From aff159f40c1abc150bf58c3644b42b0d7d19d9e7 Mon Sep 17 00:00:00 2001
From: Abtin Keshavarzian <abtink@google.com>
Date: Mon, 26 Feb 2024 18:37:46 -0800
Subject: [PATCH] [link-quality] prevent overflow in `LqiAverager` calculation
 (#9876)

This commit updates `LqiAverager::Add()` to explicitly use a `uint16_t`
local variable for calculating the new running average. This prevents
potential overflows.
---
 src/core/thread/link_quality.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/core/thread/link_quality.cpp b/src/core/thread/link_quality.cpp
index b2adbdcc7..67475401b 100644
--- a/src/core/thread/link_quality.cpp
+++ b/src/core/thread/link_quality.cpp
@@ -117,7 +117,8 @@ exit:
 
 void LqiAverager::Add(uint8_t aLqi)
 {
-    uint8_t count;
+    uint8_t  count;
+    uint16_t newAverage;
 
     if (mCount < NumericLimits<uint8_t>::kMax)
     {
@@ -126,7 +127,10 @@ void LqiAverager::Add(uint8_t aLqi)
 
     count = Min(static_cast<uint8_t>(1 << kCoeffBitShift), mCount);
 
-    mAverage = static_cast<uint8_t>(((mAverage * (count - 1)) + aLqi) / count);
+    newAverage = mAverage;
+    newAverage = (newAverage * (count - 1) + aLqi) / count;
+
+    mAverage = static_cast<uint8_t>(newAverage);
 }
 
 void LinkQualityInfo::Clear(void)