networking/udhcp/leases.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Russ Dill <Russ.Dill@asu.edu> July 2001
   4  *
   5  * Licensed under GPLv2, see file LICENSE in this source tree.
   6  */
   7 #include "common.h"
   8 #include "dhcpd.h"
   9
  10 /* Find the oldest expired lease, NULL if there are no expired leases */
  11 static struct dyn_lease *oldest_expired_lease(void)
  12 {
  13         struct dyn_lease *oldest_lease = NULL;
  14         leasetime_t oldest_time = time(NULL);
  15         unsigned i;
  16
  17         /* Unexpired leases have g_leases[i].expires >= current time
  18          * and therefore can't ever match */
  19         for (i = 0; i < server_config.max_leases; i++) {
  20                 if (g_leases[i].expires < oldest_time) {
  21                         oldest_time = g_leases[i].expires;
  22                         oldest_lease = &g_leases[i];
  23                 }
  24         }
  25         return oldest_lease;
  26 }
  27
  28 /* Clear out all leases with matching nonzero chaddr OR yiaddr.
  29  * If chaddr == NULL, this is a conflict lease.
  30  */
  31 static void clear_leases(const uint8_t *chaddr, uint32_t yiaddr)
  32 {
  33         unsigned i;
  34
  35         for (i = 0; i < server_config.max_leases; i++) {
  36                 if ((chaddr && memcmp(g_leases[i].lease_mac, chaddr, 6) == 0)
  37                  || (yiaddr && g_leases[i].lease_nip == yiaddr)
  38                 ) {
  39                         memset(&g_leases[i], 0, sizeof(g_leases[i]));
  40                 }
  41         }
  42 }
  43
  44 /* Add a lease into the table, clearing out any old ones.
  45  * If chaddr == NULL, this is a conflict lease.
  46  */
  47 struct dyn_lease* FAST_FUNC add_lease(
  48                 const uint8_t *chaddr, uint32_t yiaddr,
  49                 leasetime_t leasetime,
  50                 const char *hostname, int hostname_len)
  51 {
  52         struct dyn_lease *oldest;
  53
  54         /* clean out any old ones */
  55         clear_leases(chaddr, yiaddr);
  56
  57         oldest = oldest_expired_lease();
  58
  59         if (oldest) {
  60                 memset(oldest, 0, sizeof(*oldest));
  61                 if (hostname) {
  62                         char *p;
  63
  64                         hostname_len++; /* include NUL */
  65                         if (hostname_len > sizeof(oldest->hostname))
  66                                 hostname_len = sizeof(oldest->hostname);
  67                         p = safe_strncpy(oldest->hostname, hostname, hostname_len);
  68                         /* sanitization (s/non-ASCII/^/g) */
  69                         while (*p) {
  70                                 if (*p < ' ' || *p > 126)
  71                                         *p = '^';
  72                                 p++;
  73                         }
  74                 }
  75                 if (chaddr)
  76                         memcpy(oldest->lease_mac, chaddr, 6);
  77                 oldest->lease_nip = yiaddr;
  78                 oldest->expires = time(NULL) + leasetime;
  79         }
  80
  81         return oldest;
  82 }
  83
  84 /* True if a lease has expired */
  85 int FAST_FUNC is_expired_lease(struct dyn_lease *lease)
  86 {
  87         return (lease->expires < (leasetime_t) time(NULL));
  88 }
  89
  90 /* Find the first lease that matches MAC, NULL if no match */
  91 struct dyn_lease* FAST_FUNC find_lease_by_mac(const uint8_t *mac)
  92 {
  93         unsigned i;
  94
  95         for (i = 0; i < server_config.max_leases; i++)
  96                 if (memcmp(g_leases[i].lease_mac, mac, 6) == 0)
  97                         return &g_leases[i];
  98
  99         return NULL;
 100 }
 101
 102 /* Find the first lease that matches IP, NULL is no match */
 103 struct dyn_lease* FAST_FUNC find_lease_by_nip(uint32_t nip)
 104 {
 105         unsigned i;
 106
 107         for (i = 0; i < server_config.max_leases; i++)
 108                 if (g_leases[i].lease_nip == nip)
 109                         return &g_leases[i];
 110
 111         return NULL;
 112 }
 113
 114 /* Check if the IP is taken; if it is, add it to the lease table */
 115 static int nobody_responds_to_arp(uint32_t nip, const uint8_t *safe_mac, unsigned arpping_ms)
 116 {
 117         struct in_addr temp;
 118         int r;
 119
 120         r = arpping(nip, safe_mac,
 121                         server_config.server_nip,
 122                         server_config.server_mac,
 123                         server_config.interface,
 124                         arpping_ms);
 125         if (r)
 126                 return r;
 127
 128         temp.s_addr = nip;
 129         bb_info_msg("%s belongs to someone, reserving it for %u seconds",
 130                 inet_ntoa(temp), (unsigned)server_config.conflict_time);
 131         add_lease(NULL, nip, server_config.conflict_time, NULL, 0);
 132         return 0;
 133 }
 134
 135 /* Find a new usable (we think) address */
 136 uint32_t FAST_FUNC find_free_or_expired_nip(const uint8_t *safe_mac, unsigned arpping_ms)
 137 {
 138         uint32_t addr;
 139         struct dyn_lease *oldest_lease = NULL;
 140
 141 #if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
 142         uint32_t stop;
 143         unsigned i, hash;
 144
 145         /* hash hwaddr: use the SDBM hashing algorithm.  Seems to give good
 146          * dispersal even with similarly-valued "strings".
 147          */
 148         hash = 0;
 149         for (i = 0; i < 6; i++)
 150                 hash += safe_mac[i] + (hash << 6) + (hash << 16) - hash;
 151
 152         /* pick a seed based on hwaddr then iterate until we find a free address. */
 153         addr = server_config.start_ip
 154                 + (hash % (1 + server_config.end_ip - server_config.start_ip));
 155         stop = addr;
 156 #else
 157         addr = server_config.start_ip;
 158 #define stop (server_config.end_ip + 1)
 159 #endif
 160         do {
 161                 uint32_t nip;
 162                 struct dyn_lease *lease;
 163
 164                 /* ie, 192.168.55.0 */
 165                 if ((addr & 0xff) == 0)
 166                         goto next_addr;
 167                 /* ie, 192.168.55.255 */
 168                 if ((addr & 0xff) == 0xff)
 169                         goto next_addr;
 170                 nip = htonl(addr);
 171                 /* skip our own address */
 172                 if (nip == server_config.server_nip)
 173                         goto next_addr;
 174                 /* is this a static lease addr? */
 175                 if (is_nip_reserved(server_config.static_leases, nip))
 176                         goto next_addr;
 177
 178                 lease = find_lease_by_nip(nip);
 179                 if (!lease) {
 180 //TODO: DHCP servers do not always sit on the same subnet as clients: should *ping*, not arp-ping!
 181                         if (nobody_responds_to_arp(nip, safe_mac, arpping_ms))
 182                                 return nip;
 183                 } else {
 184                         if (!oldest_lease || lease->expires < oldest_lease->expires)
 185                                 oldest_lease = lease;
 186                 }
 187
 188  next_addr:
 189                 addr++;
 190 #if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
 191                 if (addr > server_config.end_ip)
 192                         addr = server_config.start_ip;
 193 #endif
 194         } while (addr != stop);
 195
 196         if (oldest_lease
 197          && is_expired_lease(oldest_lease)
 198          && nobody_responds_to_arp(oldest_lease->lease_nip, safe_mac, arpping_ms)
 199         ) {
 200                 return oldest_lease->lease_nip;
 201         }
 202
 203         return 0;
 204 }