/* vi: set sw=4 ts=4: */ /* clientpacket.c * * Packet generation and dispatching functions for the DHCP client. * * Russ Dill <Russ.Dill@asu.edu> July 2001 * * Licensed under GPLv2 or later, see file LICENSE in this tarball for details. */ #include "common.h" #include "dhcpd.h" #include "dhcpc.h" #include "options.h" //#include <features.h> #if (defined(__GLIBC__) && __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 1) || defined _NEWLIB_VERSION #include <netpacket/packet.h> #include <net/ethernet.h> #else #include <asm/types.h> #include <linux/if_packet.h> #include <linux/if_ether.h> #endif /* Create a random xid */ uint32_t FAST_FUNC random_xid(void) { static smallint initialized; if (!initialized) { srand(monotonic_us()); initialized = 1; } return rand(); } /* Initialize the packet with the proper defaults */ static void init_packet(struct dhcp_packet *packet, char type) { udhcp_init_header(packet, type); memcpy(packet->chaddr, client_config.client_mac, 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); if ((type != DHCPDECLINE) && (type != DHCPRELEASE)) 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_param_req_option(struct dhcp_packet *packet) { uint8_t c; int end = end_option(packet->options); int i, len = 0; for (i = 0; (c = dhcp_options[i].code) != 0; i++) { if (((dhcp_options[i].flags & OPTION_REQ) && !client_config.no_default_options) || (client_config.opt_mask[c >> 3] & (1 << (c & 7))) ) { packet->options[end + OPT_DATA + len] = c; len++; } } if (len) { packet->options[end + OPT_CODE] = DHCP_PARAM_REQ; packet->options[end + OPT_LEN] = len; packet->options[end + OPT_DATA + len] = DHCP_END; } } /* RFC 2131 * 4.4.4 Use of broadcast and unicast * * The DHCP client broadcasts DHCPDISCOVER, DHCPREQUEST and DHCPINFORM * messages, unless the client knows the address of a DHCP server. * The client unicasts DHCPRELEASE messages to the server. Because * the client is declining the use of the IP address supplied by the server, * the client broadcasts DHCPDECLINE messages. * * When the DHCP client knows the address of a DHCP server, in either * INIT or REBOOTING state, the client may use that address * in the DHCPDISCOVER or DHCPREQUEST rather than the IP broadcast address. * The client may also use unicast to send DHCPINFORM messages * to a known DHCP server. If the client receives no response to DHCP * messages sent to the IP address of a known DHCP server, the DHCP * client reverts to using the IP broadcast address. */ static int raw_bcast_from_client_config_ifindex(struct dhcp_packet *packet) { return udhcp_send_raw_packet(packet, /*src*/ INADDR_ANY, CLIENT_PORT, /*dst*/ INADDR_BROADCAST, SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex); } #if ENABLE_FEATURE_UDHCPC_ARPING /* Broadcast a DHCP decline message */ int FAST_FUNC send_decline(uint32_t xid, uint32_t server, uint32_t requested) { struct dhcp_packet packet; init_packet(&packet, DHCPDECLINE); packet.xid = xid; add_simple_option(packet.options, DHCP_REQUESTED_IP, requested); add_simple_option(packet.options, DHCP_SERVER_ID, server); bb_info_msg("Sending decline..."); return raw_bcast_from_client_config_ifindex(&packet); } #endif /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */ int FAST_FUNC send_discover(uint32_t xid, uint32_t requested) { struct dhcp_packet packet; init_packet(&packet, DHCPDISCOVER); packet.xid = xid; if (requested) add_simple_option(packet.options, DHCP_REQUESTED_IP, requested); /* Explicitly saying that we want RFC-compliant packets helps * some buggy DHCP servers to NOT send bigger packets */ add_simple_option(packet.options, DHCP_MAX_SIZE, htons(576)); add_param_req_option(&packet); bb_info_msg("Sending discover..."); return raw_bcast_from_client_config_ifindex(&packet); } /* Broadcast a DHCP request message */ /* RFC 2131 3.1 paragraph 3: * "The client _broadcasts_ a DHCPREQUEST message..." */ int FAST_FUNC send_select(uint32_t xid, uint32_t server, uint32_t requested) { struct dhcp_packet 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_param_req_option(&packet); addr.s_addr = requested; bb_info_msg("Sending select for %s...", inet_ntoa(addr)); return raw_bcast_from_client_config_ifindex(&packet); } /* Unicast or broadcast a DHCP renew message */ int FAST_FUNC send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr) { struct dhcp_packet packet; init_packet(&packet, DHCPREQUEST); packet.xid = xid; packet.ciaddr = ciaddr; add_param_req_option(&packet); bb_info_msg("Sending renew..."); if (server) return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT); return raw_bcast_from_client_config_ifindex(&packet); } /* Unicast a DHCP release message */ int FAST_FUNC send_release(uint32_t server, uint32_t ciaddr) { struct dhcp_packet packet; init_packet(&packet, DHCPRELEASE); packet.xid = random_xid(); packet.ciaddr = ciaddr; add_simple_option(packet.options, DHCP_SERVER_ID, server); bb_info_msg("Sending release..."); return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT); } /* Returns -1 on errors that are fatal for the socket, -2 for those that aren't */ int FAST_FUNC udhcp_recv_raw_packet(struct dhcp_packet *dhcp_pkt, int fd) { int bytes; struct ip_udp_dhcp_packet packet; uint16_t check; memset(&packet, 0, sizeof(packet)); bytes = safe_read(fd, &packet, sizeof(packet)); if (bytes < 0) { log1("Packet read error, ignoring"); /* NB: possible down interface, etc. Caller should pause. */ return bytes; /* returns -1 */ } if (bytes < (int) (sizeof(packet.ip) + sizeof(packet.udp))) { log1("Packet is too short, ignoring"); return -2; } if (bytes < ntohs(packet.ip.tot_len)) { /* packet is bigger than sizeof(packet), we did partial read */ log1("Oversized packet, ignoring"); 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(packet) - can't happen */ || ntohs(packet.udp.len) != (uint16_t)(bytes - sizeof(packet.ip)) ) { log1("Unrelated/bogus packet, ignoring"); return -2; } /* verify IP checksum */ check = packet.ip.check; packet.ip.check = 0; if (check != udhcp_checksum(&packet.ip, sizeof(packet.ip))) { log1("Bad IP header checksum, ignoring"); return -2; } /* verify UDP checksum. IP header has to be modified for this */ memset(&packet.ip, 0, offsetof(struct iphdr, protocol)); /* ip.xx fields which are not memset: protocol, check, saddr, daddr */ packet.ip.tot_len = packet.udp.len; /* yes, this is needed */ check = packet.udp.check; packet.udp.check = 0; if (check && check != udhcp_checksum(&packet, bytes)) { log1("Packet with bad UDP checksum received, ignoring"); return -2; } memcpy(dhcp_pkt, &packet.data, bytes - (sizeof(packet.ip) + sizeof(packet.udp))); if (dhcp_pkt->cookie != htonl(DHCP_MAGIC)) { bb_info_msg("Packet with bad magic, ignoring"); return -2; } log1("Got valid DHCP packet"); udhcp_dump_packet(dhcp_pkt); return bytes - (sizeof(packet.ip) + sizeof(packet.udp)); }