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 == 0 /* empty entry */
  21                  || g_leases[i].expires < oldest_time
  22                 ) {
  23                         oldest_time = g_leases[i].expires;
  24                         oldest_lease = &g_leases[i];
  25                 }
  26         }
  27         return oldest_lease;
  28 }
  29
  30 /* Clear out all leases with matching nonzero chaddr OR yiaddr.
  31  * If chaddr == NULL, this is a conflict lease.
  32  */
  33 static void clear_leases(const uint8_t *chaddr, uint32_t yiaddr)
  34 {
  35         unsigned i;
  36
  37         for (i = 0; i < server_config.max_leases; i++) {
  38                 if ((chaddr && memcmp(g_leases[i].lease_mac, chaddr, 6) == 0)
  39                  || (yiaddr && g_leases[i].lease_nip == yiaddr)
  40                 ) {
  41                         memset(&g_leases[i], 0, sizeof(g_leases[i]));
  42                 }
  43         }
  44 }
  45
  46 /* Add a lease into the table, clearing out any old ones.
  47  * If chaddr == NULL, this is a conflict lease.
  48  */
  49 struct dyn_lease* FAST_FUNC add_lease(
  50                 const uint8_t *chaddr, uint32_t yiaddr,
  51                 leasetime_t leasetime,
  52                 const char *hostname, int hostname_len)
  53 {
  54         struct dyn_lease *oldest;
  55
  56         /* clean out any old ones */
  57         clear_leases(chaddr, yiaddr);
  58
  59         oldest = oldest_expired_lease();
  60
  61         if (oldest) {
  62                 memset(oldest, 0, sizeof(*oldest));
  63                 if (hostname) {
  64                         char *p;
  65
  66                         hostname_len++; /* include NUL */
  67                         if (hostname_len > sizeof(oldest->hostname))
  68                                 hostname_len = sizeof(oldest->hostname);
  69                         p = safe_strncpy(oldest->hostname, hostname, hostname_len);
  70                         /*
  71                          * Sanitization (s/bad_char/./g).
  72                          * The intent is not to allow only "DNS-valid" hostnames,
  73                          * but merely make dumpleases output safe for shells to use.
  74                          * We accept "0-9A-Za-z._-", all other chars turn to dots.
  75                          */
  76                         while (*p) {
  77                                 if (!isalnum(*p) && *p != '-' && *p != '_')
  78                                         *p = '.';
  79                                 p++;
  80                         }
  81                 }
  82                 if (chaddr)
  83                         memcpy(oldest->lease_mac, chaddr, 6);
  84                 oldest->lease_nip = yiaddr;
  85                 oldest->expires = time(NULL) + leasetime;
  86         }
  87
  88         return oldest;
  89 }
  90
  91 /* True if a lease has expired */
  92 int FAST_FUNC is_expired_lease(struct dyn_lease *lease)
  93 {
  94         return (lease->expires < (leasetime_t) time(NULL));
  95 }
  96
  97 /* Find the first lease that matches MAC, NULL if no match */
  98 struct dyn_lease* FAST_FUNC find_lease_by_mac(const uint8_t *mac)
  99 {
 100         unsigned i;
 101
 102         for (i = 0; i < server_config.max_leases; i++)
 103                 if (memcmp(g_leases[i].lease_mac, mac, 6) == 0)
 104                         return &g_leases[i];
 105
 106         return NULL;
 107 }
 108
 109 /* Find the first lease that matches IP, NULL is no match */
 110 struct dyn_lease* FAST_FUNC find_lease_by_nip(uint32_t nip)
 111 {
 112         unsigned i;
 113
 114         for (i = 0; i < server_config.max_leases; i++)
 115                 if (g_leases[i].lease_nip == nip)
 116                         return &g_leases[i];
 117
 118         return NULL;
 119 }
 120
 121 /* Check if the IP is taken; if it is, add it to the lease table */
 122 static int nobody_responds_to_arp(uint32_t nip, const uint8_t *safe_mac, unsigned arpping_ms)
 123 {
 124         struct in_addr temp;
 125         int r;
 126
 127         r = arpping(nip, safe_mac,
 128                         server_config.server_nip,
 129                         server_config.server_mac,
 130                         server_config.interface,
 131                         arpping_ms);
 132         if (r)
 133                 return r;
 134
 135         temp.s_addr = nip;
 136         bb_error_msg("%s belongs to someone, reserving it for %u seconds",
 137                 inet_ntoa(temp), (unsigned)server_config.conflict_time);
 138         add_lease(NULL, nip, server_config.conflict_time, NULL, 0);
 139         return 0;
 140 }
 141
 142 /* Find a new usable (we think) address */
 143 uint32_t FAST_FUNC find_free_or_expired_nip(const uint8_t *safe_mac, unsigned arpping_ms)
 144 {
 145         uint32_t addr;
 146         struct dyn_lease *oldest_lease = NULL;
 147
 148 #if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
 149         uint32_t stop;
 150         unsigned i, hash;
 151
 152         /* hash hwaddr: use the SDBM hashing algorithm.  Seems to give good
 153          * dispersal even with similarly-valued "strings".
 154          */
 155         hash = 0;
 156         for (i = 0; i < 6; i++)
 157                 hash += safe_mac[i] + (hash << 6) + (hash << 16) - hash;
 158
 159         /* pick a seed based on hwaddr then iterate until we find a free address. */
 160         addr = server_config.start_ip
 161                 + (hash % (1 + server_config.end_ip - server_config.start_ip));
 162         stop = addr;
 163 #else
 164         addr = server_config.start_ip;
 165 #define stop (server_config.end_ip + 1)
 166 #endif
 167         do {
 168                 uint32_t nip;
 169                 struct dyn_lease *lease;
 170
 171                 /* ie, 192.168.55.0 */
 172                 if ((addr & 0xff) == 0)
 173                         goto next_addr;
 174                 /* ie, 192.168.55.255 */
 175                 if ((addr & 0xff) == 0xff)
 176                         goto next_addr;
 177                 nip = htonl(addr);
 178                 /* skip our own address */
 179                 if (nip == server_config.server_nip)
 180                         goto next_addr;
 181                 /* is this a static lease addr? */
 182                 if (is_nip_reserved(server_config.static_leases, nip))
 183                         goto next_addr;
 184
 185                 lease = find_lease_by_nip(nip);
 186                 if (!lease) {
 187 //TODO: DHCP servers do not always sit on the same subnet as clients: should *ping*, not arp-ping!
 188                         if (nobody_responds_to_arp(nip, safe_mac, arpping_ms))
 189                                 return nip;
 190                 } else {
 191                         if (!oldest_lease || lease->expires < oldest_lease->expires)
 192                                 oldest_lease = lease;
 193                 }
 194
 195  next_addr:
 196                 addr++;
 197 #if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
 198                 if (addr > server_config.end_ip)
 199                         addr = server_config.start_ip;
 200 #endif
 201         } while (addr != stop);
 202
 203         if (oldest_lease
 204          && is_expired_lease(oldest_lease)
 205          && nobody_responds_to_arp(oldest_lease->lease_nip, safe_mac, arpping_ms)
 206         ) {
 207                 return oldest_lease->lease_nip;
 208         }
 209
 210         return 0;
 211 }