networking/udhcp/arpping.c

/* vi: set sw=4 ts=4: */
/*
 * arpping.c
 *
 * Mostly stolen from: dhcpcd - DHCP client daemon
 * by Yoichi Hariguchi <yoichi@fore.com>
 */

#include <netinet/if_ether.h>
#include <net/if_arp.h>

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


struct arpMsg {
	/* Ethernet header */
	u_char   h_dest[6];			/* destination ether addr */
	u_char   h_source[6];			/* source ether addr */
	u_short  h_proto;			/* packet type ID field */

	/* ARP packet */
	uint16_t htype;				/* hardware type (must be ARPHRD_ETHER) */
	uint16_t ptype;				/* protocol type (must be ETH_P_IP) */
	uint8_t  hlen;				/* hardware address length (must be 6) */
	uint8_t  plen;				/* protocol address length (must be 4) */
	uint16_t operation;			/* ARP opcode */
	uint8_t  sHaddr[6];			/* sender's hardware address */
	uint8_t  sInaddr[4];			/* sender's IP address */
	uint8_t  tHaddr[6];			/* target's hardware address */
	uint8_t  tInaddr[4];			/* target's IP address */
	uint8_t  pad[18];			/* pad for min. Ethernet payload (60 bytes) */
} ATTRIBUTE_PACKED;

/* 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	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;


	s = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
	if (s == -1) {
		bb_perror_msg(bb_msg_can_not_create_raw_socket);
		return -1;
	}

	if (setsockopt_broadcast(s) == -1) {
		bb_perror_msg("cannot 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) {
			bb_perror_msg("error on ARPING request");
			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) &&
			    memcmp(arp.tHaddr, mac, 6) == 0 &&
			    *((uint32_t *) arp.sInaddr) == yiaddr) {
				DEBUG("Valid arp reply received for this address");
				rv = 0;
				break;
			}
		}
		timeout -= uptime() - prevTime;
		prevTime = uptime();
	}
	close(s);
	DEBUG("%salid arp replies for this address", rv ? "No v" : "V");
	return rv;
}