[radio] fix for key rotation in enhAck (#879)

Not all devices do the key rotation at the same time.
This scenario fixes the issue when Router rotates sooner than SSED.
In such case SSED still requires enhAcks to use previous key id and counter.
Added storing last value of FC when keyId changes.
If SSED uses keyId-1 ack uses the stored value instead of current mac counter value.

Signed-off-by: Marek Porwisz <[email protected]>

src/src/radio.c

@@ -140,6 +140,7 @@ static uint32_t sPendingEvents;
 
 #if OPENTHREAD_CONFIG_THREAD_VERSION >= OT_THREAD_VERSION_1_2
 static uint32_t         sMacFrameCounter;
+static uint32_t         sPrevMacFrameCounter;
 static uint8_t          sKeyId;
 static otMacKeyMaterial sPrevKey;
 static otMacKeyMaterial sCurrKey;
@@ -189,6 +190,8 @@ static void dataInit(void)
     }
 
     memset(&sAckFrame, 0, sizeof(sAckFrame));
+
+    sPrevMacFrameCounter = 0;
 }
 
 static void convertShortAddress(uint8_t *aTo, uint16_t aFrom)
@@ -273,29 +276,34 @@ static void txAckProcessSecurity(uint8_t *aAckFrame)
 
     if (keyId == sKeyId)
     {
-        key = &sCurrKey;
+        key              = &sCurrKey;
+        sAckFrameCounter = sMacFrameCounter++;
     }
     else if (keyId == sKeyId - 1)
     {
-        key = &sPrevKey;
+        key              = &sPrevKey;
+        sAckFrameCounter = sPrevMacFrameCounter++;
     }
     else if (keyId == sKeyId + 1)
     {
         key = &sNextKey;
+        // Openthread does not maintain future frame counter.
+        // Mac frame counter would be overwritten after key rotation leading to
+        // frames being dropped due to counter value lower than in acks.
+        sAckFrameCounter = 0;
     }
     else
     {
         otEXPECT(false);
     }
 
-    sAckFrameCounter    = sMacFrameCounter;
     sAckKeyId           = keyId;
     sAckedWithSecEnhAck = true;
 
     ackFrame.mInfo.mTxInfo.mAesKey = key;
 
     otMacFrameSetKeyId(&ackFrame, keyId);
-    otMacFrameSetFrameCounter(&ackFrame, sMacFrameCounter++);
+    otMacFrameSetFrameCounter(&ackFrame, sAckFrameCounter);
 
     otMacFrameProcessTransmitAesCcm(&ackFrame, &sExtAddress);
 
@@ -1308,10 +1316,11 @@ void otPlatRadioSetMacKey(otInstance             *aInstance,
 
     CRITICAL_REGION_ENTER();
 
-    sKeyId   = aKeyId;
-    sPrevKey = *aPrevKey;
-    sCurrKey = *aCurrKey;
-    sNextKey = *aNextKey;
+    sKeyId               = aKeyId;
+    sPrevKey             = *aPrevKey;
+    sCurrKey             = *aCurrKey;
+    sNextKey             = *aNextKey;
+    sPrevMacFrameCounter = sMacFrameCounter;
 
     CRITICAL_REGION_EXIT();
 }