busybox/networking/zcip.c

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