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cluarp.c
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/** @file
* Utility to generate a gratuitous ARP request on a given interface.
*/
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <ctype.h>
#include <sys/socket.h>
#include <netinet/if_ether.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#define IP_ADDR_LEN 4
#define DEFAULT_DEVICE "eth0"
#define SA_DATA_LEN 14 /* Taken from include/linux/socket.h */
/**
* ARP frame structure.
*/
struct arp_frame {
u_char ether_dest_hw_addr[ETH_ALEN];
u_char ether_src_hw_addr[ETH_ALEN];
u_short ether_packet_type;
u_short arp_hw_type;
u_short arp_proto_type;
u_char arp_hlen;
u_char arp_plen;
u_short op;
u_char arp_sender_ha[ETH_ALEN];
u_char arp_sender_ip[IP_ADDR_LEN];
u_char arp_target_ha[ETH_ALEN];
u_char arp_target_ip[IP_ADDR_LEN];
u_char padding[18];
};
/**
* Display usage information.
*/
void usage(void)
{
fprintf(stdout,
"myarp <src_ip> <src_hw> <targ_ip> <targ_hw> [device]\n");
}
/**
* Change a hardware ethernet address into an array of characters.
* Warning: Unchecked bounds in copy_to.
*
* @param addr_string NULL-terminated string in the format:
* "aa:bb:cc:dd:ee:ff"
* @param copy_to Pre-allocated array of at least 6 bytes,
* preferrably set to 0.
*/
void
parse_hw_addr(char *addr_string, u_char *copy_to)
{
char *c = addr_string, p, result=' ';
int i;
for (i = 0; i < ETH_ALEN; i++) {
/* first digit */
if (*c == ':')
c++;
p = tolower(*c++);
if (isdigit(p))
result = p - '0';
else if (p >= 'a' && p <= 'z')
result = p - 'a' + 10;
*copy_to = result << 4;
/* second digit */
if (*c == ':')
c++;
p = tolower(*c++);
if (isdigit(p))
result = p - '0';
else if (p >= 'a' && p <= 'z')
result = p - 'a' + 10;
*copy_to++ |= result;
}
return;
}
/**
* Change an IP address into an array of characters.
* Warning: Unchecked bounds in copy_to.
*
* @param addr_string NULL-terminated string in the format:
* "10.1.2.3" (standard IPv4 dotted-quad).
* @param copy_to Pre-allocated array of at least 4 bytes,
* preferrably set to 0.
*/
void
parse_ip_addr(char *addr_string, u_char *copy_to)
{
unsigned long inaddr;
inaddr = inet_addr(addr_string);
memcpy(copy_to, &inaddr, IP_ADDR_LEN);
}
/**
* Driver for cluarp.
*
* @return 0 on success, 1 on any failure.
*/
int
main(int argc, char **argv)
{
int s;
struct arp_frame arp_packet;
struct sockaddr sockaddr;
/* unsigned long inaddr; */
if ((argc != 5) && (argc != 6)) {
usage();
exit(1);
}
bzero(&arp_packet, sizeof(struct arp_frame));
parse_ip_addr(argv[1], arp_packet.arp_sender_ip);
parse_hw_addr(argv[2], arp_packet.ether_src_hw_addr);
parse_hw_addr(argv[2], arp_packet.arp_sender_ha);
parse_ip_addr(argv[3], arp_packet.arp_target_ip);
parse_hw_addr(argv[4], arp_packet.ether_dest_hw_addr);
parse_hw_addr(argv[4], arp_packet.arp_target_ha);
arp_packet.ether_packet_type = htons(ETH_P_ARP);
arp_packet.arp_hw_type = htons(ETH_P_802_3);
arp_packet.arp_proto_type = htons(ETH_P_IP);
arp_packet.arp_hlen = ETH_ALEN;
arp_packet.arp_plen = IP_ADDR_LEN;
arp_packet.op = htons(ARPOP_REPLY);
s = socket(AF_PACKET,SOCK_PACKET,htons(ETH_P_RARP));
if (argc == 5)
strncpy(sockaddr.sa_data, DEFAULT_DEVICE, SA_DATA_LEN);
else
strncpy(sockaddr.sa_data, argv[5], SA_DATA_LEN);
if (sendto(s, &arp_packet, sizeof(struct arp_frame), 0,
&sockaddr, sizeof(struct sockaddr)) < 0) {
perror("sendto");
exit(1);
}
exit(0);
}

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