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533 lines
14 KiB
C
533 lines
14 KiB
C
/* vi: set sw=4 ts=4: */
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/*
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* RFC3927 ZeroConf IPv4 Link-Local addressing
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* (see <http://www.zeroconf.org/>)
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*
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* Copyright (C) 2003 by Arthur van Hoff (avh@strangeberry.com)
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* Copyright (C) 2004 by David Brownell
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*
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* Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
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*/
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/*
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* ZCIP just manages the 169.254.*.* addresses. That network is not
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* routed at the IP level, though various proxies or bridges can
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* certainly be used. Its naming is built over multicast DNS.
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*/
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//#define DEBUG
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// TODO:
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// - more real-world usage/testing, especially daemon mode
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// - kernel packet filters to reduce scheduling noise
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// - avoid silent script failures, especially under load...
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// - link status monitoring (restart on link-up; stop on link-down)
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#include <syslog.h>
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#include <poll.h>
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#include <sys/wait.h>
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#include <netinet/ether.h>
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#include <net/ethernet.h>
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#include <net/if.h>
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#include <net/if_arp.h>
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#include <linux/if_packet.h>
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#include <linux/sockios.h>
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#include "libbb.h"
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/* We don't need more than 32 bits of the counter */
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#define MONOTONIC_US() ((unsigned)monotonic_us())
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struct arp_packet {
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struct ether_header hdr;
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struct ether_arp arp;
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} ATTRIBUTE_PACKED;
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enum {
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/* 169.254.0.0 */
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LINKLOCAL_ADDR = 0xa9fe0000,
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/* protocol timeout parameters, specified in seconds */
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PROBE_WAIT = 1,
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PROBE_MIN = 1,
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PROBE_MAX = 2,
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PROBE_NUM = 3,
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MAX_CONFLICTS = 10,
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RATE_LIMIT_INTERVAL = 60,
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ANNOUNCE_WAIT = 2,
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ANNOUNCE_NUM = 2,
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ANNOUNCE_INTERVAL = 2,
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DEFEND_INTERVAL = 10
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};
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/* States during the configuration process. */
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enum {
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PROBE = 0,
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RATE_LIMIT_PROBE,
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ANNOUNCE,
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MONITOR,
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DEFEND
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};
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#define VDBG(fmt,args...) \
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do { } while (0)
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/**
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* Pick a random link local IP address on 169.254/16, except that
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* the first and last 256 addresses are reserved.
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*/
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static void pick(struct in_addr *ip)
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{
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unsigned tmp;
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do {
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tmp = rand() & IN_CLASSB_HOST;
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} while (tmp > (IN_CLASSB_HOST - 0x0200));
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ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
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}
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/**
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* Broadcast an ARP packet.
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*/
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static void arp(int fd, struct sockaddr *saddr, int op,
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const struct ether_addr *source_addr, struct in_addr source_ip,
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const struct ether_addr *target_addr, struct in_addr target_ip)
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{
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struct arp_packet p;
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memset(&p, 0, sizeof(p));
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// ether header
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p.hdr.ether_type = htons(ETHERTYPE_ARP);
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memcpy(p.hdr.ether_shost, source_addr, ETH_ALEN);
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memset(p.hdr.ether_dhost, 0xff, ETH_ALEN);
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// arp request
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p.arp.arp_hrd = htons(ARPHRD_ETHER);
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p.arp.arp_pro = htons(ETHERTYPE_IP);
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p.arp.arp_hln = ETH_ALEN;
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p.arp.arp_pln = 4;
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p.arp.arp_op = htons(op);
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memcpy(&p.arp.arp_sha, source_addr, ETH_ALEN);
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memcpy(&p.arp.arp_spa, &source_ip, sizeof(p.arp.arp_spa));
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memcpy(&p.arp.arp_tha, target_addr, ETH_ALEN);
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memcpy(&p.arp.arp_tpa, &target_ip, sizeof(p.arp.arp_tpa));
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// send it
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xsendto(fd, &p, sizeof(p), saddr, sizeof(*saddr));
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// Currently all callers ignore errors, that's why returns are
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// commented out...
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//return 0;
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}
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/**
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* Run a script. argv[2] is already NULL.
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*/
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static int run(char *argv[3], const char *intf, struct in_addr *ip)
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{
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int status;
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VDBG("%s run %s %s\n", intf, argv[0], argv[1]);
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if (ip) {
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char *addr = inet_ntoa(*ip);
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setenv("ip", addr, 1);
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bb_info_msg("%s %s %s", argv[1], intf, addr);
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}
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status = wait4pid(spawn(argv));
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if (status < 0) {
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bb_perror_msg("%s %s", argv[1], intf);
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return -errno;
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}
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if (status != 0)
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bb_error_msg("script %s %s failed, exitcode=%d", argv[0], argv[1], status);
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return status;
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}
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/**
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* Return milliseconds of random delay, up to "secs" seconds.
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*/
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static unsigned ALWAYS_INLINE ms_rdelay(unsigned secs)
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{
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return rand() % (secs * 1000);
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}
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/**
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* main program
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*/
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int zcip_main(int argc, char **argv);
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int zcip_main(int argc, char **argv)
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{
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int state = PROBE;
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struct ether_addr eth_addr;
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const char *why;
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int fd;
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char *r_opt;
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unsigned opts;
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/* Ugly trick, but I want these zeroed in one go */
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struct {
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const struct in_addr null_ip;
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const struct ether_addr null_addr;
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struct sockaddr saddr;
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struct in_addr ip;
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struct ifreq ifr;
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char *intf;
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char *script_av[3];
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int timeout_ms; /* must be signed */
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unsigned conflicts;
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unsigned nprobes;
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unsigned nclaims;
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int ready;
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int verbose;
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} L;
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#define null_ip (L.null_ip )
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#define null_addr (L.null_addr )
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#define saddr (L.saddr )
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#define ip (L.ip )
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#define ifr (L.ifr )
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#define intf (L.intf )
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#define script_av (L.script_av )
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#define timeout_ms (L.timeout_ms)
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#define conflicts (L.conflicts )
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#define nprobes (L.nprobes )
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#define nclaims (L.nclaims )
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#define ready (L.ready )
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#define verbose (L.verbose )
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memset(&L, 0, sizeof(L));
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#define FOREGROUND (opts & 1)
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#define QUIT (opts & 2)
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// parse commandline: prog [options] ifname script
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// exactly 2 args; -v accumulates and implies -f
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opt_complementary = "=2:vv:vf";
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opts = getopt32(argv, "fqr:v", &r_opt, &verbose);
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if (!FOREGROUND) {
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/* Do it early, before all bb_xx_msg calls */
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openlog(applet_name, 0, LOG_DAEMON);
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logmode |= LOGMODE_SYSLOG;
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}
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if (opts & 4) { // -r n.n.n.n
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if (inet_aton(r_opt, &ip) == 0
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|| (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR
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) {
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bb_error_msg_and_die("invalid link address");
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}
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}
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// On NOMMU reexec early (or else we will rerun things twice)
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#if !BB_MMU
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if (!FOREGROUND)
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bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv);
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#endif
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argc -= optind;
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argv += optind;
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intf = argv[0];
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script_av[0] = argv[1];
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setenv("interface", intf, 1);
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// initialize the interface (modprobe, ifup, etc)
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script_av[1] = (char*)"init";
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if (run(script_av, intf, NULL))
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return EXIT_FAILURE;
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// initialize saddr
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//memset(&saddr, 0, sizeof(saddr));
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safe_strncpy(saddr.sa_data, intf, sizeof(saddr.sa_data));
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// open an ARP socket
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fd = xsocket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
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// bind to the interface's ARP socket
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xbind(fd, &saddr, sizeof(saddr));
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// get the interface's ethernet address
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//memset(&ifr, 0, sizeof(ifr));
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strncpy(ifr.ifr_name, intf, sizeof(ifr.ifr_name));
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xioctl(fd, SIOCGIFHWADDR, &ifr);
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memcpy(ð_addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
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// start with some stable ip address, either a function of
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// the hardware address or else the last address we used.
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// NOTE: the sequence of addresses we try changes only
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// depending on when we detect conflicts.
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srand(*(unsigned*)&ifr.ifr_hwaddr.sa_data);
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if (ip.s_addr == 0)
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pick(&ip);
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// FIXME cases to handle:
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// - zcip already running!
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// - link already has local address... just defend/update
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// daemonize now; don't delay system startup
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if (!FOREGROUND) {
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#if BB_MMU
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bb_daemonize(DAEMON_CHDIR_ROOT);
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#endif
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bb_info_msg("start, interface %s", intf);
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}
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// run the dynamic address negotiation protocol,
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// restarting after address conflicts:
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// - start with some address we want to try
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// - short random delay
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// - arp probes to see if another host else uses it
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// - arp announcements that we're claiming it
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// - use it
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// - defend it, within limits
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while (1) {
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struct pollfd fds[1];
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unsigned deadline_us;
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struct arp_packet p;
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int source_ip_conflict = 0;
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int target_ip_conflict = 0;
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fds[0].fd = fd;
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fds[0].events = POLLIN;
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fds[0].revents = 0;
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// poll, being ready to adjust current timeout
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if (!timeout_ms) {
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timeout_ms = ms_rdelay(PROBE_WAIT);
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// FIXME setsockopt(fd, SO_ATTACH_FILTER, ...) to
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// make the kernel filter out all packets except
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// ones we'd care about.
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}
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// set deadline_us to the point in time when we timeout
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deadline_us = MONOTONIC_US() + timeout_ms * 1000;
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VDBG("...wait %d %s nprobes=%u, nclaims=%u\n",
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timeout_ms, intf, nprobes, nclaims);
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switch (poll(fds, 1, timeout_ms)) {
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// timeout
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case 0:
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VDBG("state = %d\n", state);
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switch (state) {
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case PROBE:
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// timeouts in the PROBE state mean no conflicting ARP packets
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// have been received, so we can progress through the states
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if (nprobes < PROBE_NUM) {
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nprobes++;
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VDBG("probe/%u %s@%s\n",
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nprobes, intf, inet_ntoa(ip));
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arp(fd, &saddr, ARPOP_REQUEST,
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ð_addr, null_ip,
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&null_addr, ip);
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timeout_ms = PROBE_MIN * 1000;
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timeout_ms += ms_rdelay(PROBE_MAX - PROBE_MIN);
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}
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else {
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// Switch to announce state.
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state = ANNOUNCE;
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nclaims = 0;
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VDBG("announce/%u %s@%s\n",
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nclaims, intf, inet_ntoa(ip));
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arp(fd, &saddr, ARPOP_REQUEST,
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ð_addr, ip,
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ð_addr, ip);
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timeout_ms = ANNOUNCE_INTERVAL * 1000;
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}
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break;
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case RATE_LIMIT_PROBE:
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// timeouts in the RATE_LIMIT_PROBE state mean no conflicting ARP packets
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// have been received, so we can move immediately to the announce state
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state = ANNOUNCE;
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nclaims = 0;
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VDBG("announce/%u %s@%s\n",
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nclaims, intf, inet_ntoa(ip));
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arp(fd, &saddr, ARPOP_REQUEST,
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ð_addr, ip,
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ð_addr, ip);
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timeout_ms = ANNOUNCE_INTERVAL * 1000;
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break;
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case ANNOUNCE:
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// timeouts in the ANNOUNCE state mean no conflicting ARP packets
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// have been received, so we can progress through the states
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if (nclaims < ANNOUNCE_NUM) {
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nclaims++;
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VDBG("announce/%u %s@%s\n",
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nclaims, intf, inet_ntoa(ip));
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arp(fd, &saddr, ARPOP_REQUEST,
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ð_addr, ip,
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ð_addr, ip);
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timeout_ms = ANNOUNCE_INTERVAL * 1000;
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}
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else {
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// Switch to monitor state.
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state = MONITOR;
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// link is ok to use earlier
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// FIXME update filters
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script_av[1] = (char*)"config";
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run(script_av, intf, &ip);
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ready = 1;
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conflicts = 0;
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timeout_ms = -1; // Never timeout in the monitor state.
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// NOTE: all other exit paths
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// should deconfig ...
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if (QUIT)
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return EXIT_SUCCESS;
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}
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break;
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case DEFEND:
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// We won! No ARP replies, so just go back to monitor.
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state = MONITOR;
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timeout_ms = -1;
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conflicts = 0;
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break;
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default:
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// Invalid, should never happen. Restart the whole protocol.
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state = PROBE;
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pick(&ip);
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timeout_ms = 0;
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nprobes = 0;
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nclaims = 0;
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break;
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} // switch (state)
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break; // case 0 (timeout)
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// packets arriving
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case 1:
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// We need to adjust the timeout in case we didn't receive
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// a conflicting packet.
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if (timeout_ms > 0) {
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unsigned diff = deadline_us - MONOTONIC_US();
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if ((int)(diff) < 0) {
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// Current time is greater than the expected timeout time.
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// Should never happen.
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VDBG("missed an expected timeout\n");
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timeout_ms = 0;
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} else {
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VDBG("adjusting timeout\n");
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timeout_ms = diff / 1000;
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if (!timeout_ms) timeout_ms = 1;
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}
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}
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if ((fds[0].revents & POLLIN) == 0) {
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if (fds[0].revents & POLLERR) {
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// FIXME: links routinely go down;
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// this shouldn't necessarily exit.
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bb_error_msg("%s: poll error", intf);
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if (ready) {
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script_av[1] = (char*)"deconfig";
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run(script_av, intf, &ip);
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}
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return EXIT_FAILURE;
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}
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continue;
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}
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// read ARP packet
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if (recv(fd, &p, sizeof(p), 0) < 0) {
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why = "recv";
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goto bad;
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}
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if (p.hdr.ether_type != htons(ETHERTYPE_ARP))
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continue;
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#ifdef DEBUG
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{
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struct ether_addr * sha = (struct ether_addr *) p.arp.arp_sha;
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struct ether_addr * tha = (struct ether_addr *) p.arp.arp_tha;
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struct in_addr * spa = (struct in_addr *) p.arp.arp_spa;
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struct in_addr * tpa = (struct in_addr *) p.arp.arp_tpa;
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VDBG("%s recv arp type=%d, op=%d,\n",
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intf, ntohs(p.hdr.ether_type),
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ntohs(p.arp.arp_op));
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VDBG("\tsource=%s %s\n",
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ether_ntoa(sha),
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inet_ntoa(*spa));
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VDBG("\ttarget=%s %s\n",
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ether_ntoa(tha),
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inet_ntoa(*tpa));
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}
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#endif
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if (p.arp.arp_op != htons(ARPOP_REQUEST)
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&& p.arp.arp_op != htons(ARPOP_REPLY))
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continue;
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if (memcmp(p.arp.arp_spa, &ip.s_addr, sizeof(struct in_addr)) == 0 &&
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memcmp(ð_addr, &p.arp.arp_sha, ETH_ALEN) != 0) {
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source_ip_conflict = 1;
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}
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if (memcmp(p.arp.arp_tpa, &ip.s_addr, sizeof(struct in_addr)) == 0 &&
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p.arp.arp_op == htons(ARPOP_REQUEST) &&
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memcmp(ð_addr, &p.arp.arp_tha, ETH_ALEN) != 0) {
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target_ip_conflict = 1;
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}
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VDBG("state = %d, source ip conflict = %d, target ip conflict = %d\n",
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state, source_ip_conflict, target_ip_conflict);
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switch (state) {
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case PROBE:
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case ANNOUNCE:
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// When probing or announcing, check for source IP conflicts
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// and other hosts doing ARP probes (target IP conflicts).
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if (source_ip_conflict || target_ip_conflict) {
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conflicts++;
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if (conflicts >= MAX_CONFLICTS) {
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VDBG("%s ratelimit\n", intf);
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timeout_ms = RATE_LIMIT_INTERVAL * 1000;
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state = RATE_LIMIT_PROBE;
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}
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// restart the whole protocol
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pick(&ip);
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timeout_ms = 0;
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nprobes = 0;
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nclaims = 0;
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}
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break;
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case MONITOR:
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// If a conflict, we try to defend with a single ARP probe.
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if (source_ip_conflict) {
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VDBG("monitor conflict -- defending\n");
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state = DEFEND;
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timeout_ms = DEFEND_INTERVAL * 1000;
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arp(fd, &saddr,
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ARPOP_REQUEST,
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ð_addr, ip,
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ð_addr, ip);
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}
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break;
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case DEFEND:
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// Well, we tried. Start over (on conflict).
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if (source_ip_conflict) {
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state = PROBE;
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VDBG("defend conflict -- starting over\n");
|
|
ready = 0;
|
|
script_av[1] = (char*)"deconfig";
|
|
run(script_av, intf, &ip);
|
|
|
|
// restart the whole protocol
|
|
pick(&ip);
|
|
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;
|
|
pick(&ip);
|
|
timeout_ms = 0;
|
|
nprobes = 0;
|
|
nclaims = 0;
|
|
break;
|
|
} // switch state
|
|
|
|
break; // case 1 (packets arriving)
|
|
default:
|
|
why = "poll";
|
|
goto bad;
|
|
} // switch poll
|
|
}
|
|
bad:
|
|
bb_perror_msg("%s, %s", intf, why);
|
|
return EXIT_FAILURE;
|
|
}
|