From af9f7f64eef86dfe7d438ff418969c86a37c5fa7 Mon Sep 17 00:00:00 2001
From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Wed, 3 Mar 2021 10:33:12 +0100
Subject: [PATCH] dnsdist: Prevent an infinite loop when a cache shard is below
 the limit

---
 pdns/dnsdist-cache.cc              | 3 +--
 pdns/test-dnsdistpacketcache_cc.cc | 6 ++++++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/pdns/dnsdist-cache.cc b/pdns/dnsdist-cache.cc
index 8bb38c2ff7..a5a3865662 100644
--- a/pdns/dnsdist-cache.cc
+++ b/pdns/dnsdist-cache.cc
@@ -305,6 +305,7 @@ size_t DNSDistPacketCache::purgeExpired(size_t upTo, const time_t now)
 
   do {
     uint32_t shardIndex = (d_expungeIndex++ % d_shardCount);
+    scannedMaps++;
 
     WriteLock w(&d_shards.at(shardIndex).d_lock);
     auto& map = d_shards.at(shardIndex).d_map;
@@ -325,8 +326,6 @@ size_t DNSDistPacketCache::purgeExpired(size_t upTo, const time_t now)
         ++it;
       }
     }
-
-    scannedMaps++;
   }
   while (scannedMaps < d_shardCount);
 
diff --git a/pdns/test-dnsdistpacketcache_cc.cc b/pdns/test-dnsdistpacketcache_cc.cc
index c39a304d11..3ac48628aa 100644
--- a/pdns/test-dnsdistpacketcache_cc.cc
+++ b/pdns/test-dnsdistpacketcache_cc.cc
@@ -112,6 +112,9 @@ BOOST_AUTO_TEST_CASE(test_PacketCacheSimple) {
     auto removed = PC.expungeByName(DNSName(" hello"), QType::ANY, true);
     BOOST_CHECK_EQUAL(PC.getSize(), 0U);
     BOOST_CHECK_EQUAL(removed, remaining);
+
+    /* nothing to remove */
+    BOOST_CHECK_EQUAL(PC.purgeExpired(0, now), 0U);
   }
   catch (const PDNSException& e) {
     cerr<<"Had error: "<<e.reason<<endl;
@@ -209,6 +212,9 @@ BOOST_AUTO_TEST_CASE(test_PacketCacheSharded) {
     removed = PC.purgeExpired(0, now + 7200 + 3600);
     BOOST_CHECK_EQUAL(removed, 1000U);
     BOOST_CHECK_EQUAL(PC.getSize(), 0U);
+
+    /* nothing to remove */
+    BOOST_CHECK_EQUAL(PC.purgeExpired(0, now), 0U);
   }
   catch (const PDNSException& e) {
     cerr<<"Had error: "<<e.reason<<endl;
-- 
2.47.3