91 lines
2.9 KiB
C
91 lines
2.9 KiB
C
/* arp/arp.c */
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#include "arp.h"
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/* Sends an ARP request
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sockfd is the file descriptor of the socket to use to send the
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frame, should be a raw socket (AF_PACKET), which accepts ARP
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(ETH_P_ALL or ETH_P_ARP)
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ifindex is the index of the network interface
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ipaddr is the source IP address
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macaddr is the source MAC address
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target_ip is the IP address to be queried via ARP
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The function returns 0 upon success, EXIT_FAILURE otherwise.
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*/
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int send_arp_request(int sockfd, int ifindex, struct sockaddr_in *ipaddr, unsigned char *macaddr, struct in_addr target_ip)
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{
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/* DEFINITION OF THE DESTINATION */
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/* The destination of the packet is contained in a struct
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sockaddr_ll, that we fill with the broadcast address
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ff:ff:ff:ff:ff:ff */
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/* Broadcast address: */
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const unsigned char ether_broadcast_addr[]= {0xff,0xff,0xff,0xff,0xff,0xff};
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struct sockaddr_ll addr;
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addr.sll_family = AF_PACKET; /* always AF_PACKET */
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addr.sll_protocol = htons(ETH_P_ARP); /* physical-layer protocol */
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addr.sll_ifindex = ifindex; /* interface number */
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addr.sll_halen = ETHER_ADDR_LEN; /* length of address */
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/* physical-layer address: */
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memcpy(addr.sll_addr, ether_broadcast_addr, ETHER_ADDR_LEN);
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#ifdef DEBUG
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printf("[OK] Destination structure (struct sockaddr_ll) "
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"constructed successfully\n");
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#endif
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/* ====================================================================== */
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/* CONSTRUCTION OF THE FRAME */
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/* We can now build the ARP request frame, using the structures
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defined in <netinet/if_ether.h> (included by
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<netinet/ether.h>). */
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struct ether_arp request;
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request.arp_hrd = htons(ARPHRD_ETHER); /* hardware type: Ethernet */
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request.arp_pro = htons(ETH_P_IP); /* Protocol type: IP */
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request.arp_hln = ETHER_ADDR_LEN; /* Hardware address length */
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request.arp_pln = sizeof(in_addr_t); /* Protocol address length */
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request.arp_op = htons(ARPOP_REQUEST); /* Operation code */
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/* Target hardware address: 0 since this is one we want */
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memset(&request.arp_tha, 0, sizeof(request.arp_tha));
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/* Target protocol address: we put the IP address for which we want
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the layer-2 address */
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memcpy(&request.arp_tpa, &target_ip.s_addr, sizeof(request.arp_tpa));
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/* Source hardware address */
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memcpy(&request.arp_sha, macaddr, sizeof(request.arp_sha));
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/* Source protocol (IP) address */
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memcpy(&request.arp_spa, &ipaddr->sin_addr, sizeof(request.arp_spa));
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#ifdef DEBUG
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printf("[OK] ARP request structure (struct ether_arp) "
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"constructed successfully\n");
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#endif
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/* ====================================================================== */
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/* SEND THE FRAME */
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int err = sendto(sockfd, &request, sizeof(request), 0,
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(struct sockaddr *) &addr, sizeof(addr));
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if (err == -1) {
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perror("[FAIL] sendto()");
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exit(EXIT_FAILURE);
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}
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#ifdef DEBUG
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printf("[OK] Frame sent\n");
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#endif
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return 0;
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}
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