1 | /* vi: set sw=4 ts=4: */
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2 | /*
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3 | * Russ Dill <Russ.Dill@asu.edu> July 2001
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4 | *
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5 | * Licensed under GPLv2, see file LICENSE in this source tree.
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6 | */
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7 | #include "common.h"
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8 | #include "dhcpd.h"
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9 |
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10 | /* Find the oldest expired lease, NULL if there are no expired leases */
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11 | static struct dyn_lease *oldest_expired_lease(void)
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12 | {
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13 | struct dyn_lease *oldest_lease = NULL;
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14 | leasetime_t oldest_time = time(NULL);
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15 | unsigned i;
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16 |
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17 | /* Unexpired leases have g_leases[i].expires >= current time
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18 | * and therefore can't ever match */
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19 | for (i = 0; i < server_config.max_leases; i++) {
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20 | if (g_leases[i].expires == 0 /* empty entry */
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21 | || g_leases[i].expires < oldest_time
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22 | ) {
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23 | oldest_time = g_leases[i].expires;
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24 | oldest_lease = &g_leases[i];
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25 | }
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26 | }
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27 | return oldest_lease;
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28 | }
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29 |
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30 | /* Clear out all leases with matching nonzero chaddr OR yiaddr.
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31 | * If chaddr == NULL, this is a conflict lease.
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32 | */
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33 | static void clear_leases(const uint8_t *chaddr, uint32_t yiaddr)
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34 | {
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35 | unsigned i;
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36 |
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37 | for (i = 0; i < server_config.max_leases; i++) {
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38 | if ((chaddr && memcmp(g_leases[i].lease_mac, chaddr, 6) == 0)
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39 | || (yiaddr && g_leases[i].lease_nip == yiaddr)
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40 | ) {
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41 | memset(&g_leases[i], 0, sizeof(g_leases[i]));
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42 | }
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43 | }
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44 | }
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45 |
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46 | /* Add a lease into the table, clearing out any old ones.
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47 | * If chaddr == NULL, this is a conflict lease.
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48 | */
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49 | struct dyn_lease* FAST_FUNC add_lease(
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50 | const uint8_t *chaddr, uint32_t yiaddr,
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51 | leasetime_t leasetime,
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52 | const char *hostname, int hostname_len)
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53 | {
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54 | struct dyn_lease *oldest;
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55 |
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56 | /* clean out any old ones */
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57 | clear_leases(chaddr, yiaddr);
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58 |
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59 | oldest = oldest_expired_lease();
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60 |
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61 | if (oldest) {
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62 | memset(oldest, 0, sizeof(*oldest));
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63 | if (hostname) {
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64 | char *p;
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65 |
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66 | hostname_len++; /* include NUL */
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67 | if (hostname_len > sizeof(oldest->hostname))
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68 | hostname_len = sizeof(oldest->hostname);
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69 | p = safe_strncpy(oldest->hostname, hostname, hostname_len);
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70 | /*
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71 | * Sanitization (s/bad_char/./g).
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72 | * The intent is not to allow only "DNS-valid" hostnames,
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73 | * but merely make dumpleases output safe for shells to use.
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74 | * We accept "0-9A-Za-z._-", all other chars turn to dots.
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75 | */
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76 | while (*p) {
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77 | if (!isalnum(*p) && *p != '-' && *p != '_')
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78 | *p = '.';
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79 | p++;
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80 | }
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81 | }
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82 | if (chaddr)
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83 | memcpy(oldest->lease_mac, chaddr, 6);
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84 | oldest->lease_nip = yiaddr;
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85 | oldest->expires = time(NULL) + leasetime;
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86 | }
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87 |
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88 | return oldest;
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89 | }
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90 |
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91 | /* True if a lease has expired */
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92 | int FAST_FUNC is_expired_lease(struct dyn_lease *lease)
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93 | {
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94 | return (lease->expires < (leasetime_t) time(NULL));
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95 | }
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96 |
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97 | /* Find the first lease that matches MAC, NULL if no match */
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98 | struct dyn_lease* FAST_FUNC find_lease_by_mac(const uint8_t *mac)
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99 | {
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100 | unsigned i;
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101 |
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102 | for (i = 0; i < server_config.max_leases; i++)
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103 | if (memcmp(g_leases[i].lease_mac, mac, 6) == 0)
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104 | return &g_leases[i];
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105 |
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106 | return NULL;
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107 | }
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108 |
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109 | /* Find the first lease that matches IP, NULL is no match */
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110 | struct dyn_lease* FAST_FUNC find_lease_by_nip(uint32_t nip)
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111 | {
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112 | unsigned i;
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113 |
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114 | for (i = 0; i < server_config.max_leases; i++)
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115 | if (g_leases[i].lease_nip == nip)
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116 | return &g_leases[i];
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117 |
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118 | return NULL;
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119 | }
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120 |
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121 | /* Check if the IP is taken; if it is, add it to the lease table */
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122 | static int nobody_responds_to_arp(uint32_t nip, const uint8_t *safe_mac, unsigned arpping_ms)
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123 | {
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124 | struct in_addr temp;
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125 | int r;
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126 |
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127 | r = arpping(nip, safe_mac,
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128 | server_config.server_nip,
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129 | server_config.server_mac,
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130 | server_config.interface,
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131 | arpping_ms);
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132 | if (r)
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133 | return r;
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134 |
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135 | temp.s_addr = nip;
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136 | bb_error_msg("%s belongs to someone, reserving it for %u seconds",
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137 | inet_ntoa(temp), (unsigned)server_config.conflict_time);
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138 | add_lease(NULL, nip, server_config.conflict_time, NULL, 0);
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139 | return 0;
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140 | }
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141 |
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142 | /* Find a new usable (we think) address */
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143 | uint32_t FAST_FUNC find_free_or_expired_nip(const uint8_t *safe_mac, unsigned arpping_ms)
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144 | {
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145 | uint32_t addr;
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146 | struct dyn_lease *oldest_lease = NULL;
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147 |
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148 | #if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
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149 | uint32_t stop;
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150 | unsigned i, hash;
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151 |
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152 | /* hash hwaddr: use the SDBM hashing algorithm. Seems to give good
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153 | * dispersal even with similarly-valued "strings".
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154 | */
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155 | hash = 0;
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156 | for (i = 0; i < 6; i++)
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157 | hash += safe_mac[i] + (hash << 6) + (hash << 16) - hash;
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158 |
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159 | /* pick a seed based on hwaddr then iterate until we find a free address. */
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160 | addr = server_config.start_ip
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161 | + (hash % (1 + server_config.end_ip - server_config.start_ip));
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162 | stop = addr;
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163 | #else
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164 | addr = server_config.start_ip;
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165 | #define stop (server_config.end_ip + 1)
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166 | #endif
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167 | do {
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168 | uint32_t nip;
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169 | struct dyn_lease *lease;
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170 |
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171 | /* ie, 192.168.55.0 */
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172 | if ((addr & 0xff) == 0)
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173 | goto next_addr;
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174 | /* ie, 192.168.55.255 */
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175 | if ((addr & 0xff) == 0xff)
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176 | goto next_addr;
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177 | nip = htonl(addr);
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178 | /* skip our own address */
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179 | if (nip == server_config.server_nip)
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180 | goto next_addr;
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181 | /* is this a static lease addr? */
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182 | if (is_nip_reserved(server_config.static_leases, nip))
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183 | goto next_addr;
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184 |
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185 | lease = find_lease_by_nip(nip);
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186 | if (!lease) {
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187 | //TODO: DHCP servers do not always sit on the same subnet as clients: should *ping*, not arp-ping!
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188 | if (nobody_responds_to_arp(nip, safe_mac, arpping_ms))
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189 | return nip;
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190 | } else {
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191 | if (!oldest_lease || lease->expires < oldest_lease->expires)
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192 | oldest_lease = lease;
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193 | }
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194 |
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195 | next_addr:
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196 | addr++;
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197 | #if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
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198 | if (addr > server_config.end_ip)
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199 | addr = server_config.start_ip;
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200 | #endif
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201 | } while (addr != stop);
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202 |
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203 | if (oldest_lease
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204 | && is_expired_lease(oldest_lease)
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205 | && nobody_responds_to_arp(oldest_lease->lease_nip, safe_mac, arpping_ms)
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206 | ) {
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207 | return oldest_lease->lease_nip;
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208 | }
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209 |
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210 | return 0;
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211 | }
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