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hush/networking/zcip.c

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/*
* 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;
}
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