/*
 * Send gratuitous ARP, based on send_arp from the Linux fake package.
 */

/* send_arp.c

   This program sends out one ARP packet with source/target IP and Ethernet
   hardware addresses suuplied by the user.  It compiles and works on Linux
   and will probably work on any Unix that has SOCK_PACKET.

   The idea behind this program is a proof of a concept, nothing more.  It
   comes as is, no warranty.  However, you're allowed to use it under one
   condition: you must use your brain simultaneously.  If this condition is
   not met, you shall forget about this program and go RTFM immediately.

   yuri volobuev'97
   volobuev@t1.chem.umn.edu

*/

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <netdb.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <linux/if_ether.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <netinet/ether.h>
#include <sys/socket.h>
#include <netpacket/packet.h>
#include <net/ethernet.h> /* the L2 protocols */


#define ETH_HW_ADDR_LEN 6
#define IP_ADDR_LEN 4
#define ARP_FRAME_TYPE 0x0806
#define ETHER_HW_TYPE 1
#define IP_PROTO_TYPE 0x0800
#define OP_ARP_REQUEST 1
#define OP_ARP_REPLY 2

struct arp_packet {
        u_char targ_hw_addr[ETH_HW_ADDR_LEN];
        u_char src_hw_addr[ETH_HW_ADDR_LEN];
        u_short frame_type;
        u_short hw_type;
        u_short prot_type;
        u_char hw_addr_size;
        u_char prot_addr_size;
        u_short op;
        u_char sndr_hw_addr[ETH_HW_ADDR_LEN];
        u_char sndr_ip_addr[IP_ADDR_LEN];
        u_char rcpt_hw_addr[ETH_HW_ADDR_LEN];
        u_char rcpt_ip_addr[IP_ADDR_LEN];
        u_char padding[18];
};

int main(int argc,char** argv)
{
	struct arp_packet pkt = { { 0, }, };
	struct sockaddr_ll sa = {
		.sll_family = AF_PACKET,
	};
	struct ifreq ifr;
	int sock;

	if (argc != 2 && argc != 3) {
		fprintf(stderr, "usage: gratarp ifname [target_mac_address]\n");
		return 1;
	}

	sock = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_RARP));
	if (sock<0){
		perror("socket");
		exit(1);
        }

	pkt.frame_type = htons(ARP_FRAME_TYPE);
	pkt.hw_type = htons(ETHER_HW_TYPE);
	pkt.prot_type = htons(IP_PROTO_TYPE);
	pkt.hw_addr_size = ETH_HW_ADDR_LEN;
	pkt.prot_addr_size = IP_ADDR_LEN;

	memset (&ifr, 0, sizeof(ifr));
	memcpy (&ifr.ifr_name, argv[1], strlen(argv[1]));

	if (ioctl(sock, SIOCGIFINDEX, &ifr) < 0)
		perror("SIOCGIFINDEX");
	sa.sll_ifindex = ifr.ifr_ifindex;

	if (ioctl(sock, SIOCGIFHWADDR, &ifr) < 0) {
		perror("SIOCGIFHWADDR");
		return 2;
	}
	memcpy(pkt.src_hw_addr, ifr.ifr_hwaddr.sa_data, 6);
	memcpy(pkt.sndr_hw_addr, ifr.ifr_hwaddr.sa_data, 6);

	/* pickup the target mac address */
	if (argc > 2) {
		struct ether_addr *eth_addr = ether_aton(argv[2]);
		if (!eth_addr) {
			perror("ether_aton\n");
			return 4;
		}
		memcpy(pkt.targ_hw_addr, eth_addr, 6);
		memcpy(pkt.rcpt_hw_addr, eth_addr, 6);
		memcpy(sa.sll_addr, eth_addr, 6);
		pkt.op = htons(OP_ARP_REPLY);
	} else {
		pkt.op = htons(OP_ARP_REQUEST);
		memset(pkt.targ_hw_addr, 0xff, 6);
	}
	sa.sll_halen = 6;

	if (ioctl(sock, SIOCGIFADDR, &ifr) < 0) {
		perror("SIOCGIFADDR");
		return 5;
	}
	memcpy(pkt.sndr_ip_addr, &((struct sockaddr_in*)&ifr.ifr_addr)->sin_addr, 4);
	memcpy(pkt.rcpt_ip_addr, &((struct sockaddr_in*)&ifr.ifr_addr)->sin_addr, 4);

	if (sendto(sock, &pkt, sizeof(pkt), 0, (struct sockaddr*)&sa, sizeof(sa)) < 0){
		perror("sendto");
		return 4;
        }

	return 0;
}