240 lines
6.8 KiB
C
240 lines
6.8 KiB
C
/* vi: set sw=4 ts=4: */
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/* clientpacket.c
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*
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* Packet generation and dispatching functions for the DHCP client.
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*
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* Russ Dill <Russ.Dill@asu.edu> July 2001
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*
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* Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
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*/
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#include <features.h>
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#if (defined(__GLIBC__) && __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 1) || defined _NEWLIB_VERSION
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#include <netpacket/packet.h>
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#include <net/ethernet.h>
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#else
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#include <asm/types.h>
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#include <linux/if_packet.h>
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#include <linux/if_ether.h>
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#endif
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#include "common.h"
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#include "dhcpd.h"
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#include "dhcpc.h"
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#include "options.h"
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/* Create a random xid */
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uint32_t random_xid(void)
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{
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static smallint initialized;
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if (!initialized) {
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srand(monotonic_us());
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initialized = 1;
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}
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return rand();
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}
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/* initialize a packet with the proper defaults */
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static void init_packet(struct dhcpMessage *packet, char type)
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{
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udhcp_init_header(packet, type);
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memcpy(packet->chaddr, client_config.arp, 6);
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if (client_config.clientid)
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add_option_string(packet->options, client_config.clientid);
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if (client_config.hostname)
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add_option_string(packet->options, client_config.hostname);
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if (client_config.fqdn)
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add_option_string(packet->options, client_config.fqdn);
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if ((type != DHCPDECLINE) && (type != DHCPRELEASE))
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add_option_string(packet->options, client_config.vendorclass);
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}
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/* Add a parameter request list for stubborn DHCP servers. Pull the data
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* from the struct in options.c. Don't do bounds checking here because it
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* goes towards the head of the packet. */
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static void add_param_req_option(struct dhcpMessage *packet)
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{
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uint8_t c;
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int end = end_option(packet->options);
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int i, len = 0;
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packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
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for (i = 0; (c = dhcp_options[i].code) != 0; i++) {
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if ((dhcp_options[i].flags & OPTION_REQ)
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|| (client_config.opt_mask[c >> 3] & (1 << (c & 7)))
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) {
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packet->options[end + OPT_DATA + len] = c;
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len++;
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}
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}
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packet->options[end + OPT_LEN] = len;
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packet->options[end + OPT_DATA + len] = DHCP_END;
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}
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#if ENABLE_FEATURE_UDHCPC_ARPING
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/* Unicast a DHCP decline message */
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int send_decline(uint32_t xid, uint32_t server, uint32_t requested)
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{
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struct dhcpMessage packet;
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init_packet(&packet, DHCPDECLINE);
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packet.xid = xid;
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add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
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add_simple_option(packet.options, DHCP_SERVER_ID, server);
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bb_info_msg("Sending decline...");
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return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
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SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
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}
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#endif
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/* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
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int send_discover(uint32_t xid, uint32_t requested)
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{
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struct dhcpMessage packet;
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init_packet(&packet, DHCPDISCOVER);
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packet.xid = xid;
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if (requested)
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add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
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/* Explicitly saying that we want RFC-compliant packets helps
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* some buggy DHCP servers to NOT send bigger packets */
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add_simple_option(packet.options, DHCP_MAX_SIZE, htons(576));
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add_param_req_option(&packet);
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bb_info_msg("Sending discover...");
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return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
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SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
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}
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/* Broadcasts a DHCP request message */
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int send_selecting(uint32_t xid, uint32_t server, uint32_t requested)
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{
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struct dhcpMessage packet;
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struct in_addr addr;
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init_packet(&packet, DHCPREQUEST);
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packet.xid = xid;
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add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
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add_simple_option(packet.options, DHCP_SERVER_ID, server);
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add_param_req_option(&packet);
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addr.s_addr = requested;
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bb_info_msg("Sending select for %s...", inet_ntoa(addr));
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return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
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SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
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}
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/* Unicasts or broadcasts a DHCP renew message */
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int send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
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{
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struct dhcpMessage packet;
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init_packet(&packet, DHCPREQUEST);
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packet.xid = xid;
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packet.ciaddr = ciaddr;
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add_param_req_option(&packet);
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bb_info_msg("Sending renew...");
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if (server)
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return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
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return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
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SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
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}
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/* Unicasts a DHCP release message */
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int send_release(uint32_t server, uint32_t ciaddr)
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{
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struct dhcpMessage packet;
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init_packet(&packet, DHCPRELEASE);
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packet.xid = random_xid();
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packet.ciaddr = ciaddr;
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add_simple_option(packet.options, DHCP_SERVER_ID, server);
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bb_info_msg("Sending release...");
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return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
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}
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/* Returns -1 on errors that are fatal for the socket, -2 for those that aren't */
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int get_raw_packet(struct dhcpMessage *payload, int fd)
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{
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int bytes;
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struct udp_dhcp_packet packet;
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uint16_t check;
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memset(&packet, 0, sizeof(packet));
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bytes = safe_read(fd, &packet, sizeof(packet));
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if (bytes < 0) {
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DEBUG("Cannot read on raw listening socket - ignoring");
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sleep(1); /* possible down interface, looping condition */
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return bytes; /* returns -1 */
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}
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if (bytes < (int) (sizeof(packet.ip) + sizeof(packet.udp))) {
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DEBUG("Packet is too short, ignoring");
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return -2;
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}
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if (bytes < ntohs(packet.ip.tot_len)) {
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/* packet is bigger than sizeof(packet), we did partial read */
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DEBUG("Oversized packet, ignoring");
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return -2;
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}
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/* ignore any extra garbage bytes */
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bytes = ntohs(packet.ip.tot_len);
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/* make sure its the right packet for us, and that it passes sanity checks */
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if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION
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|| packet.ip.ihl != (sizeof(packet.ip) >> 2)
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|| packet.udp.dest != htons(CLIENT_PORT)
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/* || bytes > (int) sizeof(packet) - can't happen */
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|| ntohs(packet.udp.len) != (uint16_t)(bytes - sizeof(packet.ip))
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) {
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DEBUG("Unrelated/bogus packet");
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return -2;
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}
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/* verify IP checksum */
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check = packet.ip.check;
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packet.ip.check = 0;
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if (check != udhcp_checksum(&packet.ip, sizeof(packet.ip))) {
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DEBUG("Bad IP header checksum, ignoring");
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return -2;
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}
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/* verify UDP checksum. IP header has to be modified for this */
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memset(&packet.ip, 0, offsetof(struct iphdr, protocol));
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/* ip.xx fields which are not memset: protocol, check, saddr, daddr */
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packet.ip.tot_len = packet.udp.len; /* yes, this is needed */
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check = packet.udp.check;
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packet.udp.check = 0;
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if (check && check != udhcp_checksum(&packet, bytes)) {
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bb_error_msg("packet with bad UDP checksum received, ignoring");
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return -2;
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}
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memcpy(payload, &packet.data, bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
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if (payload->cookie != htonl(DHCP_MAGIC)) {
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bb_error_msg("received bogus message (bad magic), ignoring");
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return -2;
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}
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DEBUG("Got valid DHCP packet");
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return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
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}
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