arpping.c

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

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

#include "dhcpd.h"
#include "debug.h"
#include "arpping.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(u_int32_t yiaddr, u_int32_t ip, unsigned char *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) {
                LOG(LOG_ERR, "Could not open raw socket");
                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.ethhdr.h_dest, MAC_BCAST_ADDR, 6);   /* MAC DA */
        memcpy(arp.ethhdr.h_source, mac, 6);            /* MAC SA */
        arp.ethhdr.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 */
        *((u_int *) arp.sInaddr) = ip;                  /* source IP address */
        memcpy(arp.sHaddr, mac, 6);                     /* source hardware address */
        *((u_int *) arp.tInaddr) = 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;
        time(&prevTime);
        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: %s", strerror(errno));
                        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 && 
                            *((u_int *) arp.sInaddr) == yiaddr) {
                                DEBUG(LOG_INFO, "Valid arp reply receved for this address");
                                rv = 0;
                                break;
                        }
                }
                timeout -= time(NULL) - prevTime;
                time(&prevTime);
        }
        close(s);
        DEBUG(LOG_INFO, "%salid arp replies for this address", rv ? "No v" : "V");       
        return rv;
}

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