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                         /*
  69                          * Sanitization (s/bad_char/./g).
  70                          * The intent is not to allow only "DNS-valid" hostnames,
  71                          * but merely make dumpleases output safe for shells to use.
  72                          * We accept "0-9A-Za-z._-", all other chars turn to dots.
  73                          */
  74                         while (*p) {
  75                                 if (!isalnum(*p) && *p != '-' && *p != '_')
  76                                         *p = '.';
  77                                 p++;
  78                         }
  79                 }
  80                 if (chaddr)
  81                         memcpy(oldest->lease_mac, chaddr, 6);
  82                 oldest->lease_nip = yiaddr;
  83                 oldest->expires = time(NULL) + leasetime;
  84         }
  85
  86         return oldest;
  87 }
  88
  89 /* True if a lease has expired */
  90 int FAST_FUNC is_expired_lease(struct dyn_lease *lease)
  91 {
  92         return (lease->expires < (leasetime_t) time(NULL));
  93 }
  94
  95 /* Find the first lease that matches MAC, NULL if no match */
  96 struct dyn_lease* FAST_FUNC find_lease_by_mac(const uint8_t *mac)
  97 {
  98         unsigned i;
  99
 100         for (i = 0; i < server_config.max_leases; i++)
 101                 if (memcmp(g_leases[i].lease_mac, mac, 6) == 0)
 102                         return &g_leases[i];
 103
 104         return NULL;
 105 }
 106
 107 /* Find the first lease that matches IP, NULL is no match */
 108 struct dyn_lease* FAST_FUNC find_lease_by_nip(uint32_t nip)
 109 {
 110         unsigned i;
 111
 112         for (i = 0; i < server_config.max_leases; i++)
 113                 if (g_leases[i].lease_nip == nip)
 114                         return &g_leases[i];
 115
 116         return NULL;
 117 }
 118
 119 /* Check if the IP is taken; if it is, add it to the lease table */
 120 static int nobody_responds_to_arp(uint32_t nip, const uint8_t *safe_mac, unsigned arpping_ms)
 121 {
 122         struct in_addr temp;
 123         int r;
 124
 125         r = arpping(nip, safe_mac,
 126                         server_config.server_nip,
 127                         server_config.server_mac,
 128                         server_config.interface,
 129                         arpping_ms);
 130         if (r)
 131                 return r;
 132
 133         temp.s_addr = nip;
 134         bb_info_msg("%s belongs to someone, reserving it for %u seconds",
 135                 inet_ntoa(temp), (unsigned)server_config.conflict_time);
 136         add_lease(NULL, nip, server_config.conflict_time, NULL, 0);
 137         return 0;
 138 }
 139
 140 /* Find a new usable (we think) address */
 141 uint32_t FAST_FUNC find_free_or_expired_nip(const uint8_t *safe_mac, unsigned arpping_ms)
 142 {
 143         uint32_t addr;
 144         struct dyn_lease *oldest_lease = NULL;
 145
 146 #if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
 147         uint32_t stop;
 148         unsigned i, hash;
 149
 150         /* hash hwaddr: use the SDBM hashing algorithm.  Seems to give good
 151          * dispersal even with similarly-valued "strings".
 152          */
 153         hash = 0;
 154         for (i = 0; i < 6; i++)
 155                 hash += safe_mac[i] + (hash << 6) + (hash << 16) - hash;
 156
 157         /* pick a seed based on hwaddr then iterate until we find a free address. */
 158         addr = server_config.start_ip
 159                 + (hash % (1 + server_config.end_ip - server_config.start_ip));
 160         stop = addr;
 161 #else
 162         addr = server_config.start_ip;
 163 #define stop (server_config.end_ip + 1)
 164 #endif
 165         do {
 166                 uint32_t nip;
 167                 struct dyn_lease *lease;
 168
 169                 /* ie, 192.168.55.0 */
 170                 if ((addr & 0xff) == 0)
 171                         goto next_addr;
 172                 /* ie, 192.168.55.255 */
 173                 if ((addr & 0xff) == 0xff)
 174                         goto next_addr;
 175                 nip = htonl(addr);
 176                 /* skip our own address */
 177                 if (nip == server_config.server_nip)
 178                         goto next_addr;
 179                 /* is this a static lease addr? */
 180                 if (is_nip_reserved(server_config.static_leases, nip))
 181                         goto next_addr;
 182
 183                 lease = find_lease_by_nip(nip);
 184                 if (!lease) {
 185 //TODO: DHCP servers do not always sit on the same subnet as clients: should *ping*, not arp-ping!
 186                         if (nobody_responds_to_arp(nip, safe_mac, arpping_ms))
 187                                 return nip;
 188                 } else {
 189                         if (!oldest_lease || lease->expires < oldest_lease->expires)
 190                                 oldest_lease = lease;
 191                 }
 192
 193  next_addr:
 194                 addr++;
 195 #if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
 196                 if (addr > server_config.end_ip)
 197                         addr = server_config.start_ip;
 198 #endif
 199         } while (addr != stop);
 200
 201         if (oldest_lease
 202          && is_expired_lease(oldest_lease)
 203          && nobody_responds_to_arp(oldest_lease->lease_nip, safe_mac, arpping_ms)
 204         ) {
 205                 return oldest_lease->lease_nip;
 206         }
 207
 208         return 0;
 209 }