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/* 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 <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
#include "common.h"
#include "dhcpd.h"
#include "dhcpc.h"
#include "options.h"
/* Create a random xid */
uint32_t random_xid(void)
{
static smallint initialized;
if (!initialized) {
srand(monotonic_us());
initialized = 1;
}
return rand();
}
/* initialize a packet with the proper defaults */
static void init_packet(struct dhcpMessage *packet, char type)
{
udhcp_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)
{
uint8_t c;
int end = end_option(packet->options);
int i, len = 0;
packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
for (i = 0; (c = dhcp_options[i].code) != 0; i++) {
if (dhcp_options[i].flags & OPTION_REQ
|| (client_config.opt_mask[c >> 3] & (1 << (c & 7)))
) {
packet->options[end + OPT_DATA + len++] = c;
}
}
packet->options[end + OPT_LEN] = len;
packet->options[end + OPT_DATA + len] = DHCP_END;
}
#if ENABLE_FEATURE_UDHCPC_ARPING
/* Unicast a DHCP decline message */
int send_decline(uint32_t xid, uint32_t server)
{
struct dhcpMessage packet;
init_packet(&packet, DHCPDECLINE);
packet.xid = xid;
add_requests(&packet);
bb_info_msg("Sending decline...");
return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
}
#endif
/* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
int send_discover(uint32_t xid, uint32_t requested)
{
struct dhcpMessage 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_requests(&packet);
bb_info_msg("Sending discover...");
return udhcp_send_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(uint32_t xid, uint32_t server, uint32_t 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;
bb_info_msg("Sending select for %s...", inet_ntoa(addr));
return udhcp_send_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(uint32_t xid, uint32_t server, uint32_t ciaddr)
{
struct dhcpMessage packet;
init_packet(&packet, DHCPREQUEST);
packet.xid = xid;
packet.ciaddr = ciaddr;
add_requests(&packet);
bb_info_msg("Sending renew...");
if (server)
return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
}
/* Unicasts a DHCP release message */
int send_release(uint32_t server, uint32_t 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);
bb_info_msg("Sending release...");
return udhcp_send_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;
uint16_t check;
memset(&packet, 0, sizeof(struct udp_dhcp_packet));
bytes = read(fd, &packet, sizeof(struct udp_dhcp_packet));
if (bytes < 0) {
DEBUG("Cannot read on raw listening socket - ignoring");
sleep(1); /* possible down interface, looping condition */
return -1;
}
if (bytes < (int) (sizeof(struct iphdr) + sizeof(struct udphdr))) {
DEBUG("Message too short, ignoring");
return -2;
}
if (bytes < ntohs(packet.ip.tot_len)) {
DEBUG("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("Unrelated/bogus packet");
return -2;
}
/* verify IP checksum */
check = packet.ip.check;
packet.ip.check = 0;
if (check != udhcp_checksum(&packet.ip, sizeof(packet.ip))) {
DEBUG("Bad IP header checksum, ignoring");
return -1;
}
/* verify UDP checksum. IP header has to be modified for this */
memset(&packet.ip, 0, offsetof(struct iphdr, protocol));
/* 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)) {
bb_error_msg("packet with bad UDP checksum received, ignoring");
return -2;
}
memcpy(payload, &packet.data, bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
if (payload->cookie != htonl(DHCP_MAGIC)) {
bb_error_msg("received bogus message (bad magic) - ignoring");
return -2;
}
DEBUG("Got valid DHCP packet");
return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
}
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