source: MondoRescue/branches/3.2/mindi-busybox/networking/udhcp/leases.c

/* vi: set sw=4 ts=4: */
/*
 * Russ Dill <Russ.Dill@asu.edu> July 2001
 *
 * Licensed under GPLv2, see file LICENSE in this source tree.
 */
#include "common.h"
#include "dhcpd.h"

/* Find the oldest expired lease, NULL if there are no expired leases */
static struct dyn_lease *oldest_expired_lease(void)
{
    struct dyn_lease *oldest_lease = NULL;
    leasetime_t oldest_time = time(NULL);
    unsigned i;

    /* Unexpired leases have g_leases[i].expires >= current time
     * and therefore can't ever match */
    for (i = 0; i < server_config.max_leases; i++) {
        if (g_leases[i].expires < oldest_time) {
            oldest_time = g_leases[i].expires;
            oldest_lease = &g_leases[i];
        }
    }
    return oldest_lease;
}

/* Clear out all leases with matching nonzero chaddr OR yiaddr.
 * If chaddr == NULL, this is a conflict lease.
 */
static void clear_leases(const uint8_t *chaddr, uint32_t yiaddr)
{
    unsigned i;

    for (i = 0; i < server_config.max_leases; i++) {
        if ((chaddr && memcmp(g_leases[i].lease_mac, chaddr, 6) == 0)
         || (yiaddr && g_leases[i].lease_nip == yiaddr)
        ) {
            memset(&g_leases[i], 0, sizeof(g_leases[i]));
        }
    }
}

/* Add a lease into the table, clearing out any old ones.
 * If chaddr == NULL, this is a conflict lease.
 */
struct dyn_lease* FAST_FUNC add_lease(
        const uint8_t *chaddr, uint32_t yiaddr,
        leasetime_t leasetime,
        const char *hostname, int hostname_len)
{
    struct dyn_lease *oldest;

    /* clean out any old ones */
    clear_leases(chaddr, yiaddr);

    oldest = oldest_expired_lease();

    if (oldest) {
        memset(oldest, 0, sizeof(*oldest));
        if (hostname) {
            char *p;

            hostname_len++; /* include NUL */
            if (hostname_len > sizeof(oldest->hostname))
                hostname_len = sizeof(oldest->hostname);
            p = safe_strncpy(oldest->hostname, hostname, hostname_len);
            /* sanitization (s/non-ASCII/^/g) */
            while (*p) {
                if (*p < ' ' || *p > 126)
                    *p = '^';
                p++;
            }
        }
        if (chaddr)
            memcpy(oldest->lease_mac, chaddr, 6);
        oldest->lease_nip = yiaddr;
        oldest->expires = time(NULL) + leasetime;
    }

    return oldest;
}

/* True if a lease has expired */
int FAST_FUNC is_expired_lease(struct dyn_lease *lease)
{
    return (lease->expires < (leasetime_t) time(NULL));
}

/* Find the first lease that matches MAC, NULL if no match */
struct dyn_lease* FAST_FUNC find_lease_by_mac(const uint8_t *mac)
{
    unsigned i;

    for (i = 0; i < server_config.max_leases; i++)
        if (memcmp(g_leases[i].lease_mac, mac, 6) == 0)
            return &g_leases[i];

    return NULL;
}

/* Find the first lease that matches IP, NULL is no match */
struct dyn_lease* FAST_FUNC find_lease_by_nip(uint32_t nip)
{
    unsigned i;

    for (i = 0; i < server_config.max_leases; i++)
        if (g_leases[i].lease_nip == nip)
            return &g_leases[i];

    return NULL;
}

/* Check if the IP is taken; if it is, add it to the lease table */
static int nobody_responds_to_arp(uint32_t nip, const uint8_t *safe_mac)
{
    struct in_addr temp;
    int r;

    r = arpping(nip, safe_mac,
            server_config.server_nip,
            server_config.server_mac,
            server_config.interface);
    if (r)
        return r;

    temp.s_addr = nip;
    bb_info_msg("%s belongs to someone, reserving it for %u seconds",
        inet_ntoa(temp), (unsigned)server_config.conflict_time);
    add_lease(NULL, nip, server_config.conflict_time, NULL, 0);
    return 0;
}

/* Find a new usable (we think) address */
uint32_t FAST_FUNC find_free_or_expired_nip(const uint8_t *safe_mac)
{
    uint32_t addr;
    struct dyn_lease *oldest_lease = NULL;

#if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
    uint32_t stop;
    unsigned i, hash;

    /* hash hwaddr: use the SDBM hashing algorithm.  Seems to give good
     * dispersal even with similarly-valued "strings".
     */
    hash = 0;
    for (i = 0; i < 6; i++)
        hash += safe_mac[i] + (hash << 6) + (hash << 16) - hash;

    /* pick a seed based on hwaddr then iterate until we find a free address. */
    addr = server_config.start_ip
        + (hash % (1 + server_config.end_ip - server_config.start_ip));
    stop = addr;
#else
    addr = server_config.start_ip;
#define stop (server_config.end_ip + 1)
#endif
    do {
        uint32_t nip;
        struct dyn_lease *lease;

        /* ie, 192.168.55.0 */
        if ((addr & 0xff) == 0)
            goto next_addr;
        /* ie, 192.168.55.255 */
        if ((addr & 0xff) == 0xff)
            goto next_addr;
        nip = htonl(addr);
        /* skip our own address */
        if (nip == server_config.server_nip)
            goto next_addr;
        /* is this a static lease addr? */
        if (is_nip_reserved(server_config.static_leases, nip))
            goto next_addr;

        lease = find_lease_by_nip(nip);
        if (!lease) {
//TODO: DHCP servers do not always sit on the same subnet as clients: should *ping*, not arp-ping!
            if (nobody_responds_to_arp(nip, safe_mac))
                return nip;
        } else {
            if (!oldest_lease || lease->expires < oldest_lease->expires)
                oldest_lease = lease;
        }

 next_addr:
        addr++;
#if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
        if (addr > server_config.end_ip)
            addr = server_config.start_ip;
#endif
    } while (addr != stop);

    if (oldest_lease
     && is_expired_lease(oldest_lease)
     && nobody_responds_to_arp(oldest_lease->lease_nip, safe_mac)
    ) {
        return oldest_lease->lease_nip;
    }

    return 0;
}