254 lines
7.2 KiB
C
Executable File
254 lines
7.2 KiB
C
Executable File
/* 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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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#include <string.h>
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#include <sys/socket.h>
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#include <features.h>
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#if __GLIBC__ >=2 && __GLIBC_MINOR >= 1
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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 <stdlib.h>
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#include <time.h>
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#include <unistd.h>
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#include <netinet/in.h>
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#include <arpa/inet.h>
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#include <errno.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include "dhcpd.h"
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#include "packet.h"
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#include "options.h"
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#include "dhcpc.h"
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#include "debug.h"
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/* Create a random xid */
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unsigned long random_xid(void)
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{
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static int initialized;
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if (!initialized) {
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int fd;
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unsigned long seed;
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fd = open("/dev/urandom", 0);
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if (fd < 0 || read(fd, &seed, sizeof(seed)) < 0) {
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LOG(LOG_WARNING, "Could not load seed from /dev/urandom: %s",
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strerror(errno));
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seed = time(0);
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}
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if (fd >= 0) close(fd);
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srand(seed);
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initialized++;
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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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struct vendor {
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char vendor, length;
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char str[sizeof("udhcp "VERSION)];
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} vendor_id = { DHCP_VENDOR, sizeof("udhcp "VERSION) - 1, "udhcp "VERSION};
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init_header(packet, type);
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memcpy(packet->chaddr, client_config.arp, 6);
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add_option_string(packet->options, client_config.clientid);
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if (client_config.hostname) add_option_string(packet->options, client_config.hostname);
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add_option_string(packet->options, (unsigned char *) &vendor_id);
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}
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/* Add a paramater 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_requests(struct dhcpMessage *packet)
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{
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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; options[i].code; i++)
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if (options[i].flags & OPTION_REQ)
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packet->options[end + OPT_DATA + len++] = options[i].code;
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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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/* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
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int send_discover(unsigned long xid, unsigned long 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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add_requests(&packet);
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LOG(LOG_DEBUG, "Sending discover...");
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return 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(unsigned long xid, unsigned long server, unsigned long 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_requests(&packet);
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addr.s_addr = requested;
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LOG(LOG_DEBUG, "Sending select for %s...", inet_ntoa(addr));
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return 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(unsigned long xid, unsigned long server, unsigned long ciaddr)
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{
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struct dhcpMessage packet;
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int ret = 0;
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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_requests(&packet);
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LOG(LOG_DEBUG, "Sending renew...");
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if (server)
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ret = kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
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else ret = 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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return ret;
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}
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/* Unicasts a DHCP release message */
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int send_release(unsigned long server, unsigned long 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_REQUESTED_IP, ciaddr);
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add_simple_option(packet.options, DHCP_SERVER_ID, server);
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LOG(LOG_DEBUG, "Sending release...");
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return kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
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}
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/* return -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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u_int32_t source, dest;
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u_int16_t check;
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memset(&packet, 0, sizeof(struct udp_dhcp_packet));
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bytes = read(fd, &packet, sizeof(struct udp_dhcp_packet));
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if (bytes < 0) {
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DEBUG(LOG_INFO, "couldn't read on raw listening socket -- ignoring");
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usleep(500000); /* possible down interface, looping condition */
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return -1;
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}
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if (bytes < (int) (sizeof(struct iphdr) + sizeof(struct udphdr))) {
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DEBUG(LOG_INFO, "message 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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DEBUG(LOG_INFO, "Truncated packet");
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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 || packet.udp.dest != htons(CLIENT_PORT) ||
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bytes > (int) sizeof(struct udp_dhcp_packet) ||
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ntohs(packet.udp.len) != (short) (bytes - sizeof(packet.ip))) {
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DEBUG(LOG_INFO, "unrelated/bogus packet");
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return -2;
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}
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/* check IP checksum */
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check = packet.ip.check;
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packet.ip.check = 0;
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if (check != checksum(&(packet.ip), sizeof(packet.ip))) {
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DEBUG(LOG_INFO, "bad IP header checksum, ignoring");
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return -1;
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}
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/* verify the UDP checksum by replacing the header with a psuedo header */
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source = packet.ip.saddr;
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dest = packet.ip.daddr;
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check = packet.udp.check;
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packet.udp.check = 0;
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memset(&packet.ip, 0, sizeof(packet.ip));
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packet.ip.protocol = IPPROTO_UDP;
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packet.ip.saddr = source;
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packet.ip.daddr = dest;
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packet.ip.tot_len = packet.udp.len; /* cheat on the psuedo-header */
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if (check && check != checksum(&packet, bytes)) {
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DEBUG(LOG_ERR, "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 (ntohl(payload->cookie) != DHCP_MAGIC) {
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LOG(LOG_ERR, "received bogus message (bad magic) -- ignoring");
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return -2;
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}
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DEBUG(LOG_INFO, "oooooh!!! got some!");
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return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
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}
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