From 84f5dec52b305d853ecbeb0283d2ff040d78a418 Mon Sep 17 00:00:00 2001
From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Tue, 25 Oct 2022 10:47:10 +0200
Subject: [PATCH] dnsdist: Better handling of lazy backoff overflow

---
 pdns/dnsdistdist/dnsdist-backend.cc | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/pdns/dnsdistdist/dnsdist-backend.cc b/pdns/dnsdistdist/dnsdist-backend.cc
index a8a065fc15..916df4d03e 100644
--- a/pdns/dnsdistdist/dnsdist-backend.cc
+++ b/pdns/dnsdistdist/dnsdist-backend.cc
@@ -585,13 +585,16 @@ void DownstreamState::updateNextLazyHealthCheck(LazyHealthCheckStats& stats)
       stats.d_nextCheck = now + d_config.d_lazyHealthCheckFailedInterval;
     }
     else {
-      const uint16_t failedTests = currentCheckFailures;
-      size_t backOffCoeff = std::pow(2U, failedTests);
       time_t backOff = d_config.d_lazyHealthCheckMaxBackOff;
-      if ((static_cast<size_t>(std::numeric_limits<time_t>::max()) / d_config.d_lazyHealthCheckFailedInterval) >= backOffCoeff) {
-        backOff = d_config.d_lazyHealthCheckFailedInterval * backOffCoeff;
-        if (backOff > d_config.d_lazyHealthCheckMaxBackOff || (std::numeric_limits<time_t>::max() - now) <= backOff) {
-          backOff = d_config.d_lazyHealthCheckMaxBackOff;
+      const uint16_t failedTests = currentCheckFailures;
+      double backOffCoeffTmp = std::pow(2U, failedTests);
+      if (backOffCoeffTmp != HUGE_VAL && backOffCoeffTmp <= std::numeric_limits<time_t>::max()) {
+        time_t backOffCoeff = static_cast<time_t>(backOffCoeffTmp);
+        if ((std::numeric_limits<time_t>::max() / d_config.d_lazyHealthCheckFailedInterval) >= backOffCoeff) {
+          backOff = d_config.d_lazyHealthCheckFailedInterval * backOffCoeff;
+          if (backOff > d_config.d_lazyHealthCheckMaxBackOff || (std::numeric_limits<time_t>::max() - now) <= backOff) {
+            backOff = d_config.d_lazyHealthCheckMaxBackOff;
+          }
         }
       }
 
-- 
2.47.2