From 1f5cb247ecd20ba57c472138f94856aa83caf042 Mon Sep 17 00:00:00 2001
From: Mark Andrews <marka@isc.org>
Date: Tue, 1 Mar 2022 09:48:05 +1100
Subject: [PATCH] Add additional name checks when using a forwarder
When using a forwarder, check that the owner name of response
records are within the bailiwick of the forwarded name space.
(cherry picked from commit e8df2802ac62016ea68585893eb4310fc3329028)
Check that the forward declaration is unchanged and not overridden
If we are using a fowarder, in addition to checking that names to
be cached are subdomains of the forwarded namespace, we must also
check that there are no subsidiary forwarded namespaces which would
take precedence. To be safe, we don't cache any responses if the
forwarding configuration has changed since the query was sent.
(cherry picked from commit 590f8698fc876d6d72f75cf35359e7546c3af972)
Check cached names for possible "forward only" clause
When caching additional and glue data *not* from a forwarder, we must
check that there is no "forward only" clause covering the owner name
that would take precedence. Such names would normally be allowed by
baliwick rules, but a "forward only" zone introduces a new baliwick
scope.
(cherry picked from commit 4a144fae16e70517be894a971cef1d085ee68ebe)
Look for zones deeper than the current domain or forward name
When caching glue, we need to ensure that there is no closer
source of truth for the name. If the owner name for the glue
record would be answered by a locally configured zone, do not
cache.
(cherry picked from commit 42f8c538d3fb9d075b98d82688aeb71621798754)
Avoid use of compound literals
Compound literals are not used in BIND 9.11, in order to ensure backward
compatibility with ancient compilers. Rework the relevant parts of the
BIND 9.11 backport of the CVE-2021-25220 fix so that compound literals
are not used.
(cherry picked from commit d4b1efbcbd4dfb8c6ef303968992440c5bdeed15)
---
lib/dns/resolver.c | 130 +++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 125 insertions(+), 5 deletions(-)
diff --git a/lib/dns/resolver.c b/lib/dns/resolver.c
index c912f3aea8..2c68973899 100644
--- a/lib/dns/resolver.c
+++ b/lib/dns/resolver.c
@@ -63,6 +63,7 @@
#include <dns/stats.h>
#include <dns/tsig.h>
#include <dns/validator.h>
+#include <dns/zone.h>
#ifdef WANT_QUERYTRACE
#define RTRACE(m) isc_log_write(dns_lctx, \
@@ -312,6 +313,8 @@ struct fetchctx {
bool ns_ttl_ok;
uint32_t ns_ttl;
isc_counter_t * qc;
+ dns_fixedname_t fwdfname;
+ dns_name_t *fwdname;
/*%
* The number of events we're waiting for.
@@ -3393,6 +3396,7 @@ fctx_getaddresses(fetchctx_t *fctx, bool badcache) {
if (result == ISC_R_SUCCESS) {
fwd = ISC_LIST_HEAD(forwarders->fwdrs);
fctx->fwdpolicy = forwarders->fwdpolicy;
+ dns_name_copy(domain, fctx->fwdname, NULL);
if (fctx->fwdpolicy == dns_fwdpolicy_only &&
isstrictsubdomain(domain, &fctx->domain)) {
fcount_decr(fctx);
@@ -4422,6 +4426,9 @@ fctx_create(dns_resolver_t *res, dns_name_t *name, dns_rdatatype_t type,
fctx->restarts = 0;
fctx->querysent = 0;
fctx->referrals = 0;
+
+ fctx->fwdname = dns_fixedname_initname(&fctx->fwdfname);
+
TIME_NOW(&fctx->start);
fctx->timeouts = 0;
fctx->lamecount = 0;
@@ -4480,8 +4487,10 @@ fctx_create(dns_resolver_t *res, dns_name_t *name, dns_rdatatype_t type,
domain = dns_fixedname_initname(&fixed);
result = dns_fwdtable_find2(fctx->res->view->fwdtable, fwdname,
domain, &forwarders);
- if (result == ISC_R_SUCCESS)
+ if (result == ISC_R_SUCCESS) {
fctx->fwdpolicy = forwarders->fwdpolicy;
+ dns_name_copy(domain, fctx->fwdname, NULL);
+ }
if (fctx->fwdpolicy != dns_fwdpolicy_only) {
/*
@@ -6231,6 +6240,112 @@ mark_related(dns_name_t *name, dns_rdataset_t *rdataset,
rdataset->attributes |= DNS_RDATASETATTR_EXTERNAL;
}
+/*
+ * Returns true if 'name' is external to the namespace for which
+ * the server being queried can answer, either because it's not a
+ * subdomain or because it's below a forward declaration or a
+ * locally served zone.
+ */
+static inline bool
+name_external(dns_name_t *name, dns_rdatatype_t type, fetchctx_t *fctx) {
+ isc_result_t result;
+ dns_forwarders_t *forwarders = NULL;
+ dns_fixedname_t fixed, zfixed;
+ dns_name_t *fname = dns_fixedname_initname(&fixed);
+ dns_name_t *zfname = dns_fixedname_initname(&zfixed);
+ dns_name_t *apex = NULL;
+ dns_name_t suffix;
+ dns_zone_t *zone = NULL;
+ unsigned int labels;
+ dns_namereln_t rel;
+ /*
+ * The following two variables do not influence code flow; they are
+ * only necessary for calling dns_name_fullcompare().
+ */
+ int _orderp = 0;
+ unsigned int _nlabelsp = 0;
+
+ apex = ISFORWARDER(fctx->addrinfo) ? fctx->fwdname : &fctx->domain;
+
+ /*
+ * The name is outside the queried namespace.
+ */
+ rel = dns_name_fullcompare(name, apex, &_orderp, &_nlabelsp);
+ if (rel != dns_namereln_subdomain && rel != dns_namereln_equal) {
+ return (true);
+ }
+
+ /*
+ * If the record lives in the parent zone, adjust the name so we
+ * look for the correct zone or forward clause.
+ */
+ labels = dns_name_countlabels(name);
+ if (dns_rdatatype_atparent(type) && labels > 1U) {
+ dns_name_init(&suffix, NULL);
+ dns_name_getlabelsequence(name, 1, labels - 1, &suffix);
+ name = &suffix;
+ } else if (rel == dns_namereln_equal) {
+ /* If 'name' is 'apex', no further checking is needed. */
+ return (false);
+ }
+
+ /*
+ * If there is a locally served zone between 'apex' and 'name'
+ * then don't cache.
+ */
+ LOCK(&fctx->res->view->lock);
+ if (fctx->res->view->zonetable != NULL) {
+ unsigned int options = DNS_ZTFIND_NOEXACT;
+ result = dns_zt_find(fctx->res->view->zonetable, name, options,
+ zfname, &zone);
+ if (zone != NULL) {
+ dns_zone_detach(&zone);
+ }
+ if (result == ISC_R_SUCCESS || result == DNS_R_PARTIALMATCH) {
+ if (dns_name_fullcompare(zfname, apex, &_orderp,
+ &_nlabelsp) ==
+ dns_namereln_subdomain)
+ {
+ UNLOCK(&fctx->res->view->lock);
+ return (true);
+ }
+ }
+ }
+ UNLOCK(&fctx->res->view->lock);
+
+ /*
+ * Look for a forward declaration below 'name'.
+ */
+ result = dns_fwdtable_find2(fctx->res->view->fwdtable, name, fname,
+ &forwarders);
+
+ if (ISFORWARDER(fctx->addrinfo)) {
+ /*
+ * See if the forwarder declaration is better.
+ */
+ if (result == ISC_R_SUCCESS) {
+ return (!dns_name_equal(fname, fctx->fwdname));
+ }
+
+ /*
+ * If the lookup failed, the configuration must have
+ * changed: play it safe and don't cache.
+ */
+ return (true);
+ } else if (result == ISC_R_SUCCESS &&
+ forwarders->fwdpolicy == dns_fwdpolicy_only &&
+ !ISC_LIST_EMPTY(forwarders->fwdrs))
+ {
+ /*
+ * If 'name' is covered by a 'forward only' clause then we
+ * can't cache this repsonse.
+ */
+ return (true);
+ }
+
+ return (false);
+}
+
static isc_result_t
check_section(void *arg, dns_name_t *addname, dns_rdatatype_t type,
dns_section_t section)
@@ -6259,7 +6374,7 @@ check_section(void *arg, dns_name_t *addname, dns_rdatatype_t type,
result = dns_message_findname(rmessage, section, addname,
dns_rdatatype_any, 0, &name, NULL);
if (result == ISC_R_SUCCESS) {
- external = !dns_name_issubdomain(name, &fctx->domain);
+ external = name_external(name, type, fctx);
if (type == dns_rdatatype_a) {
for (rdataset = ISC_LIST_HEAD(name->list);
rdataset != NULL;
@@ -7141,6 +7256,13 @@ answer_response(fetchctx_t *fctx, dns_message_t *message) {
break;
case dns_namereln_subdomain:
+ /*
+ * Don't accept DNAME from parent namespace.
+ */
+ if (name_external(name, dns_rdatatype_dname, fctx)) {
+ continue;
+ }
+
/*
* In-scope DNAME records must have at least
* as many labels as the domain being queried.
@@ -7376,11 +7498,9 @@ answer_response(fetchctx_t *fctx, dns_message_t *message) {
*/
result = dns_message_firstname(message, DNS_SECTION_AUTHORITY);
while (!done && result == ISC_R_SUCCESS) {
- bool external;
name = NULL;
dns_message_currentname(message, DNS_SECTION_AUTHORITY, &name);
- external = !dns_name_issubdomain(name, &fctx->domain);
- if (!external) {
+ if (!name_external(name, dns_rdatatype_ns, fctx)) {
/*
* We expect to find NS or SIG NS rdatasets, and
* nothing else.
--
2.34.1