--- /dev/null
+/*
+ * 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
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+ * 02111-1307 USA
+ */
+
+/*
+ * This can build as part of BusyBox or by itself:
+ *
+ * $(CROSS_COMPILE)cc -Os -Wall -DNO_BUSYBOX -DDEBUG -o zcip zcip.c
+ *
+ * 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 <errno.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <syslog.h>
+#include <poll.h>
+#include <time.h>
+#include <unistd.h>
+
+#include <sys/ioctl.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <sys/time.h>
+#include <sys/socket.h>
+
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#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>
+
+
+struct arp_packet {
+ struct ether_header hdr;
+ // FIXME this part is netinet/if_ether.h "struct ether_arp"
+ struct arphdr arp;
+ struct ether_addr source_addr;
+ struct in_addr source_ip;
+ struct ether_addr target_addr;
+ struct in_addr target_ip;
+} __attribute__ ((__packed__));
+
+/* 169.254.0.0 */
+static const uint32_t LINKLOCAL_ADDR = 0xa9fe0000;
+
+/* protocol timeout parameters, specified in seconds */
+static const unsigned PROBE_WAIT = 1;
+static const unsigned PROBE_MIN = 1;
+static const unsigned PROBE_MAX = 2;
+static const unsigned PROBE_NUM = 3;
+static const unsigned MAX_CONFLICTS = 10;
+static const unsigned RATE_LIMIT_INTERVAL = 60;
+static const unsigned ANNOUNCE_WAIT = 2;
+static const unsigned ANNOUNCE_NUM = 2;
+static const unsigned ANNOUNCE_INTERVAL = 2;
+static const time_t DEFEND_INTERVAL = 10;
+
+static const unsigned char ZCIP_VERSION[] = "0.75 (18 April 2005)";
+static char *prog;
+
+static const struct in_addr null_ip = { 0 };
+static const struct ether_addr null_addr = { {0, 0, 0, 0, 0, 0} };
+
+static int verbose = 0;
+
+#ifdef DEBUG
+
+#define DBG(fmt,args...) \
+ fprintf(stderr, "%s: " fmt , prog , ## args)
+#define VDBG(fmt,args...) do { \
+ if (verbose) fprintf(stderr, "%s: " fmt , prog ,## args); \
+ } while (0)
+#else
+
+#define DBG(fmt,args...) \
+ do { } while (0)
+#define VDBG DBG
+#endif /* DEBUG */
+
+/**
+ * Pick a random link local IP address on 169.254/16, except that
+ * the first and last 256 addresses are reserved.
+ */
+static void
+pick(struct in_addr *ip)
+{
+ unsigned tmp;
+
+ /* use cheaper math than lrand48() mod N */
+ do {
+ tmp = (lrand48() >> 16) & IN_CLASSB_HOST;
+ } while (tmp > (IN_CLASSB_HOST - 0x0200));
+ ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
+}
+
+/**
+ * Broadcast an ARP packet.
+ */
+static int
+arp(int fd, struct sockaddr *saddr, int op,
+ const struct ether_addr *source_addr, struct in_addr source_ip,
+ const struct ether_addr *target_addr, struct in_addr target_ip)
+{
+ struct arp_packet p;
+
+ // ether header
+ p.hdr.ether_type = htons(ETHERTYPE_ARP);
+ memcpy(p.hdr.ether_shost, source_addr, ETH_ALEN);
+ memset(p.hdr.ether_dhost, 0xff, ETH_ALEN);
+
+ // arp request
+ p.arp.ar_hrd = htons(ARPHRD_ETHER);
+ p.arp.ar_pro = htons(ETHERTYPE_IP);
+ p.arp.ar_hln = ETH_ALEN;
+ p.arp.ar_pln = 4;
+ p.arp.ar_op = htons(op);
+ memcpy(&p.source_addr, source_addr, ETH_ALEN);
+ memcpy(&p.source_ip, &source_ip, sizeof (p.source_ip));
+ memcpy(&p.target_addr, target_addr, ETH_ALEN);
+ memcpy(&p.target_ip, &target_ip, sizeof (p.target_ip));
+
+ // send it
+ if (sendto(fd, &p, sizeof (p), 0, saddr, sizeof (*saddr)) < 0) {
+ perror("sendto");
+ return -errno;
+ }
+ return 0;
+}
+
+/**
+ * Run a script.
+ */
+static int
+run(char *script, char *arg, char *intf, struct in_addr *ip)
+{
+ int pid, status;
+ char *why;
+
+ if (script != NULL) {
+ VDBG("%s run %s %s\n", intf, script, arg);
+ if (ip != NULL) {
+ char *addr = inet_ntoa(*ip);
+ setenv("ip", addr, 1);
+ syslog(LOG_INFO, "%s %s %s", arg, intf, addr);
+ }
+
+ pid = vfork();
+ if (pid < 0) { // error
+ why = "vfork";
+ goto bad;
+ } else if (pid == 0) { // child
+ execl(script, script, arg, NULL);
+ perror("execl");
+ _exit(EXIT_FAILURE);
+ }
+
+ if (waitpid(pid, &status, 0) <= 0) {
+ why = "waitpid";
+ goto bad;
+ }
+ if (WEXITSTATUS(status) != 0) {
+ fprintf(stderr, "%s: script %s failed, exit=%d\n",
+ prog, script, WEXITSTATUS(status));
+ return -errno;
+ }
+ }
+ return 0;
+bad:
+ status = -errno;
+ syslog(LOG_ERR, "%s %s, %s error: %s",
+ arg, intf, why, strerror(errno));
+ return status;
+}
+
+#ifndef NO_BUSYBOX
+#include "busybox.h"
+#endif
+
+/**
+ * Print usage information.
+ */
+static void __attribute__ ((noreturn))
+usage(const char *msg)
+{
+ fprintf(stderr, "%s: %s\n", prog, msg);
+#ifdef NO_BUSYBOX
+ fprintf(stderr, "Usage: %s [OPTIONS] ifname script\n"
+ "\t-f foreground mode (implied by -v)\n"
+ "\t-q quit after address (no daemon)\n"
+ "\t-r 169.254.x.x request this address first\n"
+ "\t-v verbose; show version\n",
+ prog);
+ exit(0);
+#else
+ bb_show_usage();
+#endif
+}
+
+/**
+ * Return milliseconds of random delay, up to "secs" seconds.
+ */
+static inline unsigned
+ms_rdelay(unsigned secs)
+{
+ return lrand48() % (secs * 1000);
+}
+
+/**
+ * main program
+ */
+int
+main(int argc, char *argv[])
+ __attribute__ ((weak, alias ("zcip_main")));
+
+int zcip_main(int argc, char *argv[])
+{
+ char *intf = NULL;
+ char *script = NULL;
+ int quit = 0;
+ int foreground = 0;
+
+ char *why;
+ struct sockaddr saddr;
+ struct ether_addr addr;
+ struct in_addr ip = { 0 };
+ int fd;
+ int ready = 0;
+ suseconds_t timeout = 0; // milliseconds
+ time_t defend = 0;
+ unsigned conflicts = 0;
+ unsigned nprobes = 0;
+ unsigned nclaims = 0;
+ int t;
+
+ // parse commandline: prog [options] ifname script
+ prog = argv[0];
+ while ((t = getopt(argc, argv, "fqr:v")) != EOF) {
+ switch (t) {
+ case 'f':
+ foreground = 1;
+ continue;
+ case 'q':
+ quit = 1;
+ continue;
+ case 'r':
+ if (inet_aton(optarg, &ip) == 0
+ || (ntohl(ip.s_addr) & IN_CLASSB_NET)
+ != LINKLOCAL_ADDR) {
+ usage("invalid link address");
+ }
+ continue;
+ case 'v':
+ if (!verbose)
+ printf("%s: version %s\n", prog, ZCIP_VERSION);
+ verbose++;
+ foreground = 1;
+ continue;
+ default:
+ usage("bad option");
+ }
+ }
+ if (optind < argc - 1) {
+ intf = argv[optind++];
+ setenv("interface", intf, 1);
+ script = argv[optind++];
+ }
+ if (optind != argc || !intf)
+ usage("wrong number of arguments");
+ openlog(prog, 0, LOG_DAEMON);
+
+ // initialize the interface (modprobe, ifup, etc)
+ if (run(script, "init", intf, NULL) < 0)
+ return EXIT_FAILURE;
+
+ // initialize saddr
+ memset(&saddr, 0, sizeof (saddr));
+ strncpy(saddr.sa_data, intf, sizeof (saddr.sa_data));
+
+ // open an ARP socket
+ if ((fd = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP))) < 0) {
+ why = "open";
+fail:
+ foreground = 1;
+ goto bad;
+ }
+ // bind to the interface's ARP socket
+ if (bind(fd, &saddr, sizeof (saddr)) < 0) {
+ why = "bind";
+ goto fail;
+ } else {
+ struct ifreq ifr;
+ short seed[3];
+
+ // get the interface's ethernet address
+ memset(&ifr, 0, sizeof (ifr));
+ strncpy(ifr.ifr_name, intf, sizeof (ifr.ifr_name));
+ if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0) {
+ why = "get ethernet address";
+ goto fail;
+ }
+ memcpy(&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.
+ // NOTE: the sequence of addresses we try changes only
+ // depending on when we detect conflicts.
+ memcpy(seed, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
+ seed48(seed);
+ if (ip.s_addr == 0)
+ pick(&ip);
+ }
+
+ // 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 (daemon(0, verbose) < 0) {
+ why = "daemon";
+ goto bad;
+ }
+ syslog(LOG_INFO, "start, interface %s", 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 else uses it
+ // - arp announcements that we're claiming it
+ // - use it
+ // - defend it, within limits
+ while (1) {
+ struct pollfd fds[1];
+ struct timeval tv1;
+ struct arp_packet p;
+
+ fds[0].fd = fd;
+ fds[0].events = POLLIN;
+ fds[0].revents = 0;
+
+ // poll, being ready to adjust current timeout
+ if (timeout > 0) {
+ gettimeofday(&tv1, NULL);
+ tv1.tv_usec += (timeout % 1000) * 1000;
+ while (tv1.tv_usec > 1000000) {
+ tv1.tv_usec -= 1000000;
+ tv1.tv_sec++;
+ }
+ tv1.tv_sec += timeout / 1000;
+ } else if (timeout == 0) {
+ timeout = ms_rdelay(PROBE_WAIT);
+ // FIXME setsockopt(fd, SO_ATTACH_FILTER, ...) to
+ // make the kernel filter out all packets except
+ // ones we'd care about.
+ }
+ VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n",
+ timeout, intf, nprobes, nclaims);
+ switch (poll(fds, 1, timeout)) {
+
+ // timeouts trigger protocol transitions
+ case 0:
+ // probes
+ if (nprobes < PROBE_NUM) {
+ nprobes++;
+ VDBG("probe/%d %s@%s\n",
+ nprobes, intf, inet_ntoa(ip));
+ (void)arp(fd, &saddr, ARPOP_REQUEST,
+ &addr, null_ip,
+ &null_addr, ip);
+ if (nprobes < PROBE_NUM) {
+ timeout = PROBE_MIN * 1000;
+ timeout += ms_rdelay(PROBE_MAX
+ - PROBE_MIN);
+ } else
+ timeout = ANNOUNCE_WAIT * 1000;
+ }
+ // then announcements
+ else if (nclaims < ANNOUNCE_NUM) {
+ nclaims++;
+ VDBG("announce/%d %s@%s\n",
+ nclaims, intf, inet_ntoa(ip));
+ (void)arp(fd, &saddr, ARPOP_REQUEST,
+ &addr, ip,
+ &addr, ip);
+ if (nclaims < ANNOUNCE_NUM) {
+ timeout = ANNOUNCE_INTERVAL * 1000;
+ } else {
+ // link is ok to use earlier
+ run(script, "config", intf, &ip);
+ ready = 1;
+ conflicts = 0;
+ timeout = -1;
+
+ // NOTE: all other exit paths
+ // should deconfig ...
+ if (quit)
+ return EXIT_SUCCESS;
+ // FIXME update filters
+ }
+ }
+ break;
+
+ // packets arriving
+ case 1:
+ // maybe adjust timeout
+ if (timeout > 0) {
+ struct timeval tv2;
+
+ gettimeofday(&tv2, NULL);
+ if (timercmp(&tv1, &tv2, <)) {
+ timeout = -1;
+ } else {
+ timersub(&tv1, &tv2, &tv1);
+ timeout = 1000 * tv1.tv_sec
+ + tv1.tv_usec / 1000;
+ }
+ }
+ if ((fds[0].revents & POLLIN) == 0) {
+ if (fds[0].revents & POLLERR) {
+ // FIXME: links routinely go down;
+ // this shouldn't necessarily exit.
+ fprintf(stderr, "%s %s: poll error\n",
+ prog, intf);
+ if (ready) {
+ run(script, "deconfig",
+ intf, &ip);
+ }
+ return EXIT_FAILURE;
+ }
+ continue;
+ }
+ // read ARP packet
+ if (recv(fd, &p, sizeof (p), 0) < 0) {
+ why = "recv";
+ goto bad;
+ }
+ if (p.hdr.ether_type != htons(ETHERTYPE_ARP))
+ continue;
+
+ VDBG("%s recv arp type=%d, op=%d,\n",
+ intf, ntohs(p.hdr.ether_type),
+ ntohs(p.arp.ar_op));
+ VDBG("\tsource=%s %s\n",
+ ether_ntoa(&p.source_addr),
+ inet_ntoa(p.source_ip));
+ VDBG("\ttarget=%s %s\n",
+ ether_ntoa(&p.target_addr),
+ inet_ntoa(p.target_ip));
+ if (p.arp.ar_op != htons(ARPOP_REQUEST)
+ && p.arp.ar_op != htons(ARPOP_REPLY))
+ continue;
+
+ // some cases are always conflicts
+ if ((p.source_ip.s_addr == ip.s_addr)
+ && (memcmp(&addr, &p.source_addr,
+ ETH_ALEN) != 0)) {
+collision:
+ VDBG("%s ARP conflict from %s\n", intf,
+ ether_ntoa(&p.source_addr));
+ if (ready) {
+ time_t now = time(0);
+
+ if ((defend + DEFEND_INTERVAL)
+ < now) {
+ defend = now;
+ (void)arp(fd, &saddr,
+ ARPOP_REQUEST,
+ &addr, ip,
+ &addr, ip);
+ VDBG("%s defend\n", intf);
+ timeout = -1;
+ continue;
+ }
+ defend = now;
+ ready = 0;
+ run(script, "deconfig", intf, &ip);
+ // FIXME rm filters: setsockopt(fd,
+ // SO_DETACH_FILTER, ...)
+ }
+ conflicts++;
+ if (conflicts >= MAX_CONFLICTS) {
+ VDBG("%s ratelimit\n", intf);
+ sleep(RATE_LIMIT_INTERVAL);
+ }
+ // restart the whole protocol
+ pick(&ip);
+ timeout = 0;
+ nprobes = 0;
+ nclaims = 0;
+ }
+ // two hosts probing one address is a collision too
+ else if (p.target_ip.s_addr == ip.s_addr
+ && nclaims == 0
+ && p.arp.ar_op == htons(ARPOP_REQUEST)
+ && memcmp(&addr, &p.target_addr,
+ ETH_ALEN) != 0) {
+ goto collision;
+ }
+ break;
+
+ default:
+ why = "poll";
+ goto bad;
+ }
+ }
+bad:
+ if (foreground)
+ perror(why);
+ else
+ syslog(LOG_ERR, "%s %s, %s error: %s",
+ prog, intf, why, strerror(errno));
+ return EXIT_FAILURE;
+}
projects / oweals / busybox.git / commitdiff