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busybox/networking/zcip.c
Denis Vlasenko 3538b9a882 Implement optional syslog logging using ordinary 
bb_xx_msg calls, and convert networking/* to it.
The rest of bbox will be converted gradually.
2006-09-06 18:36:50 +00:00

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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 "busybox.h"
#include <errno.h>
#include <string.h>
#include <syslog.h>
#include <poll.h>
#include <time.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>
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
};
#define VDBG(fmt,args...) \
do { } while (0)
static unsigned long opts;
#define FOREGROUND (opts & 1)
#define QUIT (opts & 2)
/**
* 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);
}
/* TODO: we need a flag to direct bb_[p]error_msg output to stderr. */
/**
* Broadcast an ARP packet.
*/
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);
memcpy(&p.arp.arp_spa, &source_ip, sizeof (p.arp.arp_spa));
memcpy(&p.arp.arp_tha, target_addr, ETH_ALEN);
memcpy(&p.arp.arp_tpa, &target_ip, sizeof (p.arp.arp_tpa));
// send it
if (sendto(fd, &p, sizeof (p), 0, saddr, sizeof (*saddr)) < 0) {
bb_perror_msg("sendto");
//return -errno;
}
// Currently all callers ignore errors, that's why returns are
// commented out...
//return 0;
}
/**
* Run a script.
*/
static int run(char *script, char *arg, char *intf, struct in_addr *ip)
{
int pid, status;
char *why;
if(1) { //always true: if (script != NULL)
VDBG("%s run %s %s\n", intf, script, arg);
if (ip != NULL) {
char *addr = inet_ntoa(*ip);
setenv("ip", addr, 1);
bb_info_msg("%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);
bb_perror_msg("execl");
_exit(EXIT_FAILURE);
}
if (waitpid(pid, &status, 0) <= 0) {
why = "waitpid";
goto bad;
}
if (WEXITSTATUS(status) != 0) {
bb_error_msg("script %s failed, exit=%d",
script, WEXITSTATUS(status));
return -errno;
}
}
return 0;
bad:
status = -errno;
bb_perror_msg("%s %s, %s", arg, intf, why);
return status;
}
/**
* Return milliseconds of random delay, up to "secs" seconds.
*/
static unsigned ATTRIBUTE_ALWAYS_INLINE ms_rdelay(unsigned secs)
{
return lrand48() % (secs * 1000);
}
/**
* main program
*/
/* Used to be auto variables on main() stack, but
* most of them were zero-inited. Moving them to bss
* is more space-efficient.
*/
static const struct in_addr null_ip; // = { 0 };
static const struct ether_addr null_addr; // = { {0, 0, 0, 0, 0, 0} };
static struct sockaddr saddr; // memset(0);
static struct in_addr ip; // = { 0 };
static struct ifreq ifr; //memset(0);
static char *intf; // = NULL;
static char *script; // = NULL;
static suseconds_t timeout; // = 0; // milliseconds
static unsigned conflicts; // = 0;
static unsigned nprobes; // = 0;
static unsigned nclaims; // = 0;
static int ready; // = 0;
static int verbose; // = 0;
static int state = PROBE;
int zcip_main(int argc, char *argv[])
{
struct ether_addr eth_addr;
char *why;
int fd;
// parse commandline: prog [options] ifname script
char *r_opt;
bb_opt_complementally = "vv:vf"; // -v accumulates and implies -f
opts = bb_getopt_ulflags(argc, argv, "fqr:v", &r_opt, &verbose);
if (!FOREGROUND) {
/* Do it early, before all bb_xx_msg calls */
logmode = LOGMODE_SYSLOG;
openlog(bb_applet_name, 0, LOG_DAEMON);
}
if (opts & 4) { // -r n.n.n.n
if (inet_aton(r_opt, &ip) == 0
|| (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR) {
bb_error_msg_and_die("invalid link address");
}
}
argc -= optind;
argv += optind;
if (argc != 2)
bb_show_usage();
intf = argv[0];
script = argv[1];
setenv("interface", intf, 1);
// initialize the interface (modprobe, ifup, etc)
if (run(script, "init", intf, NULL) < 0)
return EXIT_FAILURE;
// initialize saddr
//memset(&saddr, 0, sizeof (saddr));
safe_strncpy(saddr.sa_data, intf, sizeof (saddr.sa_data));
// open an ARP socket
fd = xsocket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
// bind to the interface's ARP socket
xbind(fd, &saddr, sizeof (saddr));
// 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) {
bb_perror_msg_and_die("get ethernet address");
}
memcpy(&eth_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.
// (SVID 3 bogon: who says that "short" is always 16 bits?)
seed48( (unsigned short*)&ifr.ifr_hwaddr.sa_data );
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) {
setsid();
xdaemon(0, 0);
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];
struct timeval tv1;
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;
// poll, being ready to adjust current timeout
if (!timeout) {
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.
}
// set tv1 to the point in time when we timeout
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;
VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n",
timeout, intf, nprobes, nclaims);
switch (poll(fds, 1, timeout)) {
// timeout
case 0:
VDBG("state = %d\n", state);
switch (state) {
case PROBE:
// 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/%d %s@%s\n",
nprobes, intf, inet_ntoa(ip));
arp(fd, &saddr, ARPOP_REQUEST,
&eth_addr, null_ip,
&null_addr, ip);
timeout = PROBE_MIN * 1000;
timeout += ms_rdelay(PROBE_MAX
- PROBE_MIN);
}
else {
// Switch to announce state.
state = ANNOUNCE;
nclaims = 0;
VDBG("announce/%d %s@%s\n",
nclaims, intf, inet_ntoa(ip));
arp(fd, &saddr, ARPOP_REQUEST,
&eth_addr, ip,
&eth_addr, ip);
timeout = ANNOUNCE_INTERVAL * 1000;
}
break;
case RATE_LIMIT_PROBE:
// 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/%d %s@%s\n",
nclaims, intf, inet_ntoa(ip));
arp(fd, &saddr, ARPOP_REQUEST,
&eth_addr, ip,
&eth_addr, ip);
timeout = ANNOUNCE_INTERVAL * 1000;
break;
case ANNOUNCE:
// 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/%d %s@%s\n",
nclaims, intf, inet_ntoa(ip));
arp(fd, &saddr, ARPOP_REQUEST,
&eth_addr, ip,
&eth_addr, ip);
timeout = ANNOUNCE_INTERVAL * 1000;
}
else {
// Switch to monitor state.
state = MONITOR;
// link is ok to use earlier
// FIXME update filters
run(script, "config", intf, &ip);
ready = 1;
conflicts = 0;
timeout = -1; // Never timeout in the monitor state.
// NOTE: all other exit paths
// should deconfig ...
if (QUIT)
return EXIT_SUCCESS;
}
break;
case DEFEND:
// We won! No ARP replies, so just go back to monitor.
state = MONITOR;
timeout = -1;
conflicts = 0;
break;
default:
// Invalid, should never happen. Restart the whole protocol.
state = PROBE;
pick(&ip);
timeout = 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 > 0) {
struct timeval tv2;
gettimeofday(&tv2, NULL);
if (timercmp(&tv1, &tv2, <)) {
// Current time is greater than the expected timeout time.
// Should never happen.
VDBG("missed an expected timeout\n");
timeout = 0;
} else {
VDBG("adjusting timeout\n");
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.
bb_error_msg("%s: poll error", 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;
#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;
}
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 = RATE_LIMIT_INTERVAL * 1000;
state = RATE_LIMIT_PROBE;
}
// restart the whole protocol
pick(&ip);
timeout = 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 = DEFEND_INTERVAL * 1000;
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;
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;
}
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