73 lines
2.6 KiB
Diff
73 lines
2.6 KiB
Diff
From 589c06568e3036bfe713d42b53c8e88005ce17e4 Mon Sep 17 00:00:00 2001
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From: Evan Hunt <each@isc.org>
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Date: Thu, 25 May 2023 23:53:50 -0700
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Subject: [PATCH 2/3] Stale answer lookups could loop when over recursion quota
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When a query was aborted because of the recursion quota being exceeded,
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but triggered a stale answer response and a stale data refresh query,
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it could cause named to loop back where we are iterating and following
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a delegation. Having no good answer in cache, we would fall back to
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using serve-stale again, use the stale data, try to refresh the RRset,
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and loop back again, without ever terminating until crashing due to
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stack overflow.
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This happens because in the functions 'query_notfound()' and
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'query_delegation_recurse()', we check whether we can fall back to
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serving stale data. We shouldn't do so if we are already refreshing
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an RRset due to having prioritized stale data in cache.
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In other words, we need to add an extra check to 'query_usestale()' to
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disallow serving stale data if we are currently refreshing a stale
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RRset.
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As an additional mitigation to prevent looping, we now use the result
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code ISC_R_ALREADYRUNNING rather than ISC_R_FAILURE when a recursion
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loop is encountered, and we check for that condition in
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'query_usestale()' as well.
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(cherry picked from commit 0101e28f91fb36b6a16a0049d3b3e2b7846f23f0)
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---
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lib/ns/query.c | 17 ++++++++++++++---
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1 file changed, 14 insertions(+), 3 deletions(-)
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diff --git a/lib/ns/query.c b/lib/ns/query.c
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index c169e22bf4..1eb662ea4d 100644
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--- a/lib/ns/query.c
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+++ b/lib/ns/query.c
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@@ -6229,7 +6229,7 @@ ns_query_recurse(ns_client_t *client, dns_rdatatype_t qtype, dns_name_t *qname,
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if (recparam_match(&client->query.recparam, qtype, qname, qdomain)) {
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ns_client_log(client, NS_LOGCATEGORY_CLIENT, NS_LOGMODULE_QUERY,
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ISC_LOG_INFO, "recursion loop detected");
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- return (ISC_R_FAILURE);
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+ return (ISC_R_ALREADYRUNNING);
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}
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recparam_update(&client->query.recparam, qtype, qname, qdomain);
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@@ -7205,10 +7205,21 @@ query_usestale(query_ctx_t *qctx, isc_result_t result) {
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return (false);
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}
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- if (result == DNS_R_DUPLICATE || result == DNS_R_DROP) {
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+ if (qctx->refresh_rrset) {
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+ /*
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+ * This is a refreshing query, we have already prioritized
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+ * stale data, so don't enable serve-stale again.
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+ */
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+ return (false);
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+ }
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+
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+ if (result == DNS_R_DUPLICATE || result == DNS_R_DROP ||
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+ result == ISC_R_ALREADYRUNNING)
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+ {
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/*
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* Don't enable serve-stale if the result signals a duplicate
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- * query or query that is being dropped.
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+ * query or a query that is being dropped or can't proceed
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+ * because of a recursion loop.
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*/
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return (false);
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}
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--
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2.40.1
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