From cde2b1ce4feb646dabe926bd1b78551b5669b468 Mon Sep 17 00:00:00 2001
From: Rongli Sun <rongli@google.com>
Date: Tue, 8 Oct 2019 11:28:30 +0800
Subject: [PATCH] [key-manager] only start guard timer on switch to next key
 index (#4296)

---
 src/core/thread/key_manager.cpp | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/src/core/thread/key_manager.cpp b/src/core/thread/key_manager.cpp
index cc70c472c..062273ddc 100644
--- a/src/core/thread/key_manager.cpp
+++ b/src/core/thread/key_manager.cpp
@@ -162,11 +162,16 @@ void KeyManager::SetCurrentKeySequence(uint32_t aKeySequence)
 {
     VerifyOrExit(aKeySequence != mKeySequence, Get<Notifier>().SignalIfFirst(OT_CHANGED_THREAD_KEY_SEQUENCE_COUNTER));
 
-    // Check if the guard timer has expired if key rotation is requested.
-    if ((aKeySequence == (mKeySequence + 1)) && (mKeySwitchGuardTime != 0) && mKeyRotationTimer.IsRunning() &&
-        mKeySwitchGuardEnabled)
+    if ((aKeySequence == (mKeySequence + 1)) && mKeyRotationTimer.IsRunning())
     {
-        VerifyOrExit(mHoursSinceKeyRotation >= mKeySwitchGuardTime);
+        if (mKeySwitchGuardEnabled)
+        {
+            // Check if the guard timer has expired if key rotation is requested.
+            VerifyOrExit(mHoursSinceKeyRotation >= mKeySwitchGuardTime);
+            StartKeyRotationTimer();
+        }
+
+        mKeySwitchGuardEnabled = true;
     }
 
     mKeySequence = aKeySequence;
@@ -175,12 +180,6 @@ void KeyManager::SetCurrentKeySequence(uint32_t aKeySequence)
     mMacFrameCounter = 0;
     mMleFrameCounter = 0;
 
-    if (mKeyRotationTimer.IsRunning())
-    {
-        mKeySwitchGuardEnabled = true;
-        StartKeyRotationTimer();
-    }
-
     Get<Notifier>().Signal(OT_CHANGED_THREAD_KEY_SEQUENCE_COUNTER);
 
 exit: