ip_nat_snmp_basic.c

linux-2.6.15.6

	
	x =~ x & 0xFFFF;
	csum[0] = x / 256;
	csum[1] = x & 0xFF;
}

/* 
 * Mangle IP address.
 * 	- begin points to the start of the snmp messgae
 *      - addr points to the start of the address
 */
static inline void mangle_address(unsigned char *begin,
                                  unsigned char *addr,
                                  const struct oct1_map *map,
                                  u_int16_t *check)
{
	if (map->from == NOCT1(*addr)) {
		u_int32_t old;
		
		if (debug)
			memcpy(&old, (unsigned char *)addr, sizeof(old));
			
		*addr = map->to;
		
		/* Update UDP checksum if being used */
		if (*check) {
			unsigned char odd = !((addr - begin) % 2);
			
			fast_csum((unsigned char *)check,
			          &map->from, &map->to, odd);
			          
		}
		
		if (debug)
			printk(KERN_DEBUG "bsalg: mapped %u.%u.%u.%u to "
			       "%u.%u.%u.%u\n", NIPQUAD(old), NIPQUAD(*addr));
	}
}

static unsigned char snmp_trap_decode(struct asn1_ctx *ctx,
                                      struct snmp_v1_trap *trap,
                                      const struct oct1_map *map,
                                      u_int16_t *check)
{
	unsigned int cls, con, tag, len;
	unsigned char *end;

	if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
		return 0;
		
	if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
		return 0;
	
	if (!asn1_oid_decode(ctx, end, &trap->id, &trap->id_len))
		return 0;
		
	if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
		goto err_id_free;

	if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_IPA) ||
	      (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_OTS)))
		goto err_id_free;
	
	if (!asn1_octets_decode(ctx, end, (unsigned char **)&trap->ip_address, &len))
		goto err_id_free;
	
	/* IPv4 only */
	if (len != 4)
		goto err_addr_free;
	
	mangle_address(ctx->begin, ctx->pointer - 4, map, check);
	
	if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
		goto err_addr_free;
		
	if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
		goto err_addr_free;
		
	if (!asn1_uint_decode(ctx, end, &trap->general))
		goto err_addr_free;
		
	if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
		goto err_addr_free;
	
	if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
		goto err_addr_free;
		
	if (!asn1_uint_decode(ctx, end, &trap->specific))
		goto err_addr_free;
		
	if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
		goto err_addr_free;
		
	if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_TIT) ||
	      (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_INT)))
		goto err_addr_free;
		
	if (!asn1_ulong_decode(ctx, end, &trap->time))
		goto err_addr_free;
		
	return 1;

err_id_free:
	kfree(trap->id);

err_addr_free:
	kfree((unsigned long *)trap->ip_address);
	
	return 0;
}

/*****************************************************************************
 *
 * Misc. routines
 *
 *****************************************************************************/

static void hex_dump(unsigned char *buf, size_t len)
{
	size_t i;
	
	for (i = 0; i < len; i++) {
		if (i && !(i % 16))
			printk("\n");
		printk("%02x ", *(buf + i));
	}
	printk("\n");
}

/*
 * Parse and mangle SNMP message according to mapping.
 * (And this is the fucking 'basic' method).
 */
static int snmp_parse_mangle(unsigned char *msg,
                             u_int16_t len,
                             const struct oct1_map *map,
                             u_int16_t *check)
{
	unsigned char *eoc, *end;
	unsigned int cls, con, tag, vers, pdutype;
	struct asn1_ctx ctx;
	struct asn1_octstr comm;
	struct snmp_object **obj;
	
	if (debug > 1)
		hex_dump(msg, len);

	asn1_open(&ctx, msg, len);
	
	/* 
	 * Start of SNMP message.
	 */
	if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
		return 0;
	if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
		return 0;
	
	/* 
	 * Version 1 or 2 handled.
	 */
	if (!asn1_header_decode(&ctx, &end, &cls, &con, &tag))
		return 0;
	if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
		return 0;
	if (!asn1_uint_decode (&ctx, end, &vers))
		return 0;
	if (debug > 1)
		printk(KERN_DEBUG "bsalg: snmp version: %u\n", vers + 1);
	if (vers > 1)
		return 1;
	
	/*
	 * Community.
	 */
	if (!asn1_header_decode (&ctx, &end, &cls, &con, &tag))
		return 0;
	if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OTS)
		return 0;
	if (!asn1_octets_decode(&ctx, end, &comm.data, &comm.len))
		return 0;
	if (debug > 1) {
		unsigned int i;
		
		printk(KERN_DEBUG "bsalg: community: ");
		for (i = 0; i < comm.len; i++)
			printk("%c", comm.data[i]);
		printk("\n");
	}
	kfree(comm.data);
	
	/*
	 * PDU type
	 */
	if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &pdutype))
		return 0;
	if (cls != ASN1_CTX || con != ASN1_CON)
		return 0;
	if (debug > 1) {
		unsigned char *pdus[] = {
			[SNMP_PDU_GET] = "get",
			[SNMP_PDU_NEXT] = "get-next",
			[SNMP_PDU_RESPONSE] = "response",
			[SNMP_PDU_SET] = "set",
			[SNMP_PDU_TRAP1] = "trapv1",
			[SNMP_PDU_BULK] = "bulk",
			[SNMP_PDU_INFORM] = "inform",
			[SNMP_PDU_TRAP2] = "trapv2"
		};
		
		if (pdutype > SNMP_PDU_TRAP2)
			printk(KERN_DEBUG "bsalg: bad pdu type %u\n", pdutype);
		else
			printk(KERN_DEBUG "bsalg: pdu: %s\n", pdus[pdutype]);
	}
	if (pdutype != SNMP_PDU_RESPONSE &&
	    pdutype != SNMP_PDU_TRAP1 && pdutype != SNMP_PDU_TRAP2)
		return 1;
	
	/*
	 * Request header or v1 trap
	 */
	if (pdutype == SNMP_PDU_TRAP1) {
		struct snmp_v1_trap trap;
		unsigned char ret = snmp_trap_decode(&ctx, &trap, map, check);
		
		/* Discard trap allocations regardless */
		kfree(trap.id);
		kfree((unsigned long *)trap.ip_address);
		
		if (!ret)
			return ret;
		
	} else {
		struct snmp_request req;
		
		if (!snmp_request_decode(&ctx, &req))
			return 0;
			
		if (debug > 1)
			printk(KERN_DEBUG "bsalg: request: id=0x%lx error_status=%u "
			"error_index=%u\n", req.id, req.error_status,
			req.error_index);
	}
	
	/*
	 * Loop through objects, look for IP addresses to mangle.
	 */
	if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
		return 0;
		
	if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
		return 0;
	
	obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
	if (obj == NULL) {
		if (net_ratelimit())
			printk(KERN_WARNING "OOM in bsalg(%d)\n", __LINE__);
		return 0;	
	}

	while (!asn1_eoc_decode(&ctx, eoc)) {
		unsigned int i;
		
		if (!snmp_object_decode(&ctx, obj)) {
			if (*obj) {
				kfree((*obj)->id);
				kfree(*obj);
			}	
			kfree(obj);
			return 0;
		}

		if (debug > 1) {
			printk(KERN_DEBUG "bsalg: object: ");
			for (i = 0; i < (*obj)->id_len; i++) {
				if (i > 0)
					printk(".");
				printk("%lu", (*obj)->id[i]);
			}
			printk(": type=%u\n", (*obj)->type);
			
		}

		if ((*obj)->type == SNMP_IPADDR)
			mangle_address(ctx.begin, ctx.pointer - 4 , map, check);
		
		kfree((*obj)->id);
		kfree(*obj);
	}
	kfree(obj);
	
	if (!asn1_eoc_decode(&ctx, eoc))
		return 0;
		
	return 1;
}

/*****************************************************************************
 *
 * NAT routines.
 *
 *****************************************************************************/

/* 
 * SNMP translation routine.
 */
static int snmp_translate(struct ip_conntrack *ct,
                          enum ip_conntrack_info ctinfo,
                          struct sk_buff **pskb)
{
	struct iphdr *iph = (*pskb)->nh.iph;
	struct udphdr *udph = (struct udphdr *)((u_int32_t *)iph + iph->ihl);
	u_int16_t udplen = ntohs(udph->len);
	u_int16_t paylen = udplen - sizeof(struct udphdr);
	int dir = CTINFO2DIR(ctinfo);
	struct oct1_map map;

	/*
	 * Determine mappping for application layer addresses based
	 * on NAT manipulations for the packet.
	 */
	if (dir == IP_CT_DIR_ORIGINAL) {
		/* SNAT traps */
		map.from = NOCT1(ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip);
		map.to = NOCT1(ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.ip);
	} else {
		/* DNAT replies */
		map.from = NOCT1(ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.ip);
		map.to = NOCT1(ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.ip);
	}
	
	if (map.from == map.to)
		return NF_ACCEPT;
	
	if (!snmp_parse_mangle((unsigned char *)udph + sizeof(struct udphdr),
	                       paylen, &map, &udph->check)) {
		if (net_ratelimit())
			printk(KERN_WARNING "bsalg: parser failed\n");
		return NF_DROP;
	}
	return NF_ACCEPT;
}

/* We don't actually set up expectations, just adjust internal IP
 * addresses if this is being NATted */
static int help(struct sk_buff **pskb,
		struct ip_conntrack *ct,
		enum ip_conntrack_info ctinfo)
{
	int dir = CTINFO2DIR(ctinfo);
	unsigned int ret;
	struct iphdr *iph = (*pskb)->nh.iph;
	struct udphdr *udph = (struct udphdr *)((u_int32_t *)iph + iph->ihl);

	/* SNMP replies and originating SNMP traps get mangled */
	if (udph->source == ntohs(SNMP_PORT) && dir != IP_CT_DIR_REPLY)
		return NF_ACCEPT;
	if (udph->dest == ntohs(SNMP_TRAP_PORT) && dir != IP_CT_DIR_ORIGINAL)
		return NF_ACCEPT;

	/* No NAT? */
	if (!(ct->status & IPS_NAT_MASK))
		return NF_ACCEPT;

	/* 
	 * Make sure the packet length is ok.  So far, we were only guaranteed
	 * to have a valid length IP header plus 8 bytes, which means we have
	 * enough room for a UDP header.  Just verify the UDP length field so we
	 * can mess around with the payload.
	 */
	if (ntohs(udph->len) != (*pskb)->len - (iph->ihl << 2)) {
		 if (net_ratelimit())
			 printk(KERN_WARNING "SNMP: dropping malformed packet "
				"src=%u.%u.%u.%u dst=%u.%u.%u.%u\n",
				NIPQUAD(iph->saddr), NIPQUAD(iph->daddr));
		 return NF_DROP;
	}

	if (!skb_make_writable(pskb, (*pskb)->len))
		return NF_DROP;

	spin_lock_bh(&snmp_lock);
	ret = snmp_translate(ct, ctinfo, pskb);
	spin_unlock_bh(&snmp_lock);
	return ret;
}

static struct ip_conntrack_helper snmp_helper = {
	.max_expected = 0,
	.timeout = 180,
	.me = THIS_MODULE,
	.help = help,
	.name = "snmp",

	.tuple = { .src = { .u = { __constant_htons(SNMP_PORT) } },
		   .dst = { .protonum = IPPROTO_UDP },
	},
	.mask = { .src = { .u = { 0xFFFF } },
		 .dst = { .protonum = 0xFF },
	},
};

static struct ip_conntrack_helper snmp_trap_helper = {
	.max_expected = 0,
	.timeout = 180,
	.me = THIS_MODULE,
	.help = help,
	.name = "snmp_trap",

	.tuple = { .src = { .u = { __constant_htons(SNMP_TRAP_PORT) } },
		   .dst = { .protonum = IPPROTO_UDP },
	},
	.mask = { .src = { .u = { 0xFFFF } },
		 .dst = { .protonum = 0xFF },
	},
};

/*****************************************************************************
 *
 * Module stuff.
 *
 *****************************************************************************/
 
static int __init init(void)
{
	int ret = 0;

	ret = ip_conntrack_helper_register(&snmp_helper);
	if (ret < 0)
		return ret;
	ret = ip_conntrack_helper_register(&snmp_trap_helper);
	if (ret < 0) {
		ip_conntrack_helper_unregister(&snmp_helper);
		return ret;
	}
	return ret;
}

static void __exit fini(void)
{
	ip_conntrack_helper_unregister(&snmp_helper);
	ip_conntrack_helper_unregister(&snmp_trap_helper);
}

module_init(init);
module_exit(fini);

module_param(debug, bool, 0600);