/* 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));

}
