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|
From: Debian DNS Team <team+dns@tracker.debian.org>
Date: Mon, 14 Mar 2022 15:31:10 +0100
Subject: CVE-2021-25220
---
lib/dns/resolver.c | 125 ++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 120 insertions(+), 5 deletions(-)
diff --git a/lib/dns/resolver.c b/lib/dns/resolver.c
index bfc1ae2..cabcbdc 100644
--- a/lib/dns/resolver.c
+++ b/lib/dns/resolver.c
@@ -68,6 +68,7 @@
#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, \
@@ -314,6 +315,8 @@ 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.
@@ -3304,6 +3307,7 @@ 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);
@@ -4334,6 +4338,9 @@ 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;
@@ -4386,8 +4393,10 @@ 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) {
/*
@@ -6144,6 +6153,107 @@ 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;
+
+ apex = ISFORWARDER(fctx->addrinfo) ? fctx->fwdname : &fctx->domain;
+
+ /*
+ * The name is outside the queried namespace.
+ */
+ rel = dns_name_fullcompare(name, apex, &(int){ 0 },
+ &(unsigned int){ 0U });
+ 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, &(int){ 0 },
+ &(unsigned int){ 0U }) ==
+ 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)
@@ -6170,7 +6280,7 @@ check_section(void *arg, dns_name_t *addname, dns_rdatatype_t type,
result = dns_message_findname(fctx->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;
@@ -7018,6 +7128,13 @@ answer_response(fetchctx_t *fctx) {
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.
@@ -7246,11 +7363,9 @@ answer_response(fetchctx_t *fctx) {
*/
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.
|
