/*
* nf_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 <jmorris@intercode.com.au>
*/
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/udp.h>
#include <net/checksum.h>
#include <net/udp.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_nat_helper.h>
MODULE_LICENSE("GPL");
MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
MODULE_DESCRIPTION("Basic SNMP Application Layer Gateway");
MODULE_ALIAS("ip_nat_snmp_basic");
#define SNMP_PORT 161
#define SNMP_TRAP_PORT 162
#define NOCT1(n) (*(u8 *)(n))
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
{