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rrl.c
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rrl.c
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/* rrl.c - Response Rate Limiting for NSD.
* By W.C.A. Wijngaards
* Copyright 2012, NLnet Labs.
* BSD, see LICENSE.
*/
#include "config.h"
#include <errno.h>
#include "rrl.h"
#include "util.h"
#include "lookup3.h"
#include "options.h"
#ifdef RATELIMIT
#ifdef HAVE_MMAP
#include <sys/mman.h>
#if defined(MAP_ANON) && !defined(MAP_ANONYMOUS)
#define MAP_ANONYMOUS MAP_ANON
#endif
#endif /* HAVE_MMAP */
/**
* The rate limiting data structure bucket, this represents one rate of
* packets from a single source.
* Smoothed average rates.
*/
struct rrl_bucket {
/* the source netmask */
uint64_t source;
/* rate, in queries per second, which due to rate=r(t)+r(t-1)/2 is
* equal to double the queries per second */
uint32_t rate;
/* the full hash */
uint32_t hash;
/* counter for queries arrived in this second */
uint32_t counter;
/* timestamp, which time is the time of the counter, the rate is from
* one timestep before that. */
int32_t stamp;
/* flags for the source mask and type */
uint16_t flags;
};
/* the (global) array of RRL buckets */
static struct rrl_bucket* rrl_array = NULL;
static size_t rrl_array_size = RRL_BUCKETS;
static uint32_t rrl_ratelimit = RRL_LIMIT; /* 2x qps */
static uint8_t rrl_slip_ratio = RRL_SLIP;
static uint8_t rrl_ipv4_prefixlen = RRL_IPV4_PREFIX_LENGTH;
static uint8_t rrl_ipv6_prefixlen = RRL_IPV6_PREFIX_LENGTH;
static uint64_t rrl_ipv6_mask; /* max prefixlen 64 */
static uint32_t rrl_whitelist_ratelimit = RRL_WLIST_LIMIT; /* 2x qps */
/* the array of mmaps for the children (saved between reloads) */
static void** rrl_maps = NULL;
static size_t rrl_maps_num = 0;
void rrl_mmap_init(int numch, size_t numbuck, size_t lm, size_t wlm, size_t sm,
size_t plf, size_t pls)
{
#ifdef HAVE_MMAP
size_t i;
#endif
if(numbuck != 0)
rrl_array_size = numbuck;
rrl_ratelimit = lm*2;
rrl_slip_ratio = sm;
rrl_ipv4_prefixlen = plf;
rrl_ipv6_prefixlen = pls;
if (pls <= 32) {
rrl_ipv6_mask = ((uint64_t) htonl(0xffffffff << (32-pls))) << 32;
} else {
rrl_ipv6_mask = ((uint64_t) htonl(0xffffffff << (64-pls))) |
(((uint64_t)0xffffffff)<<32);
}
rrl_whitelist_ratelimit = wlm*2;
#ifdef HAVE_MMAP
/* allocate the ratelimit hashtable in a memory map so it is
* preserved across reforks (every child its own table) */
rrl_maps_num = (size_t)numch;
rrl_maps = (void**)xmallocarray(rrl_maps_num, sizeof(void*));
for(i=0; i<rrl_maps_num; i++) {
rrl_maps[i] = mmap(NULL,
sizeof(struct rrl_bucket)*rrl_array_size,
PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
if(rrl_maps[i] == MAP_FAILED) {
log_msg(LOG_ERR, "rrl: mmap failed: %s",
strerror(errno));
exit(1);
}
memset(rrl_maps[i], 0,
sizeof(struct rrl_bucket)*rrl_array_size);
}
#else
(void)numch;
rrl_maps_num = 0;
rrl_maps = NULL;
#endif
}
void rrl_mmap_deinit(void)
{
#ifdef HAVE_MMAP
size_t i;
for(i=0; i<rrl_maps_num; i++) {
munmap(rrl_maps[i], sizeof(struct rrl_bucket)*rrl_array_size);
rrl_maps[i] = NULL;
}
free(rrl_maps);
rrl_maps = NULL;
#endif
}
void rrl_mmap_deinit_keep_mmap(void)
{
#ifdef HAVE_MMAP
free(rrl_maps);
rrl_maps = NULL;
#endif
}
void rrl_set_limit(size_t lm, size_t wlm, size_t sm)
{
rrl_ratelimit = lm*2;
rrl_whitelist_ratelimit = wlm*2;
rrl_slip_ratio = sm;
}
void rrl_init(size_t ch)
{
if(!rrl_maps || ch >= rrl_maps_num)
rrl_array = xalloc_array_zero(sizeof(struct rrl_bucket),
rrl_array_size);
#ifdef HAVE_MMAP
else rrl_array = (struct rrl_bucket*)rrl_maps[ch];
#endif
}
void rrl_deinit(size_t ch)
{
if(!rrl_maps || ch >= rrl_maps_num)
free(rrl_array);
rrl_array = NULL;
}
/** return the source netblock of the query, this is the genuine source
* for genuine queries and the target for reflected packets */
static uint64_t rrl_get_source(query_type* query, uint16_t* c2)
{
/* note there is an IPv6 subnet, that maps
* to the same buckets as IPv4 space, but there is a flag in c2
* that makes the hash different */
#ifdef INET6
if( ((struct sockaddr_in*)&query->client_addr)->sin_family == AF_INET) {
*c2 = 0;
return ((struct sockaddr_in*)&query->client_addr)->
sin_addr.s_addr & htonl(0xffffffff << (32-rrl_ipv4_prefixlen));
} else {
uint64_t s;
*c2 = rrl_ip6;
memmove(&s, &((struct sockaddr_in6*)&query->client_addr)->sin6_addr,
sizeof(s));
return s & rrl_ipv6_mask;
}
#else
*c2 = 0;
return query->client_addr.sin_addr.s_addr & htonl(0xffffffff << (32-rrl_ipv4_prefixlen));
#endif
}
/** debug source to string */
static const char* rrlsource2str(uint64_t s, uint16_t c2)
{
static char buf[64];
struct in_addr a4;
#ifdef INET6
if(c2) {
/* IPv6 */
struct in6_addr a6;
memset(&a6, 0, sizeof(a6));
memmove(&a6, &s, sizeof(s));
if(!inet_ntop(AF_INET6, &a6, buf, sizeof(buf)))
strlcpy(buf, "[ip6 ntop failed]", sizeof(buf));
else {
static char prefix[5];
snprintf(prefix, sizeof(prefix), "/%d", rrl_ipv6_prefixlen);
strlcat(buf, &prefix[0], sizeof(buf));
}
return buf;
}
#else
(void)c2;
#endif
/* ipv4 */
a4.s_addr = (uint32_t)s;
if(!inet_ntop(AF_INET, &a4, buf, sizeof(buf)))
strlcpy(buf, "[ip4 ntop failed]", sizeof(buf));
else {
static char prefix[5];
snprintf(prefix, sizeof(prefix), "/%d", rrl_ipv4_prefixlen);
strlcat(buf, &prefix[0], sizeof(buf));
}
return buf;
}
enum rrl_type rrlstr2type(const char* s)
{
if(strcmp(s, "nxdomain")==0) return rrl_type_nxdomain;
else if(strcmp(s, "error")==0) return rrl_type_error;
else if(strcmp(s, "referral")==0) return rrl_type_referral;
else if(strcmp(s, "any")==0) return rrl_type_any;
else if(strcmp(s, "wildcard")==0) return rrl_type_wildcard;
else if(strcmp(s, "nodata")==0) return rrl_type_nodata;
else if(strcmp(s, "dnskey")==0) return rrl_type_dnskey;
else if(strcmp(s, "positive")==0) return rrl_type_positive;
else if(strcmp(s, "rrsig")==0) return rrl_type_rrsig;
else if(strcmp(s, "all")==0) return rrl_type_all;
return 0; /* unknown */
}
const char* rrltype2str(enum rrl_type c)
{
switch(c & 0x0fff) {
case rrl_type_nxdomain: return "nxdomain";
case rrl_type_error: return "error";
case rrl_type_referral: return "referral";
case rrl_type_any: return "any";
case rrl_type_wildcard: return "wildcard";
case rrl_type_nodata: return "nodata";
case rrl_type_dnskey: return "dnskey";
case rrl_type_positive: return "positive";
case rrl_type_rrsig: return "rrsig";
case rrl_type_all: return "all";
}
return "unknown";
}
/** classify the query in a number of different types, each has separate
* ratelimiting, so that positive queries are not impeded by others */
static uint16_t rrl_classify(query_type* query, const uint8_t** d,
size_t* d_len)
{
if(RCODE(query->packet) == RCODE_NXDOMAIN) {
if(query->zone && query->zone->apex) {
*d = dname_name(domain_dname(query->zone->apex));
*d_len = domain_dname(query->zone->apex)->name_size;
}
return rrl_type_nxdomain;
}
if(RCODE(query->packet) != RCODE_OK) {
if(query->zone && query->zone->apex) {
*d = dname_name(domain_dname(query->zone->apex));
*d_len = domain_dname(query->zone->apex)->name_size;
}
return rrl_type_error;
}
if(query->delegation_domain) {
*d = dname_name(domain_dname(query->delegation_domain));
*d_len = domain_dname(query->delegation_domain)->name_size;
return rrl_type_referral;
}
if(query->qtype == TYPE_ANY) {
if(query->qname) {
*d = dname_name(query->qname);
*d_len = query->qname->name_size;
}
return rrl_type_any;
}
if(query->qtype == TYPE_RRSIG) {
if(query->qname) {
*d = dname_name(query->qname);
*d_len = query->qname->name_size;
}
return rrl_type_rrsig;
}
if(query->wildcard_domain) {
*d = dname_name(domain_dname(query->wildcard_domain));
*d_len = domain_dname(query->wildcard_domain)->name_size;
return rrl_type_wildcard;
}
if(ANCOUNT(query->packet) == 0) {
if(query->zone && query->zone->apex) {
*d = dname_name(domain_dname(query->zone->apex));
*d_len = domain_dname(query->zone->apex)->name_size;
}
return rrl_type_nodata;
}
if(query->qtype == TYPE_DNSKEY) {
if(query->qname) {
*d = dname_name(query->qname);
*d_len = query->qname->name_size;
}
return rrl_type_dnskey;
}
/* positive */
if(query->qname) {
*d = dname_name(query->qname);
*d_len = query->qname->name_size;
}
return rrl_type_positive;
}
/** Examine the query and return hash and source of netblock. */
static void examine_query(query_type* query, uint32_t* hash, uint64_t* source,
uint16_t* flags, uint32_t* lm)
{
/* compile a binary string representing the query */
uint16_t c, c2;
/* size with 16 bytes to spare */
uint8_t buf[MAXDOMAINLEN + sizeof(*source) + sizeof(c) + 16];
const uint8_t* dname = NULL; size_t dname_len = 0;
uint32_t r = 0x267fcd16;
*source = rrl_get_source(query, &c2);
c = rrl_classify(query, &dname, &dname_len);
if(query->zone && query->zone->opts &&
(query->zone->opts->pattern->rrl_whitelist & c))
*lm = rrl_whitelist_ratelimit;
if(*lm == 0) return;
c |= c2;
*flags = c;
memmove(buf, source, sizeof(*source));
memmove(buf+sizeof(*source), &c, sizeof(c));
DEBUG(DEBUG_QUERY, 1, (LOG_INFO, "rrl_examine type %s name %s", rrltype2str(c), dname?wiredname2str(dname):"NULL"));
/* and hash it */
if(dname && dname_len <= MAXDOMAINLEN) {
memmove(buf+sizeof(*source)+sizeof(c), dname, dname_len);
*hash = hashlittle(buf, sizeof(*source)+sizeof(c)+dname_len, r);
} else
*hash = hashlittle(buf, sizeof(*source)+sizeof(c), r);
}
/* age the bucket because elapsed time steps have gone by */
static void rrl_attenuate_bucket(struct rrl_bucket* b, int32_t elapsed)
{
if(elapsed > 16) {
b->rate = 0;
} else {
/* divide rate /2 for every elapsed time step, because
* the counters in the inbetween steps were 0 */
/* r(t) = 0 + 0/2 + 0/4 + .. + oldrate/2^dt */
b->rate >>= elapsed;
/* we know that elapsed >= 2 */
b->rate += (b->counter>>(elapsed-1));
}
}
/** log a message about ratelimits */
static void
rrl_msg(query_type* query, const char* str)
{
uint16_t c, c2, wl = 0;
const uint8_t* d = NULL;
size_t d_len;
uint64_t s;
char address[128];
if(verbosity < 1) return;
addr2str(&query->client_addr, address, sizeof(address));
s = rrl_get_source(query, &c2);
c = rrl_classify(query, &d, &d_len) | c2;
if(query->zone && query->zone->opts &&
(query->zone->opts->pattern->rrl_whitelist & c))
wl = 1;
log_msg(LOG_INFO, "ratelimit %s %s type %s%s target %s query %s %s",
str, d?wiredname2str(d):"", rrltype2str(c),
wl?"(whitelisted)":"", rrlsource2str(s, c2),
address, rrtype_to_string(query->qtype));
}
/** true if the query used to be blocked by the ratelimit */
static int
used_to_block(uint32_t rate, uint32_t counter, uint32_t lm)
{
return rate >= lm || counter+rate/2 >= lm;
}
/** update the rate in a ratelimit bucket, return actual rate */
uint32_t rrl_update(query_type* query, uint32_t hash, uint64_t source,
uint16_t flags, int32_t now, uint32_t lm)
{
struct rrl_bucket* b = &rrl_array[hash % rrl_array_size];
DEBUG(DEBUG_QUERY, 1, (LOG_INFO, "source %llx hash %x oldrate %d oldcount %d stamp %d",
(long long unsigned)source, hash, b->rate, b->counter, b->stamp));
/* check if different source */
if(b->source != source || b->flags != flags || b->hash != hash) {
/* initialise */
/* potentially the wrong limit here, used lower nonwhitelim */
if(verbosity >= 1 &&
used_to_block(b->rate, b->counter, rrl_ratelimit)) {
char address[128];
addr2str(&query->client_addr, address, sizeof(address));
log_msg(LOG_INFO, "ratelimit unblock ~ type %s target %s query %s %s (%s collision)",
rrltype2str(b->flags),
rrlsource2str(b->source, b->flags),
address, rrtype_to_string(query->qtype),
(b->hash!=hash?"bucket":"hash"));
}
b->hash = hash;
b->source = source;
b->flags = flags;
b->counter = 1;
b->rate = 0;
b->stamp = now;
return 1;
}
/* this is the same source */
/* check if old, zero or smooth it */
/* circular arith for time */
if(now - b->stamp == 1) {
/* very busy bucket and time just stepped one step */
int oldblock = used_to_block(b->rate, b->counter, lm);
b->rate = b->rate/2 + b->counter;
if(oldblock && b->rate < lm)
rrl_msg(query, "unblock");
b->counter = 1;
b->stamp = now;
} else if(now - b->stamp > 0) {
/* older bucket */
int olderblock = used_to_block(b->rate, b->counter, lm);
rrl_attenuate_bucket(b, now - b->stamp);
if(olderblock && b->rate < lm)
rrl_msg(query, "unblock");
b->counter = 1;
b->stamp = now;
} else if(now != b->stamp) {
/* robust, timestamp from the future */
if(used_to_block(b->rate, b->counter, lm))
rrl_msg(query, "unblock");
b->rate = 0;
b->counter = 1;
b->stamp = now;
} else {
/* bucket is from the current timestep, update counter */
b->counter ++;
/* log what is blocked for operational debugging */
if(b->counter + b->rate/2 == lm && b->rate < lm)
rrl_msg(query, "block");
}
/* return max from current rate and projected next-value for rate */
/* so that if the rate increases suddenly very high, it is
* stopped halfway into the time step */
if(b->counter > b->rate/2)
return b->counter + b->rate/2;
return b->rate;
}
int rrl_process_query(query_type* query)
{
uint64_t source;
uint32_t hash;
/* we can use circular arithmetic here, so int32 works after 2038 */
int32_t now = (int32_t)time(NULL);
uint32_t lm = rrl_ratelimit;
uint16_t flags;
if(rrl_ratelimit == 0 && rrl_whitelist_ratelimit == 0)
return 0;
/* examine query */
examine_query(query, &hash, &source, &flags, &lm);
if(lm == 0)
return 0; /* no limit for this */
/* update rate */
return (rrl_update(query, hash, source, flags, now, lm) >= lm);
}
query_state_type rrl_slip(query_type* query)
{
/* discard number the packets, randomly */
#ifdef HAVE_ARC4RANDOM_UNIFORM
if((rrl_slip_ratio > 0) && ((rrl_slip_ratio == 1) || ((arc4random_uniform(rrl_slip_ratio)) == 0))) {
#elif HAVE_ARC4RANDOM
if((rrl_slip_ratio > 0) && ((rrl_slip_ratio == 1) || ((arc4random() % rrl_slip_ratio) == 0))) {
#else
if((rrl_slip_ratio > 0) && ((rrl_slip_ratio == 1) || ((random() % rrl_slip_ratio) == 0))) {
#endif
/* set TC on the rest */
TC_SET(query->packet);
ANCOUNT_SET(query->packet, 0);
NSCOUNT_SET(query->packet, 0);
ARCOUNT_SET(query->packet, 0);
if(query->qname)
/* header, type, class, qname */
buffer_set_position(query->packet,
QHEADERSZ+4+query->qname->name_size);
else buffer_set_position(query->packet, QHEADERSZ);
return QUERY_PROCESSED;
}
return QUERY_DISCARDED;
}
#endif /* RATELIMIT */