/* clientpacket.c * * Packet generation and dispatching functions for the DHCP client. * * Russ Dill <Russ.Dill@asu.edu> July 2001 * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ #include <string.h> #include <sys/socket.h> #include <features.h> #if __GLIBC__ >=2 && __GLIBC_MINOR >= 1 #include <netpacket/packet.h> #include <net/ethernet.h> #else #include <asm/types.h> #include <linux/if_packet.h> #include <linux/if_ether.h> #endif #include <stdlib.h> #include <time.h> #include <unistd.h> #include <netinet/in.h> #include <arpa/inet.h> #include <fcntl.h> #include "dhcpd.h" #include "clientpacket.h" #include "options.h" #include "dhcpc.h" #include "common.h" /* Create a random xid */ unsigned long random_xid(void) { static int initialized; if (!initialized) { int fd; unsigned long seed; fd = open("/dev/urandom", 0); if (fd < 0 || read(fd, &seed, sizeof(seed)) < 0) { LOG(LOG_WARNING, "Could not load seed from /dev/urandom: %m"); seed = time(0); } if (fd >= 0) close(fd); srand(seed); initialized++; } return rand(); } /* initialize a packet with the proper defaults */ static void init_packet(struct dhcpMessage *packet, char type) { init_header(packet, type); memcpy(packet->chaddr, client_config.arp, 6); if (client_config.clientid) add_option_string(packet->options, client_config.clientid); if (client_config.hostname) add_option_string(packet->options, client_config.hostname); if (client_config.fqdn) add_option_string(packet->options, client_config.fqdn); add_option_string(packet->options, client_config.vendorclass); } /* Add a parameter request list for stubborn DHCP servers. Pull the data * from the struct in options.c. Don't do bounds checking here because it * goes towards the head of the packet. */ static void add_requests(struct dhcpMessage *packet) { int end = end_option(packet->options); int i, len = 0; packet->options[end + OPT_CODE] = DHCP_PARAM_REQ; for (i = 0; dhcp_options[i].code; i++) if (dhcp_options[i].flags & OPTION_REQ) packet->options[end + OPT_DATA + len++] = dhcp_options[i].code; packet->options[end + OPT_LEN] = len; packet->options[end + OPT_DATA + len] = DHCP_END; } /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */ int send_discover(unsigned long xid, unsigned long requested) { struct dhcpMessage packet; init_packet(&packet, DHCPDISCOVER); packet.xid = xid; if (requested) add_simple_option(packet.options, DHCP_REQUESTED_IP, requested); add_requests(&packet); LOG(LOG_DEBUG, "Sending discover..."); return raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST, SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex); } /* Broadcasts a DHCP request message */ int send_selecting(unsigned long xid, unsigned long server, unsigned long requested) { struct dhcpMessage packet; struct in_addr addr; init_packet(&packet, DHCPREQUEST); packet.xid = xid; add_simple_option(packet.options, DHCP_REQUESTED_IP, requested); add_simple_option(packet.options, DHCP_SERVER_ID, server); add_requests(&packet); addr.s_addr = requested; LOG(LOG_DEBUG, "Sending select for %s...", inet_ntoa(addr)); return raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST, SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex); } /* Unicasts or broadcasts a DHCP renew message */ int send_renew(unsigned long xid, unsigned long server, unsigned long ciaddr) { struct dhcpMessage packet; int ret = 0; init_packet(&packet, DHCPREQUEST); packet.xid = xid; packet.ciaddr = ciaddr; add_requests(&packet); LOG(LOG_DEBUG, "Sending renew..."); if (server) ret = kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT); else ret = raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST, SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex); return ret; } /* Unicasts a DHCP release message */ int send_release(unsigned long server, unsigned long ciaddr) { struct dhcpMessage packet; init_packet(&packet, DHCPRELEASE); packet.xid = random_xid(); packet.ciaddr = ciaddr; add_simple_option(packet.options, DHCP_REQUESTED_IP, ciaddr); add_simple_option(packet.options, DHCP_SERVER_ID, server); LOG(LOG_DEBUG, "Sending release..."); return kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT); } /* return -1 on errors that are fatal for the socket, -2 for those that aren't */ int get_raw_packet(struct dhcpMessage *payload, int fd) { int bytes; struct udp_dhcp_packet packet; uint32_t source, dest; uint16_t check; memset(&packet, 0, sizeof(struct udp_dhcp_packet)); bytes = read(fd, &packet, sizeof(struct udp_dhcp_packet)); if (bytes < 0) { DEBUG(LOG_INFO, "couldn't read on raw listening socket -- ignoring"); usleep(500000); /* possible down interface, looping condition */ return -1; } if (bytes < (int) (sizeof(struct iphdr) + sizeof(struct udphdr))) { DEBUG(LOG_INFO, "message too short, ignoring"); return -2; } if (bytes < ntohs(packet.ip.tot_len)) { DEBUG(LOG_INFO, "Truncated packet"); return -2; } /* ignore any extra garbage bytes */ bytes = ntohs(packet.ip.tot_len); /* Make sure its the right packet for us, and that it passes sanity checks */ if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION || packet.ip.ihl != sizeof(packet.ip) >> 2 || packet.udp.dest != htons(CLIENT_PORT) || bytes > (int) sizeof(struct udp_dhcp_packet) || ntohs(packet.udp.len) != (uint16_t) (bytes - sizeof(packet.ip))) { DEBUG(LOG_INFO, "unrelated/bogus packet"); return -2; } /* check IP checksum */ check = packet.ip.check; packet.ip.check = 0; if (check != checksum(&(packet.ip), sizeof(packet.ip))) { DEBUG(LOG_INFO, "bad IP header checksum, ignoring"); return -1; } /* verify the UDP checksum by replacing the header with a psuedo header */ source = packet.ip.saddr; dest = packet.ip.daddr; check = packet.udp.check; packet.udp.check = 0; memset(&packet.ip, 0, sizeof(packet.ip)); packet.ip.protocol = IPPROTO_UDP; packet.ip.saddr = source; packet.ip.daddr = dest; packet.ip.tot_len = packet.udp.len; /* cheat on the psuedo-header */ if (check && check != checksum(&packet, bytes)) { DEBUG(LOG_ERR, "packet with bad UDP checksum received, ignoring"); return -2; } memcpy(payload, &(packet.data), bytes - (sizeof(packet.ip) + sizeof(packet.udp))); if (ntohl(payload->cookie) != DHCP_MAGIC) { LOG(LOG_ERR, "received bogus message (bad magic) -- ignoring"); return -2; } DEBUG(LOG_INFO, "oooooh!!! got some!"); return bytes - (sizeof(packet.ip) + sizeof(packet.udp)); }