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// gcc -O2 -o derspan derspan.c -lpcap -std=gnu99 -Wall
#include <pcap.h>
#include <stdlib.h>
#include <netinet/ip.h>
#include <stdint.h>
#include <stdio.h>
int rawsock;
void my_callback(u_char *user, const struct pcap_pkthdr *h, const u_char *bytes)
{
int len = h->caplen;
if (len < 40) {
//printf("skipped short packet\n");
return;
}
if (bytes[14] != 0x88 || bytes[15] != 0xbe) {
//printf("skipped non-ethernet packet\n");
return;
}
if (bytes[36] != 0x08 || bytes[37] != 0x00) {
//printf("skipped non-IPv4 packet\n");
return;
}
struct sockaddr_in self;
self.sin_family = AF_INET;
self.sin_addr.s_addr = htonl(0x7f000001); // localhost
self.sin_port = htons(1337);
sendto(rawsock, bytes + 38, len - 38, 0, (struct sockaddr *)&self, sizeof(self));
}
int main(int argc, char **argv)
{
rawsock = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);
if (rawsock == -1) {
perror("socket");
exit(0);
}
pcap_t *pcap = pcap_open_live(argv[1], 1500, 1, 1000, NULL);
pcap_activate(pcap);
pcap_loop(pcap, -1, my_callback, NULL);
return 0;
}
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