ars.c

VC＋＋源代码

/* Copyright (C) 2000,2001 Salvatore Sanfilippo <[e-mail]>
 * See the LICENSE file for more information.
 * 
 * TODO:
 * o Functions to add addresses and timestamps for some IP and TCP option
 * o IGMP support
 * o DNS support
 * o ARS add_build_layer() facility and Co., read the PROPOSAL file.
 */

/* $Id: ars.c,v 1.4 2003/07/28 09:00:54 njombart Exp $ */

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>
#include <sys/types.h>

#ifndef WIN32
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#else
#include <winsock2.h>
#include <ws2tcpip.h>
#endif

#include <unistd.h>
#include "ars.h"

/* prototypes */
int ars_compiler_ip(struct ars_packet *pkt, int layer);
int ars_compiler_ipopt(struct ars_packet *pkt, int layer);
int ars_compiler_tcp(struct ars_packet *pkt, int layer);
int ars_compiler_tcpopt(struct ars_packet *pkt, int layer);
int ars_compiler_udp(struct ars_packet *pkt, int layer);
int ars_compiler_icmp(struct ars_packet *pkt, int layer);
int ars_compiler_abort(struct ars_packet *pkt, int layer) { return 0; }

/* Initialize a packets context:
 * must be called before to work with the packet's layers */
int ars_init(struct ars_packet *pkt)
{
	int j;

	pkt->p_error = NULL;
	pkt->p_layer_nr = 0;
	for (j = 0; j < ARS_MAX_LAYER; j++) {
		pkt->p_layer[j].l_size = 0;
		pkt->p_layer[j].l_flags = 0;
		pkt->p_layer[j].l_type = ARS_TYPE_NULL;
		pkt->p_layer[j].l_data = NULL;
		pkt->p_layer[j].l_packet = pkt;
	}
	for (j = 0; j < ARS_TYPE_SIZE; j++)
		pkt->p_default[j] = NULL;
	return -ARS_OK;
}

/* Destroy (free the allocated memory) a packet context */
int ars_destroy(struct ars_packet *pkt)
{
	int j;

	free(pkt->p_error);
	for (j = 0; j < ARS_MAX_LAYER; j++) {
		if (pkt->p_layer[j].l_type != ARS_TYPE_NULL &&
		    pkt->p_layer[j].l_data != NULL)
			free(pkt->p_layer[j].l_data);
	}
	return ars_init(pkt); /* Re-initialize it */
}

/* THe out of memory message must be statically allocated */
char *ars_error_nomem = "Out of memory";

/* Set the error description */
int ars_set_error(struct ars_packet *pkt, char *error)
{
	if (pkt == NULL)
		return -ARS_OK;

	free(pkt->p_error); /* p_error is initialized to NULL */
	if ((pkt->p_error = strdup(error)) == NULL) {
		/* To put the error description for the -KO_NOMEM
		 * error we needs a statically allocated error message:
		 * Note that all other functions don't need to report
		 * a statically allocated error message for -KO_NOMEM
		 * it will be auto-selected if strdup() returns NULL */
		pkt->p_error = ars_error_nomem;
	}
	return -ARS_OK; /* report anyway success */
}

/* Set the default for a layer */
int ars_set_default(struct ars_packet *pkt, int layer_type, void *def)
{
	pkt->p_default[layer_type] = def;
	return -ARS_OK;
}

/* return nonzero if the packet is full */
int ars_nospace(struct ars_packet *pkt)
{
	return (pkt->p_layer_nr == ARS_MAX_LAYER);
}

/* Check if the layer number is valid */
int ars_valid_layer(int layer)
{
	if (layer < 0 || layer >= ARS_MAX_LAYER)
		return -ARS_INVALID;
	return -ARS_OK;
}

/* Add an a generic layer */
int ars_add_generic(struct ars_packet *pkt, size_t size, int type)
{
	int layer;

	if (ars_nospace(pkt)) {
		ars_set_error(pkt, "No space for the next layer");
		return -ARS_NOSPACE;
	}
	layer = pkt->p_layer_nr;
	/* You may want to create a 0 len layer and then realloc */
	if (size != 0) {
		pkt->p_layer[layer].l_data = malloc(size);
		if (pkt->p_layer[layer].l_data == NULL) {
			ars_set_error(pkt, "Out of memory adding a new layer");
			return -ARS_NOMEM;
		}
		memset(pkt->p_layer[layer].l_data, 0, size);
		/* Copy the default if any */
		if (pkt->p_default[type] != NULL) {
			memcpy(pkt->p_layer[layer].l_data,
			       pkt->p_default[type], size);
		}
	}
	pkt->p_layer[layer].l_type = type;
	pkt->p_layer[layer].l_size = size;
	return -ARS_OK;
}

/* Add an IP layer */
void *ars_add_iphdr(struct ars_packet *pkt, int unused)
{
	int retval;

	retval = ars_add_generic(pkt, sizeof(struct ars_iphdr), ARS_TYPE_IP);
	if (retval != -ARS_OK)
		return NULL;
	pkt->p_layer_nr++;
	return pkt->p_layer[pkt->p_layer_nr-1].l_data;
}

/* Add on IP option */
void *ars_add_ipopt(struct ars_packet *pkt, int option)
{
	int retval;
	struct ars_ipopt *ipopt;
	int opt_len;

	switch(option) {
	case ARS_IPOPT_END:
	case ARS_IPOPT_NOOP:
		opt_len = 1;
		break;
	case ARS_IPOPT_SEC:
		opt_len = 11;
		break;
	case ARS_IPOPT_SID:
		opt_len = 4;
		break;
	case ARS_IPOPT_LSRR:
	case ARS_IPOPT_SSRR:
	case ARS_IPOPT_RR:
	case ARS_IPOPT_TIMESTAMP:
		/* We allocate the max (40 bytes) but the real layer size
		 * may be modified by ars_ipopt_set*() functions */
		opt_len = 40;
		break;
	default:
		return NULL; /* Unsupported option */
		break;
	}

	retval = ars_add_generic(pkt, opt_len, ARS_TYPE_IPOPT);
	if (retval != -ARS_OK)
		return NULL;
	ipopt = pkt->p_layer[pkt->p_layer_nr].l_data;
	pkt->p_layer_nr++;

	ipopt->kind = option;
	ipopt->len = opt_len; /* the default, can be modified inside switch() */
	/* Perform some special operation for some option */
	switch(option) {
	case ARS_IPOPT_LSRR: /* ars_ipopt_setls() will change some field */
	case ARS_IPOPT_SSRR: /* ars_ipopt_setss() will change some field */
	case ARS_IPOPT_RR:   /* ars_ipopt_setrr() will change some field */
		/* RFC 791 needs the roomlen - 3 octects, so the gateways
		 * can compare len and ptr to check for room.
		 * Try to break this to stress lame TCP/IP implementation */
		ipopt->len = opt_len - 2 - 3;
		ipopt->un.rr.ptr = 4;
		break;
	case ARS_IPOPT_TIMESTAMP:
		ipopt->un.tstamp.ptr = 5;
		ipopt->un.tstamp.flags = ARS_IPOPT_TS_TSONLY; /* default */
		break;
	}
	return ipopt;
}

/* Add a UDP layer */
void *ars_add_udphdr(struct ars_packet *pkt, int unused)
{
	int retval;

	retval = ars_add_generic(pkt, sizeof(struct ars_udphdr), ARS_TYPE_UDP);
	if (retval != -ARS_OK)
		return NULL;
	pkt->p_layer_nr++;
	return pkt->p_layer[pkt->p_layer_nr-1].l_data;
}

/* Add a TCP layer */
void *ars_add_tcphdr(struct ars_packet *pkt, int unused)
{
	int retval;

	retval = ars_add_generic(pkt, sizeof(struct ars_tcphdr), ARS_TYPE_TCP);
	if (retval != -ARS_OK)
		return NULL;
	pkt->p_layer_nr++;
	return pkt->p_layer[pkt->p_layer_nr-1].l_data;
}

/* Add TCP options */
void *ars_add_tcpopt(struct ars_packet *pkt, int option)
{
	int retval;
	struct ars_tcpopt *tcpopt;
	int opt_len;

	switch(option) {
	case ARS_TCPOPT_NOP:
	case ARS_TCPOPT_EOL:
		opt_len = 1;
		break;
	case ARS_TCPOPT_MAXSEG:
		opt_len = 4;
		break;
	case ARS_TCPOPT_WINDOW:
		opt_len = 3;
		break;
	case ARS_TCPOPT_SACK_PERM: /* ars_tcpopt_setsack() must change this */
	case ARS_TCPOPT_SACK:
		opt_len = 2;
		break;
	case ARS_TCPOPT_ECHOREQUEST:
	case ARS_TCPOPT_ECHOREPLY:
		opt_len = 6;
		break;
	case ARS_TCPOPT_TIMESTAMP:
		opt_len = 10;
		break;
	default:
		return NULL; /* Unsupported option */
		break;
	}

	retval = ars_add_generic(pkt, opt_len, ARS_TYPE_TCPOPT);
	if (retval != -ARS_OK)
		return NULL;
	tcpopt = pkt->p_layer[pkt->p_layer_nr].l_data;
	pkt->p_layer_nr++;

	tcpopt->kind = option;
	/* EOL and NOP lacks the len field */
	if (option != ARS_TCPOPT_EOL && option != ARS_TCPOPT_NOP)
		tcpopt->len = opt_len;

	/* Perform some special operation for the option */
	switch(option) {
	case ARS_TCPOPT_ECHOREQUEST:
	case ARS_TCPOPT_ECHOREPLY:
		memset(tcpopt->un.echo.info, 0, 4);
		break;
	case ARS_TCPOPT_TIMESTAMP:
		memset(tcpopt->un.timestamp.tsval, 0, 4);
		memset(tcpopt->un.timestamp.tsecr, 0, 4);
		break;
	}
	return tcpopt;
}

/* Add an ICMP layer */
void *ars_add_icmphdr(struct ars_packet *pkt, int unused)
{
	int retval;
	struct ars_icmphdr *icmp;

	retval = ars_add_generic(pkt, sizeof(struct ars_icmphdr),ARS_TYPE_ICMP);
	if (retval != -ARS_OK)
		return NULL;
	icmp = pkt->p_layer[pkt->p_layer_nr].l_data;
	pkt->p_layer_nr++;
	return (struct ars_icmphdr*) pkt->p_layer[pkt->p_layer_nr-1].l_data;
}

/* Add data, for IP-RAW, TCP, UDP, and so on */
void *ars_add_data(struct ars_packet *pkt, int size)
{
	int retval;
	void *boguspointer = "zzappt"; /* we can't return NULL for size == 0 */

	if (size < 0) {
		ars_set_error(pkt, "Tryed to add a DATA layer with size < 0");
		return NULL;
	}
	retval = ars_add_generic(pkt, size, ARS_TYPE_DATA);
	if (retval != -ARS_OK)
		return NULL;
	pkt->p_layer_nr++;
	if (size > 0)
		return pkt->p_layer[pkt->p_layer_nr-1].l_data;
	else
		return boguspointer;
}

/* Remove a layer */
int ars_remove_layer(struct ars_packet *pkt, int layer)
{
	if (layer == ARS_LAST_LAYER)
		layer = pkt->p_layer_nr -1;
	if (ars_valid_layer(layer) != -ARS_OK)
		return -ARS_INVALID;

	free(pkt->p_layer[layer].l_data); /* No problem if it's NULL */
	pkt->p_layer[layer].l_type = ARS_TYPE_NULL;
	pkt->p_layer[layer].l_size = 0;
	pkt->p_layer[layer].l_flags = 0;
	pkt->p_layer[layer].l_data = NULL;
	pkt->p_layer[layer].l_packet = pkt;
	return -ARS_OK;
}

/* Return the sum of the size of the specifed layer and of all the
 * following layers */
size_t ars_relative_size(struct ars_packet *pkt, int layer_nr)
{
	int j = layer_nr, rel_size = 0;

	while (j < ARS_MAX_LAYER && pkt->p_layer[j].l_type != ARS_TYPE_NULL) {
		rel_size += pkt->p_layer[j].l_size;
		j++;
	}
	return rel_size;
}

/* Just a short cut for ars_relative_size(), to get the total size */
size_t ars_packet_size(struct ars_packet *pkt)
{
	return ars_relative_size(pkt, 0);
}

/* from R. Stevens's Network Programming */
u_int16_t ars_cksum(void *vbuf, size_t nbytes)
{
	u_int16_t *buf = (u_int16_t*) vbuf;
	u_int32_t sum;
	u_int16_t oddbyte;

	sum = 0;
	while (nbytes > 1) {
		sum += *buf++;
		nbytes -= 2;
	}
	if (nbytes == 1) {
		oddbyte = 0;
		*((u_int16_t *) &oddbyte) = *(u_int8_t *) buf;
		sum += oddbyte;
	}
	sum = (sum >> 16) + (sum & 0xffff);
	sum += (sum >> 16);
	return (u_int16_t) ~sum;
}

/* Multiple buffers checksum facility */
u_int16_t ars_multi_cksum(struct mc_context *c, int op, void *vbuf,
							size_t nbytes)
{
	u_int16_t *buf = (u_int16_t*) vbuf;
	u_int32_t sum;
	u_int16_t oddbyte;
	void *tmp;

	if (op == ARS_MC_INIT) {
		c->oddbyte_flag = 0;
		c->old = 0;
		return -ARS_OK;
	} else if (op == ARS_MC_UPDATE) {
		if (c->oddbyte_flag) {
			u_int8_t *x = (u_int8_t*)&oddbyte;
			oddbyte = 0;
			*((u_int16_t *) &oddbyte) = c->oddbyte << 8;
			*((u_int16_t *) &oddbyte) |= *(u_int8_t *) buf;
			oddbyte = (x[0] << 8) | x[1]; /* fix endianess */
			c->old += oddbyte;
			nbytes--;
			c->oddbyte_flag = 0;
			/* We need to stay aligned -- bad slowdown, fix? */
			tmp = alloca(nbytes);
			memcpy(tmp, vbuf+1, nbytes);
			buf = tmp;
		}
		sum = c->old;
		while (nbytes > 1) {
			sum += *buf++;
			nbytes -= 2;
		}
		c->old = sum;
		if (nbytes == 1) {
			c->oddbyte = *(u_int8_t*) buf;
			c->oddbyte_flag++;
		}
		return -ARS_OK;
	} else if (op == ARS_MC_FINAL) {
		sum = c->old;
		if (c->oddbyte_flag == 1) {
			oddbyte = 0;
			*((u_int16_t *) &oddbyte) = c->oddbyte;
			sum += oddbyte;
		}
		sum = (sum >> 16) + (sum & 0xffff);
		sum += (sum >> 16);
		return (u_int16_t) ~sum;
	} else {
		assert("else reached in ars_multi_cksum()" == "");
	}
	return 0; /* unreached, here to prevent warnings */
}

/* The ARS compiler table is just a function pointers array:
 * For example to select the right function to compile an IP
 * layer use: ars_compiler[ARS_TYPE_IP](pkt, layer);
 * You can, of course, add your protocols and compilers:
 *
 * WARNING: take it syncronized with ars.h ARS_TYPE_* defines
 */
struct ars_layer_info ars_linfo[ARS_TYPE_SIZE] = {
	/* NAME			COMPILER		ID *
	 * ----                 --------                -- */
	{ "NULL",		ars_compiler_abort,	0 },
	{ "IP",			ars_compiler_ip,	1 },
	{ "IPOPT",		ars_compiler_ipopt,	2 },
	{ "ICMP",		ars_compiler_icmp,	3 },
	{ "UDP",		ars_compiler_udp,	4 },