ip_nat_snmp_basic.c

linux-2.6.15.6

/*
 * ip_nat_snmp_basic.c
 *
 * Basic SNMP Application Layer Gateway
 *
 * This IP NAT module is intended for use with SNMP network 
 * discovery and monitoring applications where target networks use 
 * conflicting private address realms.
 *
 * Static NAT is used to remap the networks from the view of the network 
 * management system at the IP layer, and this module remaps some application
 * layer addresses to match.
 *
 * The simplest form of ALG is performed, where only tagged IP addresses
 * are modified.  The module does not need to be MIB aware and only scans
 * messages at the ASN.1/BER level.
 *
 * Currently, only SNMPv1 and SNMPv2 are supported.
 *
 * More information on ALG and associated issues can be found in
 * RFC 2962
 *
 * The ASB.1/BER parsing code is derived from the gxsnmp package by Gregory 
 * McLean & Jochen Friedrich, stripped down for use in the kernel.
 *
 * Copyright (c) 2000 RP Internet (www.rpi.net.au).
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
 *
 * Author: James Morris <[e-mail]>
 *
 * Updates:
 * 2000-08-06: Convert to new helper API (Harald Welte).
 *
 */
#include <linux/config.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/moduleparam.h>
#include <linux/netfilter_ipv4.h>
#include <linux/netfilter_ipv4/ip_nat.h>
#include <linux/netfilter_ipv4/ip_conntrack_helper.h>
#include <linux/netfilter_ipv4/ip_nat_helper.h>
#include <linux/ip.h>
#include <net/checksum.h>
#include <net/udp.h>
#include <asm/uaccess.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("James Morris <[e-mail]>");
MODULE_DESCRIPTION("Basic SNMP Application Layer Gateway");

#define SNMP_PORT 161
#define SNMP_TRAP_PORT 162
#define NOCT1(n) (u_int8_t )((n) & 0xff)

static int debug;
static DEFINE_SPINLOCK(snmp_lock);

/* 
 * Application layer address mapping mimics the NAT mapping, but 
 * only for the first octet in this case (a more flexible system
 * can be implemented if needed).
 */
struct oct1_map
{
	u_int8_t from;
	u_int8_t to;
};

                                  
/*****************************************************************************
 *
 * Basic ASN.1 decoding routines (gxsnmp author Dirk Wisse)
 *
 *****************************************************************************/

/* Class */
#define ASN1_UNI	0	/* Universal */
#define ASN1_APL	1	/* Application */
#define ASN1_CTX	2	/* Context */
#define ASN1_PRV	3	/* Private */

/* Tag */
#define ASN1_EOC	0	/* End Of Contents */
#define ASN1_BOL	1	/* Boolean */
#define ASN1_INT	2	/* Integer */
#define ASN1_BTS	3	/* Bit String */
#define ASN1_OTS	4	/* Octet String */
#define ASN1_NUL	5	/* Null */
#define ASN1_OJI	6	/* Object Identifier  */
#define ASN1_OJD	7	/* Object Description */
#define ASN1_EXT	8	/* External */
#define ASN1_SEQ	16	/* Sequence */
#define ASN1_SET	17	/* Set */
#define ASN1_NUMSTR	18	/* Numerical String */
#define ASN1_PRNSTR	19	/* Printable String */
#define ASN1_TEXSTR	20	/* Teletext String */
#define ASN1_VIDSTR	21	/* Video String */
#define ASN1_IA5STR	22	/* IA5 String */
#define ASN1_UNITIM	23	/* Universal Time */
#define ASN1_GENTIM	24	/* General Time */
#define ASN1_GRASTR	25	/* Graphical String */
#define ASN1_VISSTR	26	/* Visible String */
#define ASN1_GENSTR	27	/* General String */

/* Primitive / Constructed methods*/
#define ASN1_PRI	0	/* Primitive */
#define ASN1_CON	1	/* Constructed */

/*
 * Error codes.
 */
#define ASN1_ERR_NOERROR		0
#define ASN1_ERR_DEC_EMPTY		2
#define ASN1_ERR_DEC_EOC_MISMATCH	3
#define ASN1_ERR_DEC_LENGTH_MISMATCH	4
#define ASN1_ERR_DEC_BADVALUE		5

/* 
 * ASN.1 context.
 */
struct asn1_ctx
{
	int error;			/* Error condition */
	unsigned char *pointer;		/* Octet just to be decoded */
	unsigned char *begin;		/* First octet */
	unsigned char *end;		/* Octet after last octet */
};

/*
 * Octet string (not null terminated)
 */
struct asn1_octstr
{
	unsigned char *data;
	unsigned int len;
};
	
static void asn1_open(struct asn1_ctx *ctx,
                      unsigned char *buf,
                      unsigned int len)
{
	ctx->begin = buf;
	ctx->end = buf + len;
	ctx->pointer = buf;
	ctx->error = ASN1_ERR_NOERROR;
}

static unsigned char asn1_octet_decode(struct asn1_ctx *ctx, unsigned char *ch)
{
	if (ctx->pointer >= ctx->end) {
		ctx->error = ASN1_ERR_DEC_EMPTY;
		return 0;
	}
	*ch = *(ctx->pointer)++;
	return 1;
}

static unsigned char asn1_tag_decode(struct asn1_ctx *ctx, unsigned int *tag)
{
	unsigned char ch;
	
	*tag = 0;
	
	do
	{
		if (!asn1_octet_decode(ctx, &ch))
			return 0;
		*tag <<= 7;
		*tag |= ch & 0x7F;
	} while ((ch & 0x80) == 0x80);
	return 1;
}

static unsigned char asn1_id_decode(struct asn1_ctx *ctx, 
                                    unsigned int *cls,
                                    unsigned int *con,
                                    unsigned int *tag)
{
	unsigned char ch;
	
	if (!asn1_octet_decode(ctx, &ch))
		return 0;
		
	*cls = (ch & 0xC0) >> 6;
	*con = (ch & 0x20) >> 5;
	*tag = (ch & 0x1F);
	
	if (*tag == 0x1F) {
		if (!asn1_tag_decode(ctx, tag))
			return 0;
	}
	return 1;
}

static unsigned char asn1_length_decode(struct asn1_ctx *ctx,
                                        unsigned int *def,
                                        unsigned int *len)
{
	unsigned char ch, cnt;
	
	if (!asn1_octet_decode(ctx, &ch))
		return 0;
		
	if (ch == 0x80)
		*def = 0;
	else {
		*def = 1;
		
		if (ch < 0x80)
			*len = ch;
		else {
			cnt = (unsigned char) (ch & 0x7F);
			*len = 0;
			
			while (cnt > 0) {
				if (!asn1_octet_decode(ctx, &ch))
					return 0;
				*len <<= 8;
				*len |= ch;
				cnt--;
			}
		}
	}
	return 1;
}

static unsigned char asn1_header_decode(struct asn1_ctx *ctx,
                                        unsigned char **eoc,
                                        unsigned int *cls,
                                        unsigned int *con,
                                        unsigned int *tag)
{
	unsigned int def, len;
	
	if (!asn1_id_decode(ctx, cls, con, tag))
		return 0;
		
	if (!asn1_length_decode(ctx, &def, &len))
		return 0;
		
	if (def)
		*eoc = ctx->pointer + len;
	else
		*eoc = NULL;
	return 1;
}

static unsigned char asn1_eoc_decode(struct asn1_ctx *ctx, unsigned char *eoc)
{
	unsigned char ch;
	
	if (eoc == 0) {
		if (!asn1_octet_decode(ctx, &ch))
			return 0;
			
		if (ch != 0x00) {
			ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
			return 0;
		}
		
		if (!asn1_octet_decode(ctx, &ch))
			return 0;
			
		if (ch != 0x00) {
			ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
			return 0;
		}
		return 1;
	} else {
		if (ctx->pointer != eoc) {
			ctx->error = ASN1_ERR_DEC_LENGTH_MISMATCH;
			return 0;
		}
		return 1;
	}
}

static unsigned char asn1_null_decode(struct asn1_ctx *ctx, unsigned char *eoc)
{
	ctx->pointer = eoc;
	return 1;
}

static unsigned char asn1_long_decode(struct asn1_ctx *ctx,
                                      unsigned char *eoc,
                                      long *integer)
{
	unsigned char ch;
	unsigned int  len;
	
	if (!asn1_octet_decode(ctx, &ch))
		return 0;
		
	*integer = (signed char) ch;
	len = 1;
	
	while (ctx->pointer < eoc) {
		if (++len > sizeof (long)) {
			ctx->error = ASN1_ERR_DEC_BADVALUE;
			return 0;
		}
		
		if (!asn1_octet_decode(ctx, &ch))
			return 0;
			
		*integer <<= 8;
		*integer |= ch;
	}
	return 1;
}

static unsigned char asn1_uint_decode(struct asn1_ctx *ctx,
                                      unsigned char *eoc,
                                      unsigned int *integer)
{
	unsigned char ch;
	unsigned int  len;
	
	if (!asn1_octet_decode(ctx, &ch))
		return 0;
		
	*integer = ch;
	if (ch == 0) len = 0;
	else len = 1;
	
	while (ctx->pointer < eoc) {
		if (++len > sizeof (unsigned int)) {
			ctx->error = ASN1_ERR_DEC_BADVALUE;
			return 0;
		}
		
		if (!asn1_octet_decode(ctx, &ch))
			return 0;
			
		*integer <<= 8;
		*integer |= ch;
	}
	return 1;
}

static unsigned char asn1_ulong_decode(struct asn1_ctx *ctx,
                                       unsigned char *eoc,
                                       unsigned long *integer)
{
	unsigned char ch;
	unsigned int  len;
	
	if (!asn1_octet_decode(ctx, &ch))
		return 0;
		
	*integer = ch;
	if (ch == 0) len = 0;
	else len = 1;
	
	while (ctx->pointer < eoc) {
		if (++len > sizeof (unsigned long)) {
			ctx->error = ASN1_ERR_DEC_BADVALUE;
			return 0;
		}
		
		if (!asn1_octet_decode(ctx, &ch))
			return 0;
			
		*integer <<= 8;
		*integer |= ch;
	}
	return 1;
}

static unsigned char asn1_octets_decode(struct asn1_ctx *ctx,
                                        unsigned char *eoc,
                                        unsigned char **octets,
                                        unsigned int *len)
{
	unsigned char *ptr;
	
	*len = 0;
	
	*octets = kmalloc(eoc - ctx->pointer, GFP_ATOMIC);
	if (*octets == NULL) {
		if (net_ratelimit())
			printk("OOM in bsalg (%d)\n", __LINE__);
		return 0;
	}
	
	ptr = *octets;
	while (ctx->pointer < eoc) {
		if (!asn1_octet_decode(ctx, (unsigned char *)ptr++)) {
			kfree(*octets);
			*octets = NULL;
			return 0;
		}
		(*len)++;
	}
	return 1;
}

static unsigned char asn1_subid_decode(struct asn1_ctx *ctx,
                                       unsigned long *subid)
{
	unsigned char ch;
	
	*subid = 0;
	
	do {
		if (!asn1_octet_decode(ctx, &ch))
			return 0;
		
		*subid <<= 7;
		*subid |= ch & 0x7F;
	} while ((ch & 0x80) == 0x80);
	return 1;
}

static unsigned char asn1_oid_decode(struct asn1_ctx *ctx,
                                     unsigned char *eoc,
                                     unsigned long **oid,
                                     unsigned int *len)
{
	unsigned long subid;
	unsigned int  size;
	unsigned long *optr;
	
	size = eoc - ctx->pointer + 1;
	*oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);
	if (*oid == NULL) {
		if (net_ratelimit())
			printk("OOM in bsalg (%d)\n", __LINE__);
		return 0;
	}
	
	optr = *oid;
	
	if (!asn1_subid_decode(ctx, &subid)) {
		kfree(*oid);
		*oid = NULL;