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/*
handle ARP
At startup, we make a synchronous request for the local router.
We'll wait several seconds for a response, but abort the program
if we don't receive a response.
*/
#include "rawsock.h"
#include "string_s.h"
#include "logger.h"
#define VERIFY_REMAINING(n) if (offset+(n) > max) return;
struct ARP_IncomingRequest
{
unsigned is_valid;
unsigned opcode;
unsigned hardware_type;
unsigned protocol_type;
unsigned hardware_length;
unsigned protocol_length;
unsigned ip_src;
unsigned ip_dst;
const unsigned char *mac_src;
const unsigned char *mac_dst;
};
/****************************************************************************
****************************************************************************/
static void
proto_arp_parse(struct ARP_IncomingRequest *arp,
const unsigned char px[], unsigned offset, unsigned max)
{
/*
* parse the header
*/
VERIFY_REMAINING(8);
arp->is_valid = 0; /* not valid yet */
arp->hardware_type = px[offset]<<8 | px[offset+1];
arp->protocol_type = px[offset+2]<<8 | px[offset+3];
arp->hardware_length = px[offset+4];
arp->protocol_length = px[offset+5];
arp->opcode = px[offset+6]<<8 | px[offset+7];
offset += 8;
/* We only support IPv4 and Ethernet addresses */
if (arp->protocol_length != 4 && arp->hardware_length != 6)
return;
if (arp->protocol_type != 0x0800)
return;
if (arp->hardware_type != 1 && arp->hardware_type != 6)
return;
/*
* parse the addresses
*/
VERIFY_REMAINING(2 * arp->hardware_length + 2 * arp->protocol_length);
arp->mac_src = px+offset;
offset += arp->hardware_length;
arp->ip_src = px[offset+0]<<24 | px[offset+1]<<16 | px[offset+2]<<8 | px[offset+3];
offset += arp->protocol_length;
arp->mac_dst = px+offset;
offset += arp->hardware_length;
arp->ip_dst = px[offset+0]<<24 | px[offset+1]<<16 | px[offset+2]<<8 | px[offset+3];
//offset += arp->protocol_length;
arp->is_valid = 1;
}
/****************************************************************************
****************************************************************************/
int arp_resolve_sync(struct RawAdapter *adapter,
unsigned my_ipv4, const unsigned char *my_mac_address,
unsigned your_ipv4, unsigned char *your_mac_address)
{
unsigned char arp_packet[64];
unsigned i;
time_t start;
unsigned is_arp_notice_given = 0;
struct ARP_IncomingRequest response;
memset(&response, 0, sizeof(response));
/* zero out bytes in packet to avoid leaking stuff in the padding
* (ARP is 42 byte packet, Ethernet is 60 byte minimum) */
memset(arp_packet, 0, sizeof(arp_packet));
/*
* Create the request packet
*/
memcpy(arp_packet + 0, "\xFF\xFF\xFF\xFF\xFF\xFF", 6);
memcpy(arp_packet + 6, my_mac_address, 6);
memcpy(arp_packet + 12, "\x08\x06", 2);
memcpy(arp_packet + 14,
"\x00\x01" /* hardware = Ethernet */
"\x08\x00" /* protocol = IPv4 */
"\x06\x04" /* MAC length = 6, IPv4 length = 4 */
"\x00\x01" /* opcode = request */
, 8);
memcpy(arp_packet + 22, my_mac_address, 6);
arp_packet[28] = (unsigned char)(my_ipv4 >> 24);
arp_packet[29] = (unsigned char)(my_ipv4 >> 16);
arp_packet[30] = (unsigned char)(my_ipv4 >> 8);
arp_packet[31] = (unsigned char)(my_ipv4 >> 0);
memcpy(arp_packet + 32, "\x00\x00\x00\x00\x00\x00", 6);
arp_packet[38] = (unsigned char)(your_ipv4 >> 24);
arp_packet[39] = (unsigned char)(your_ipv4 >> 16);
arp_packet[40] = (unsigned char)(your_ipv4 >> 8);
arp_packet[41] = (unsigned char)(your_ipv4 >> 0);
/*
* Now loop for a few seconds looking for the response
*/
rawsock_send_packet(adapter, arp_packet, 60, 1);
start = time(0);
i = 0;
for (;;) {
unsigned length;
unsigned secs;
unsigned usecs;
const unsigned char *px;
int err;
if (time(0) != start) {
start = time(0);
rawsock_send_packet(adapter, arp_packet, 60, 1);
if (i++ >= 10)
break; /* timeout */
}
/* If we aren't getting a response back to our ARP, then print a
* status message */
if (time(0) > start+1 && !is_arp_notice_given) {
fprintf(stderr, "ARPing local router %u.%u.%u.%u\n",
(unsigned char)(your_ipv4>>24),
(unsigned char)(your_ipv4>>16),
(unsigned char)(your_ipv4>> 8),
(unsigned char)(your_ipv4>> 0)
);
is_arp_notice_given = 1;
}
err = rawsock_recv_packet(
adapter,
&length,
&secs,
&usecs,
&px);
if (err != 0)
continue;
if (px[13] != 6)
continue;
/*
* Parse the response as an ARP packet
*/
proto_arp_parse(&response, px, 14, length);
/* Is this an ARP packet? */
if (!response.is_valid) {
LOG(2, "arp: etype=0x%04x, not ARP\n", px[12]*256 + px[13]);
continue;
}
/* Is this an ARP "reply"? */
if (response.opcode != 2) {
LOG(2, "arp: opcode=%u, not reply(2)\n", response.opcode);
continue;
}
/* Is this response directed at us? */
if (response.ip_dst != my_ipv4) {
LOG(2, "arp: dst=%08x, not my ip 0x%08x\n", response.ip_dst, my_ipv4);
continue;
}
if (memcmp(response.mac_dst, my_mac_address, 6) != 0)
continue;
/* Is this the droid we are looking for? */
if (response.ip_src != your_ipv4) {
LOG(2, "arp: target=%08x, not desired 0x%08x\n", response.ip_src, your_ipv4);
continue;
}
/*
* GOT IT!
* we've got a valid response, so save the results and
* return.
*/
memcpy(your_mac_address, response.mac_src, 6);
return 0;
}
return 1;
}
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