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/*
 * Copyright (C) 2013  Internet Systems Consortium, Inc. ("ISC")
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
 * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */


#ifndef DNS_RRL_H
#define DNS_RRL_H 1

/*
 * Rate limit DNS responses.
 */

#include <isc/lang.h>

#include <dns/fixedname.h>
#include <dns/rdata.h>
#include <dns/types.h>

ISC_LANG_BEGINDECLS


/*
 * Memory allocation or other failures.
 */
#define DNS_RRL_LOG_FAIL	ISC_LOG_WARNING
/*
 * dropped or slipped responses.
 */
#define DNS_RRL_LOG_DROP	ISC_LOG_INFO
/*
 * Major events in dropping or slipping.
 */
#define DNS_RRL_LOG_DEBUG1	ISC_LOG_DEBUG(3)
/*
 * Limit computations.
 */
#define DNS_RRL_LOG_DEBUG2	ISC_LOG_DEBUG(4)
/*
 * Even less interesting.
 */
#define DNS_RRL_LOG_DEBUG3	ISC_LOG_DEBUG(9)


#define DNS_RRL_LOG_ERR_LEN	64
#define DNS_RRL_LOG_BUF_LEN	(sizeof("would continue limiting") +	\
				 DNS_RRL_LOG_ERR_LEN +			\
				 sizeof(" responses to ") +		\
				 ISC_NETADDR_FORMATSIZE +		\
				 sizeof("/128 for IN ") +		\
				 DNS_RDATATYPE_FORMATSIZE +		\
				 DNS_NAME_FORMATSIZE)


typedef struct dns_rrl_hash dns_rrl_hash_t;

/*
 * Response types.
 */
typedef enum {
	DNS_RRL_RTYPE_FREE = 0,
	DNS_RRL_RTYPE_QUERY,
	DNS_RRL_RTYPE_REFERRAL,
	DNS_RRL_RTYPE_NODATA,
	DNS_RRL_RTYPE_NXDOMAIN,
	DNS_RRL_RTYPE_ERROR,
	DNS_RRL_RTYPE_ALL,
	DNS_RRL_RTYPE_TCP,
} dns_rrl_rtype_t;

/*
 * A rate limit bucket key.
 * This should be small to limit the total size of the database.
 * The hash of the qname should be wide enough to make the probability
 * of collisions among requests from a single IP address block less than 50%.
 * We need a 32-bit hash value for 10000 qps (e.g. random qnames forged
 * by attacker) to collide with legitimate qnames from the target with
 * probability at most 1%.
 */
#define DNS_RRL_MAX_PREFIX  64
typedef union dns_rrl_key dns_rrl_key_t;
union dns_rrl_key {
	struct {
		isc_uint32_t	    ip[DNS_RRL_MAX_PREFIX/32];
		isc_uint32_t	    qname_hash;
		dns_rdatatype_t	    qtype;
		isc_uint8_t         qclass;
		dns_rrl_rtype_t	    rtype   :4; /* 3 bits + sign bit */
		isc_boolean_t	    ipv6    :1;
	} s;
	isc_uint16_t	w[1];
};

/*
 * A rate-limit entry.
 * This should be small to limit the total size of the table of entries.
 */
typedef struct dns_rrl_entry dns_rrl_entry_t;
typedef ISC_LIST(dns_rrl_entry_t) dns_rrl_bin_t;
struct dns_rrl_entry {
	ISC_LINK(dns_rrl_entry_t) lru;
	ISC_LINK(dns_rrl_entry_t) hlink;
	dns_rrl_key_t	key;
# define DNS_RRL_RESPONSE_BITS	24
	signed int	responses   :DNS_RRL_RESPONSE_BITS;
# define DNS_RRL_QNAMES_BITS	8
	unsigned int	log_qname   :DNS_RRL_QNAMES_BITS;

# define DNS_RRL_TS_GEN_BITS	2
	unsigned int	ts_gen	    :DNS_RRL_TS_GEN_BITS;
	isc_boolean_t	ts_valid    :1;
# define DNS_RRL_HASH_GEN_BITS	1
	unsigned int	hash_gen    :DNS_RRL_HASH_GEN_BITS;
	isc_boolean_t	logged	    :1;
# define DNS_RRL_LOG_BITS	11
	unsigned int	log_secs    :DNS_RRL_LOG_BITS;

# define DNS_RRL_TS_BITS	12
	unsigned int	ts	    :DNS_RRL_TS_BITS;

# define DNS_RRL_MAX_SLIP	10
	unsigned int	slip_cnt    :4;
};

#define DNS_RRL_MAX_TIME_TRAVEL	5
#define DNS_RRL_FOREVER		(1<<DNS_RRL_TS_BITS)
#define DNS_RRL_MAX_TS		(DNS_RRL_FOREVER - 1)

#define DNS_RRL_MAX_RESPONSES	((1<<(DNS_RRL_RESPONSE_BITS-1))-1)
#define DNS_RRL_MAX_WINDOW	3600
#if DNS_RRL_MAX_WINDOW >= DNS_RRL_MAX_TS
#error "DNS_RRL_MAX_WINDOW is too large"
#endif
#define DNS_RRL_MAX_RATE	1000
#if DNS_RRL_MAX_RATE >= (DNS_RRL_MAX_RESPONSES / DNS_RRL_MAX_WINDOW)
#error "DNS_RRL_MAX_rate is too large"
#endif

#if (1<<DNS_RRL_LOG_BITS) >= DNS_RRL_FOREVER
#error DNS_RRL_LOG_BITS is too big
#endif
#define DNS_RRL_MAX_LOG_SECS	1800
#if DNS_RRL_MAX_LOG_SECS >= (1<<DNS_RRL_LOG_BITS)
#error "DNS_RRL_MAX_LOG_SECS is too large"
#endif
#define DNS_RRL_STOP_LOG_SECS	60
#if DNS_RRL_STOP_LOG_SECS >= (1<<DNS_RRL_LOG_BITS)
#error "DNS_RRL_STOP_LOG_SECS is too large"
#endif


/*
 * A hash table of rate-limit entries.
 */
struct dns_rrl_hash {
	isc_stdtime_t	check_time;
	unsigned int	gen	    :DNS_RRL_HASH_GEN_BITS;
	int		length;
	dns_rrl_bin_t	bins[1];
};

/*
 * A block of rate-limit entries.
 */
typedef struct dns_rrl_block dns_rrl_block_t;
struct dns_rrl_block {
	ISC_LINK(dns_rrl_block_t) link;
	int		size;
	dns_rrl_entry_t	entries[1];
};

/*
 * A rate limited qname buffer.
 */
typedef struct dns_rrl_qname_buf dns_rrl_qname_buf_t;
struct dns_rrl_qname_buf {
	ISC_LINK(dns_rrl_qname_buf_t) link;
	const dns_rrl_entry_t *e;
	unsigned int	    index;
	dns_fixedname_t	    qname;
};

typedef struct dns_rrl_rate dns_rrl_rate_t;
struct dns_rrl_rate {
	int	    r;
	int	    scaled;
	const char  *str;
};

/*
 * Per-view query rate limit parameters and a pointer to database.
 */
typedef struct dns_rrl dns_rrl_t;
struct dns_rrl {
	isc_mutex_t	lock;
	isc_mem_t	*mctx;

	isc_boolean_t	log_only;
	dns_rrl_rate_t	responses_per_second;
	dns_rrl_rate_t	referrals_per_second;
	dns_rrl_rate_t	nodata_per_second;
	dns_rrl_rate_t	nxdomains_per_second;
	dns_rrl_rate_t	errors_per_second;
	dns_rrl_rate_t	all_per_second;
	dns_rrl_rate_t	slip;
	int		window;
	double		qps_scale;
	int		max_entries;

	dns_acl_t	*exempt;

	int		num_entries;

	int		qps_responses;
	isc_stdtime_t	qps_time;
	double		qps;

	unsigned int	probes;
	unsigned int	searches;

	ISC_LIST(dns_rrl_block_t) blocks;
	ISC_LIST(dns_rrl_entry_t) lru;

	dns_rrl_hash_t	*hash;
	dns_rrl_hash_t	*old_hash;
	unsigned int	hash_gen;

	unsigned int	ts_gen;
# define DNS_RRL_TS_BASES   (1<<DNS_RRL_TS_GEN_BITS)
	isc_stdtime_t	ts_bases[DNS_RRL_TS_BASES];

	int		ipv4_prefixlen;
	isc_uint32_t	ipv4_mask;
	int		ipv6_prefixlen;
	isc_uint32_t	ipv6_mask[4];

	isc_stdtime_t	log_stops_time;
	dns_rrl_entry_t	*last_logged;
	int		num_logged;
	int		num_qnames;
	ISC_LIST(dns_rrl_qname_buf_t) qname_free;
# define DNS_RRL_QNAMES	    (1<<DNS_RRL_QNAMES_BITS)
	dns_rrl_qname_buf_t *qnames[DNS_RRL_QNAMES];
};

typedef enum {
	DNS_RRL_RESULT_OK,
	DNS_RRL_RESULT_DROP,
	DNS_RRL_RESULT_SLIP,
} dns_rrl_result_t;

dns_rrl_result_t
dns_rrl(dns_view_t *view,
	const isc_sockaddr_t *client_addr, isc_boolean_t is_tcp,
	dns_rdataclass_t rdclass, dns_rdatatype_t qtype,
	dns_name_t *qname, isc_result_t resp_result, isc_stdtime_t now,
	isc_boolean_t wouldlog, char *log_buf, unsigned int log_buf_len);

void
dns_rrl_view_destroy(dns_view_t *view);

isc_result_t
dns_rrl_init(dns_rrl_t **rrlp, dns_view_t *view, int min_entries);

ISC_LANG_ENDDECLS

#endif /* DNS_RRL_H */