Adding upstream version 5.6.0.upstream/5.6.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1366 insertions, 0 deletions

diff --git a/lib/layer/validate.c b/lib/layer/validate.c
new file mode 100644
index 0000000..93f1d4f
--- /dev/null
+++ b/lib/layer/validate.c
@@ -0,0 +1,1366 @@
+/*  Copyright (C) CZ.NIC, z.s.p.o. <knot-resolver@labs.nic.cz>
+ *  SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include <errno.h>
+#include <sys/time.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <contrib/cleanup.h>
+#include <libknot/packet/wire.h>
+#include <libknot/rrtype/rdname.h>
+#include <libknot/rrtype/rrsig.h>
+#include <libdnssec/error.h>
+
+#include "lib/dnssec/nsec.h"
+#include "lib/dnssec/nsec3.h"
+#include "lib/dnssec/ta.h"
+#include "lib/dnssec.h"
+#include "lib/layer.h"
+#include "lib/resolve.h"
+#include "lib/rplan.h"
+#include "lib/utils.h"
+#include "lib/defines.h"
+#include "lib/module.h"
+#include "lib/selection.h"
+
+#define VERBOSE_MSG(qry, ...) kr_log_q(qry, VALIDATOR, __VA_ARGS__)
+
+#define MAX_REVALIDATION_CNT 2
+
+/**
+ * Search in section for given type.
+ * @param sec  Packet section.
+ * @param type Type to search for.
+ * @return     True if found.
+ */
+static bool section_has_type(const knot_pktsection_t *sec, uint16_t type)
+{
+	if (!sec) {
+		return false;
+	}
+
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *rr = knot_pkt_rr(sec, i);
+		if (rr->type == type) {
+			return true;
+		}
+	}
+
+	return false;
+}
+
+static bool pkt_has_type(const knot_pkt_t *pkt, uint16_t type)
+{
+	if (!pkt) {
+		return false;
+	}
+
+	if (section_has_type(knot_pkt_section(pkt, KNOT_ANSWER), type)) {
+		return true;
+	}
+	if (section_has_type(knot_pkt_section(pkt, KNOT_AUTHORITY), type)) {
+		return true;
+	}
+	return section_has_type(knot_pkt_section(pkt, KNOT_ADDITIONAL), type);
+}
+
+static void log_bogus_rrsig(kr_rrset_validation_ctx_t *vctx,
+			    const knot_rrset_t *rr, const char *msg) {
+	if (kr_log_is_debug_qry(VALIDATOR, vctx->log_qry)) {
+		auto_free char *name_text = kr_dname_text(rr->owner);
+		auto_free char *type_text = kr_rrtype_text(rr->type);
+		VERBOSE_MSG(vctx->log_qry, ">< %s: %s %s "
+			    "(%u matching RRSIGs, %u expired, %u not yet valid, "
+			    "%u invalid signer, %u invalid label count, %u invalid key, "
+			    "%u invalid crypto, %u invalid NSEC)\n",
+			    msg, name_text, type_text, vctx->rrs_counters.matching_name_type,
+			    vctx->rrs_counters.expired, vctx->rrs_counters.notyet,
+			    vctx->rrs_counters.signer_invalid, vctx->rrs_counters.labels_invalid,
+			    vctx->rrs_counters.key_invalid, vctx->rrs_counters.crypto_invalid,
+			    vctx->rrs_counters.nsec_invalid);
+	}
+}
+
+/** Check that given CNAME could be generated by given DNAME (no DNSSEC validation). */
+static bool cname_matches_dname(const knot_rrset_t *rr_cn, const knot_rrset_t *rr_dn)
+{
+	if (kr_fails_assert(rr_cn->type == KNOT_RRTYPE_CNAME && rr_dn->type == KNOT_RRTYPE_DNAME))
+		return false;
+	/* When DNAME substitution happens, let's consider the "prefix"
+	 * that is carried over and the "suffix" that is replaced.
+	 * (Here we consider the label order used in wire and presentation.) */
+	const int prefix_labels = knot_dname_in_bailiwick(rr_cn->owner, rr_dn->owner);
+	if (prefix_labels < 1)
+		return false;
+	const knot_dname_t *cn_target = knot_cname_name(rr_cn->rrs.rdata);
+	const knot_dname_t *dn_target = knot_dname_target(rr_dn->rrs.rdata);
+		/* ^ We silently use the first RR in each RRset.  Could be e.g. logged. */
+	/* Check that the suffixes are correct - and even prefix label counts. */
+	if (knot_dname_in_bailiwick(cn_target, dn_target) != prefix_labels)
+		return false;
+	/* Check that prefixes match.  Find end of the first one and compare. */
+	const knot_dname_t *cn_se = rr_cn->owner;
+	for (int i = 0; i < prefix_labels; ++i)
+		cn_se += 1 + *cn_se;
+	return strncmp((const char *)rr_cn->owner, (const char *)cn_target,
+			cn_se - rr_cn->owner) == 0;
+		/* ^ We use the fact that dnames are always zero-terminated
+		 * to avoid any possible over-read in cn_target. */
+}
+
+static void mark_insecure_parents(const struct kr_query *qry);
+static void rank_records(struct kr_query *qry, bool any_rank, enum kr_rank rank_to_set,
+			 const knot_dname_t *bailiwick);
+
+static bool maybe_downgrade_nsec3(const ranked_rr_array_entry_t *e, struct kr_query *qry,
+				  const kr_rrset_validation_ctx_t *vctx)
+{
+	bool required_conditions =
+		e->rr->type == KNOT_RRTYPE_NSEC3
+		&& kr_rank_test(e->rank, KR_RANK_SECURE)
+		// extra careful: avoid downgrade if SNAME isn't in bailiwick of signer
+		&& knot_dname_in_bailiwick(qry->sname, vctx->zone_name) >= 0;
+	if (!required_conditions)
+		return false;
+
+	const knot_rdataset_t *rrs = &e->rr->rrs;
+	knot_rdata_t *rd = rrs->rdata;
+	for (int j = 0; j < rrs->count; ++j, rd = knot_rdataset_next(rd)) {
+		if (knot_nsec3_iters(rd) > KR_NSEC3_MAX_ITERATIONS)
+			goto do_downgrade;
+	}
+	return false;
+
+do_downgrade: // we do this deep inside calls because of having signer name available
+	VERBOSE_MSG(qry, "<= DNSSEC downgraded due to NSEC3 iterations %d > %d\n",
+			(int)knot_nsec3_iters(rd), (int)KR_NSEC3_MAX_ITERATIONS);
+	qry->flags.DNSSEC_WANT = false;
+	qry->flags.DNSSEC_INSECURE = true;
+	rank_records(qry, true, KR_RANK_INSECURE, vctx->zone_name);
+	mark_insecure_parents(qry);
+	return true;
+}
+
+#define KNOT_EDOWNGRADED (KNOT_ERROR_MIN - 1)
+
+static int validate_section(kr_rrset_validation_ctx_t *vctx, struct kr_query *qry,
+			    knot_mm_t *pool)
+{
+	struct kr_request *req = qry->request;
+	if (!vctx) {
+		return kr_error(EINVAL);
+	}
+
+	/* Can't use qry->zone_cut.name directly, as this name can
+	 * change when updating cut information before validation.
+	 */
+	vctx->zone_name = vctx->keys ? vctx->keys->owner : NULL;
+
+	for (ssize_t i = 0; i < vctx->rrs->len; ++i) {
+		ranked_rr_array_entry_t *entry = vctx->rrs->at[i];
+		knot_rrset_t * const rr = entry->rr;
+
+		if (entry->yielded || vctx->qry_uid != entry->qry_uid) {
+			continue;
+		}
+
+		if (kr_rank_test(entry->rank, KR_RANK_OMIT)
+		    || kr_rank_test(entry->rank, KR_RANK_SECURE)) {
+			continue; /* these are already OK */
+		}
+
+		if (!knot_dname_is_equal(qry->zone_cut.name, rr->owner)/*optim.*/
+		    && !kr_ta_closest(qry->request->ctx, rr->owner, rr->type)) {
+			/* We have NTA "between" our (perceived) zone cut and the RR. */
+			kr_rank_set(&entry->rank, KR_RANK_INSECURE);
+			continue;
+		}
+
+		if (rr->type == KNOT_RRTYPE_RRSIG) {
+			const knot_dname_t *signer_name = knot_rrsig_signer_name(rr->rrs.rdata);
+			if (!knot_dname_is_equal(vctx->zone_name, signer_name)) {
+				kr_rank_set(&entry->rank, KR_RANK_MISMATCH);
+				vctx->err_cnt += 1;
+				break;
+			}
+			if (!kr_rank_test(entry->rank, KR_RANK_BOGUS))
+				kr_rank_set(&entry->rank, KR_RANK_OMIT);
+			continue;
+		}
+
+		uint8_t rank_orig = entry->rank;
+		int validation_result = kr_rrset_validate(vctx, rr);
+
+		/* Handle the case of CNAMEs synthesized from DNAMEs (they don't have RRSIGs). */
+		if (rr->type == KNOT_RRTYPE_CNAME && validation_result == kr_error(ENOENT)) {
+			for (ssize_t j = 0; j < vctx->rrs->len; ++j) {
+				ranked_rr_array_entry_t *e_dname = vctx->rrs->at[j];
+				if ((e_dname->rr->type == KNOT_RRTYPE_DNAME)
+				    /* If the order is wrong, we will need two passes. */
+				    && kr_rank_test(e_dname->rank, KR_RANK_SECURE)
+				    && cname_matches_dname(rr, e_dname->rr)) {
+					/* Now we believe the CNAME is OK. */
+					validation_result = kr_ok();
+					break;
+				}
+			}
+			if (validation_result != kr_ok()) {
+				vctx->cname_norrsig_cnt += 1;
+			}
+		}
+
+		if (validation_result == kr_ok()) {
+			kr_rank_set(&entry->rank, KR_RANK_SECURE);
+
+			/* Downgrade zone to insecure if certain NSEC3 record occurs. */
+			if (unlikely(maybe_downgrade_nsec3(entry, qry, vctx)))
+				return kr_error(KNOT_EDOWNGRADED);
+
+		} else if (kr_rank_test(rank_orig, KR_RANK_TRY)) {
+			/* RFC 4035 section 2.2:
+			 * NS RRsets that appear at delegation points (...)
+			 * MUST NOT be signed */
+			if (vctx->rrs_counters.matching_name_type > 0)
+				log_bogus_rrsig(vctx, rr,
+					"found unexpected signatures for non-authoritative data which failed to validate, continuing");
+			vctx->result = kr_ok();
+			kr_rank_set(&entry->rank, KR_RANK_TRY);
+			/* ^^ BOGUS would be more accurate, but it might change
+			 * to MISMATCH on revalidation, e.g. in test val_referral_nods :-/
+			 */
+
+		} else if (validation_result == kr_error(ENOENT)
+				&& vctx->rrs_counters.matching_name_type == 0) {
+			/* no RRSIGs found */
+			kr_rank_set(&entry->rank, KR_RANK_MISSING);
+			vctx->err_cnt += 1;
+			kr_request_set_extended_error(req, KNOT_EDNS_EDE_RRSIG_MISS, "JZAJ");
+			log_bogus_rrsig(vctx, rr, "no valid RRSIGs found");
+		} else {
+			kr_rank_set(&entry->rank, KR_RANK_BOGUS);
+			vctx->err_cnt += 1;
+			if (vctx->rrs_counters.expired > 0)
+				kr_request_set_extended_error(req, KNOT_EDNS_EDE_SIG_EXPIRED, "YFJ2");
+			else if (vctx->rrs_counters.notyet > 0)
+				kr_request_set_extended_error(req, KNOT_EDNS_EDE_SIG_NOTYET, "UBBS");
+			else
+				kr_request_set_extended_error(req, KNOT_EDNS_EDE_BOGUS, "I74V");
+			log_bogus_rrsig(vctx, rr, "bogus signatures");
+		}
+	}
+	return kr_ok();
+}
+
+static int validate_records(struct kr_request *req, knot_pkt_t *answer, knot_mm_t *pool, bool has_nsec3)
+{
+	struct kr_query *qry = req->current_query;
+	if (!qry->zone_cut.key) {
+		VERBOSE_MSG(qry, "<= no DNSKEY, can't validate\n");
+		return kr_error(EBADMSG);
+	}
+
+	kr_rrset_validation_ctx_t vctx = {
+		.pkt		= answer,
+		.rrs		= &req->answ_selected,
+		.section_id	= KNOT_ANSWER,
+		.keys		= qry->zone_cut.key,
+		.zone_name	= qry->zone_cut.name,
+		.timestamp	= qry->timestamp.tv_sec,
+		.ttl_min	= req->ctx->cache.ttl_min,
+		.qry_uid	= qry->uid,
+		.has_nsec3	= has_nsec3,
+		.flags		= 0,
+		.err_cnt	= 0,
+		.cname_norrsig_cnt = 0,
+		.result		= 0,
+		.log_qry	= qry,
+	};
+
+	int ret = validate_section(&vctx, qry, pool);
+	if (vctx.err_cnt && vctx.err_cnt == vctx.cname_norrsig_cnt) {
+		VERBOSE_MSG(qry, ">< all validation errors are missing RRSIGs on CNAMES, trying again in hope for DNAMEs\n");
+		vctx.err_cnt = vctx.cname_norrsig_cnt = vctx.result = 0;
+		ret = validate_section(&vctx, qry, pool);
+	}
+	req->answ_validated = (vctx.err_cnt == 0);
+	if (ret != kr_ok()) {
+		return ret;
+	}
+
+	uint32_t an_flags = vctx.flags;
+	vctx.rrs	  = &req->auth_selected;
+	vctx.section_id   = KNOT_AUTHORITY;
+	vctx.flags	  = 0;
+	vctx.err_cnt	  = 0;
+	vctx.result	  = 0;
+
+	ret = validate_section(&vctx, qry, pool);
+	req->auth_validated = (vctx.err_cnt == 0);
+	if (ret != kr_ok()) {
+		return ret;
+	}
+
+	/* Records were validated.
+	 * If there is wildcard expansion in answer,
+	 * or optout - flag the query.
+         */
+	if (an_flags & KR_DNSSEC_VFLG_WEXPAND) {
+		qry->flags.DNSSEC_WEXPAND = true;
+	}
+	if (an_flags & KR_DNSSEC_VFLG_OPTOUT) {
+		qry->flags.DNSSEC_OPTOUT = true;
+	}
+
+	return ret;
+}
+
+static int validate_keyset(struct kr_request *req, knot_pkt_t *answer, bool has_nsec3)
+{
+	/* Merge DNSKEY records from answer that are below/at current cut. */
+	struct kr_query *qry = req->current_query;
+	bool updated_key = false;
+	const knot_pktsection_t *an = knot_pkt_section(answer, KNOT_ANSWER);
+	for (unsigned i = 0; i < an->count; ++i) {
+		const knot_rrset_t *rr = knot_pkt_rr(an, i);
+		if (rr->type != KNOT_RRTYPE_DNSKEY
+		    || knot_dname_in_bailiwick(rr->owner, qry->zone_cut.name) < 0) {
+			continue;
+		}
+		/* Merge with zone cut (or replace ancestor key). */
+		if (!qry->zone_cut.key || !knot_dname_is_equal(qry->zone_cut.key->owner, rr->owner)) {
+			qry->zone_cut.key = knot_rrset_copy(rr, qry->zone_cut.pool);
+			if (!qry->zone_cut.key) {
+				return kr_error(ENOMEM);
+			}
+			updated_key = true;
+		} else {
+			int ret = knot_rdataset_merge(&qry->zone_cut.key->rrs,
+			                              &rr->rrs, qry->zone_cut.pool);
+			if (ret != 0) {
+				knot_rrset_free(qry->zone_cut.key, qry->zone_cut.pool);
+				qry->zone_cut.key = NULL;
+				return ret;
+			}
+			updated_key = true;
+		}
+	}
+
+	/* Check if there's a key for current TA. */
+	if (updated_key && !(qry->flags.CACHED)) {
+		/* Find signatures for the DNSKEY; selected by iterator from ANSWER. */
+		int sig_index = -1;
+		for (int i = req->answ_selected.len - 1; i >= 0; --i) {
+			const knot_rrset_t *rrsig = req->answ_selected.at[i]->rr;
+			const bool ok = req->answ_selected.at[i]->qry_uid == qry->uid
+				&& rrsig->type == KNOT_RRTYPE_RRSIG
+				&& knot_rrsig_type_covered(rrsig->rrs.rdata)
+					== KNOT_RRTYPE_DNSKEY
+				&& rrsig->rclass == KNOT_CLASS_IN
+				&& knot_dname_is_equal(rrsig->owner,
+							qry->zone_cut.key->owner);
+			if (ok) {
+				sig_index = i;
+				break;
+			}
+		}
+		if (sig_index < 0) {
+			kr_request_set_extended_error(req, KNOT_EDNS_EDE_RRSIG_MISS, "EZDC");
+			return kr_error(ENOENT);
+		}
+		const knot_rdataset_t *sig_rds = &req->answ_selected.at[sig_index]->rr->rrs;
+
+		kr_rrset_validation_ctx_t vctx = {
+			.pkt		= answer,
+			.rrs		= &req->answ_selected,
+			.section_id	= KNOT_ANSWER,
+			.keys		= qry->zone_cut.key,
+			.zone_name	= qry->zone_cut.name,
+			.timestamp	= qry->timestamp.tv_sec,
+			.ttl_min	= req->ctx->cache.ttl_min,
+			.qry_uid	= qry->uid,
+			.has_nsec3	= has_nsec3,
+			.flags		= 0,
+			.result		= 0,
+			.log_qry	= qry,
+		};
+		int ret = kr_dnskeys_trusted(&vctx, sig_rds, qry->zone_cut.trust_anchor);
+		/* Set rank of the RRSIG.  This may be needed, but I don't know why.
+		 * In particular, black_ent.rpl may get broken otherwise. */
+		kr_rank_set(&req->answ_selected.at[sig_index]->rank,
+				ret == 0 ? KR_RANK_SECURE : KR_RANK_BOGUS);
+
+		if (ret != 0) {
+			log_bogus_rrsig(&vctx, qry->zone_cut.key, "bogus key");
+			knot_rrset_free(qry->zone_cut.key, qry->zone_cut.pool);
+			qry->zone_cut.key = NULL;
+			if (vctx.rrs_counters.expired > 0)
+				kr_request_set_extended_error(req, KNOT_EDNS_EDE_SIG_EXPIRED, "6GJV");
+			else if (vctx.rrs_counters.notyet > 0)
+				kr_request_set_extended_error(req, KNOT_EDNS_EDE_SIG_NOTYET, "4DJQ");
+			else
+				kr_request_set_extended_error(req, KNOT_EDNS_EDE_BOGUS, "EXRU");
+			return ret;
+		}
+
+		if (vctx.flags & KR_DNSSEC_VFLG_WEXPAND) {
+			qry->flags.DNSSEC_WEXPAND = true;
+		}
+		if (vctx.flags & KR_DNSSEC_VFLG_OPTOUT) {
+			qry->flags.DNSSEC_OPTOUT = true;
+		}
+
+	}
+	return kr_ok();
+}
+
+static knot_rrset_t *update_ds(struct kr_zonecut *cut, const knot_pktsection_t *sec)
+{
+	/* Aggregate DS records (if using multiple keys) */
+	knot_rrset_t *new_ds = NULL;
+	for (unsigned i = 0; i < sec->count; ++i) {
+		const knot_rrset_t *rr = knot_pkt_rr(sec, i);
+		if (rr->type != KNOT_RRTYPE_DS) {
+			continue;
+		}
+		int ret = 0;
+		if (new_ds) {
+			ret = knot_rdataset_merge(&new_ds->rrs, &rr->rrs, cut->pool);
+		} else {
+			new_ds = knot_rrset_copy(rr, cut->pool);
+			if (!new_ds) {
+				return NULL;
+			}
+		}
+		if (ret != 0) {
+			knot_rrset_free(new_ds, cut->pool);
+			return NULL;
+		}
+	}
+	return new_ds;
+}
+
+static void mark_insecure_parents(const struct kr_query *qry)
+{
+	/* If there is a chain of DS queries mark all of them,
+	 * then mark first non-DS parent.
+	 * Stop if parent is waiting for ns address.
+	 * NS can be located at unsigned zone, but still will return
+	 * valid DNSSEC records for initial query. */
+	struct kr_query *parent = qry->parent;
+	while (parent && !parent->flags.AWAIT_IPV4 && !parent->flags.AWAIT_IPV6) {
+		parent->flags.DNSSEC_WANT = false;
+		parent->flags.DNSSEC_INSECURE = true;
+		if (parent->stype != KNOT_RRTYPE_DS &&
+		    parent->stype != KNOT_RRTYPE_RRSIG) {
+			break;
+		}
+		parent = parent->parent;
+	}
+}
+
+static int update_parent_keys(struct kr_request *req, uint16_t answer_type)
+{
+	struct kr_query *qry = req->current_query;
+	struct kr_query *parent = qry->parent;
+	if (kr_fails_assert(parent))
+		return KR_STATE_FAIL;
+	switch(answer_type) {
+	case KNOT_RRTYPE_DNSKEY:
+		VERBOSE_MSG(qry, "<= parent: updating DNSKEY\n");
+		parent->zone_cut.key = knot_rrset_copy(qry->zone_cut.key, parent->zone_cut.pool);
+		if (!parent->zone_cut.key) {
+			return KR_STATE_FAIL;
+		}
+		break;
+	case KNOT_RRTYPE_DS:
+		VERBOSE_MSG(qry, "<= parent: updating DS\n");
+		if (qry->flags.DNSSEC_INSECURE) { /* DS non-existence proven. */
+			mark_insecure_parents(qry);
+		} else if (qry->flags.DNSSEC_NODS && !qry->flags.FORWARD) {
+			if (qry->flags.DNSSEC_OPTOUT) {
+				mark_insecure_parents(qry);
+			} else {
+				int ret = kr_dnssec_matches_name_and_type(&req->auth_selected, qry->uid,
+									  qry->sname, KNOT_RRTYPE_NS);
+				if (ret == kr_ok()) {
+					mark_insecure_parents(qry);
+				}
+			}
+		} else if (qry->flags.DNSSEC_NODS && qry->flags.FORWARD) {
+			int ret = kr_dnssec_matches_name_and_type(&req->auth_selected, qry->uid,
+								  qry->sname, KNOT_RRTYPE_NS);
+			if (ret == kr_ok()) {
+				mark_insecure_parents(qry);
+			}
+		} else { /* DS existence proven. */
+			parent->zone_cut.trust_anchor = knot_rrset_copy(qry->zone_cut.trust_anchor, parent->zone_cut.pool);
+			if (!parent->zone_cut.trust_anchor) {
+				return KR_STATE_FAIL;
+			}
+		}
+		break;
+	default: break;
+	}
+	return kr_ok();
+}
+
+static int update_delegation(struct kr_request *req, struct kr_query *qry, knot_pkt_t *answer, bool has_nsec3)
+{
+	struct kr_zonecut *cut = &qry->zone_cut;
+
+	/* RFC4035 3.1.4. authoritative must send either DS or proof of non-existence.
+	 * If it contains neither, resolver must query the parent for the DS (RFC4035 5.2.).
+	 * If DS exists, the referral is OK,
+	 * otherwise referral is bogus (or an attempted downgrade attack).
+	 */
+
+
+	unsigned section = KNOT_ANSWER;
+	const bool referral = !knot_wire_get_aa(answer->wire);
+	if (referral) {
+		section = KNOT_AUTHORITY;
+	} else if (knot_pkt_qtype(answer) == KNOT_RRTYPE_DS &&
+		   !(qry->flags.CNAME) &&
+		   (knot_wire_get_rcode(answer->wire) != KNOT_RCODE_NXDOMAIN)) {
+		section = KNOT_ANSWER;
+	} else { /* N/A */
+		return kr_ok();
+	}
+
+	int ret = 0;
+	const knot_dname_t *proved_name = knot_pkt_qname(answer);
+	/* Aggregate DS records (if using multiple keys) */
+	knot_rrset_t *new_ds = update_ds(cut, knot_pkt_section(answer, section));
+	if (!new_ds) {
+		/* No DS provided, check for proof of non-existence. */
+		if (!has_nsec3) {
+			if (referral) {
+				/* Check if it is referral to unsigned, rfc4035 5.2 */
+				ret = kr_nsec_ref_to_unsigned(&req->auth_selected,
+								qry->uid, proved_name);
+			} else {
+				/* No-data answer */
+				ret = kr_nsec_negative(&req->auth_selected, qry->uid,
+							proved_name, KNOT_RRTYPE_DS);
+				if (ret >= 0) {
+					if (ret == PKT_NODATA) {
+						ret = kr_ok();
+					} else {
+						ret = kr_error(ENOENT); // suspicious
+					}
+				}
+			}
+		} else {
+			if (referral) {
+				/* Check if it is referral to unsigned, rfc5155 8.9 */
+				ret = kr_nsec3_ref_to_unsigned(answer);
+			} else {
+				/* No-data answer, QTYPE is DS, rfc5155 8.6 */
+				ret = kr_nsec3_no_data(answer, KNOT_AUTHORITY, proved_name, KNOT_RRTYPE_DS);
+			}
+			if (ret == kr_error(KNOT_ERANGE)) {
+				/* Not bogus, going insecure due to optout */
+				ret = 0;
+			}
+		}
+
+		if (referral && qry->stype != KNOT_RRTYPE_DS &&
+		    ret == DNSSEC_NOT_FOUND) {
+			/* referral,
+			 * qtype is not KNOT_RRTYPE_DS, NSEC\NSEC3 were not found.
+			 * Check if DS already was fetched. */
+			knot_rrset_t *ta = cut->trust_anchor;
+			if (knot_dname_is_equal(cut->name, ta->owner)) {
+				/* DS is OK */
+				ret = 0;
+			}
+		} else if (ret != 0) {
+			VERBOSE_MSG(qry, "<= bogus proof of DS non-existence\n");
+			kr_request_set_extended_error(req, KNOT_EDNS_EDE_BOGUS, "Z4I6");
+			qry->flags.DNSSEC_BOGUS = true;
+		} else if (proved_name[0] != '\0') { /* don't go to insecure for . DS */
+			qry->flags.DNSSEC_NODS = true;
+			/* Rank the corresponding nonauth NS as insecure. */
+			for (int i = 0; i < req->auth_selected.len; ++i) {
+				ranked_rr_array_entry_t *ns = req->auth_selected.at[i];
+				if (ns->qry_uid != qry->uid
+				    || !ns->rr
+				    || ns->rr->type != KNOT_RRTYPE_NS) {
+					continue;
+				}
+				if (!referral && !knot_dname_is_equal(qry->sname, ns->rr->owner)) {
+					continue;
+				}
+				/* Found the record.  Note: this is slightly fragile
+				 * in case there were more NS records in the packet.
+				 * As it is now for referrals, kr_nsec*_ref_to_unsigned consider
+				 * (only) the first NS record in the packet. */
+				if (!kr_rank_test(ns->rank, KR_RANK_AUTH)) { /* sanity */
+					ns->rank = KR_RANK_INSECURE;
+				}
+				break;
+			}
+		}
+		return ret;
+	} else if (qry->flags.FORWARD && qry->parent) {
+		struct kr_query *parent = qry->parent;
+		parent->zone_cut.name = knot_dname_copy(qry->sname, parent->zone_cut.pool);
+	}
+
+	/* Extend trust anchor */
+	VERBOSE_MSG(qry, "<= DS: OK\n");
+	cut->trust_anchor = new_ds;
+	return ret;
+}
+
+static const knot_dname_t *find_first_signer(ranked_rr_array_t *arr, struct kr_query *qry)
+{
+	for (size_t i = 0; i < arr->len; ++i) {
+		ranked_rr_array_entry_t *entry = arr->at[i];
+		const knot_rrset_t *rr = entry->rr;
+		if (entry->yielded ||
+		    (!kr_rank_test(entry->rank, KR_RANK_INITIAL) &&
+		     !kr_rank_test(entry->rank, KR_RANK_TRY) &&
+		     !kr_rank_test(entry->rank, KR_RANK_MISMATCH))) {
+			continue;
+		}
+		if (rr->type != KNOT_RRTYPE_RRSIG) {
+			continue;
+		}
+		const knot_dname_t *signame = knot_rrsig_signer_name(rr->rrs.rdata);
+		if (knot_dname_in_bailiwick(rr->owner, signame) >= 0) {
+			return signame;
+		} else {
+			/* otherwise it's some nonsense, so we skip it */
+			kr_log_q(qry, VALIDATOR, "protocol violation: "
+					"out-of-bailiwick RRSIG signer, skipping\n");
+		}
+	}
+	return NULL;
+}
+
+static const knot_dname_t *signature_authority(struct kr_request *req)
+{
+	const knot_dname_t *signer_name = find_first_signer(&req->answ_selected, req->current_query);
+	if (!signer_name) {
+		signer_name = find_first_signer(&req->auth_selected, req->current_query);
+	}
+	return signer_name;
+}
+
+static int rrsig_not_found(const kr_layer_t * const ctx, const knot_pkt_t * const pkt,
+				const knot_rrset_t * const rr)
+{
+	/* Signatures are missing.  There might be a zone cut that we've skipped
+	 * and transitions to insecure.  That can commonly happen when iterating
+	 * and both sides of that cut are served by the same IP address(es).
+	 * We'll try proving that the name truly is insecure - by spawning
+	 * a DS sub-query on a suitable QNAME.
+	 */
+	struct kr_request * const req = ctx->req;
+	struct kr_query * const qry = req->current_query;
+
+	if (qry->flags.FORWARD || qry->flags.STUB) {
+		/* Undiscovered signed cuts can't happen in the current forwarding
+		 * algorithm, so this function shouldn't be able to help. */
+		return KR_STATE_FAIL;
+	}
+
+	/* Find cut_next: the name at which to try finding the "missing" zone cut. */
+	const knot_dname_t * const cut_top = qry->zone_cut.name;
+	const int next_depth = knot_dname_in_bailiwick(rr->owner, cut_top);
+	if (next_depth <= 0) {
+		return KR_STATE_FAIL; // shouldn't happen, I think
+	}
+	/* Add one extra label to cur_top, i.e. descend one level below current zone cut */
+	const knot_dname_t * const cut_next = rr->owner +
+		knot_dname_prefixlen(rr->owner, next_depth - 1, NULL);
+
+	/* Spawn that DS sub-query. */
+	struct kr_query * const next = kr_rplan_push(&req->rplan, qry, cut_next,
+						rr->rclass, KNOT_RRTYPE_DS);
+	if (!next) {
+		return KR_STATE_FAIL;
+	}
+	kr_zonecut_init(&next->zone_cut, qry->zone_cut.name, &req->pool);
+	kr_zonecut_copy(&next->zone_cut, &qry->zone_cut);
+	kr_zonecut_copy_trust(&next->zone_cut, &qry->zone_cut);
+	next->flags.DNSSEC_WANT = true;
+	return KR_STATE_YIELD;
+}
+
+static int check_validation_result(kr_layer_t *ctx, const knot_pkt_t *pkt, ranked_rr_array_t *arr)
+{
+	int ret = KR_STATE_DONE;
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+	ranked_rr_array_entry_t *invalid_entry = NULL;
+	for (size_t i = 0; i < arr->len; ++i) {
+		ranked_rr_array_entry_t *entry = arr->at[i];
+		if (entry->yielded || entry->qry_uid != qry->uid) {
+			continue;
+		}
+		if (kr_rank_test(entry->rank, KR_RANK_MISMATCH)) {
+			invalid_entry = entry;
+			break;
+		} else if (kr_rank_test(entry->rank, KR_RANK_MISSING) &&
+			   !invalid_entry) {
+			invalid_entry = entry;
+		} else if (kr_rank_test(entry->rank, KR_RANK_OMIT)) {
+			continue;
+		} else if (!kr_rank_test(entry->rank, KR_RANK_SECURE) &&
+			   !invalid_entry) {
+			invalid_entry = entry;
+		}
+	}
+
+	if (!invalid_entry) {
+		return ret;
+	}
+
+	if (!kr_rank_test(invalid_entry->rank, KR_RANK_SECURE) &&
+	    (++(invalid_entry->revalidation_cnt) > MAX_REVALIDATION_CNT)) {
+		VERBOSE_MSG(qry, "<= continuous revalidation, fails\n");
+		kr_request_set_extended_error(req, KNOT_EDNS_EDE_OTHER,
+			"4T4L: continuous revalidation");
+		qry->flags.DNSSEC_BOGUS = true;
+		return KR_STATE_FAIL;
+	}
+
+	const knot_rrset_t *rr = invalid_entry->rr;
+	if (kr_rank_test(invalid_entry->rank, KR_RANK_MISMATCH)) {
+		const knot_dname_t *signer_name = knot_rrsig_signer_name(rr->rrs.rdata);
+		if (knot_dname_in_bailiwick(signer_name, qry->zone_cut.name) > 0) {
+			qry->zone_cut.name = knot_dname_copy(signer_name, &req->pool);
+			qry->flags.AWAIT_CUT = true;
+		} else if (!knot_dname_is_equal(signer_name, qry->zone_cut.name)) {
+			if (qry->zone_cut.parent) {
+				memcpy(&qry->zone_cut, qry->zone_cut.parent, sizeof(qry->zone_cut));
+			} else {
+				qry->flags.AWAIT_CUT = true;
+			}
+			qry->zone_cut.name = knot_dname_copy(signer_name, &req->pool);
+		}
+		VERBOSE_MSG(qry, ">< cut changed (new signer), needs revalidation\n");
+		ret = KR_STATE_YIELD;
+	} else if (kr_rank_test(invalid_entry->rank, KR_RANK_MISSING)) {
+		ret = rrsig_not_found(ctx, pkt, rr);
+	} else if (!kr_rank_test(invalid_entry->rank, KR_RANK_SECURE)) {
+		kr_request_set_extended_error(req, KNOT_EDNS_EDE_BOGUS, "NXJA");
+		qry->flags.DNSSEC_BOGUS = true;
+		ret = KR_STATE_FAIL;
+	}
+
+	return ret;
+}
+
+static bool check_empty_answer(kr_layer_t *ctx, knot_pkt_t *pkt)
+{
+	struct kr_request *req	= ctx->req;
+	struct kr_query *qry	= req->current_query;
+	ranked_rr_array_t *arr	= &req->answ_selected;
+	size_t num_entries = 0;
+	for (size_t i = 0; i < arr->len; ++i) {
+		ranked_rr_array_entry_t *entry = arr->at[i];
+		const knot_rrset_t *rr = entry->rr;
+		if (rr->type == KNOT_RRTYPE_RRSIG && qry->stype != KNOT_RRTYPE_RRSIG) {
+			continue;
+		}
+		if (entry->qry_uid == qry->uid) {
+			++num_entries;
+		}
+	}
+	const knot_pktsection_t *an = knot_pkt_section(pkt, KNOT_ANSWER);
+	return ((an->count != 0) && (num_entries == 0)) ? false : true;
+}
+
+static int unsigned_forward(kr_layer_t *ctx, knot_pkt_t *pkt)
+{
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+	const uint16_t qtype = knot_pkt_qtype(pkt);
+	const uint8_t pkt_rcode = knot_wire_get_rcode(pkt->wire);
+	bool nods = false;
+	bool ns_exist = true;
+	for (int i = 0; i < req->rplan.resolved.len; ++i) {
+		struct kr_query *q = req->rplan.resolved.at[i];
+		if (q->sclass == qry->sclass &&
+		    q->stype == KNOT_RRTYPE_DS &&
+		    knot_dname_is_equal(q->sname, qry->sname)) {
+			nods = true;
+			if (!(q->flags.DNSSEC_OPTOUT)) {
+				int ret = kr_dnssec_matches_name_and_type(&req->auth_selected, q->uid,
+									  qry->sname, KNOT_RRTYPE_NS);
+				ns_exist = (ret == kr_ok());
+			}
+		}
+	}
+
+	if (nods && ns_exist && qtype == KNOT_RRTYPE_NS) {
+		qry->flags.DNSSEC_WANT = false;
+		qry->flags.DNSSEC_INSECURE = true;
+		if (qry->forward_flags.CNAME) {
+			if (kr_fails_assert(qry->cname_parent))
+				return KR_STATE_FAIL;
+			qry->cname_parent->flags.DNSSEC_WANT = false;
+			qry->cname_parent->flags.DNSSEC_INSECURE = true;
+		} else if (pkt_rcode == KNOT_RCODE_NOERROR && qry->parent != NULL) {
+			const knot_pktsection_t *sec = knot_pkt_section(pkt, KNOT_ANSWER);
+			const knot_rrset_t *rr = knot_pkt_rr(sec, 0);
+			if (rr->type == KNOT_RRTYPE_NS) {
+				qry->parent->zone_cut.name = knot_dname_copy(rr->owner, &req->pool);
+				qry->parent->flags.DNSSEC_WANT = false;
+				qry->parent->flags.DNSSEC_INSECURE = true;
+			}
+		}
+		while (qry->parent) {
+			qry = qry->parent;
+			qry->flags.DNSSEC_WANT = false;
+			qry->flags.DNSSEC_INSECURE = true;
+			if (qry->forward_flags.CNAME) {
+				if (kr_fails_assert(qry->cname_parent))
+					return KR_STATE_FAIL;
+				qry->cname_parent->flags.DNSSEC_WANT = false;
+				qry->cname_parent->flags.DNSSEC_INSECURE = true;
+			}
+		}
+		return KR_STATE_DONE;
+	}
+
+	if (ctx->state == KR_STATE_YIELD) {
+		return KR_STATE_DONE;
+	}
+
+	if (!nods && qtype != KNOT_RRTYPE_DS) {
+		struct kr_rplan *rplan = &req->rplan;
+		struct kr_query *next = kr_rplan_push(rplan, qry, qry->sname, qry->sclass, KNOT_RRTYPE_DS);
+		if (!next) {
+			return KR_STATE_FAIL;
+		}
+		kr_zonecut_set(&next->zone_cut, qry->zone_cut.name);
+		kr_zonecut_copy_trust(&next->zone_cut, &qry->zone_cut);
+		next->flags.DNSSEC_WANT = true;
+	}
+
+	return KR_STATE_YIELD;
+}
+
+static int check_signer(kr_layer_t *ctx, knot_pkt_t *pkt)
+{
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+	const knot_dname_t *ta_name = qry->zone_cut.trust_anchor ? qry->zone_cut.trust_anchor->owner : NULL;
+	const knot_dname_t *signer = signature_authority(req);
+	if (ta_name && (!signer || !knot_dname_is_equal(ta_name, signer))) {
+		/* check all newly added RRSIGs */
+		if (!signer) {
+			if (qry->flags.FORWARD) {
+				return unsigned_forward(ctx, pkt);
+			}
+			/* Not a DNSSEC-signed response. */
+			if (ctx->state == KR_STATE_YIELD) {
+				/* Already yielded for revalidation.
+				 * It means that trust chain is OK and
+				 * transition to INSECURE hasn't occurred.
+				 * Let the validation logic ask about RRSIG. */
+				return KR_STATE_DONE;
+			}
+			/* Ask parent for DS
+			 * to prove transition to INSECURE. */
+			const uint16_t qtype = knot_pkt_qtype(pkt);
+			const knot_dname_t *qname = knot_pkt_qname(pkt);
+			if (qtype == KNOT_RRTYPE_NS &&
+			    knot_dname_in_bailiwick(qname, qry->zone_cut.name) > 0) {
+				/* Server is authoritative
+				 * for both parent and child,
+				 * and child zone is not signed. */
+				qry->zone_cut.name = knot_dname_copy(qname, &req->pool);
+			}
+		} else if (knot_dname_in_bailiwick(signer, qry->zone_cut.name) > 0) {
+			if (!(qry->flags.FORWARD)) {
+				/* Key signer is below current cut, advance and refetch keys. */
+				qry->zone_cut.name = knot_dname_copy(signer, &req->pool);
+			} else {
+				/* Check if DS does not exist. */
+				struct kr_query *q = kr_rplan_find_resolved(&req->rplan, NULL,
+									    signer, qry->sclass, KNOT_RRTYPE_DS);
+				if (q && q->flags.DNSSEC_NODS) {
+					qry->flags.DNSSEC_WANT = false;
+					qry->flags.DNSSEC_INSECURE = true;
+					if (qry->parent) {
+						qry->parent->flags.DNSSEC_WANT = false;
+						qry->parent->flags.DNSSEC_INSECURE = true;
+					}
+				} else if (qry->stype != KNOT_RRTYPE_DS) {
+					struct kr_rplan *rplan = &req->rplan;
+					struct kr_query *next = kr_rplan_push(rplan, qry, qry->sname,
+									      qry->sclass, KNOT_RRTYPE_DS);
+					if (!next) {
+						return KR_STATE_FAIL;
+					}
+					kr_zonecut_set(&next->zone_cut, qry->zone_cut.name);
+					kr_zonecut_copy_trust(&next->zone_cut, &qry->zone_cut);
+					next->flags.DNSSEC_WANT = true;
+				}
+			}
+		} else if (!knot_dname_is_equal(signer, qry->zone_cut.name)) {
+			/* Key signer is above the current cut, so we can't validate it. This happens when
+			   a server is authoritative for both grandparent, parent and child zone.
+			   Ascend to parent cut, and refetch authority for signer. */
+			if (qry->zone_cut.parent) {
+				memcpy(&qry->zone_cut, qry->zone_cut.parent, sizeof(qry->zone_cut));
+			} else {
+				qry->flags.AWAIT_CUT = true;
+			}
+			qry->zone_cut.name = knot_dname_copy(signer, &req->pool);
+		}
+
+		/* zone cut matches, but DS/DNSKEY doesn't => refetch. */
+		VERBOSE_MSG(qry, ">< cut changed, needs revalidation\n");
+		if ((qry->flags.FORWARD) && qry->stype != KNOT_RRTYPE_DS) {
+			struct kr_rplan *rplan = &req->rplan;
+			struct kr_query *next = kr_rplan_push(rplan, qry, signer,
+							qry->sclass, KNOT_RRTYPE_DS);
+			if (!next) {
+				return KR_STATE_FAIL;
+			}
+			kr_zonecut_set(&next->zone_cut, qry->zone_cut.name);
+			kr_zonecut_copy_trust(&next->zone_cut, &qry->zone_cut);
+			next->flags.DNSSEC_WANT = true;
+			return KR_STATE_YIELD;
+		}
+		if (!(qry->flags.FORWARD)) {
+			return KR_STATE_YIELD;
+		}
+	}
+	return KR_STATE_DONE;
+}
+
+/** Change ranks of RRs from this single iteration:
+ * _INITIAL or _TRY or _MISSING -> rank_to_set.  Or any rank, if any_rank == true.
+ *
+ * Optionally do this only in a `bailiwick` (if not NULL).
+ * Iterator shouldn't have selected such records, but we check to be sure. */
+static void rank_records(struct kr_query *qry, bool any_rank, enum kr_rank rank_to_set,
+			 const knot_dname_t *bailiwick)
+{
+	struct kr_request *req = qry->request;
+	ranked_rr_array_t *ptrs[2] = { &req->answ_selected, &req->auth_selected };
+	for (size_t i = 0; i < 2; ++i) {
+		ranked_rr_array_t *arr = ptrs[i];
+		for (size_t j = 0; j < arr->len; ++j) {
+			ranked_rr_array_entry_t *entry = arr->at[j];
+			if (entry->qry_uid != qry->uid) {
+				continue;
+			}
+			if (bailiwick && knot_dname_in_bailiwick(entry->rr->owner,
+								 bailiwick) < 0) {
+				continue;
+			}
+			if (any_rank
+			    || kr_rank_test(entry->rank, KR_RANK_INITIAL)
+			    || kr_rank_test(entry->rank, KR_RANK_TRY)
+			    || kr_rank_test(entry->rank, KR_RANK_MISSING)) {
+				kr_rank_set(&entry->rank, rank_to_set);
+			}
+		}
+	}
+}
+
+static void check_wildcard(kr_layer_t *ctx)
+{
+	struct kr_request *req	   = ctx->req;
+	struct kr_query *qry	   = req->current_query;
+	ranked_rr_array_t *ptrs[2] = { &req->answ_selected, &req->auth_selected };
+
+	for (int i = 0; i < 2; ++i) {
+		ranked_rr_array_t *arr = ptrs[i];
+		for (ssize_t j = 0; j < arr->len; ++j) {
+			ranked_rr_array_entry_t *entry = arr->at[j];
+			const knot_rrset_t *rrsigs = entry->rr;
+
+			if (qry->uid != entry->qry_uid) {
+				continue;
+			}
+
+			if (rrsigs->type != KNOT_RRTYPE_RRSIG) {
+				continue;
+			}
+
+			int owner_labels = knot_dname_labels(rrsigs->owner, NULL);
+
+			knot_rdata_t *rdata_k = rrsigs->rrs.rdata;
+			for (int k = 0; k < rrsigs->rrs.count;
+					++k, rdata_k = knot_rdataset_next(rdata_k)) {
+				if (knot_rrsig_labels(rdata_k) != owner_labels) {
+					qry->flags.DNSSEC_WEXPAND = true;
+				}
+			}
+		}
+	}
+}
+
+/** Just for wildcard_adjust_to_wire() */
+static bool rr_is_for_wildcard(const ranked_rr_array_entry_t *entry)
+{
+	switch (kr_rrset_type_maysig(entry->rr)) {
+	case KNOT_RRTYPE_NSEC:
+	case KNOT_RRTYPE_NSEC3:
+		return true;
+	default:
+		return false;
+	}
+}
+/** In case of wildcard expansion, mark required authority RRs by to_wire. */
+static int wildcard_adjust_to_wire(struct kr_request *req, const struct kr_query *qry)
+{
+	if (!qry->parent && qry->flags.DNSSEC_WEXPAND) {
+		return kr_ranked_rrarray_set_wire(&req->auth_selected, true,
+				qry->uid, true, &rr_is_for_wildcard);
+	}
+	return kr_ok();
+}
+
+static int validate(kr_layer_t *ctx, knot_pkt_t *pkt)
+{
+	int ret = 0;
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+
+	/* Ignore faulty or unprocessed responses. */
+	if (ctx->state & (KR_STATE_FAIL|KR_STATE_CONSUME)) {
+		return ctx->state;
+	}
+
+	/* Pass-through if user doesn't want secure answer or stub. */
+	if (qry->flags.STUB) {
+		rank_records(qry, false, KR_RANK_OMIT, NULL);
+		return ctx->state;
+	}
+	uint8_t pkt_rcode = knot_wire_get_rcode(pkt->wire);
+	if ((qry->flags.FORWARD) &&
+	    pkt_rcode != KNOT_RCODE_NOERROR &&
+	    pkt_rcode != KNOT_RCODE_NXDOMAIN) {
+		do {
+			qry->flags.DNSSEC_BOGUS = true;
+			if (qry->cname_parent) {
+				qry->cname_parent->flags.DNSSEC_BOGUS = true;
+			}
+			qry = qry->parent;
+		} while (qry);
+		ctx->state = KR_STATE_DONE;
+		return ctx->state;
+	}
+
+	if (!(qry->flags.DNSSEC_WANT)) {
+		const bool is_insec = qry->flags.CACHED && qry->flags.DNSSEC_INSECURE;
+		if ((qry->flags.DNSSEC_INSECURE)) {
+			rank_records(qry, true, KR_RANK_INSECURE, qry->zone_cut.name);
+		}
+		if (is_insec && qry->parent != NULL) {
+			/* We have got insecure answer from cache.
+			 * Mark parent(s) as insecure. */
+			mark_insecure_parents(qry);
+			VERBOSE_MSG(qry, "<= cached insecure response, going insecure\n");
+			ctx->state = KR_STATE_DONE;
+		} else if (ctx->state == KR_STATE_YIELD) {
+			/* Transition to insecure state
+			   occurred during revalidation.
+			   if state remains YIELD, answer will not be cached.
+			   Let cache layers to work. */
+			ctx->state = KR_STATE_DONE;
+		}
+		return ctx->state;
+	}
+
+	/* Pass-through if CD bit is set. */
+	if (knot_wire_get_cd(req->qsource.packet->wire)) {
+		check_wildcard(ctx);
+		wildcard_adjust_to_wire(req, qry);
+		rank_records(qry, false, KR_RANK_OMIT, NULL);
+		return ctx->state;
+	}
+	/* Answer for RRSIG may not set DO=1, but all records MUST still validate. */
+	bool use_signatures = (knot_pkt_qtype(pkt) != KNOT_RRTYPE_RRSIG);
+	if (!(qry->flags.CACHED) && !knot_pkt_has_dnssec(pkt) && !use_signatures) {
+		VERBOSE_MSG(qry, "<= got insecure response\n");
+		kr_request_set_extended_error(req, KNOT_EDNS_EDE_BOGUS, "MISQ");
+		qry->flags.DNSSEC_BOGUS = true;
+		return KR_STATE_FAIL;
+	}
+
+	/* Check if this is a DNSKEY answer, check trust chain and store. */
+	uint16_t qtype = knot_pkt_qtype(pkt);
+	bool has_nsec3 = pkt_has_type(pkt, KNOT_RRTYPE_NSEC3);
+	const knot_pktsection_t *an = knot_pkt_section(pkt, KNOT_ANSWER);
+	const bool referral = (an->count == 0 && !knot_wire_get_aa(pkt->wire));
+
+	if (!(qry->flags.CACHED) && knot_wire_get_aa(pkt->wire)) {
+		/* Check if answer if not empty,
+		 * but iterator has not selected any records. */
+		if (!check_empty_answer(ctx, pkt)) {
+			VERBOSE_MSG(qry, "<= no useful RR in authoritative answer\n");
+			kr_request_set_extended_error(req, KNOT_EDNS_EDE_BOGUS, "MJX6");
+			qry->flags.DNSSEC_BOGUS = true;
+			return KR_STATE_FAIL;
+		}
+		/* Track difference between current TA and signer name.
+		 * This indicates that the NS is auth for both parent-child,
+		 * and we must update DS/DNSKEY to validate it.
+		 */
+		ret = check_signer(ctx, pkt);
+		if (ret != KR_STATE_DONE) {
+			return ret;
+		}
+		if (qry->flags.FORWARD && qry->flags.DNSSEC_INSECURE) {
+			return KR_STATE_DONE;
+		}
+	}
+
+	if (knot_wire_get_aa(pkt->wire) && qtype == KNOT_RRTYPE_DNSKEY) {
+		const knot_rrset_t *ds = qry->zone_cut.trust_anchor;
+		if (ds && !kr_ds_algo_support(ds)) {
+			VERBOSE_MSG(qry, ">< all DS entries use unsupported algorithm pairs, going insecure\n");
+			/* ^ the message is a bit imprecise to avoid being too verbose */
+			kr_request_set_extended_error(req, KNOT_EDNS_EDE_OTHER, "LSLC: unsupported digest/key");
+			qry->flags.DNSSEC_WANT = false;
+			qry->flags.DNSSEC_INSECURE = true;
+			rank_records(qry, true, KR_RANK_INSECURE, qry->zone_cut.name);
+			mark_insecure_parents(qry);
+			return KR_STATE_DONE;
+		}
+
+		ret = validate_keyset(req, pkt, has_nsec3);
+		if (ret == kr_error(EAGAIN)) {
+			VERBOSE_MSG(qry, ">< cut changed, needs revalidation\n");
+			return KR_STATE_YIELD;
+		} else if (ret != 0) {
+			VERBOSE_MSG(qry, "<= bad keys, broken trust chain\n");
+			/* EDE code already set in validate_keyset() */
+			qry->flags.DNSSEC_BOGUS = true;
+			return KR_STATE_FAIL;
+		}
+	}
+
+	/* Validate all records, fail as bogus if it doesn't match.
+	 * Do not revalidate data from cache, as it's already trusted.
+	 * TTLs of RRsets may get lowered. */
+	if (!(qry->flags.CACHED)) {
+		ret = validate_records(req, pkt, req->rplan.pool, has_nsec3);
+		if (ret == KNOT_EDOWNGRADED) {
+			return KR_STATE_DONE;
+		} else if (ret != 0) {
+			/* something exceptional - no DNS key, empty pointers etc
+			 * normally it shouldn't happen */
+			VERBOSE_MSG(qry, "<= couldn't validate RRSIGs\n");
+			kr_request_set_extended_error(req, KNOT_EDNS_EDE_OTHER,
+				"O4TP: couldn't validate RRSIGs");
+			qry->flags.DNSSEC_BOGUS = true;
+			return KR_STATE_FAIL;
+		}
+		/* check validation state and spawn subrequests */
+		if (!req->answ_validated) {
+			ret = check_validation_result(ctx, pkt, &req->answ_selected);
+			if (ret != KR_STATE_DONE) {
+				return ret;
+			}
+		}
+		if (!req->auth_validated) {
+			ret = check_validation_result(ctx, pkt, &req->auth_selected);
+			if (ret != KR_STATE_DONE) {
+				return ret;
+			}
+		}
+	}
+
+	/* Validate non-existence proof if not positive answer.
+	 * In case of CNAME, iterator scheduled a sibling query for the target,
+	 * so we just drop the negative piece of information and don't try to prove it.
+	 * TODO: not ideal; with aggressive cache we'll at least avoid the extra packet. */
+	if (!qry->flags.CACHED && pkt_rcode == KNOT_RCODE_NXDOMAIN && !qry->flags.CNAME) {
+		/* @todo If knot_pkt_qname(pkt) is used instead of qry->sname then the tests crash. */
+		if (!has_nsec3) {
+			ret = kr_nsec_negative(&req->auth_selected, qry->uid,
+						qry->sname, KNOT_RRTYPE_NULL);
+			if (ret >= 0) {
+				if (ret & PKT_NXDOMAIN) {
+					ret = kr_ok();
+				} else {
+					ret = kr_error(ENOENT); // probably proved NODATA
+				}
+			}
+		} else {
+			ret = kr_nsec3_name_error_response_check(pkt, KNOT_AUTHORITY, qry->sname);
+		}
+		if (has_nsec3 && (ret == kr_error(KNOT_ERANGE))) {
+			/* NXDOMAIN proof is OK,
+			 * but NSEC3 that covers next closer name
+			 * (or wildcard at next closer name) has opt-out flag.
+			 * RFC5155 9.2; AD flag can not be set */
+			qry->flags.DNSSEC_OPTOUT = true;
+			VERBOSE_MSG(qry, "<= can't prove NXDOMAIN due to optout, going insecure\n");
+		} else if (ret != 0) {
+			VERBOSE_MSG(qry, "<= bad NXDOMAIN proof\n");
+			kr_request_set_extended_error(req, KNOT_EDNS_EDE_NSEC_MISS, "3WKM");
+			qry->flags.DNSSEC_BOGUS = true;
+			return KR_STATE_FAIL;
+		}
+	}
+
+	/* @todo WTH, this needs API that just tries to find a proof and the caller
+	 * doesn't have to worry about NSEC/NSEC3
+	 * @todo rework this
+	 * CNAME: same as the NXDOMAIN case above */
+	if (!qry->flags.CACHED && pkt_rcode == KNOT_RCODE_NOERROR && !qry->flags.CNAME) {
+		bool no_data = (an->count == 0 && knot_wire_get_aa(pkt->wire));
+		if (no_data) {
+			/* @todo
+			 * ? quick mechanism to determine which check to preform first
+			 * ? merge the functionality together to share code/resources
+			 */
+			if (!has_nsec3) {
+				ret = kr_nsec_negative(&req->auth_selected, qry->uid,
+							knot_pkt_qname(pkt), knot_pkt_qtype(pkt));
+				if (ret >= 0) {
+					if (ret == PKT_NODATA) {
+						ret = kr_ok();
+					} else {
+						ret = kr_error(ENOENT); // suspicious
+					}
+				}
+			} else {
+				ret = kr_nsec3_no_data(pkt, KNOT_AUTHORITY, knot_pkt_qname(pkt), knot_pkt_qtype(pkt));
+			}
+			if (ret != 0) {
+				if (has_nsec3 && (ret == kr_error(KNOT_ERANGE))) {
+					VERBOSE_MSG(qry, "<= can't prove NODATA due to optout, going insecure\n");
+					qry->flags.DNSSEC_OPTOUT = true;
+					/* Could not return from here,
+					 * we must continue, validate NSEC\NSEC3 and
+					 * call update_parent_keys() to mark
+					 * parent queries as insecure */
+				} else {
+					VERBOSE_MSG(qry, "<= bad NODATA proof\n");
+					kr_request_set_extended_error(req, KNOT_EDNS_EDE_NSEC_MISS, "AHXI");
+					qry->flags.DNSSEC_BOGUS = true;
+					return KR_STATE_FAIL;
+				}
+			}
+		}
+	}
+
+	wildcard_adjust_to_wire(req, qry);
+
+	/* Check and update current delegation point security status. */
+	ret = update_delegation(req, qry, pkt, has_nsec3);
+	if (ret == DNSSEC_NOT_FOUND && qry->stype != KNOT_RRTYPE_DS) {
+		if (ctx->state == KR_STATE_YIELD) {
+			VERBOSE_MSG(qry, "<= can't validate referral\n");
+			kr_request_set_extended_error(req, KNOT_EDNS_EDE_BOGUS, "XLE4");
+			qry->flags.DNSSEC_BOGUS = true;
+			return KR_STATE_FAIL;
+		} else {
+			/* Check the trust chain and query DS\DNSKEY if needed. */
+			VERBOSE_MSG(qry, "<= DS\\NSEC was not found, querying for DS\n");
+			return KR_STATE_YIELD;
+		}
+	} else if (ret != 0) {
+		return KR_STATE_FAIL;
+	} else if (pkt_rcode == KNOT_RCODE_NOERROR &&
+		   referral &&
+		   ((!qry->flags.DNSSEC_WANT && qry->flags.DNSSEC_INSECURE) ||
+		   (qry->flags.DNSSEC_NODS))) {
+		/* referral with proven DS non-existence */
+		qtype = KNOT_RRTYPE_DS;
+	}
+	/* Update parent query zone cut */
+	if (qry->parent) {
+		if (update_parent_keys(req, qtype) != 0) {
+			return KR_STATE_FAIL;
+		}
+	}
+
+	if (qry->flags.FORWARD && qry->parent) {
+		if (pkt_rcode == KNOT_RCODE_NXDOMAIN) {
+			qry->parent->forward_flags.NO_MINIMIZE = true;
+		}
+	}
+	VERBOSE_MSG(qry, "<= answer valid, OK\n");
+	return KR_STATE_DONE;
+}
+
+/** Hide RRsets which did not validate from clients. */
+static int hide_bogus(kr_layer_t *ctx) {
+	if (knot_wire_get_cd(ctx->req->qsource.packet->wire)) {
+		return ctx->state;
+	}
+	/* We don't want to send bogus answers to clients, not even in SERVFAIL
+	 * answers, but we cannot drop whole sections. If a CNAME chain
+	 * SERVFAILs somewhere, the steps that were OK should be put into
+	 * answer.
+	 *
+	 * There is one specific issue: currently we follow CNAME *before*
+	 * we validate it, because... iterator comes before validator.
+	 * Therefore some rrsets might be added into req->*_selected before
+	 * we detected failure in validator.
+	 * TODO: better approach, probably during work on parallel queries.
+	 */
+	const ranked_rr_array_t *sel[] = kr_request_selected(ctx->req);
+	for (knot_section_t sect = KNOT_ANSWER; sect <= KNOT_ADDITIONAL; ++sect) {
+		for (size_t i = 0; i < sel[sect]->len; ++i) {
+			ranked_rr_array_entry_t *e = sel[sect]->at[i];
+			e->to_wire = e->to_wire
+				&& !kr_rank_test(e->rank, KR_RANK_INDET)
+				&& !kr_rank_test(e->rank, KR_RANK_BOGUS)
+				&& !kr_rank_test(e->rank, KR_RANK_MISMATCH)
+				&& !kr_rank_test(e->rank, KR_RANK_MISSING);
+		}
+	}
+	return ctx->state;
+}
+
+static int validate_wrapper(kr_layer_t *ctx, knot_pkt_t *pkt) {
+	// Wrapper for now.
+	int ret = validate(ctx, pkt);
+	struct kr_request *req = ctx->req;
+	struct kr_query *qry = req->current_query;
+	if (ret & KR_STATE_FAIL && qry->flags.DNSSEC_BOGUS)
+		qry->server_selection.error(qry, req->upstream.transport, KR_SELECTION_DNSSEC_ERROR);
+	if (ret & KR_STATE_DONE && !qry->flags.DNSSEC_BOGUS) {
+		/* Don't report extended DNS errors related to validation
+		 * when it managed to succeed (e.g. by trying different auth). */
+		switch (req->extended_error.info_code) {
+		case KNOT_EDNS_EDE_BOGUS:
+		case KNOT_EDNS_EDE_NSEC_MISS:
+		case KNOT_EDNS_EDE_RRSIG_MISS:
+		case KNOT_EDNS_EDE_SIG_EXPIRED:
+		case KNOT_EDNS_EDE_SIG_NOTYET:
+			kr_request_set_extended_error(req, KNOT_EDNS_EDE_NONE, NULL);
+			break;
+		case KNOT_EDNS_EDE_DNSKEY_MISS:
+		case KNOT_EDNS_EDE_DNSKEY_BIT:
+			kr_assert(false);  /* These EDE codes aren't used. */
+			break;
+		default: break;  /* Remaining codes don't indicate hard DNSSEC failure. */
+		}
+	}
+	return ret;
+}
+
+
+/** Module implementation. */
+int validate_init(struct kr_module *self)
+{
+	static const kr_layer_api_t layer = {
+		.consume = &validate_wrapper,
+		.answer_finalize = &hide_bogus,
+	};
+	self->layer = &layer;
+	return kr_ok();
+}
+
+KR_MODULE_EXPORT(validate) /* useless for builtin module, but let's be consistent */
+
+#undef VERBOSE_MSG