slitheen/server/flow.c

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <pthread.h>
#include <errno.h>
#include "flow.h"
#include "crypto.h"
#include "slitheen.h"

static flow_table *table;
static session_cache *sessions;

/* Initialize the table of tagged flows */
int init_flow_table(void) {

	table = malloc(sizeof(flow_table));
	
	table->table = (flow *) malloc(sizeof(flow)*MAX_FLOWS);
	if( table->table == NULL){
		fprintf(stderr, "malloc failed.\n");
		return 1;
	}
	table->len = 0;
	table->max_len = MAX_FLOWS;

	return 0;
}


/* Add a new flow to the tagged flow table */
flow *add_flow(flow newFlow) {
	flow *ptr;

	if(table->len == table->max_len){
		//grow_table();
		NULL;
	}
	printf("there are %d flows in the table\n", table->len);

	ptr = table->table + table->len;
	newFlow.state = TLS_CLNT_HELLO;
	newFlow.in_encrypted = 0;
	newFlow.out_encrypted = 0;
	newFlow.application = 0;
	newFlow.resume_session = 0;
	newFlow.current_session = NULL;
	newFlow.packet_chain = NULL;
	newFlow.censored_queue = NULL;
	newFlow.outbox_len = 0;

	newFlow.finish_md_ctx = EVP_MD_CTX_create();
	const EVP_MD *md = EVP_sha384();
	EVP_DigestInit_ex(newFlow.finish_md_ctx, md, NULL);

	memset(newFlow.read_seq, 0, 8);
	memset(newFlow.write_seq, 0, 8);
	*ptr = newFlow;

	table->len ++;

	return ptr;
}

/** Observes TLS handshake messages and updates the state of
 *  the flow
 *
 *  Inputs:
 *  	f: the tagged flow
 *
 *  Output:
 *  	0 on success, 1 on failure
 */
int update_flow(flow *f) {
	uint8_t *record;
	const struct record_header *record_hdr;
	const struct handshake_header *handshake_hdr;

	uint8_t *p = f->packet_chain->data;

	record_hdr = (struct record_header*) p;
	int record_len;
	int data_len;

	record_len = RECORD_LEN(record_hdr)+RECORD_HEADER_LEN;
	data_len = f->packet_chain->data_len;
	packet *current = f->packet_chain;
	int incoming = current->incoming;
	record = calloc(1, record_len);
	
	for(int i=0; (i<data_len) && (i<record_len); i++){
		record[i] = p[i];
	}

	while(record_len > data_len) {
		if(current->next == NULL){
			free(record);
			return 0;
		}
		if(current->next->seq_num != current->seq_num + current->len){
			printf("Missing packet: seq_num= %d, datalen= %d, nextseq= %d\n", current->seq_num, current->len, current->next->seq_num);
			free(record);
			return 0;
		}

		current = current->next;
		p = current->data;
		int i;
		for(i=0; (i<current->data_len) && (i+data_len < record_len); i++){

			record[data_len+i] = p[i];
		}
		data_len += current->data_len;
	}

	switch(record_hdr->type){
		case HS:
			p = record;
			p += RECORD_HEADER_LEN;

			if((incoming && f->in_encrypted) || (!incoming && f->out_encrypted)){
				int32_t n = encrypt(f, p, p, record_len - RECORD_HEADER_LEN, incoming, 0x16, 0);
				p += EVP_GCM_TLS_EXPLICIT_IV_LEN;
				update_context(f, p, n, incoming, 0x16, 0);
				if(incoming) f->in_encrypted = 2;
				else f->out_encrypted = 2;
			}
			handshake_hdr = (struct handshake_header*) p;
			f->state = handshake_hdr->type;

			switch(f->state){
				case TLS_CLNT_HELLO: 
					update_finish_hash(f, p);
					check_session(f, p, HANDSHAKE_MESSAGE_LEN(handshake_hdr));
					printf("Shaking hands...\n");
					break;
				case TLS_SERV_HELLO:
					printf("Received server hello\n");
					if(f->resume_session){
						verify_session_id(f,p);
					} else {
						save_session_id(f,p);
					}
					extract_server_random(f, p);
					update_finish_hash(f, p);
					break;
				case TLS_NEW_SESS:
					printf("Received new session\n");
					save_session_ticket(f, p, HANDSHAKE_MESSAGE_LEN(handshake_hdr));
					update_finish_hash(f, p);
					break;
				case TLS_CERT:
					printf("Received cert\n");
					update_finish_hash(f, p);
					break;
				case TLS_SRVR_KEYEX:
					update_finish_hash(f, p);

					if(extract_parameters(f, p)){
						printf("Error extracting params\n");
					}
					if(compute_master_secret(f)){
						printf("Error computing master secret\n");
					}
					break;
				case TLS_CERT_REQ:
					update_finish_hash(f, p);
					break;
				case TLS_SRVR_HELLO_DONE:
					printf("Received server hello done\n");
					update_finish_hash(f, p);
					break;
				case TLS_CERT_VERIFY:
					printf("received cert verify\n");
					update_finish_hash(f, p);
					break;
				case TLS_CLNT_KEYEX:
					printf("Received client key exchange\n");
					update_finish_hash(f, p);
					break;
				case TLS_FINISHED:
					verify_finish_hash(f,p, incoming);
					update_finish_hash(f, p);
					if((f->in_encrypted == 2) && (f->out_encrypted == 2)){
						printf("Handshake complete!\n");
						f->application = 1;
						if(current->incoming)
							f->seq_num = current->seq_num + current->len;
						while(current->next != NULL){
							current = current->next;
							if(current->incoming)
								f->seq_num = current->seq_num+ current->len;
						}
					}
					break;
				default:
					printf("Error? %02x\n",p[0]);
					break;
			}
			break;
		case APP:
			printf("Application Data\n");
			break;
		case CCS:
			printf("CCS\n");
			if(incoming){
				f->in_encrypted = 1;
			} else {
				f->out_encrypted = 1;
			}
			
			/*Initialize ciphers */
			init_ciphers(f);
			break;
		case ALERT:
			p = record;
			p += RECORD_HEADER_LEN;

			encrypt(f, p, p, record_len - RECORD_HEADER_LEN, incoming, 0x16, 0);
			p += EVP_GCM_TLS_EXPLICIT_IV_LEN;
			printf("Alert: %02x %02x\n", p[0], p[1]);
			break;
		case HB:
			printf("Heartbeat\n");
			break;
		default:
			printf("Error: Not a Record\n");
			//TODO: later figure this out, for now delete
			f->packet_chain = f->packet_chain->next;

			if( f->packet_chain != NULL){
				update_flow(f);
			}
			return 0;
	}

	if(!f->application){
	f->seq_num = current->seq_num;

	if(record_len == data_len){
		/* record ended on packet boundary */
		f->packet_chain = current->next;
	} else {
		/* need to update data */
		f->packet_chain = current;
		current->data = current->data + (current->data_len - (data_len - record_len));
		current->data_len = data_len - record_len;
		update_flow(f);
	}
	}

	free(record);
	return 0;
}

/** Removes the tagged flow from the flow table: happens when
 *  the station receives a TCP RST or FIN packet
 *
 *  Input:
 *  	index: the index into the flow table of the tagged flow
 *
 *  Output:
 *  	0 on success, 1 on failure
 */
int remove_flow(int index) {
	int i;
	flow *ptr;

	if(index){
		ptr = table->table + index -1;
		for(i=0; i< table->len - index; i++){
			ptr += i;
			*ptr = *(ptr + 1);
		}
		table->len --;
	} else {
		return 1;
	}

	printf("flow removed!\n");
	return 0;
}

/** Expands the flow table when we run out of space
 *  TODO: implement and test
 */
int grow_table() {
	return 0;
}

/** Returns the index of a flow in the flow table if
 *  it exists, returns 0 if it is not present.
 *
 *  Inputs:
 *  	observed: details for the observed flow
 *
 *  Output:
 *  	index of flow in table or 0 if it doesn't exist
 */
int check_flow(flow observed){
	/* Loop through flows in table and see if it exists */
	int i;
	flow *candidate = table->table;

	/* Check first in this direction */
	for(i=0; i<table->len; i++){
		candidate += i;
		if(candidate->src_ip.s_addr == observed.src_ip.s_addr){
			if(candidate->dst_ip.s_addr == observed.dst_ip.s_addr){
				if(candidate->src_port == observed.src_port){
					if(candidate->dst_port == observed.dst_port){
						return i+1;
					}
				}
			}
		}
	}


	candidate = table->table;
	/* Then in the other direction */
	for(i=0; i<table->len; i++){
		candidate += i;
		if(candidate->src_ip.s_addr == observed.dst_ip.s_addr){
			if(candidate->dst_ip.s_addr == observed.src_ip.s_addr){
				if(candidate->src_port == observed.dst_port){
					if(candidate->dst_port == observed.src_port){
						return i+1;
					}
				}
			}
		}
	}

	return 0;
}

/** Returns the flow in the flow table at a specified index
 *
 *  Input:
 *  	index: the desired index of the flow table
 *
 *  Output:
 *  	the flow at the specified index
 */
flow *get_flow(int index){
	if(index < table->len){
		return table->table+index;
	} else {
		return NULL;
	}
}

int init_session_cache(void){
	sessions = malloc(sizeof(session_cache));
	sessions->length = 0;
	sessions->first_session = NULL;

	return 0;
}

/** Called from ServerHello, verifies that the session id returned matches
 *  the session id requested from the client hello
 *
 *  Input:
 *  	f: the tagged flow
 *  	hs: a pointer to the ServerHello message
 *
 *  Output:
 *  	0 if success, 1 if failed
 */
int verify_session_id(flow *f, uint8_t *hs){
	
	//increment pointer to point to sessionid
	uint8_t *p = hs + HANDSHAKE_HEADER_LEN;
	p += 2; //skip version
	p += SSL3_RANDOM_SIZE; //skip random

	uint8_t id_len = (uint8_t) p[0];
	p ++;
	
	//check to see if it matches flow's session id set by ClientHello
	if(f->current_session != NULL && f->current_session->session_id_len > 0 && !memcmp(f->current_session->session_id, p, id_len)){
		//if it matched, update flow with master secret :D
		session *last = sessions->first_session;
		int found = 0;
		for(int i=0; ((i<sessions->length) && (!found)); i++){
			if(!memcmp(last->session_id, f->current_session->session_id, id_len)){
				memcpy(f->master_secret, last->master_secret, SSL3_MASTER_SECRET_SIZE);
				found = 1;
			}
			last = last->next;
		}
		if((!found) && (f->current_session->session_ticket_len > 0)){
			last = sessions->first_session;
			for(int i=0; ((i<sessions->length) && (!found)); i++){
				if(!memcmp(last->session_ticket, f->current_session->session_ticket, f->current_session->session_ticket_len)){
					memcpy(f->master_secret, last->master_secret, SSL3_MASTER_SECRET_SIZE);
					found = 1;
				}
				last = last->next;
			}
		}

	} else if (f->current_session != NULL &&  f->current_session->session_id_len > 0){
		//check to see if server's hello extension matches the ticket
		save_session_id(f, p);
	}

	//now check 

	return 0;

}

/* Called from ClientHello. Checks to see if the session id len is > 0. If so,
 * saves sessionid for later verification. Also checks to see if a session
 * ticket is included as an extension.
 *
 *  Input:
 *  	f: the tagged flow
 *  	hs: a pointer to the ServerHello message
 *
 *  Output:
 *  	0 if success, 1 if failed
 */
int check_session(flow *f, uint8_t *hs, uint32_t len){

	uint8_t *p = hs + HANDSHAKE_HEADER_LEN;
	p += 2; //skip version
	p += SSL3_RANDOM_SIZE; //skip random

	session *new_session = calloc(1, sizeof(session));
	new_session->session_id_len = (uint8_t) p[0];
	new_session->session_ticket_len = 0;
	p  ++;

	if(new_session->session_id_len > 0){
		f->resume_session = 1;
		memcpy(new_session->session_id, p, new_session->session_id_len);
		new_session->next = NULL;

		f->current_session = new_session;
	}

	p += new_session->session_id_len;
	
	//check to see if there is a session ticket included

	//skip to extensions
	uint16_t ciphersuite_len = (p[0] << 8) + p[1];
	p += 2 + ciphersuite_len;
	uint8_t compress_meth_len = p[0];
	p += 1 + compress_meth_len;
	
	//search for SessionTicket TLS extension
	if(2 + SSL3_RANDOM_SIZE + new_session->session_id_len + 1 + 2 + ciphersuite_len + 1 + compress_meth_len > len){
		//no extension
		if(f->current_session == NULL)
			free(new_session);
		return 0;
	}
	uint16_t extensions_len = (p[0] << 8) + p[1];
	p += 2;
	while(extensions_len > 0){
		uint16_t type = (p[0] << 8) + p[1];
		p += 2;
		uint16_t ext_len = (p[0] << 8) + p[1];
		p += 2;
		if(type == 0x23){
			if(ext_len > 0){
				f->resume_session = 1;
				new_session->session_ticket_len = ext_len;
				new_session->session_ticket = calloc(1, ext_len);
				memcpy(new_session->session_ticket, p, ext_len);
				f->current_session = new_session;
				
			}
		}
		p += ext_len;
		extensions_len -= (4 + ext_len);
	}

	if(!f->resume_session){
		//see if a ticket is incuded
		free(new_session);
	}

	return 0;
}
	

/* Called from ServerHello during full handshake. Adds the session id to the
 * cache for later resumptions
 *
 *  Input:
 *  	f: the tagged flow
 *  	hs: a pointer to the ServerHello message
 *
 *  Output:
 *  	0 if success, 1 if failed
 */
int save_session_id(flow *f, uint8_t *hs){
	printf("saving session id\n");

	//increment pointer to point to sessionid
	uint8_t *p = hs + HANDSHAKE_HEADER_LEN;
	p += 2; //skip version
	p += SSL3_RANDOM_SIZE; //skip random
	
	session *new_session = calloc(1, sizeof(session));
	new_session->session_id_len = (uint8_t) p[0];
	if(new_session->session_id_len <= 0){
		//if this value is zero, the session is non-resumable or the
		//server will issue a NewSessionTicket handshake message
		printf("USING TLS SESSION TICKET\n");
		free(new_session);
		return 0;
	}
	p++;
	memcpy(new_session->session_id, p, new_session->session_id_len);
	new_session->next = NULL;

	f->current_session = new_session;

	if(sessions->first_session == NULL){
		sessions->first_session = new_session;
	} else {
		session *last = sessions->first_session;

		for(int i=0; i< sessions->length; i++){
			if(last == NULL)
				printf("UH OH: last is null?\n");
			last = last->next;
		}
		last->next = new_session;
	}

	sessions->length ++;

	printf("Saved session id:");
	for(int i=0; i< new_session->session_id_len; i++){
		printf(" %02x", p[i]);
	}
	printf("\n");

	printf("THERE ARE NOW %d saved sessions\n", sessions->length);

	return 0;

}

/* Called from NewSessionTicket. Adds the session ticket to the
 * cache for later resumptions
 *
 *  Input:
 *  	f: the tagged flow
 *  	hs: a pointer to the ServerHello message
 *
 *  Output:
 *  	0 if success, 1 if failed
 */
int save_session_ticket(flow *f, uint8_t *hs, uint32_t len){
	uint8_t *p = hs + HANDSHAKE_HEADER_LEN;
	p += 4; //skip lifetime TODO: add to session struct
	session *new_session = calloc(1,sizeof(session));
	new_session->session_id_len = 0;
	
	new_session->session_ticket_len = (p[0] << 8) + p[1];
	printf("saving ticket of size %d\n", new_session->session_ticket_len);
	p += 2;

	uint8_t *ticket = calloc(1, new_session->session_ticket_len);
	memcpy(ticket, p, new_session->session_ticket_len);
	new_session->session_ticket = ticket;
	memcpy(new_session->master_secret, f->master_secret, SSL3_MASTER_SECRET_SIZE);

	if(sessions->first_session == NULL){
		sessions->first_session = new_session;
	} else {
		session *last = sessions->first_session;

		for(int i=0; i< sessions->length; i++){
			if(last == NULL)
				printf("UH OH: last is null?\n");
			last = last->next;
		}
		last->next = new_session;
	}

	sessions->length ++;

	printf("Saved session ticket:");
	for(int i=0; i< new_session->session_ticket_len; i++){
		printf(" %02x", p[i]);
	}
	printf("\n");

	printf("Saved session master secret:");
	for(int i=0; i< SSL3_MASTER_SECRET_SIZE; i++){
		printf(" %02x", new_session->master_secret[i]);
	}
	printf("\n");

	printf("THERE ARE NOW %d saved sessions\n", sessions->length);

	return 0;
}

/* Adds a packet the flow's packet chain */
int add_packet(flow *f, struct packet_info *info){
	packet *new_packet = malloc(sizeof(packet));

	if (info->tcp_hdr == NULL){
		return 0;
	}

	new_packet->seq_num = htonl(info->tcp_hdr->sequence_num);
	new_packet->len = info->app_data_len;
	new_packet->data = info->app_data;
	new_packet->data_len = new_packet->len;
	new_packet->next = NULL;
	new_packet->incoming = 
		(info->ip_hdr->src.s_addr == f->src_ip.s_addr) ? 0 : 1;

	/* Find appropriate place in chain */
	if(new_packet->data_len > 0){
		packet *previous = NULL;
		packet *next = f->packet_chain;
		while(next != NULL && (next->seq_num <= new_packet->seq_num)){
			previous = next;
			next = next->next;
		}

		//place packet after current
		if(previous == NULL){
			//goes at the beginning of chain
			new_packet->next = f->packet_chain;
			f->packet_chain = new_packet;
		} else {
			new_packet->next = next;
			previous->next = new_packet;
		}

	}
	
	return 0;

}