[3320] | 1 | /* vi: set sw=4 ts=4: */
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| 2 | /* Port to Busybox Copyright (C) 2006 Jesse Dutton <jessedutton@gmail.com>
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| 3 | *
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| 4 | * Licensed under GPLv2, see file LICENSE in this source tree.
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| 5 | *
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| 6 | * DHCP Relay for 'DHCPv4 Configuration of IPSec Tunnel Mode' support
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| 7 | * Copyright (C) 2002 Mario Strasser <mast@gmx.net>,
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| 8 | * Zuercher Hochschule Winterthur,
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| 9 | * Netbeat AG
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| 10 | * Upstream has GPL v2 or later
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| 11 | */
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| 12 | #include "common.h"
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| 13 |
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| 14 | #define SERVER_PORT 67
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| 15 |
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| 16 | /* lifetime of an xid entry in sec. */
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| 17 | #define MAX_LIFETIME 2*60
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| 18 | /* select timeout in sec. */
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| 19 | #define SELECT_TIMEOUT (MAX_LIFETIME / 8)
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| 20 |
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| 21 | /* This list holds information about clients. The xid_* functions manipulate this list. */
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| 22 | struct xid_item {
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| 23 | unsigned timestamp;
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| 24 | int client;
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| 25 | uint32_t xid;
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| 26 | struct sockaddr_in ip;
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| 27 | struct xid_item *next;
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| 28 | };
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| 29 |
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| 30 | #define dhcprelay_xid_list (*(struct xid_item*)&bb_common_bufsiz1)
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| 31 |
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| 32 | static struct xid_item *xid_add(uint32_t xid, struct sockaddr_in *ip, int client)
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| 33 | {
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| 34 | struct xid_item *item;
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| 35 |
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| 36 | /* create new xid entry */
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| 37 | item = xmalloc(sizeof(struct xid_item));
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| 38 |
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| 39 | /* add xid entry */
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| 40 | item->ip = *ip;
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| 41 | item->xid = xid;
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| 42 | item->client = client;
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| 43 | item->timestamp = monotonic_sec();
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| 44 | item->next = dhcprelay_xid_list.next;
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| 45 | dhcprelay_xid_list.next = item;
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| 46 |
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| 47 | return item;
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| 48 | }
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| 49 |
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| 50 | static void xid_expire(void)
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| 51 | {
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| 52 | struct xid_item *item = dhcprelay_xid_list.next;
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| 53 | struct xid_item *last = &dhcprelay_xid_list;
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| 54 | unsigned current_time = monotonic_sec();
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| 55 |
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| 56 | while (item != NULL) {
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| 57 | if ((current_time - item->timestamp) > MAX_LIFETIME) {
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| 58 | last->next = item->next;
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| 59 | free(item);
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| 60 | item = last->next;
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| 61 | } else {
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| 62 | last = item;
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| 63 | item = item->next;
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| 64 | }
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| 65 | }
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| 66 | }
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| 67 |
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| 68 | static struct xid_item *xid_find(uint32_t xid)
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| 69 | {
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| 70 | struct xid_item *item = dhcprelay_xid_list.next;
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| 71 | while (item != NULL) {
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| 72 | if (item->xid == xid) {
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| 73 | break;
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| 74 | }
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| 75 | item = item->next;
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| 76 | }
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| 77 | return item;
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| 78 | }
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| 79 |
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| 80 | static void xid_del(uint32_t xid)
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| 81 | {
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| 82 | struct xid_item *item = dhcprelay_xid_list.next;
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| 83 | struct xid_item *last = &dhcprelay_xid_list;
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| 84 | while (item != NULL) {
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| 85 | if (item->xid == xid) {
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| 86 | last->next = item->next;
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| 87 | free(item);
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| 88 | item = last->next;
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| 89 | } else {
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| 90 | last = item;
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| 91 | item = item->next;
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| 92 | }
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| 93 | }
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| 94 | }
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| 95 |
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| 96 | /**
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| 97 | * get_dhcp_packet_type - gets the message type of a dhcp packet
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| 98 | * p - pointer to the dhcp packet
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| 99 | * returns the message type on success, -1 otherwise
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| 100 | */
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| 101 | static int get_dhcp_packet_type(struct dhcp_packet *p)
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| 102 | {
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| 103 | uint8_t *op;
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| 104 |
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| 105 | /* it must be either a BOOTREQUEST or a BOOTREPLY */
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| 106 | if (p->op != BOOTREQUEST && p->op != BOOTREPLY)
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| 107 | return -1;
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| 108 | /* get message type option */
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| 109 | op = udhcp_get_option(p, DHCP_MESSAGE_TYPE);
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| 110 | if (op != NULL)
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| 111 | return op[0];
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| 112 | return -1;
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| 113 | }
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| 114 |
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| 115 | /**
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| 116 | * make_iface_list - parses client/server interface names
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| 117 | * returns array
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| 118 | */
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| 119 | static char **make_iface_list(char **client_and_server_ifaces, int *client_number)
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| 120 | {
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| 121 | char *s, **iface_list;
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| 122 | int i, cn;
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| 123 |
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| 124 | /* get number of items */
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| 125 | cn = 2; /* 1 server iface + at least 1 client one */
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| 126 | s = client_and_server_ifaces[0]; /* list of client ifaces */
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| 127 | while (*s) {
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| 128 | if (*s == ',')
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| 129 | cn++;
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| 130 | s++;
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| 131 | }
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| 132 | *client_number = cn;
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| 133 |
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| 134 | /* create vector of pointers */
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| 135 | iface_list = xzalloc(cn * sizeof(iface_list[0]));
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| 136 |
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| 137 | iface_list[0] = client_and_server_ifaces[1]; /* server iface */
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| 138 |
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| 139 | i = 1;
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| 140 | s = xstrdup(client_and_server_ifaces[0]); /* list of client ifaces */
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| 141 | goto store_client_iface_name;
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| 142 |
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| 143 | while (i < cn) {
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| 144 | if (*s++ == ',') {
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| 145 | s[-1] = '\0';
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| 146 | store_client_iface_name:
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| 147 | iface_list[i++] = s;
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| 148 | }
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| 149 | }
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| 150 |
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| 151 | return iface_list;
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| 152 | }
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| 153 |
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| 154 | /* Creates listen sockets (in fds) bound to client and server ifaces,
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| 155 | * and returns numerically max fd.
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| 156 | */
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| 157 | static int init_sockets(char **iface_list, int num_clients, int *fds)
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| 158 | {
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| 159 | int i, n;
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| 160 |
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| 161 | n = 0;
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| 162 | for (i = 0; i < num_clients; i++) {
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| 163 | fds[i] = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT, iface_list[i]);
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| 164 | if (n < fds[i])
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| 165 | n = fds[i];
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| 166 | }
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| 167 | return n;
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| 168 | }
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| 169 |
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| 170 | static int sendto_ip4(int sock, const void *msg, int msg_len, struct sockaddr_in *to)
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| 171 | {
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| 172 | int err;
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| 173 |
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| 174 | errno = 0;
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| 175 | err = sendto(sock, msg, msg_len, 0, (struct sockaddr*) to, sizeof(*to));
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| 176 | err -= msg_len;
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| 177 | if (err)
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| 178 | bb_perror_msg("sendto");
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| 179 | return err;
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| 180 | }
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| 181 |
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| 182 | /**
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| 183 | * pass_to_server() - forwards dhcp packets from client to server
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| 184 | * p - packet to send
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| 185 | * client - number of the client
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| 186 | */
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| 187 | static void pass_to_server(struct dhcp_packet *p, int packet_len, int client, int *fds,
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| 188 | struct sockaddr_in *client_addr, struct sockaddr_in *server_addr)
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| 189 | {
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| 190 | int type;
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| 191 |
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| 192 | /* check packet_type */
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| 193 | type = get_dhcp_packet_type(p);
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| 194 | if (type != DHCPDISCOVER && type != DHCPREQUEST
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| 195 | && type != DHCPDECLINE && type != DHCPRELEASE
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| 196 | && type != DHCPINFORM
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| 197 | ) {
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| 198 | return;
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| 199 | }
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| 200 |
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| 201 | /* create new xid entry */
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| 202 | xid_add(p->xid, client_addr, client);
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| 203 |
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| 204 | /* forward request to server */
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| 205 | /* note that we send from fds[0] which is bound to SERVER_PORT (67).
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| 206 | * IOW: we send _from_ SERVER_PORT! Although this may look strange,
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| 207 | * RFC 1542 not only allows, but prescribes this for BOOTP relays.
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| 208 | */
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| 209 | sendto_ip4(fds[0], p, packet_len, server_addr);
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| 210 | }
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| 211 |
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| 212 | /**
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| 213 | * pass_to_client() - forwards dhcp packets from server to client
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| 214 | * p - packet to send
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| 215 | */
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| 216 | static void pass_to_client(struct dhcp_packet *p, int packet_len, int *fds)
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| 217 | {
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| 218 | int type;
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| 219 | struct xid_item *item;
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| 220 |
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| 221 | /* check xid */
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| 222 | item = xid_find(p->xid);
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| 223 | if (!item) {
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| 224 | return;
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| 225 | }
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| 226 |
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| 227 | /* check packet type */
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| 228 | type = get_dhcp_packet_type(p);
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| 229 | if (type != DHCPOFFER && type != DHCPACK && type != DHCPNAK) {
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| 230 | return;
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| 231 | }
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| 232 |
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| 233 | //TODO: also do it if (p->flags & htons(BROADCAST_FLAG)) is set!
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| 234 | if (item->ip.sin_addr.s_addr == htonl(INADDR_ANY))
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| 235 | item->ip.sin_addr.s_addr = htonl(INADDR_BROADCAST);
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| 236 |
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| 237 | if (sendto_ip4(fds[item->client], p, packet_len, &item->ip) != 0) {
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| 238 | return; /* send error occurred */
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| 239 | }
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| 240 |
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| 241 | /* remove xid entry */
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| 242 | xid_del(p->xid);
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| 243 | }
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| 244 |
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| 245 | int dhcprelay_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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| 246 | int dhcprelay_main(int argc, char **argv)
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| 247 | {
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| 248 | struct sockaddr_in server_addr;
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| 249 | char **iface_list;
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| 250 | int *fds;
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| 251 | int num_sockets, max_socket;
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| 252 | uint32_t our_nip;
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| 253 |
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| 254 | server_addr.sin_family = AF_INET;
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| 255 | server_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
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| 256 | server_addr.sin_port = htons(SERVER_PORT);
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| 257 |
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| 258 | /* dhcprelay CLIENT_IFACE1[,CLIENT_IFACE2...] SERVER_IFACE [SERVER_IP] */
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| 259 | if (argc == 4) {
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| 260 | if (!inet_aton(argv[3], &server_addr.sin_addr))
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| 261 | bb_perror_msg_and_die("bad server IP");
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| 262 | } else if (argc != 3) {
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| 263 | bb_show_usage();
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| 264 | }
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| 265 |
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| 266 | iface_list = make_iface_list(argv + 1, &num_sockets);
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| 267 |
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| 268 | fds = xmalloc(num_sockets * sizeof(fds[0]));
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| 269 |
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| 270 | /* Create sockets and bind one to every iface */
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| 271 | max_socket = init_sockets(iface_list, num_sockets, fds);
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| 272 |
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| 273 | /* Get our IP on server_iface */
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| 274 | if (udhcp_read_interface(argv[2], NULL, &our_nip, NULL))
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| 275 | return 1;
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| 276 |
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| 277 | /* Main loop */
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| 278 | while (1) {
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| 279 | // reinit stuff from time to time? go back to make_iface_list
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| 280 | // every N minutes?
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| 281 | fd_set rfds;
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| 282 | struct timeval tv;
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| 283 | int i;
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| 284 |
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| 285 | FD_ZERO(&rfds);
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| 286 | for (i = 0; i < num_sockets; i++)
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| 287 | FD_SET(fds[i], &rfds);
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| 288 | tv.tv_sec = SELECT_TIMEOUT;
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| 289 | tv.tv_usec = 0;
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| 290 | if (select(max_socket + 1, &rfds, NULL, NULL, &tv) > 0) {
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| 291 | int packlen;
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| 292 | struct dhcp_packet dhcp_msg;
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| 293 |
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| 294 | /* server */
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| 295 | if (FD_ISSET(fds[0], &rfds)) {
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| 296 | packlen = udhcp_recv_kernel_packet(&dhcp_msg, fds[0]);
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| 297 | if (packlen > 0) {
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| 298 | pass_to_client(&dhcp_msg, packlen, fds);
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| 299 | }
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| 300 | }
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| 301 |
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| 302 | /* clients */
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| 303 | for (i = 1; i < num_sockets; i++) {
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| 304 | struct sockaddr_in client_addr;
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| 305 | socklen_t addr_size;
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| 306 |
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| 307 | if (!FD_ISSET(fds[i], &rfds))
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| 308 | continue;
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| 309 |
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| 310 | addr_size = sizeof(client_addr);
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| 311 | packlen = recvfrom(fds[i], &dhcp_msg, sizeof(dhcp_msg), 0,
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| 312 | (struct sockaddr *)(&client_addr), &addr_size);
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| 313 | if (packlen <= 0)
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| 314 | continue;
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| 315 |
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| 316 | /* Get our IP on corresponding client_iface */
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| 317 | // RFC 1542
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| 318 | // 4.1 General BOOTP Processing for Relay Agents
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| 319 | // 4.1.1 BOOTREQUEST Messages
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| 320 | // If the relay agent does decide to relay the request, it MUST examine
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| 321 | // the 'giaddr' ("gateway" IP address) field. If this field is zero,
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| 322 | // the relay agent MUST fill this field with the IP address of the
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| 323 | // interface on which the request was received. If the interface has
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| 324 | // more than one IP address logically associated with it, the relay
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| 325 | // agent SHOULD choose one IP address associated with that interface and
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| 326 | // use it consistently for all BOOTP messages it relays. If the
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| 327 | // 'giaddr' field contains some non-zero value, the 'giaddr' field MUST
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| 328 | // NOT be modified. The relay agent MUST NOT, under any circumstances,
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| 329 | // fill the 'giaddr' field with a broadcast address as is suggested in
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| 330 | // [1] (Section 8, sixth paragraph).
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| 331 |
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| 332 | // but why? what if server can't route such IP? Client ifaces may be, say, NATed!
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| 333 |
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| 334 | // 4.1.2 BOOTREPLY Messages
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| 335 | // BOOTP relay agents relay BOOTREPLY messages only to BOOTP clients.
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| 336 | // It is the responsibility of BOOTP servers to send BOOTREPLY messages
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| 337 | // directly to the relay agent identified in the 'giaddr' field.
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| 338 | // (yeah right, unless it is impossible... see comment above)
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| 339 | // Therefore, a relay agent may assume that all BOOTREPLY messages it
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| 340 | // receives are intended for BOOTP clients on its directly-connected
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| 341 | // networks.
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| 342 | //
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| 343 | // When a relay agent receives a BOOTREPLY message, it should examine
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| 344 | // the BOOTP 'giaddr', 'yiaddr', 'chaddr', 'htype', and 'hlen' fields.
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| 345 | // These fields should provide adequate information for the relay agent
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| 346 | // to deliver the BOOTREPLY message to the client.
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| 347 | //
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| 348 | // The 'giaddr' field can be used to identify the logical interface from
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| 349 | // which the reply must be sent (i.e., the host or router interface
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| 350 | // connected to the same network as the BOOTP client). If the content
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| 351 | // of the 'giaddr' field does not match one of the relay agent's
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| 352 | // directly-connected logical interfaces, the BOOTREPLY messsage MUST be
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| 353 | // silently discarded.
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| 354 | if (udhcp_read_interface(iface_list[i], NULL, &dhcp_msg.gateway_nip, NULL)) {
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| 355 | /* Fall back to our IP on server iface */
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| 356 | // this makes more sense!
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| 357 | dhcp_msg.gateway_nip = our_nip;
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| 358 | }
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| 359 | // maybe dhcp_msg.hops++? drop packets with too many hops (RFC 1542 says 4 or 16)?
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| 360 | pass_to_server(&dhcp_msg, packlen, i, fds, &client_addr, &server_addr);
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| 361 | }
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| 362 | }
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| 363 | xid_expire();
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| 364 | } /* while (1) */
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| 365 |
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| 366 | /* return 0; - not reached */
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| 367 | }
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