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/* TODO: act proper if interface is promisc (only reply to packets
send to local host */
#include <arpa/inet.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <malloc.h>
#include <net/ethernet.h>
#include <net/if.h>
#include <netpacket/packet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>
#define BLEN 512
const char *payloads[] = {
// redirect using javascript with Meta-Refresh as fallback (works
// only with browsers, sends dangerous HTTP 200 independent of the
// request):
"HTTP/1.0 200 OK\r\n"
"Refresh: 1; url=https://%s/forcessl_nojs\r\n"
"Content-type: text/html\r\n"
"\r\n"
"<html><body>"
"<script language=\"Javascript\">"
"location.href = location.href.replace(/^http/i, \"https\");"
"</script>"
"enabling crypto..."
"</body></html>",
// redirect using 301 (closer to standart, friendly to non-browser
// HTTP clients):
"HTTP/1.0 301 Not enough crypto to process request\r\n"
"Location: https://%s/forcessl_nojs\r\n"
"Content-type: text/html"
"\r\n"
"<html><body>"
"enabling crypto..."
"</body></html>" };
#define AP0(x) if (!(x)) { perror(NULL); exit(EXIT_FAILURE); }
#define APN(x) if ((x) < 0) { perror(NULL); exit(EXIT_FAILURE); }
unsigned chksum(unsigned short *buf, int length) {
unsigned sum = 0;
for (; length > 1; length -= 2)
sum += *buf++;
return sum;
}
unsigned short ipchksum(struct iphdr *ip) {
unsigned sum = chksum((unsigned short *) ip, sizeof(struct iphdr));
sum = (sum >> 16) + (sum & 0xFFFF);
sum += (sum >> 16);
return ~sum;
}
unsigned short tcpchksum(struct iphdr *ip, struct tcphdr *tcp, int length) {
unsigned sum =
chksum((unsigned short*) &(ip->saddr), sizeof(ip->saddr)) +
chksum((unsigned short*) &(ip->daddr), sizeof(ip->daddr)) +
((length + ip->protocol) << 8) +
chksum((unsigned short*) tcp, length);
if (length % 2)
sum += *(((char*) tcp) + length - 1);
sum = (sum >> 16) + (sum & 0xFFFF);
sum += (sum >> 16);
return ~sum;
}
void printopts(char **argv) {
printf("Usage: %s -i interface [-3|-j] [-p port] [-h target-host]\n"
"\t-i interface to listen on\n"
"\t-3 use HTTP 301 reponses for redirection\n"
"\t-j use Javascript with Meta-Refresh as fallback for redirection (default)\n"
"\t-p port to listen (default: 80)\n"
"\t-h hostname of the redirection target; if unspecified the request destination IP is used\n",
argv[0]);
exit(EXIT_FAILURE);
}
int main(int argc, char **argv) {
// parse cmd line args
int opt,
port = htons(80);
char *target_host = NULL,
*output_device = NULL;
const char *raw_payload = payloads[0];
while ((opt = getopt(argc, argv, "3jp:h:i:")) != -1) {
switch (opt) {
case 'p':
port = htons(atoi(optarg));
break;
case 'h':
AP0(target_host = strdup(optarg));
break;
case 'i':
AP0(output_device = strdup(optarg));
break;
case '3':
raw_payload = payloads[1];
break;
case 'j':
raw_payload = payloads[0];
break;
default:
printopts(argv);
}
}
if (!output_device)
printopts(argv);
// prepare input buffer
char *ibuf = malloc(BLEN);
AP0(ibuf);
struct ethhdr *i_eth = (struct ethhdr*) ibuf;
struct iphdr *i_ip = (struct iphdr*) (i_eth + 1);
struct tcphdr *i_tcp = (struct tcphdr*) (i_ip + 1);
//char *i_pld = (char*) (i_tcp + 1);
// prepare output buffer
const size_t os =
sizeof(struct ethhdr) +
sizeof(struct iphdr) +
sizeof(struct tcphdr) +
strlen(raw_payload) - 1 +
(target_host ? strlen(target_host) : 15);
char *obuf = malloc(os);
AP0(obuf);
struct ethhdr *o_eth = (struct ethhdr*) obuf;
struct iphdr *o_ip = (struct iphdr*) (o_eth + 1);
struct tcphdr *o_tcp = (struct tcphdr*) (o_ip + 1);
char *o_pld = (char*) (o_tcp + 1);
if (os - sizeof(struct ethhdr) > 512)
fprintf(stderr, "warning: resulting packet size %ld exceeds MTU 512\n",
os - sizeof(struct ethhdr));
// setup sock
int fd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP));
APN(fd);
// retrieve interface idx (for send())
int ifidx;
{
struct ifreq req;
strcpy((char*) &(req.ifr_name), output_device);
APN(ioctl(fd, SIOCGIFINDEX, &req));
ifidx = req.ifr_ifindex;
}
// bind to interface
struct sockaddr_ll sall;
sall.sll_family = AF_PACKET;
sall.sll_ifindex = ifidx;
sall.sll_halen = 6;
memcpy(&(sall.sll_addr), &(o_eth->h_dest), sall.sll_halen);
sall.sll_protocol = sall.sll_hatype = sall.sll_pkttype = 0;
APN(bind(fd, (struct sockaddr*) &sall, sizeof(sall)));
// prefill static output
o_eth->h_proto = htons(ETH_P_IP);
o_ip->ihl = 5;
o_ip->version = 4;
o_ip->tos = 0;
o_ip->id = 0;
o_ip->frag_off = 0;
o_ip->ttl = 255;
o_ip->protocol = 6;
o_tcp->source = port;
o_tcp->res1 = 0;
o_tcp->doff = 5;
o_tcp->ack = 1;
o_tcp->rst = 0;
o_tcp->psh = 1;
o_tcp->urg = 0;
o_tcp->ece = 0;
o_tcp->cwr = 0;
o_tcp->urg_ptr = 0;
o_tcp->window = htons(4); // first 4 byte are harmless (and we won't ack them)
if (target_host)
snprintf(o_pld, strlen(raw_payload) + strlen(target_host) - 1,
raw_payload, target_host);
// read packets forever
while (1) {
int is = recv(fd, ibuf, BLEN, 0);
APN(is);
if ((is >= sizeof(struct ethhdr) + sizeof(struct iphdr)
+ sizeof(struct tcphdr)) && // packet long enough?
(i_eth->h_proto == htons(ETH_P_IP)) && // ip protocol?
(i_ip->ihl == 5) && // no IP options
(i_ip->protocol == 6) && // tcp protocol?
(i_tcp->dest == port)) { // port 80?
int size = 0;
// eth & IP are common for all responses
memcpy(&(o_eth->h_dest), &(i_eth->h_source), ETH_ALEN);
memcpy(&(o_eth->h_source), &(i_eth->h_dest), ETH_ALEN);
o_ip->check = 0;
memcpy(&(o_ip->saddr), &(i_ip->daddr), sizeof(o_ip->saddr));
memcpy(&(o_ip->daddr), &(i_ip->saddr), sizeof(o_ip->daddr));
o_tcp->dest = i_tcp->source;
o_tcp->check = 0;
if (i_tcp->syn && !i_tcp->ack) { // first packet of a handshake?
size = os - strlen(o_pld);
o_tcp->seq = i_tcp->seq;
o_tcp->ack_seq = htonl(ntohl(i_tcp->seq) + 1);
o_tcp->fin = 0;
o_tcp->syn = 1;
}else if (i_tcp->ack) {
size = os;
o_tcp->seq = htonl(ntohl(i_tcp->ack_seq));
o_tcp->ack_seq = htonl(ntohl(i_tcp->ack_seq));
o_tcp->fin = 1;
o_tcp->syn = 0;
if (!target_host) {
struct in_addr ba;
ba.s_addr = i_ip->daddr;
char *sa = inet_ntoa(ba);
snprintf(o_pld, os - (o_pld - (char*) o_eth),
raw_payload, sa);
size = size - 15 + strlen(sa);
}
}
if (size > 0) {
o_ip->tot_len = htons(size - sizeof(struct ethhdr));
o_ip->check = ipchksum(o_ip);
o_tcp->check = tcpchksum(o_ip, o_tcp, size - sizeof(struct ethhdr) - sizeof(struct iphdr));
if (sendto(fd, o_eth, size, 0, (struct sockaddr*) &sall, sizeof(struct sockaddr_ll)) != size) {
perror(NULL);
exit(EXIT_FAILURE);
}
}
}
}
}
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