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From bf2ea6d8525bfd96a84dad221ba9e004adb710a8 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Micha=C5=82=20K=C4=99pie=C5=84?= <michal@isc.org>
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Date: Thu, 8 Sep 2022 11:11:30 +0200
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Subject: [PATCH] Bound the amount of work performed for delegations
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Limit the amount of database lookups that can be triggered in
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fctx_getaddresses() (i.e. when determining the name server addresses to
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query next) by setting a hard limit on the number of NS RRs processed
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for any delegation encountered. Without any limit in place, named can
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be forced to perform large amounts of database lookups per each query
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received, which severely impacts resolver performance.
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The limit used (20) is an arbitrary value that is considered to be big
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enough for any sane DNS delegation.
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(cherry picked from commit 3a44097fd6c6c260765b628cd1d2c9cb7efb0b2a)
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---
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lib/dns/resolver.c | 12 ++++++++++++
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1 file changed, 12 insertions(+)
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diff --git a/lib/dns/resolver.c b/lib/dns/resolver.c
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index d2cf14bbc8..73a0ee9f77 100644
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--- a/lib/dns/resolver.c
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+++ b/lib/dns/resolver.c
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@@ -195,6 +195,12 @@
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*/
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#define NS_FAIL_LIMIT 4
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#define NS_RR_LIMIT 5
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+/*
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+ * IP address lookups are performed for at most NS_PROCESSING_LIMIT NS RRs in
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+ * any NS RRset encountered, to avoid excessive resource use while processing
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+ * large delegations.
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+ */
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+#define NS_PROCESSING_LIMIT 20
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/* Number of hash buckets for zone counters */
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#ifndef RES_DOMAIN_BUCKETS
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@@ -3711,6 +3717,7 @@ fctx_getaddresses(fetchctx_t *fctx, bool badcache) {
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bool need_alternate = false;
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bool all_spilled = true;
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unsigned int no_addresses = 0;
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+ unsigned int ns_processed = 0;
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FCTXTRACE5("getaddresses", "fctx->depth=", fctx->depth);
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@@ -3902,6 +3909,11 @@ normal_nses:
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dns_rdata_reset(&rdata);
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dns_rdata_freestruct(&ns);
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+
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+ if (++ns_processed >= NS_PROCESSING_LIMIT) {
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+ result = ISC_R_NOMORE;
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+ break;
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+ }
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}
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if (result != ISC_R_NOMORE) {
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return (result);
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--
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2.37.3
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