nf_nat_snmp_basic.c

linux 内核源代码

	unsigned int cls, con, tag, len, idlen;
	unsigned short type;
	unsigned char *eoc, *end, *p;
	unsigned long *lp, *id;
	unsigned long ul;
	long l;

	*obj = NULL;
	id = NULL;

	if (!asn1_header_decode(ctx, &eoc, &cls, &con, &tag))
		return 0;

	if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
		return 0;

	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, &id, &idlen))
		return 0;

	if (!asn1_header_decode(ctx, &end, &cls, &con, &tag)) {
		kfree(id);
		return 0;
	}

	if (con != ASN1_PRI) {
		kfree(id);
		return 0;
	}

	type = 0;
	if (!snmp_tag_cls2syntax(tag, cls, &type)) {
		kfree(id);
		return 0;
	}

	l = 0;
	switch (type) {
		case SNMP_INTEGER:
			len = sizeof(long);
			if (!asn1_long_decode(ctx, end, &l)) {
				kfree(id);
				return 0;
			}
			*obj = kmalloc(sizeof(struct snmp_object) + len,
				       GFP_ATOMIC);
			if (*obj == NULL) {
				kfree(id);
				if (net_ratelimit())
					printk("OOM in bsalg (%d)\n", __LINE__);
				return 0;
			}
			(*obj)->syntax.l[0] = l;
			break;
		case SNMP_OCTETSTR:
		case SNMP_OPAQUE:
			if (!asn1_octets_decode(ctx, end, &p, &len)) {
				kfree(id);
				return 0;
			}
			*obj = kmalloc(sizeof(struct snmp_object) + len,
				       GFP_ATOMIC);
			if (*obj == NULL) {
				kfree(id);
				if (net_ratelimit())
					printk("OOM in bsalg (%d)\n", __LINE__);
				return 0;
			}
			memcpy((*obj)->syntax.c, p, len);
			kfree(p);
			break;
		case SNMP_NULL:
		case SNMP_NOSUCHOBJECT:
		case SNMP_NOSUCHINSTANCE:
		case SNMP_ENDOFMIBVIEW:
			len = 0;
			*obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
			if (*obj == NULL) {
				kfree(id);
				if (net_ratelimit())
					printk("OOM in bsalg (%d)\n", __LINE__);
				return 0;
			}
			if (!asn1_null_decode(ctx, end)) {
				kfree(id);
				kfree(*obj);
				*obj = NULL;
				return 0;
			}
			break;
		case SNMP_OBJECTID:
			if (!asn1_oid_decode(ctx, end, (unsigned long **)&lp, &len)) {
				kfree(id);
				return 0;
			}
			len *= sizeof(unsigned long);
			*obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
			if (*obj == NULL) {
				kfree(lp);
				kfree(id);
				if (net_ratelimit())
					printk("OOM in bsalg (%d)\n", __LINE__);
				return 0;
			}
			memcpy((*obj)->syntax.ul, lp, len);
			kfree(lp);
			break;
		case SNMP_IPADDR:
			if (!asn1_octets_decode(ctx, end, &p, &len)) {
				kfree(id);
				return 0;
			}
			if (len != 4) {
				kfree(p);
				kfree(id);
				return 0;
			}
			*obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
			if (*obj == NULL) {
				kfree(p);
				kfree(id);
				if (net_ratelimit())
					printk("OOM in bsalg (%d)\n", __LINE__);
				return 0;
			}
			memcpy((*obj)->syntax.uc, p, len);
			kfree(p);
			break;
		case SNMP_COUNTER:
		case SNMP_GAUGE:
		case SNMP_TIMETICKS:
			len = sizeof(unsigned long);
			if (!asn1_ulong_decode(ctx, end, &ul)) {
				kfree(id);
				return 0;
			}
			*obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
			if (*obj == NULL) {
				kfree(id);
				if (net_ratelimit())
					printk("OOM in bsalg (%d)\n", __LINE__);
				return 0;
			}
			(*obj)->syntax.ul[0] = ul;
			break;
		default:
			kfree(id);
			return 0;
	}

	(*obj)->syntax_len = len;
	(*obj)->type = type;
	(*obj)->id = id;
	(*obj)->id_len = idlen;

	if (!asn1_eoc_decode(ctx, eoc)) {
		kfree(id);
		kfree(*obj);
		*obj = NULL;
		return 0;
	}
	return 1;
}

static unsigned char snmp_request_decode(struct asn1_ctx *ctx,
					 struct snmp_request *request)
{
	unsigned int cls, con, tag;
	unsigned char *end;

	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_ulong_decode(ctx, end, &request->id))
		return 0;

	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, &request->error_status))
		return 0;

	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, &request->error_index))
		return 0;

	return 1;
}

/*
 * Fast checksum update for possibly oddly-aligned UDP byte, from the
 * code example in the draft.
 */
static void fast_csum(__sum16 *csum,
		      const unsigned char *optr,
		      const unsigned char *nptr,
		      int offset)
{
	unsigned char s[4];

	if (offset & 1) {
		s[0] = s[2] = 0;
		s[1] = ~*optr;
		s[3] = *nptr;
	} else {
		s[1] = s[3] = 0;
		s[0] = ~*optr;
		s[2] = *nptr;
	}

	*csum = csum_fold(csum_partial(s, 4, ~csum_unfold(*csum)));
}

/*
 * 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,
				  __sum16 *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) {
			fast_csum(check,
				  &map->from, &map->to, addr - begin);

		}

		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,
				      __sum16 *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_addr_free:
	kfree((unsigned long *)trap->ip_address);

err_id_free:
	kfree(trap->id);

	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,
			     __sum16 *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);

		if (ret) {
			kfree(trap.id);
			kfree((unsigned long *)trap.ip_address);
		} else
			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 nf_conn *ct,
			  enum ip_conntrack_info ctinfo,
			  struct sk_buff *skb)
{
	struct iphdr *iph = ip_hdr(skb);
	struct udphdr *udph = (struct udphdr *)((__be32 *)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[dir].tuple.src.u3.ip);
		map.to = NOCT1(&ct->tuplehash[!dir].tuple.dst.u3.ip);
	} else {
		/* DNAT replies */
		map.from = NOCT1(&ct->tuplehash[dir].tuple.src.u3.ip);
		map.to = NOCT1(&ct->tuplehash[!dir].tuple.dst.u3.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 *skb, unsigned int protoff,
		struct nf_conn *ct,
		enum ip_conntrack_info ctinfo)
{
	int dir = CTINFO2DIR(ctinfo);
	unsigned int ret;
	struct iphdr *iph = ip_hdr(skb);
	struct udphdr *udph = (struct udphdr *)((u_int32_t *)iph + iph->ihl);

	/* SNMP replies and originating SNMP traps get mangled */
	if (udph->source == htons(SNMP_PORT) && dir != IP_CT_DIR_REPLY)
		return NF_ACCEPT;
	if (udph->dest == htons(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) != skb->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(skb, skb->len))
		return NF_DROP;

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

static struct nf_conntrack_helper snmp_helper __read_mostly = {
	.max_expected		= 0,
	.timeout		= 180,
	.me			= THIS_MODULE,
	.help			= help,
	.name			= "snmp",
	.tuple.src.l3num	= AF_INET,
	.tuple.src.u.udp.port	= __constant_htons(SNMP_PORT),
	.tuple.dst.protonum	= IPPROTO_UDP,
};

static struct nf_conntrack_helper snmp_trap_helper __read_mostly = {
	.max_expected		= 0,
	.timeout		= 180,
	.me			= THIS_MODULE,
	.help			= help,
	.name			= "snmp_trap",
	.tuple.src.l3num	= AF_INET,
	.tuple.src.u.udp.port	= __constant_htons(SNMP_TRAP_PORT),
	.tuple.dst.protonum	= IPPROTO_UDP,
};

/*****************************************************************************
 *
 * Module stuff.
 *
 *****************************************************************************/

static int __init nf_nat_snmp_basic_init(void)
{
	int ret = 0;

	ret = nf_conntrack_helper_register(&snmp_helper);
	if (ret < 0)
		return ret;
	ret = nf_conntrack_helper_register(&snmp_trap_helper);
	if (ret < 0) {
		nf_conntrack_helper_unregister(&snmp_helper);
		return ret;
	}
	return ret;
}

static void __exit nf_nat_snmp_basic_fini(void)
{
	nf_conntrack_helper_unregister(&snmp_helper);
	nf_conntrack_helper_unregister(&snmp_trap_helper);
}

module_init(nf_nat_snmp_basic_init);
module_exit(nf_nat_snmp_basic_fini);

module_param(debug, int, 0600);