Now: argv[0]:intf argv[1]:script argv[2]:junk argv[3]:NULL */ #define argv_intf (argv[0]) xsetenv("interface", argv_intf); // initialize the interface (modprobe, ifup, etc) if (run(argv, "init", NULL)) return EXIT_FAILURE; // initialize saddr // saddr is: { u16 sa_family; u8 sa_data[14]; } //memset(&saddr, 0, sizeof(saddr)); //TODO: are we leaving sa_family == 0 (AF_UNSPEC)?! safe_strncpy(saddr.sa_data, argv_intf, sizeof(saddr.sa_data)); // bind to the interface's ARP socket xbind(sock_fd, &saddr, sizeof(saddr)); // get the interface's ethernet address //memset(&ifr, 0, sizeof(ifr)); strncpy_IFNAMSIZ(ifr.ifr_name, argv_intf); xioctl(sock_fd, SIOCGIFHWADDR, &ifr); memcpy(ð_addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN); // start with some stable ip address, either a function of // the hardware address or else the last address we used. // we are taking low-order four bytes, as top-order ones // aren't random enough. // NOTE: the sequence of addresses we try changes only // depending on when we detect conflicts. { uint32_t t; move_from_unaligned32(t, ((char *)ð_addr + 2)); srand(t); } if (ip.s_addr == 0) ip.s_addr = pick(); // FIXME cases to handle: // - zcip already running! // - link already has local address... just defend/update // daemonize now; don't delay system startup if (!FOREGROUND) { #if BB_MMU bb_daemonize(0 /*was: DAEMON_CHDIR_ROOT*/); #endif bb_info_msg("start, interface %s", argv_intf); } // run the dynamic address negotiation protocol, // restarting after address conflicts: // - start with some address we want to try // - short random delay // - arp probes to see if another host uses it // - arp announcements that we're claiming it // - use it // - defend it, within limits // exit if: // - address is successfully obtained and -q was given: // run "<script> config", then exit with exitcode 0 // - poll error (when does this happen?) // - read error (when does this happen?) // - sendto error (in arp()) (when does this happen?) // - revents & POLLERR (link down). run "<script> deconfig" first state = PROBE; while (1) { struct pollfd fds[1]; unsigned deadline_us; struct arp_packet p; int source_ip_conflict; int target_ip_conflict; fds[0].fd = sock_fd; fds[0].events = POLLIN; fds[0].revents = 0; // poll, being ready to adjust current timeout if (!timeout_ms) { timeout_ms = random_delay_ms(PROBE_WAIT); // FIXME setsockopt(sock_fd, SO_ATTACH_FILTER, ...) to // make the kernel filter out all packets except // ones we'd care about. } // set deadline_us to the point in time when we timeout deadline_us = MONOTONIC_US() + timeout_ms * 1000; VDBG("...wait %d %s nprobes=%u, nclaims=%u\n", timeout_ms, argv_intf, nprobes, nclaims); switch (safe_poll(fds, 1, timeout_ms)) { default: //bb_perror_msg("poll"); - done in safe_poll return EXIT_FAILURE; // timeout case 0: VDBG("state = %d\n", state); switch (state) { case PROBE: // timeouts in the PROBE state mean no conflicting ARP packets // have been received, so we can progress through the states if (nprobes < PROBE_NUM) { nprobes++; VDBG("probe/%u %s@%s\n", nprobes, argv_intf, inet_ntoa(ip)); arp(/* ARPOP_REQUEST, */ /* ð_addr, */ null_ip, &null_addr, ip); timeout_ms = PROBE_MIN * 1000; timeout_ms += random_delay_ms(PROBE_MAX - PROBE_MIN); } else { // Switch to announce state. state = ANNOUNCE; nclaims = 0; VDBG("announce/%u %s@%s\n", nclaims, argv_intf, inet_ntoa(ip)); arp(/* ARPOP_REQUEST, */ /* ð_addr, */ ip, ð_addr, ip); timeout_ms = ANNOUNCE_INTERVAL * 1000; } break; case RATE_LIMIT_PROBE: // timeouts in the RATE_LIMIT_PROBE state mean no conflicting ARP packets // have been received, so we can move immediately to the announce state state = ANNOUNCE; nclaims = 0; VDBG("announce/%u %s@%s\n", nclaims, argv_intf, inet_ntoa(ip)); arp(/* ARPOP_REQUEST, */ /* ð_addr, */ ip, ð_addr, ip); timeout_ms = ANNOUNCE_INTERVAL * 1000; break; case ANNOUNCE: // timeouts in the ANNOUNCE state mean no conflicting ARP packets // have been received, so we can progress through the states if (nclaims < ANNOUNCE_NUM) { nclaims++; VDBG("announce/%u %s@%s\n", nclaims, argv_intf, inet_ntoa(ip)); arp(/* ARPOP_REQUEST, */ /* ð_addr, */ ip, ð_addr, ip); timeout_ms = ANNOUNCE_INTERVAL * 1000; } else { // Switch to monitor state. state = MONITOR; // link is ok to use earlier // FIXME update filters run(argv, "config", &ip); ready = 1; conflicts = 0; timeout_ms = -1; // Never timeout in the monitor state. // NOTE: all other exit paths // should deconfig ... if (QUIT) return EXIT_SUCCESS; } break; case DEFEND: // We won! No ARP replies, so just go back to monitor. state = MONITOR; timeout_ms = -1; conflicts = 0; break; default: // Invalid, should never happen. Restart the whole protocol. state = PROBE; ip.s_addr = pick(); timeout_ms = 0; nprobes = 0; nclaims = 0; break; } // switch (state) break; // case 0 (timeout) // packets arriving, or link went down case 1: // We need to adjust the timeout in case we didn't receive // a conflicting packet. if (timeout_ms > 0) { unsigned diff = deadline_us - MONOTONIC_US(); if ((int)(diff) < 0) { // Current time is greater than the expected timeout time. // Should never happen. VDBG("missed an expected timeout\n"); timeout_ms = 0; } else { VDBG("adjusting timeout\n"); timeout_ms = (diff / 1000) | 1; /* never 0 */ } } if ((fds[0].revents & POLLIN) == 0) { if (fds[0].revents & POLLERR) { // FIXME: links routinely go down; // this shouldn't necessarily exit. bb_error_msg("iface %s is down", argv_intf); if (ready) { run(argv, "deconfig", &ip); } return EXIT_FAILURE; } continue; } // read ARP packet if (safe_read(sock_fd, &p, sizeof(p)) < 0) { bb_perror_msg_and_die(bb_msg_read_error); } if (p.eth.ether_type != htons(ETHERTYPE_ARP)) continue; #ifdef DEBUG { struct ether_addr *sha = (struct ether_addr *) p.arp.arp_sha; struct ether_addr *tha = (struct ether_addr *) p.arp.arp_tha; struct in_addr *spa = (struct in_addr *) p.arp.arp_spa; struct in_addr *tpa = (struct in_addr *) p.arp.arp_tpa; VDBG("%s recv arp type=%d, op=%d,\n", argv_intf, ntohs(p.eth.ether_type), ntohs(p.arp.arp_op)); VDBG("\tsource=%s %s\n", ether_ntoa(sha), inet_ntoa(*spa)); VDBG("\ttarget=%s %s\n", ether_ntoa(tha), inet_ntoa(*tpa)); } #endif if (p.arp.arp_op != htons(ARPOP_REQUEST) && p.arp.arp_op != htons(ARPOP_REPLY)) continue; source_ip_conflict = 0; target_ip_conflict = 0; if (memcmp(p.arp.arp_spa, &ip.s_addr, sizeof(struct in_addr)) == 0 && memcmp(&p.arp.arp_sha, ð_addr, ETH_ALEN) != 0 ) { source_ip_conflict = 1; } if (p.arp.arp_op == htons(ARPOP_REQUEST) && memcmp(p.arp.arp_tpa, &ip.s_addr, sizeof(struct in_addr)) == 0 && memcmp(&p.arp.arp_tha, ð_addr, ETH_ALEN) != 0 ) { target_ip_conflict = 1; } VDBG("state = %d, source ip conflict = %d, target ip conflict = %d\n", state, source_ip_conflict, target_ip_conflict); switch (state) { case PROBE: case ANNOUNCE: // When probing or announcing, check for source IP conflicts // and other hosts doing ARP probes (target IP conflicts). if (source_ip_conflict || target_ip_conflict) { conflicts++; if (conflicts >= MAX_CONFLICTS) { VDBG("%s ratelimit\n", argv_intf); timeout_ms = RATE_LIMIT_INTERVAL * 1000; state = RATE_LIMIT_PROBE; } // restart the whole protocol ip.s_addr = pick(); timeout_ms = 0; nprobes = 0; nclaims = 0; } break; case MONITOR: // If a conflict, we try to defend with a single ARP probe. if (source_ip_conflict) { VDBG("monitor conflict -- defending\n"); state = DEFEND; timeout_ms = DEFEND_INTERVAL * 1000; arp(/* ARPOP_REQUEST, */ /* ð_addr, */ ip, ð_addr, ip); } break; case DEFEND: // Well, we tried. Start over (on conflict). if (source_ip_conflict) { state = PROBE; VDBG("defend conflict -- starting over\n"); ready = 0; run(argv, "deconfig", &ip); // restart the whole protocol ip.s_addr = pick(); timeout_ms = 0; nprobes = 0; nclaims = 0; } break; default: // Invalid, should never happen. Restart the whole protocol. VDBG("invalid state -- starting over\n"); state = PROBE; ip.s_addr = pick(); timeout_ms = 0; nprobes = 0; nclaims = 0; break; } // switch state break; // case 1 (packets arriving) } // switch poll } // while (1) #undef argv_intf }