linux/net/ipv4/netfilter/nf_nat_snmp_basic_main.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * 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).
 *
 * Author: James Morris <[email protected]>
 *
 * Copyright (c) 2006-2010 Patrick McHardy <[email protected]>
 */
#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 <linux/netfilter/nf_conntrack_snmp.h>
#include "nf_nat_snmp_basic.asn1.h"

MODULE_LICENSE(…) …;
MODULE_AUTHOR(…) …;
MODULE_DESCRIPTION(…) …;
MODULE_ALIAS(…) …;
MODULE_ALIAS_NFCT_HELPER(…) …;

#define SNMP_PORT …
#define SNMP_TRAP_PORT …

static DEFINE_SPINLOCK(snmp_lock);

struct snmp_ctx { … };

static void fast_csum(struct snmp_ctx *ctx, unsigned char offset)
{ … }

int snmp_version(void *context, size_t hdrlen, unsigned char tag,
		 const void *data, size_t datalen)
{ … }

int snmp_helper(void *context, size_t hdrlen, unsigned char tag,
		const void *data, size_t datalen)
{ … }

static int snmp_translate(struct nf_conn *ct, int dir, struct sk_buff *skb)
{ … }

/* We don't actually set up expectations, just adjust internal IP
 * addresses if this is being NATted
 */
static int help(struct sk_buff *skb, unsigned int protoff,
		struct nf_conn *ct,
		enum ip_conntrack_info ctinfo)
{ … }

static const struct nf_conntrack_expect_policy snmp_exp_policy = …;

static struct nf_conntrack_helper snmp_trap_helper __read_mostly = …;

static int __init nf_nat_snmp_basic_init(void)
{ … }

static void __exit nf_nat_snmp_basic_fini(void)
{ … }

module_init(…) …;
module_exit(nf_nat_snmp_basic_fini);