source: MondoRescue/branches/stable/mindi-busybox/networking/zcip.c

/* 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())

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)

/**
 * 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;

    do {
        tmp = rand() & IN_CLASSB_HOST;
    } while (tmp > (IN_CLASSB_HOST - 0x0200));
    ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
}

/**
 * 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
    xsendto(fd, &p, sizeof(p), saddr, sizeof(*saddr));

    // 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));

#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 */
        openlog(applet_name, 0, LOG_DAEMON);
        logmode |= LOGMODE_SYSLOG;
    }
    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");
        }
    }
    // 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
    argc -= optind;
    argv += optind;

    intf = argv[0];
    script_av[0] = argv[1];
    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
    //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));
    xioctl(fd, SIOCGIFHWADDR, &ifr);
    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.
    srand(*(unsigned*)&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) {
#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;

        // 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;

        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:
                // 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));
                    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));
                    arp(fd, &saddr, ARPOP_REQUEST,
                            &eth_addr, ip,
                            &eth_addr, ip);
                    timeout_ms = 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/%u %s@%s\n",
                        nclaims, intf, inet_ntoa(ip));
                arp(fd, &saddr, ARPOP_REQUEST,
                        &eth_addr, ip,
                        &eth_addr, ip);
                timeout_ms = 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/%u %s@%s\n",
                            nclaims, intf, inet_ntoa(ip));
                    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.

                    // 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_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
            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_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;
                    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;
}