From 7fd7a393b6aebba9303efdbcd714ce84c1f8d5ab Mon Sep 17 00:00:00 2001
From: Julien <291750+roidelapluie@users.noreply.github.com>
Date: Tue, 31 Mar 2026 14:23:17 +0200
Subject: [PATCH] convertnhcb: reject NaN bucket boundary in SetBucketCount
 (#18383)

Signed-off-by: Julien Pivotto <291750+roidelapluie@users.noreply.github.com>
---
 util/convertnhcb/convertnhcb.go      |  5 +++++
 util/convertnhcb/convertnhcb_test.go | 13 +++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/util/convertnhcb/convertnhcb.go b/util/convertnhcb/convertnhcb.go
index 64ec9054a3..60d5414a4a 100644
--- a/util/convertnhcb/convertnhcb.go
+++ b/util/convertnhcb/convertnhcb.go
@@ -26,6 +26,7 @@ import (
 
 var (
 	errNegativeBucketCount = errors.New("bucket count must be non-negative")
+	errNaNBucket           = errors.New("bucket boundary must not be NaN")
 	errNegativeCount       = errors.New("count must be non-negative")
 	errCountMismatch       = errors.New("count mismatch")
 	errCountNotCumulative  = errors.New("count is not cumulative")
@@ -71,6 +72,10 @@ func (h *TempHistogram) SetBucketCount(boundary, count float64) error {
 	if h.err != nil {
 		return h.err
 	}
+	if math.IsNaN(boundary) {
+		h.err = errNaNBucket
+		return h.err
+	}
 	if count < 0 {
 		h.err = fmt.Errorf("%w: le=%g, count=%g", errNegativeBucketCount, boundary, count)
 		return h.err
diff --git a/util/convertnhcb/convertnhcb_test.go b/util/convertnhcb/convertnhcb_test.go
index 710d47385a..3ec4b9cb0e 100644
--- a/util/convertnhcb/convertnhcb_test.go
+++ b/util/convertnhcb/convertnhcb_test.go
@@ -147,6 +147,19 @@ func TestNHCBConvert(t *testing.T) {
 			},
 			expectedErr: errNegativeCount,
 		},
+		"NaN bucket upper bound": {
+			setup: func() *TempHistogram {
+				h := NewTempHistogram()
+				// Add a real bucket first so that the NaN call reaches the
+				// default branch of the switch in SetBucketCount; without an
+				// existing bucket, len(h.buckets)==0 and the NaN is silently
+				// appended without triggering the panic.
+				h.SetBucketCount(1.0, 5)
+				h.SetBucketCount(math.NaN(), 10)
+				return &h
+			},
+			expectedErr: errNaNBucket,
+		},
 		"mixed order": {
 			setup: func() *TempHistogram {
 				h := NewTempHistogram()