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From 165181b794e185af8621300e2a68777a04af8358 Mon Sep 17 00:00:00 2001
From: Petr Mensik <pemensik@redhat.com>
Date: Fri, 15 May 2020 14:55:26 +0200
Subject: [PATCH] CVE-2020-8616
5395. [security] Further limit the number of queries that can be
triggered from a request. Root and TLD servers
are no longer exempt from max-recursion-queries.
Fetches for missing name server address records
are limited to 4 for any domain. (CVE-2020-8616)
[GL #1388]
---
lib/dns/adb.c | 33 +++++++++++++----------
lib/dns/include/dns/adb.h | 4 +++
lib/dns/resolver.c | 55 ++++++++++++++++++++++++++-------------
3 files changed, 60 insertions(+), 32 deletions(-)
diff --git a/lib/dns/adb.c b/lib/dns/adb.c
index 3d12221..ec183d0 100644
--- a/lib/dns/adb.c
+++ b/lib/dns/adb.c
@@ -404,14 +404,13 @@ static void log_quota(dns_adbentry_t *entry, const char *fmt, ...)
*/
#define FIND_WANTEVENT(fn) (((fn)->options & DNS_ADBFIND_WANTEVENT) != 0)
#define FIND_WANTEMPTYEVENT(fn) (((fn)->options & DNS_ADBFIND_EMPTYEVENT) != 0)
-#define FIND_AVOIDFETCHES(fn) (((fn)->options & DNS_ADBFIND_AVOIDFETCHES) \
- != 0)
-#define FIND_STARTATZONE(fn) (((fn)->options & DNS_ADBFIND_STARTATZONE) \
- != 0)
-#define FIND_HINTOK(fn) (((fn)->options & DNS_ADBFIND_HINTOK) != 0)
-#define FIND_GLUEOK(fn) (((fn)->options & DNS_ADBFIND_GLUEOK) != 0)
-#define FIND_HAS_ADDRS(fn) (!ISC_LIST_EMPTY((fn)->list))
-#define FIND_RETURNLAME(fn) (((fn)->options & DNS_ADBFIND_RETURNLAME) != 0)
+#define FIND_AVOIDFETCHES(fn) (((fn)->options & DNS_ADBFIND_AVOIDFETCHES) != 0)
+#define FIND_STARTATZONE(fn) (((fn)->options & DNS_ADBFIND_STARTATZONE) != 0)
+#define FIND_HINTOK(fn) (((fn)->options & DNS_ADBFIND_HINTOK) != 0)
+#define FIND_GLUEOK(fn) (((fn)->options & DNS_ADBFIND_GLUEOK) != 0)
+#define FIND_HAS_ADDRS(fn) (!ISC_LIST_EMPTY((fn)->list))
+#define FIND_RETURNLAME(fn) (((fn)->options & DNS_ADBFIND_RETURNLAME) != 0)
+#define FIND_NOFETCH(fn) (((fn)->options & DNS_ADBFIND_NOFETCH) != 0)
/*
* These are currently used on simple unsigned ints, so they are
@@ -3155,21 +3154,26 @@ dns_adb_createfind2(dns_adb_t *adb, isc_task_t *task, isc_taskaction_t action,
* Listen to negative cache hints, and don't start
* another query.
*/
- if (NCACHE_RESULT(result) || AUTH_NX(result))
+ if (NCACHE_RESULT(result) || AUTH_NX(result)) {
goto fetch;
+ }
- if (!NAME_FETCH_V6(adbname))
+ if (!NAME_FETCH_V6(adbname)) {
wanted_fetches |= DNS_ADBFIND_INET6;
+ }
}
fetch:
if ((WANT_INET(wanted_addresses) && NAME_HAS_V4(adbname)) ||
(WANT_INET6(wanted_addresses) && NAME_HAS_V6(adbname)))
+ {
have_address = true;
- else
+ } else {
have_address = false;
- if (wanted_fetches != 0 &&
- ! (FIND_AVOIDFETCHES(find) && have_address)) {
+ }
+ if (wanted_fetches != 0 && !(FIND_AVOIDFETCHES(find) && have_address) &&
+ !FIND_NOFETCH(find))
+ {
/*
* We're missing at least one address family. Either the
* caller hasn't instructed us to avoid fetches, or we don't
@@ -3177,8 +3181,9 @@ dns_adb_createfind2(dns_adb_t *adb, isc_task_t *task, isc_taskaction_t action,
* be acceptable so we have to launch fetches.
*/
- if (FIND_STARTATZONE(find))
+ if (FIND_STARTATZONE(find)) {
start_at_zone = true;
+ }
/*
* Start V4.
diff --git a/lib/dns/include/dns/adb.h b/lib/dns/include/dns/adb.h
index ca35bac..3e27c9e 100644
--- a/lib/dns/include/dns/adb.h
+++ b/lib/dns/include/dns/adb.h
@@ -207,6 +207,10 @@ struct dns_adbfind {
* lame for this query.
*/
#define DNS_ADBFIND_OVERQUOTA 0x00000400
+/*%
+ * Don't perform a fetch even if there are no address records available.
+ */
+#define DNS_ADBFIND_NOFETCH 0x00000800
/*%
* The answers to queries come back as a list of these.
diff --git a/lib/dns/resolver.c b/lib/dns/resolver.c
index 164fc01..79ad212 100644
--- a/lib/dns/resolver.c
+++ b/lib/dns/resolver.c
@@ -173,6 +173,14 @@
#define DEFAULT_MAX_QUERIES 75
#endif
+/*
+ * After NS_FAIL_LIMIT attempts to fetch a name server address,
+ * if the number of addresses in the NS RRset exceeds NS_RR_LIMIT,
+ * stop trying to fetch, in order to avoid wasting resources.
+ */
+#define NS_FAIL_LIMIT 4
+#define NS_RR_LIMIT 5
+
/* Number of hash buckets for zone counters */
#ifndef RES_DOMAIN_BUCKETS
#define RES_DOMAIN_BUCKETS 523
@@ -3121,8 +3129,7 @@ sort_finds(dns_adbfindlist_t *findlist, unsigned int bias) {
static void
findname(fetchctx_t *fctx, dns_name_t *name, in_port_t port,
unsigned int options, unsigned int flags, isc_stdtime_t now,
- bool *overquota, bool *need_alternate)
-{
+ bool *overquota, bool *need_alternate, unsigned int *no_addresses) {
dns_adbaddrinfo_t *ai;
dns_adbfind_t *find;
dns_resolver_t *res;
@@ -3210,7 +3217,12 @@ findname(fetchctx_t *fctx, dns_name_t *name, in_port_t port,
find->result_v6 != DNS_R_NXDOMAIN) ||
(res->dispatches6 == NULL &&
find->result_v4 != DNS_R_NXDOMAIN)))
+ {
*need_alternate = true;
+ }
+ if (no_addresses != NULL) {
+ (*no_addresses)++;
+ }
} else {
if ((find->options & DNS_ADBFIND_OVERQUOTA) != 0) {
if (overquota != NULL)
@@ -3261,6 +3273,7 @@ fctx_getaddresses(fetchctx_t *fctx, bool badcache) {
dns_rdata_ns_t ns;
bool need_alternate = false;
bool all_spilled = true;
+ unsigned int no_addresses = 0;
FCTXTRACE5("getaddresses", "fctx->depth=", fctx->depth);
@@ -3428,20 +3441,28 @@ fctx_getaddresses(fetchctx_t *fctx, bool badcache) {
* Extract the name from the NS record.
*/
result = dns_rdata_tostruct(&rdata, &ns, NULL);
- if (result != ISC_R_SUCCESS)
+ if (result != ISC_R_SUCCESS) {
continue;
+ }
- findname(fctx, &ns.name, 0, stdoptions, 0, now,
- &overquota, &need_alternate);
+ if (no_addresses > NS_FAIL_LIMIT &&
+ dns_rdataset_count(&fctx->nameservers) > NS_RR_LIMIT)
+ {
+ stdoptions |= DNS_ADBFIND_NOFETCH;
+ }
+ findname(fctx, &ns.name, 0, stdoptions, 0, now, &overquota,
+ &need_alternate, &no_addresses);
- if (!overquota)
+ if (!overquota) {
all_spilled = false;
+ }
dns_rdata_reset(&rdata);
dns_rdata_freestruct(&ns);
}
- if (result != ISC_R_NOMORE)
+ if (result != ISC_R_NOMORE) {
return (result);
+ }
/*
* Do we need to use 6 to 4?
@@ -3456,7 +3477,7 @@ fctx_getaddresses(fetchctx_t *fctx, bool badcache) {
if (!a->isaddress) {
findname(fctx, &a->_u._n.name, a->_u._n.port,
stdoptions, FCTX_ADDRINFO_FORWARDER,
- now, NULL, NULL);
+ now, NULL, NULL, NULL);
continue;
}
if (isc_sockaddr_pf(&a->_u.addr) != family)
@@ -3818,16 +3839,14 @@ fctx_try(fetchctx_t *fctx, bool retrying, bool badcache) {
}
}
- if (dns_name_countlabels(&fctx->domain) > 2) {
- result = isc_counter_increment(fctx->qc);
- if (result != ISC_R_SUCCESS) {
- isc_log_write(dns_lctx, DNS_LOGCATEGORY_RESOLVER,
- DNS_LOGMODULE_RESOLVER, ISC_LOG_DEBUG(3),
- "exceeded max queries resolving '%s'",
- fctx->info);
- fctx_done(fctx, DNS_R_SERVFAIL, __LINE__);
- return;
- }
+ result = isc_counter_increment(fctx->qc);
+ if (result != ISC_R_SUCCESS) {
+ isc_log_write(dns_lctx, DNS_LOGCATEGORY_RESOLVER,
+ DNS_LOGMODULE_RESOLVER, ISC_LOG_DEBUG(3),
+ "exceeded max queries resolving '%s'",
+ fctx->info);
+ fctx_done(fctx, DNS_R_SERVFAIL, __LINE__);
+ return;
}
bucketnum = fctx->bucketnum;
--
2.21.1
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