[821] | 1 | /* clientpacket.c
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| 2 | *
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| 3 | * Packet generation and dispatching functions for the DHCP client.
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| 4 | *
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| 5 | * Russ Dill <Russ.Dill@asu.edu> July 2001
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| 6 | *
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| 7 | * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
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| 8 | */
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| 9 |
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| 10 | #include <string.h>
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| 11 | #include <sys/socket.h>
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| 12 | #include <features.h>
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| 13 | #if (__GLIBC__ >= 2 && __GLIBC_MINOR >= 1) || defined _NEWLIB_VERSION
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| 14 | #include <netpacket/packet.h>
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| 15 | #include <net/ethernet.h>
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| 16 | #else
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| 17 | #include <asm/types.h>
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| 18 | #include <linux/if_packet.h>
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| 19 | #include <linux/if_ether.h>
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| 20 | #endif
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| 21 | #include <stdlib.h>
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| 22 | #include <time.h>
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| 23 | #include <unistd.h>
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| 24 | #include <netinet/in.h>
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| 25 | #include <arpa/inet.h>
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| 26 | #include <fcntl.h>
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| 27 |
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| 28 |
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| 29 | #include "dhcpd.h"
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| 30 | #include "clientpacket.h"
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| 31 | #include "options.h"
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| 32 | #include "dhcpc.h"
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| 33 | #include "common.h"
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| 34 |
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| 35 |
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| 36 | /* Create a random xid */
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| 37 | unsigned long random_xid(void)
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| 38 | {
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| 39 | static int initialized;
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| 40 | if (!initialized) {
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| 41 | int fd;
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| 42 | unsigned long seed;
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| 43 |
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| 44 | fd = open("/dev/urandom", 0);
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| 45 | if (fd < 0 || read(fd, &seed, sizeof(seed)) < 0) {
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| 46 | LOG(LOG_WARNING, "Could not load seed from /dev/urandom: %m");
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| 47 | seed = time(0);
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| 48 | }
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| 49 | if (fd >= 0) close(fd);
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| 50 | srand(seed);
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| 51 | initialized++;
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| 52 | }
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| 53 | return rand();
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| 54 | }
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| 55 |
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| 56 |
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| 57 | /* initialize a packet with the proper defaults */
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| 58 | static void init_packet(struct dhcpMessage *packet, char type)
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| 59 | {
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| 60 | udhcp_init_header(packet, type);
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| 61 | memcpy(packet->chaddr, client_config.arp, 6);
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| 62 | if (client_config.clientid)
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| 63 | add_option_string(packet->options, client_config.clientid);
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| 64 | if (client_config.hostname) add_option_string(packet->options, client_config.hostname);
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| 65 | if (client_config.fqdn) add_option_string(packet->options, client_config.fqdn);
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| 66 | add_option_string(packet->options, client_config.vendorclass);
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| 67 | }
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| 68 |
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| 69 |
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| 70 | /* Add a parameter request list for stubborn DHCP servers. Pull the data
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| 71 | * from the struct in options.c. Don't do bounds checking here because it
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| 72 | * goes towards the head of the packet. */
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| 73 | static void add_requests(struct dhcpMessage *packet)
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| 74 | {
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| 75 | int end = end_option(packet->options);
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| 76 | int i, len = 0;
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| 77 |
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| 78 | packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
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| 79 | for (i = 0; dhcp_options[i].code; i++)
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| 80 | if (dhcp_options[i].flags & OPTION_REQ)
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| 81 | packet->options[end + OPT_DATA + len++] = dhcp_options[i].code;
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| 82 | packet->options[end + OPT_LEN] = len;
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| 83 | packet->options[end + OPT_DATA + len] = DHCP_END;
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| 84 |
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| 85 | }
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| 86 |
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| 87 |
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| 88 | /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
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| 89 | int send_discover(unsigned long xid, unsigned long requested)
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| 90 | {
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| 91 | struct dhcpMessage packet;
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| 92 |
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| 93 | init_packet(&packet, DHCPDISCOVER);
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| 94 | packet.xid = xid;
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| 95 | if (requested)
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| 96 | add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
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| 97 |
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| 98 | add_requests(&packet);
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| 99 | LOG(LOG_DEBUG, "Sending discover...");
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| 100 | return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
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| 101 | SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
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| 102 | }
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| 103 |
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| 104 |
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| 105 | /* Broadcasts a DHCP request message */
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| 106 | int send_selecting(unsigned long xid, unsigned long server, unsigned long requested)
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| 107 | {
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| 108 | struct dhcpMessage packet;
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| 109 | struct in_addr addr;
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| 110 |
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| 111 | init_packet(&packet, DHCPREQUEST);
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| 112 | packet.xid = xid;
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| 113 |
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| 114 | add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
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| 115 | add_simple_option(packet.options, DHCP_SERVER_ID, server);
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| 116 |
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| 117 | add_requests(&packet);
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| 118 | addr.s_addr = requested;
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| 119 | LOG(LOG_DEBUG, "Sending select for %s...", inet_ntoa(addr));
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| 120 | return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
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| 121 | SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
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| 122 | }
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| 123 |
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| 124 |
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| 125 | /* Unicasts or broadcasts a DHCP renew message */
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| 126 | int send_renew(unsigned long xid, unsigned long server, unsigned long ciaddr)
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| 127 | {
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| 128 | struct dhcpMessage packet;
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| 129 | int ret = 0;
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| 130 |
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| 131 | init_packet(&packet, DHCPREQUEST);
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| 132 | packet.xid = xid;
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| 133 | packet.ciaddr = ciaddr;
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| 134 |
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| 135 | add_requests(&packet);
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| 136 | LOG(LOG_DEBUG, "Sending renew...");
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| 137 | if (server)
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| 138 | ret = udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
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| 139 | else ret = udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
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| 140 | SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
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| 141 | return ret;
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| 142 | }
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| 143 |
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| 144 |
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| 145 | /* Unicasts a DHCP release message */
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| 146 | int send_release(unsigned long server, unsigned long ciaddr)
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| 147 | {
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| 148 | struct dhcpMessage packet;
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| 149 |
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| 150 | init_packet(&packet, DHCPRELEASE);
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| 151 | packet.xid = random_xid();
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| 152 | packet.ciaddr = ciaddr;
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| 153 |
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| 154 | add_simple_option(packet.options, DHCP_REQUESTED_IP, ciaddr);
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| 155 | add_simple_option(packet.options, DHCP_SERVER_ID, server);
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| 156 |
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| 157 | LOG(LOG_DEBUG, "Sending release...");
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| 158 | return udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
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| 159 | }
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| 160 |
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| 161 |
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| 162 | /* return -1 on errors that are fatal for the socket, -2 for those that aren't */
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| 163 | int get_raw_packet(struct dhcpMessage *payload, int fd)
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| 164 | {
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| 165 | int bytes;
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| 166 | struct udp_dhcp_packet packet;
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| 167 | uint32_t source, dest;
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| 168 | uint16_t check;
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| 169 |
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| 170 | memset(&packet, 0, sizeof(struct udp_dhcp_packet));
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| 171 | bytes = read(fd, &packet, sizeof(struct udp_dhcp_packet));
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| 172 | if (bytes < 0) {
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| 173 | DEBUG(LOG_INFO, "couldn't read on raw listening socket -- ignoring");
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| 174 | usleep(500000); /* possible down interface, looping condition */
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| 175 | return -1;
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| 176 | }
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| 177 |
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| 178 | if (bytes < (int) (sizeof(struct iphdr) + sizeof(struct udphdr))) {
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| 179 | DEBUG(LOG_INFO, "message too short, ignoring");
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| 180 | return -2;
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| 181 | }
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| 182 |
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| 183 | if (bytes < ntohs(packet.ip.tot_len)) {
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| 184 | DEBUG(LOG_INFO, "Truncated packet");
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| 185 | return -2;
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| 186 | }
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| 187 |
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| 188 | /* ignore any extra garbage bytes */
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| 189 | bytes = ntohs(packet.ip.tot_len);
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| 190 |
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| 191 | /* Make sure its the right packet for us, and that it passes sanity checks */
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| 192 | if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION ||
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| 193 | packet.ip.ihl != sizeof(packet.ip) >> 2 || packet.udp.dest != htons(CLIENT_PORT) ||
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| 194 | bytes > (int) sizeof(struct udp_dhcp_packet) ||
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| 195 | ntohs(packet.udp.len) != (uint16_t) (bytes - sizeof(packet.ip))) {
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| 196 | DEBUG(LOG_INFO, "unrelated/bogus packet");
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| 197 | return -2;
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| 198 | }
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| 199 |
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| 200 | /* check IP checksum */
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| 201 | check = packet.ip.check;
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| 202 | packet.ip.check = 0;
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| 203 | if (check != udhcp_checksum(&(packet.ip), sizeof(packet.ip))) {
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| 204 | DEBUG(LOG_INFO, "bad IP header checksum, ignoring");
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| 205 | return -1;
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| 206 | }
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| 207 |
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| 208 | /* verify the UDP checksum by replacing the header with a psuedo header */
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| 209 | source = packet.ip.saddr;
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| 210 | dest = packet.ip.daddr;
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| 211 | check = packet.udp.check;
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| 212 | packet.udp.check = 0;
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| 213 | memset(&packet.ip, 0, sizeof(packet.ip));
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| 214 |
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| 215 | packet.ip.protocol = IPPROTO_UDP;
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| 216 | packet.ip.saddr = source;
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| 217 | packet.ip.daddr = dest;
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| 218 | packet.ip.tot_len = packet.udp.len; /* cheat on the psuedo-header */
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| 219 | if (check && check != udhcp_checksum(&packet, bytes)) {
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| 220 | DEBUG(LOG_ERR, "packet with bad UDP checksum received, ignoring");
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| 221 | return -2;
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| 222 | }
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| 223 |
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| 224 | memcpy(payload, &(packet.data), bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
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| 225 |
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| 226 | if (ntohl(payload->cookie) != DHCP_MAGIC) {
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| 227 | LOG(LOG_ERR, "received bogus message (bad magic) -- ignoring");
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| 228 | return -2;
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| 229 | }
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| 230 | DEBUG(LOG_INFO, "oooooh!!! got some!");
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| 231 | return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
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| 232 |
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| 233 | }
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