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/* Copyright (C) 2022 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
#include "knot/include/module.h"
#include "knot/nameserver/process_query.h" // Dependency on qdata->extra!
#include "knot/modules/rrl/functions.h"
#define MOD_RATE_LIMIT "\x0A""rate-limit"
#define MOD_SLIP "\x04""slip"
#define MOD_TBL_SIZE "\x0A""table-size"
#define MOD_WHITELIST "\x09""whitelist"
const yp_item_t rrl_conf[] = {
{ MOD_RATE_LIMIT, YP_TINT, YP_VINT = { 1, INT32_MAX } },
{ MOD_SLIP, YP_TINT, YP_VINT = { 0, 100, 1 } },
{ MOD_TBL_SIZE, YP_TINT, YP_VINT = { 1, INT32_MAX, 393241 } },
{ MOD_WHITELIST, YP_TNET, YP_VNONE, YP_FMULTI },
{ NULL }
};
int rrl_conf_check(knotd_conf_check_args_t *args)
{
knotd_conf_t limit = knotd_conf_check_item(args, MOD_RATE_LIMIT);
if (limit.count == 0) {
args->err_str = "no rate limit specified";
return KNOT_EINVAL;
}
return KNOT_EOK;
}
typedef struct {
rrl_table_t *rrl;
int slip;
knotd_conf_t whitelist;
} rrl_ctx_t;
static const knot_dname_t *name_from_rrsig(const knot_rrset_t *rr)
{
if (rr == NULL) {
return NULL;
}
if (rr->type != KNOT_RRTYPE_RRSIG) {
return NULL;
}
// This is a signature.
return knot_rrsig_signer_name(rr->rrs.rdata);
}
static const knot_dname_t *name_from_authrr(const knot_rrset_t *rr)
{
if (rr == NULL) {
return NULL;
}
if (rr->type != KNOT_RRTYPE_NS && rr->type != KNOT_RRTYPE_SOA) {
return NULL;
}
// This is a valid authority RR.
return rr->owner;
}
static knotd_state_t ratelimit_apply(knotd_state_t state, knot_pkt_t *pkt,
knotd_qdata_t *qdata, knotd_mod_t *mod)
{
assert(pkt && qdata && mod);
rrl_ctx_t *ctx = knotd_mod_ctx(mod);
// Rate limit is applied to pure UDP only.
if (qdata->params->proto != KNOTD_QUERY_PROTO_UDP) {
return state;
}
// Rate limit is not applied to responses with a valid cookie.
if (qdata->params->flags & KNOTD_QUERY_FLAG_COOKIE) {
return state;
}
// Exempt clients.
if (knotd_conf_addr_range_match(&ctx->whitelist, knotd_qdata_remote_addr(qdata))) {
return state;
}
rrl_req_t req = {
.wire = pkt->wire,
.query = qdata->query
};
if (!EMPTY_LIST(qdata->extra->wildcards)) {
req.flags = RRL_REQ_WILDCARD;
}
// Take the zone name if known.
const knot_dname_t *zone_name = knotd_qdata_zone_name(qdata);
// Take the signer name as zone name if there is an RRSIG.
if (zone_name == NULL) {
const knot_pktsection_t *ans = knot_pkt_section(pkt, KNOT_ANSWER);
for (int i = 0; i < ans->count; i++) {
zone_name = name_from_rrsig(knot_pkt_rr(ans, i));
if (zone_name != NULL) {
break;
}
}
}
// Take the NS or SOA owner name if there is no RRSIG.
if (zone_name == NULL) {
const knot_pktsection_t *auth = knot_pkt_section(pkt, KNOT_AUTHORITY);
for (int i = 0; i < auth->count; i++) {
zone_name = name_from_authrr(knot_pkt_rr(auth, i));
if (zone_name != NULL) {
break;
}
}
}
if (rrl_query(ctx->rrl, knotd_qdata_remote_addr(qdata), &req, zone_name, mod) == KNOT_EOK) {
// Rate limiting not applied.
return state;
}
if (rrl_slip_roll(ctx->slip)) {
// Slip the answer.
knotd_mod_stats_incr(mod, qdata->params->thread_id, 0, 0, 1);
qdata->err_truncated = true;
return KNOTD_STATE_FAIL;
} else {
// Drop the answer.
knotd_mod_stats_incr(mod, qdata->params->thread_id, 1, 0, 1);
return KNOTD_STATE_NOOP;
}
}
static void ctx_free(rrl_ctx_t *ctx)
{
assert(ctx);
rrl_destroy(ctx->rrl);
free(ctx);
}
int rrl_load(knotd_mod_t *mod)
{
// Create RRL context.
rrl_ctx_t *ctx = calloc(1, sizeof(rrl_ctx_t));
if (ctx == NULL) {
return KNOT_ENOMEM;
}
// Create table.
uint32_t rate = knotd_conf_mod(mod, MOD_RATE_LIMIT).single.integer;
size_t size = knotd_conf_mod(mod, MOD_TBL_SIZE).single.integer;
ctx->rrl = rrl_create(size, rate);
if (ctx->rrl == NULL) {
ctx_free(ctx);
return KNOT_ENOMEM;
}
// Get slip.
ctx->slip = knotd_conf_mod(mod, MOD_SLIP).single.integer;
// Get whitelist.
ctx->whitelist = knotd_conf_mod(mod, MOD_WHITELIST);
// Set up statistics counters.
int ret = knotd_mod_stats_add(mod, "slipped", 1, NULL);
if (ret != KNOT_EOK) {
ctx_free(ctx);
return ret;
}
ret = knotd_mod_stats_add(mod, "dropped", 1, NULL);
if (ret != KNOT_EOK) {
ctx_free(ctx);
return ret;
}
knotd_mod_ctx_set(mod, ctx);
return knotd_mod_hook(mod, KNOTD_STAGE_END, ratelimit_apply);
}
void rrl_unload(knotd_mod_t *mod)
{
rrl_ctx_t *ctx = knotd_mod_ctx(mod);
knotd_conf_free(&ctx->whitelist);
ctx_free(ctx);
}
KNOTD_MOD_API(rrl, KNOTD_MOD_FLAG_SCOPE_ANY,
rrl_load, rrl_unload, rrl_conf, rrl_conf_check);
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