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549 lines
14 KiB
C
549 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 "busybox.h"
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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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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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static unsigned opts;
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#define FOREGROUND (opts & 1)
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#define QUIT (opts & 2)
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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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/* use cheaper math than lrand48() mod N */
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do {
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tmp = (lrand48() >> 16) & 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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/* TODO: we need a flag to direct bb_[p]error_msg output to stderr. */
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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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if (sendto(fd, &p, sizeof(p), 0, saddr, sizeof(*saddr)) < 0) {
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bb_perror_msg("sendto");
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//return -errno;
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}
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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.
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*/
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static int run(const char *script, const char *arg, const char *intf, struct in_addr *ip)
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{
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int pid, status;
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const char *why;
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if(1) { //always true: if (script != NULL)
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VDBG("%s run %s %s\n", intf, script, arg);
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if (ip != NULL) {
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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", arg, intf, addr);
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}
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pid = vfork();
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if (pid < 0) { // error
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why = "vfork";
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goto bad;
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} else if (pid == 0) { // child
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execl(script, script, arg, NULL);
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bb_perror_msg("execl");
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_exit(EXIT_FAILURE);
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}
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if (waitpid(pid, &status, 0) <= 0) {
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why = "waitpid";
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goto bad;
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}
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if (WEXITSTATUS(status) != 0) {
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bb_error_msg("script %s failed, exit=%d",
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script, WEXITSTATUS(status));
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return -errno;
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}
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}
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return 0;
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bad:
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status = -errno;
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bb_perror_msg("%s %s, %s", arg, intf, why);
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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 ATTRIBUTE_ALWAYS_INLINE ms_rdelay(unsigned secs)
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{
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return lrand48() % (secs * 1000);
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}
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/**
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* main program
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*/
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/* Used to be auto variables on main() stack, but
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* most of them were zero-inited. Moving them to bss
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* is more space-efficient.
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*/
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static const struct in_addr null_ip; // = { 0 };
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static const struct ether_addr null_addr; // = { {0, 0, 0, 0, 0, 0} };
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static struct sockaddr saddr; // memset(0);
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static struct in_addr ip; // = { 0 };
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static struct ifreq ifr; //memset(0);
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static char *intf; // = NULL;
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static char *script; // = NULL;
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static suseconds_t timeout; // = 0; // milliseconds
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static unsigned conflicts; // = 0;
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static unsigned nprobes; // = 0;
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static unsigned nclaims; // = 0;
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static int ready; // = 0;
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static int verbose; // = 0;
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static int state = PROBE;
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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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struct ether_addr eth_addr;
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const char *why;
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int fd;
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// parse commandline: prog [options] ifname script
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char *r_opt;
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opt_complementary = "vv:vf"; // -v accumulates and implies -f
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opts = getopt32(argc, 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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logmode = LOGMODE_SYSLOG;
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openlog(applet_name, 0, LOG_DAEMON);
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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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argc -= optind;
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argv += optind;
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if (argc != 2)
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bb_show_usage();
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intf = argv[0];
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script = argv[1];
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setenv("interface", intf, 1);
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// initialize the interface (modprobe, ifup, etc)
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if (run(script, "init", intf, NULL) < 0)
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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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if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0) {
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bb_perror_msg_and_die("get ethernet address");
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}
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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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// (SVID 3 bogon: who says that "short" is always 16 bits?)
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seed48( (unsigned short*)&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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/* bb_daemonize(); - bad, will close fd! */
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xdaemon(0, 0);
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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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struct timeval tv1;
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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) {
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timeout = 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 tv1 to the point in time when we timeout
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gettimeofday(&tv1, NULL);
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tv1.tv_usec += (timeout % 1000) * 1000;
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while (tv1.tv_usec > 1000000) {
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tv1.tv_usec -= 1000000;
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tv1.tv_sec++;
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}
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tv1.tv_sec += timeout / 1000;
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VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n",
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timeout, intf, nprobes, nclaims);
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switch (poll(fds, 1, timeout)) {
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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/%d %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 = PROBE_MIN * 1000;
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timeout += ms_rdelay(PROBE_MAX
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- 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/%d %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 = 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/%d %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 = 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/%d %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 = 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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run(script, "config", intf, &ip);
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ready = 1;
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conflicts = 0;
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timeout = -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 = -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 = 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 > 0) {
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struct timeval tv2;
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gettimeofday(&tv2, NULL);
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if (timercmp(&tv1, &tv2, <)) {
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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 = 0;
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} else {
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VDBG("adjusting timeout\n");
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timersub(&tv1, &tv2, &tv1);
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timeout = 1000 * tv1.tv_sec
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+ tv1.tv_usec / 1000;
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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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run(script, "deconfig",
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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 = 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 = 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 = DEFEND_INTERVAL * 1000;
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|
arp(fd, &saddr,
|
|
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(script, "deconfig", intf, &ip);
|
|
|
|
// restart the whole protocol
|
|
pick(&ip);
|
|
timeout = 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 = 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;
|
|
}
|