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arpping.c

/*
 * arpping.c
 *
 * Mostly stolen from: dhcpcd - DHCP client daemon
 * by Yoichi Hariguchi <yoichi@fore.com>
 */

#include <sys/time.h>
#include <time.h>
#include <sys/socket.h>
#include <netinet/if_ether.h>
#include <net/if_arp.h>
#include <netinet/in.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>

#include "dhcpd.h"
#include "arpping.h"
#include "common.h"

/* args:    yiaddr - what IP to ping
 *          ip - our ip
 *          mac - our arp address
 *          interface - interface to use
 * retn:    1 addr free
 *          0 addr used
 *          -1 error
 */

/* FIXME: match response against chaddr */
int arpping(uint32_t yiaddr, uint32_t ip, uint8_t *mac, char *interface)
{

      int   timeout = 2;
      int   optval = 1;
      int   s;                /* socket */
      int   rv = 1;                 /* return value */
      struct sockaddr addr;         /* for interface name */
      struct arpMsg     arp;
      fd_set            fdset;
      struct timeval    tm;
      time_t            prevTime;


      if ((s = socket (PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP))) == -1) {
#ifdef IN_BUSYBOX
            LOG(LOG_ERR, bb_msg_can_not_create_raw_socket);
#else
            LOG(LOG_ERR, "Could not open raw socket");
#endif
            return -1;
      }

      if (setsockopt(s, SOL_SOCKET, SO_BROADCAST, &optval, sizeof(optval)) == -1) {
            LOG(LOG_ERR, "Could not setsocketopt on raw socket");
            close(s);
            return -1;
      }

      /* send arp request */
      memset(&arp, 0, sizeof(arp));
      memcpy(arp.h_dest, MAC_BCAST_ADDR, 6);          /* MAC DA */
      memcpy(arp.h_source, mac, 6);             /* MAC SA */
      arp.h_proto = htons(ETH_P_ARP);                 /* protocol type (Ethernet) */
      arp.htype = htons(ARPHRD_ETHER);          /* hardware type */
      arp.ptype = htons(ETH_P_IP);              /* protocol type (ARP message) */
      arp.hlen = 6;                             /* hardware address length */
      arp.plen = 4;                             /* protocol address length */
      arp.operation = htons(ARPOP_REQUEST);           /* ARP op code */
      memcpy(arp.sInaddr, &ip, sizeof(ip));           /* source IP address */
      memcpy(arp.sHaddr, mac, 6);               /* source hardware address */
      memcpy(arp.tInaddr, &yiaddr, sizeof(yiaddr));   /* target IP address */

      memset(&addr, 0, sizeof(addr));
      strcpy(addr.sa_data, interface);
      if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0)
            rv = 0;

      /* wait arp reply, and check it */
      tm.tv_usec = 0;
      prevTime = uptime();
      while (timeout > 0) {
            FD_ZERO(&fdset);
            FD_SET(s, &fdset);
            tm.tv_sec = timeout;
            if (select(s + 1, &fdset, (fd_set *) NULL, (fd_set *) NULL, &tm) < 0) {
                  DEBUG(LOG_ERR, "Error on ARPING request: %m");
                  if (errno != EINTR) rv = 0;
            } else if (FD_ISSET(s, &fdset)) {
                  if (recv(s, &arp, sizeof(arp), 0) < 0 ) rv = 0;
                  if (arp.operation == htons(ARPOP_REPLY) &&
                      bcmp(arp.tHaddr, mac, 6) == 0 &&
                      *((uint32_t *) arp.sInaddr) == yiaddr) {
                        DEBUG(LOG_INFO, "Valid arp reply receved for this address");
                        rv = 0;
                        break;
                  }
            }
            timeout -= uptime() - prevTime;
            prevTime = uptime();
      }
      close(s);
      DEBUG(LOG_INFO, "%salid arp replies for this address", rv ? "No v" : "V");    
      return rv;
}

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