Check only one response in Link Accept handler (#653)

* Compare Response TLV in Link Accept with appropriate Challenge value.

* Invalidate Challenge value from multicast Link Request after timeout.

src/core/thread/mle_constants.hpp

@@ -58,6 +58,7 @@ enum
     kUdpPort                    = 19788, ///< MLE UDP Port
     kParentRequestRouterTimeout = 1000,  ///< Router Request timeout
     kParentRequestChildTimeout  = 2000,  ///< End Device Request timeout
+    kMaxResponseDelay           = 1000,  ///< Maximum delay before responding to a multicast request
 };
 
 enum

src/core/thread/mle_router.cpp

@@ -57,6 +57,7 @@ MleRouter::MleRouter(ThreadNetif &aThreadNetif):
     mAddressRelease(OPENTHREAD_URI_ADDRESS_RELEASE, &MleRouter::HandleAddressRelease, this),
     mCoapServer(aThreadNetif.GetCoapServer())
 {
+    mChallengeTimeout = 0;
     mNextChildId = kMaxChildId;
     mRouterIdSequence = 0;
     memset(mChildren, 0, sizeof(mChildren));
@@ -533,6 +534,8 @@ ThreadError MleRouter::SendLinkRequest(Neighbor *aNeighbor)
             mChallenge[i] = static_cast<uint8_t>(otPlatRandomGet());
         }
 
+        mChallengeTimeout = (((2 * kMaxResponseDelay) + kStateUpdatePeriod - 1) / kStateUpdatePeriod);
+
         SuccessOrExit(error = AppendChallenge(*message, mChallenge, sizeof(mChallenge)));
         destination.mFields.m8[0] = 0xff;
         destination.mFields.m8[1] = 0x02;
@@ -545,7 +548,8 @@ ThreadError MleRouter::SendLinkRequest(Neighbor *aNeighbor)
             aNeighbor->mPending.mChallenge[i] = static_cast<uint8_t>(otPlatRandomGet());
         }
 
-        SuccessOrExit(error = AppendChallenge(*message, mChallenge, sizeof(mChallenge)));
+        SuccessOrExit(error = AppendChallenge(*message, aNeighbor->mPending.mChallenge,
+                                              sizeof(aNeighbor->mPending.mChallenge)));
         destination.mFields.m16[0] = HostSwap16(0xfe80);
         destination.SetIid(aNeighbor->mMacAddr);
     }
@@ -835,9 +839,21 @@ ThreadError MleRouter::HandleLinkAccept(const Message &aMessage, const Ip6::Mess
     }
 
     // verify response
-    VerifyOrExit(memcmp(mChallenge, response.GetResponse(), sizeof(mChallenge)) == 0 ||
-                 memcmp(neighbor->mPending.mChallenge, response.GetResponse(), sizeof(neighbor->mPending.mChallenge)) == 0,
-                 error = kThreadError_Error);
+    switch (neighbor->mState)
+    {
+    case Neighbor::kStateLinkRequest:
+        VerifyOrExit(memcmp(neighbor->mPending.mChallenge, response.GetResponse(), sizeof(neighbor->mPending.mChallenge)) == 0,
+                     error = kThreadError_Error);
+        break;
+
+    case Neighbor::kStateInvalid:
+        VerifyOrExit((mChallengeTimeout > 0) && (memcmp(mChallenge, response.GetResponse(), sizeof(mChallenge)) == 0),
+                     error = kThreadError_Error);
+        break;
+
+    default:
+        ExitNow(error = kThreadError_InvalidState);
+    }
 
     switch (mDeviceState)
     {
@@ -1620,6 +1636,11 @@ void MleRouter::HandleStateUpdateTimer(void *aContext)
 
 void MleRouter::HandleStateUpdateTimer(void)
 {
+    if (mChallengeTimeout > 0)
+    {
+        mChallengeTimeout--;
+    }
+
     switch (GetDeviceState())
     {
     case kDeviceStateDisabled:

src/core/thread/mle_router.hpp

@@ -577,6 +577,7 @@ private:
     uint8_t mMaxChildrenAllowed;
     Child mChildren[kMaxChildren];
 
+    uint8_t mChallengeTimeout;
     uint8_t mChallenge[8];
     uint16_t mNextChildId;
     uint8_t mNetworkIdTimeout;