slitheen/server/slitheen-proxy.c

#include <pcap.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <pthread.h>
#include <openssl/ssl.h>
#include "rserv.h"
#include "flow.h"
#include "slitheen.h"
#include "util.h"
#include "relay.h"

void got_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *packet);
void check_handshake(struct packet_info *info, flow f);
void *sniff_packets(void *);
void process_packet(uint8_t *packet, struct packet_info *info);
void extract_packet_headers(const uint8_t *packet, struct packet_info *info);

/** Checks a handshake message to see if it is tagged or a
 *  recognized flow.
 *  Inputs: The tcp header for the message, its associated flow,
 *  a pointer to the handshake header, and the length of
 *  the record.
 */
void check_handshake(struct packet_info *info, flow f){

	FILE *fp;
	int res, i, code;
	uint8_t *hello_rand;
	const struct handshake_header *handshake_hdr;

    byte privkey[PTWIST_BYTES];
	byte key[16];

	uint8_t *p = info->app_data + RECORD_HEADER_LEN;
	handshake_hdr = (struct handshake_header*) p;

	code = handshake_hdr->type;

	if (code == 0x01){
		p += CLIENT_HELLO_HEADER_LEN;
		//now pointing to hello random :D
		hello_rand = p;
		p += 4; //skipping time bytes
		/* Load the private key */
		fp = fopen("privkey", "rb");
		if (fp == NULL) {
			perror("fopen");
			exit(1);
		}
		res = fread(privkey, PTWIST_BYTES, 1, fp);
		if (res < 1) {
			perror("fread");
			exit(1);
		}
		fclose(fp);

		/* check tag*/ 
		res = check_tag(key, privkey, p, (const byte *)"context", 7);
		if (res) {
			printf("Untagged\n");
		} else {
			fp = fopen("tags", "wb");
			if (fp == NULL) {
				perror("fopen");
				exit(1);
			}
			//Write tag to file
			for(i=0; i< 28; i++){
				fprintf(fp, "%02x ", p[i]);
			}
			fclose(fp);

			//Write key to file
			fp = fopen("sharedkey", "wb");
			if (fp == NULL) {
				perror("fopen");
				exit(1);
			}
			for(i=0; i<16;i++){
			    fprintf(fp, "%02x", key[i]);
			}
			fclose(fp);

			/* Save flow in table */
			flow *flow_ptr = add_flow(f);
			for(int i=0; i<16; i++){
				flow_ptr->key[i] = key[i];
			}

			memcpy(flow_ptr->client_random, hello_rand, SSL3_RANDOM_SIZE);
			
			printf("Saved new flow\n");

		}
	}

}

void got_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *packet){
	pcap_t *handle = (pcap_t *) args;

	//might modify packet, copy to new pointer
	//uint8_t *modified_packet = calloc(1, header->len);
	//memcpy(modified_packet, packet, header->len);

	struct packet_info *info = calloc(1, sizeof(struct packet_info));
	extract_packet_headers(packet, info);

	// Check to make sure it is an IP packet 
	if(info->ip_hdr == NULL)
		goto end;

	/* Packet may be split over multiple frames. In this case,
	 // reconstruct the packet before trying to read TLS records
	if((htons(info->ip_hdr->flagsoff)&MF) || (htons(info->ip_hdr->flagsoff) &0x1fff) ){ // this is a fragment 
		printf("MF: %d, OFF: %d.\n", htons(info->ip_hdr->flagsoff)&MF, htons(info->ip_hdr->flagsoff)&0x1fff);
		printf("Received packet fragment.\n");
		u_char *complete_packet;
		//save packet fragment
		complete_packet = malloc(65535);

		int success = report_fragment(p, complete_packet, header->len);
		if(success){
			process_packet(complete_packet, info);
		}
		// TODO: handle errors 
		
	} else { //not a fragment, add to packet chain */
	process_packet(packet, info);

end:
	if((pcap_inject(handle, packet, header->len)) < 0 ){
		fprintf(stderr, "Error: %s\n", pcap_geterr(handle));
	}
	free(info);//Note: don't free this while a thread is using it
#ifdef DEBUG
	fprintf(stderr, "injected the following packet:\n");
	for(int i=0; i< header->len; i++){
		fprintf(stderr, "%02x ", packet[i]);
	}
	fprintf(stderr, "\n");
#endif

	//free(modified_packet);
}

void usage(void){
	printf("Usage: slitheen-proxy [internal network interface] [NAT interface]\n");
}

int main(int argc, char *argv[]){
	pthread_t t1, t2;
	char filter1[33] = "ether src host 08:00:27:e8:9d:d4";
	char filter2[33] = "ether src host 08:00:27:e8:9d:d4";

	char *dev1 = NULL; /* Device that leads to the internal network */
	char *dev2 = NULL; /* Device that leads out to the world */

	struct sniff_args outbound;
	struct sniff_args inbound;

	if (argc != 3) { 
		usage();
		return(2);
	}
	dev1 = argv[1];
	dev2 = argv[2];

	snprintf(filter1, 33, "ether src host %s", macaddr);
	snprintf(filter2, 33, "ether dst host %s", macaddr);

	init_flow_table();
	init_fragment_table();

	/* Create threads */
	outbound.readdev = dev1;
	outbound.writedev = dev2;
	outbound.filter = filter1;
	inbound.readdev = dev2;
	inbound.writedev = dev1;
	inbound.filter = filter2;
	pthread_create(&t1, NULL, sniff_packets, (void *) &outbound);
	pthread_create(&t2, NULL, sniff_packets, (void *) &inbound);

	pthread_join(t1, NULL);
	pthread_join(t2, NULL);
	
	return(0);
}

void *sniff_packets(void *args){
	pcap_t *rd_handle;
	pcap_t *wr_handle;
	char rd_errbuf[BUFSIZ];
	char wr_errbuf[BUFSIZ];
	struct bpf_program fp;
	bpf_u_int32 mask;
	bpf_u_int32 net;

	char *readdev, *writedev, *filter;
	struct sniff_args *arg_st = (struct sniff_args *) args;
	readdev = arg_st->readdev;
	writedev = arg_st->writedev;
	filter = arg_st->filter;

	if (pcap_lookupnet(readdev, &net, &mask, rd_errbuf) == -1){
		fprintf(stderr, "Can't get netmask for device %s\n", readdev);
		exit(2);
	}

	rd_handle = pcap_open_live(readdev, BUFSIZ, 1, 0, rd_errbuf);
	if (rd_handle == NULL){
		fprintf(stderr, "Couldn't open device %s: %s\n", readdev, rd_errbuf);
	}

	if(pcap_datalink(rd_handle) != DLT_EN10MB) {
		fprintf(stderr, "Device %s does not provide Ethernet headers - not supported\n", readdev);
		exit(2);
	}

	if(pcap_compile(rd_handle, &fp, filter, 0 , net) == -1){
		fprintf(stderr, "Couldn't parse filter %s: %s\n", filter, pcap_geterr(rd_handle));
		exit(2);
	}

	if (pcap_setfilter(rd_handle, &fp) == -1) {
		fprintf(stderr, "Couldn't install filter %s: %s\n", filter, pcap_geterr(rd_handle));
		exit(2);
	}

	wr_handle = pcap_open_live(writedev, BUFSIZ, 1, 0, wr_errbuf);
	if (wr_handle == NULL){
		fprintf(stderr, "Couldn't open device %s: %s\n", writedev, wr_errbuf);
	}
	/*callback function*/
	pcap_loop(rd_handle, -1, got_packet, (unsigned char *) wr_handle);

	/*Sniff a packet*/
	pcap_close(rd_handle);

	return NULL;
}

/* This function receives a full ip packet and then:
 * 	1) identifies the flow
 * 	2) adds the packet to the flow's data chain
 * 	3) updates the flow's state
 */
void process_packet(uint8_t *packet, struct packet_info *info){
	int index;

	flow newFlow;

	if (info->tcp_hdr != NULL){

		newFlow.src_ip = info->ip_hdr->src;
		newFlow.dst_ip = info->ip_hdr->dst;
		newFlow.src_port = info->tcp_hdr->src_port;
		newFlow.dst_port = info->tcp_hdr->dst_port;

		newFlow.seq_num = info->tcp_hdr->sequence_num;

		/* Checks to see if this is a possibly tagged hello msg */
		if ((info->record_hdr != NULL) && (info->record_hdr->type == HS)){ /* This is a TLS handshake */
			check_handshake(info, newFlow);
		}
	}

	/* Now if flow is in table, update state */
	if((index = check_flow(newFlow))){
		flow *observed = get_flow(index-1);
	
		if(observed->application){
			replace_packet(observed, info);
		} else {

			/* Pass data to packet chain */
			add_packet(observed, info);

			/* Update flow state */
			if(observed->packet_chain != NULL){
					update_flow(observed);

			}
		}

		/* Update TCP state */
		if(info->tcp_hdr->flags & (FIN | RST) ){
			/* Remove flow from table, connection ended */
			remove_flow(index);
		}

	}

}

/** This function extracts the ip, tcp, and tls record headers
 * 	from a received packet (if they exist), and put them in 
 * 	a packet_info struct
 * 	
 */
void extract_packet_headers(const uint8_t *packet, struct packet_info *info){

	/* First fill in IP header */
	const uint8_t *p = packet;
	p += ETHER_HEADER_LEN; //skip ethernet header
	info->ip_hdr = (struct ip_header*) p;
	info->size_ip_hdr = IP_HEADER_LEN(info->ip_hdr);
	
	/* Verify this is an IP packet */
	if( (info->ip_hdr->versionihl >>4) != 4){
		info->ip_hdr = NULL;
		info->size_ip_hdr = 0;
		info->tcp_hdr = NULL;
		info->size_tcp_hdr = 0;
		info->record_hdr = NULL;
		return;
	}

	/* If this is a TCP segment, fill in TCP header */
	if (info->ip_hdr->proto == IPPROTO_TCP){
		p += info->size_ip_hdr;	//skip IP header

		info->tcp_hdr = (struct tcp_header*) p;
		info->size_tcp_hdr = TCP_HEADER_LEN(info->tcp_hdr);
		p += info->size_tcp_hdr;
	} else {
		info->tcp_hdr = NULL;
		info->size_tcp_hdr = 0;
		info->record_hdr = NULL;
		return;
	}


	/* If the application data contains a TLS record, fill in hdr */
	info->app_data_len = htons(info->ip_hdr->len) - (info->size_ip_hdr + info->size_tcp_hdr);
	if(info->app_data_len > 0){
		info->app_data = p;
		info->record_hdr = (struct tls_header*) p;
		
		//check to see if this is a valid record
		if((info->record_hdr->type < 0x14) || (info->record_hdr->type > 0x18)){
			info->record_hdr = NULL;
		}

	} else {
		info->record_hdr = NULL;
		info->app_data = NULL;
	}

	return;

}