Implement SessionHolder auto shifting

src/lib/core/CASEAuthTag.h

@@ -17,6 +17,8 @@
 
 #pragma once
 
+#include <array>
+
 #include <lib/core/CHIPConfig.h>
 #include <lib/core/CHIPEncoding.h>
 #include <lib/core/NodeId.h>
@@ -35,11 +37,11 @@ static constexpr size_t kMaxSubjectCATAttributeCount = CHIP_CONFIG_CERT_MAX_RDN_
 
 struct CATValues
 {
-    CASEAuthTag values[kMaxSubjectCATAttributeCount] = { kUndefinedCAT };
+    std::array<CASEAuthTag, kMaxSubjectCATAttributeCount> values = { kUndefinedCAT };
 
     /* @brief Returns size of the CAT values array.
      */
-    static constexpr size_t size() { return ArraySize(values); }
+    static constexpr size_t size() { return std::tuple_size<decltype(values)>::value; }
 
     /* @brief Returns true if subject input checks against one of the CATs in the values array.
      */
@@ -58,6 +60,8 @@ struct CATValues
         return false;
     }
 
+    bool operator==(const CATValues & that) const { return values == that.values; }
+
     static constexpr size_t kSerializedLength = kMaxSubjectCATAttributeCount * sizeof(CASEAuthTag);
     typedef uint8_t Serialized[kSerializedLength];
 

src/transport/SecureSession.cpp

@@ -26,6 +26,36 @@ void SecureSessionDeleter::Release(SecureSession * entry)
     entry->mTable.ReleaseSession(entry);
 }
 
+void SecureSession::Activate(const ScopedNodeId & localNode, const ScopedNodeId & peerNode, CATValues peerCATs,
+                             uint16_t peerSessionId, const ReliableMessageProtocolConfig & config)
+{
+    VerifyOrDie(mState == State::kEstablishing);
+    VerifyOrDie(peerNode.GetFabricIndex() == localNode.GetFabricIndex());
+
+    // PASE sessions must always start unassociated with a Fabric!
+    VerifyOrDie(!((mSecureSessionType == Type::kPASE) && (peerNode.GetFabricIndex() != kUndefinedFabricIndex)));
+    // CASE sessions must always start "associated" a given Fabric!
+    VerifyOrDie(!((mSecureSessionType == Type::kCASE) && (peerNode.GetFabricIndex() == kUndefinedFabricIndex)));
+    // CASE sessions can only be activated against operational node IDs!
+    VerifyOrDie(!((mSecureSessionType == Type::kCASE) &&
+                  (!IsOperationalNodeId(peerNode.GetNodeId()) || !IsOperationalNodeId(localNode.GetNodeId()))));
+
+    mPeerNodeId    = peerNode.GetNodeId();
+    mLocalNodeId   = localNode.GetNodeId();
+    mPeerCATs      = peerCATs;
+    mPeerSessionId = peerSessionId;
+    mMRPConfig     = config;
+    SetFabricIndex(peerNode.GetFabricIndex());
+
+    Retain(); // This ref is released inside MarkForEviction
+    MoveToState(State::kActive);
+
+    if (mSecureSessionType == Type::kCASE)
+        mTable.NewerSessionAvailable(this);
+
+    ChipLogDetail(Inet, "SecureSession[%p]: Activated - Type:%d LSID:%d", this, to_underlying(mSecureSessionType), mLocalSessionId);
+}
+
 const char * SecureSession::StateToString(State state) const
 {
     switch (state)
@@ -200,5 +230,22 @@ void SecureSession::Release()
     ReferenceCounted<SecureSession, SecureSessionDeleter, 0, uint16_t>::Release();
 }
 
+void SecureSession::NewerSessionAvailable(const SessionHandle & session)
+{
+    // Shift to the new session, checks are performed by the the caller SecureSessionTable::NewerSessionAvailable.
+    IntrusiveList<SessionHolder>::Iterator iter = mHolders.begin();
+    while (iter != mHolders.end())
+    {
+        // The iterator can be invalid once the session holder is migrated to another session. So we store its next value before
+        // notifying the holder.
+        IntrusiveList<SessionHolder>::Iterator next = iter;
+        ++next;
+
+        iter->ShiftToSession(session);
+
+        iter = next;
+    }
+}
+
 } // namespace Transport
 } // namespace chip

src/transport/SecureSession.h

@@ -101,31 +101,8 @@ class SecureSession : public Session, public ReferenceCounted<SecureSession, Sec
      *   discovered during session establishment.
      */
     void Activate(const ScopedNodeId & localNode, const ScopedNodeId & peerNode, CATValues peerCATs, uint16_t peerSessionId,
-                  const ReliableMessageProtocolConfig & config)
-    {
-        VerifyOrDie(mState == State::kEstablishing);
-        VerifyOrDie(peerNode.GetFabricIndex() == localNode.GetFabricIndex());
-
-        // PASE sessions must always start unassociated with a Fabric!
-        VerifyOrDie(!((mSecureSessionType == Type::kPASE) && (peerNode.GetFabricIndex() != kUndefinedFabricIndex)));
-        // CASE sessions must always start "associated" a given Fabric!
-        VerifyOrDie(!((mSecureSessionType == Type::kCASE) && (peerNode.GetFabricIndex() == kUndefinedFabricIndex)));
-        // CASE sessions can only be activated against operational node IDs!
-        VerifyOrDie(!((mSecureSessionType == Type::kCASE) &&
-                      (!IsOperationalNodeId(peerNode.GetNodeId()) || !IsOperationalNodeId(localNode.GetNodeId()))));
-
-        mPeerNodeId    = peerNode.GetNodeId();
-        mLocalNodeId   = localNode.GetNodeId();
-        mPeerCATs      = peerCATs;
-        mPeerSessionId = peerSessionId;
-        mMRPConfig     = config;
-        SetFabricIndex(peerNode.GetFabricIndex());
-
-        Retain(); // This ref is released inside MarkForEviction
-        MoveToState(State::kActive);
-        ChipLogDetail(Inet, "SecureSession[%p]: Activated - Type:%d LSID:%d", this, to_underlying(mSecureSessionType),
-                      mLocalSessionId);
-    }
+                  const ReliableMessageProtocolConfig & config);
+
     ~SecureSession() override
     {
         ChipLogDetail(Inet, "SecureSession[%p]: Released - Type:%d LSID:%d", this, to_underlying(mSecureSessionType),
@@ -213,7 +190,7 @@ class SecureSession : public Session, public ReferenceCounted<SecureSession, Sec
     NodeId GetPeerNodeId() const { return mPeerNodeId; }
     NodeId GetLocalNodeId() const { return mLocalNodeId; }
 
-    CATValues GetPeerCATs() const { return mPeerCATs; }
+    const CATValues & GetPeerCATs() const { return mPeerCATs; }
 
     void SetMRPConfig(const ReliableMessageProtocolConfig & config) { mMRPConfig = config; }
 
@@ -262,6 +239,11 @@ class SecureSession : public Session, public ReferenceCounted<SecureSession, Sec
 
     SessionMessageCounter & GetSessionMessageCounter() { return mSessionMessageCounter; }
 
+    // This should be a private API, only meant to be called by SecureSessionTable
+    // Session holders to this session may shift to the target session regarding SessionDelegate::GetNewSessionHandlingPolicy.
+    // It requires that the target sessoin is also a CASE session, having the same peer and CATs as this session.
+    void NewerSessionAvailable(const SessionHandle & session);
+
 private:
     enum class State : uint8_t
     {

src/transport/SecureSessionTable.h

@@ -94,6 +94,32 @@ class SecureSessionTable
     CHECK_RETURN_VALUE
     Optional<SessionHandle> FindSecureSessionByLocalKey(uint16_t localSessionId);
 
+    // Select SessionHolders which are pointing to a session with the same peer as the given session. Shift them to the given
+    // session.
+    // This is an internal API, using raw pointer to a session is allowed here.
+    void NewerSessionAvailable(SecureSession * session)
+    {
+        VerifyOrDie(session->GetSecureSessionType() == SecureSession::Type::kCASE);
+        mEntries.ForEachActiveObject([&](SecureSession * oldSession) {
+            if (session == oldSession)
+                return Loop::Continue;
+
+            SessionHandle ref(*oldSession);
+
+            // This will give all SessionHolders pointing to oldSession a chance to switch to the provided session
+            //
+            // See documentation for SessionDelegate::GetNewSessionHandlingPolicy about how session auto-shifting works, and how
+            // to disable it for a specific SessionHolder in a specific scenario.
+            if (oldSession->GetSecureSessionType() == SecureSession::Type::kCASE && oldSession->GetPeer() == session->GetPeer() &&
+                oldSession->GetPeerCATs() == session->GetPeerCATs())
+            {
+                oldSession->NewerSessionAvailable(SessionHandle(*session));
+            }
+
+            return Loop::Continue;
+        });
+    }
+
 private:
     friend class TestSecureSessionTable;
 

src/transport/Session.h

@@ -114,14 +114,15 @@ class Session
         SessionHandle session(*this);
         while (!mHolders.Empty())
         {
-            mHolders.begin()->OnSessionReleased(); // OnSessionReleased must remove the item from the linked list
+            mHolders.begin()->SessionReleased(); // SessionReleased must remove the item from the linked list
         }
     }
 
     void SetFabricIndex(FabricIndex index) { mFabricIndex = index; }
 
-private:
     IntrusiveList<SessionHolder> mHolders;
+
+private:
     FabricIndex mFabricIndex = kUndefinedFabricIndex;
 };
 

src/transport/SessionDelegate.h

@@ -36,8 +36,16 @@ class DLL_EXPORT SessionDelegate
      *   Called when a new secure session to the same peer is established, over the delegate of SessionHolderWithDelegate object. It
      *   is suggested to shift to the newly created session.
      *
+     *   Our security model is built upon Exchanges and Sessions, but not SessionHolders, such that SessionHolders should be able to
+     *   shift to a new session freely. If an application is holding a session which is not intended to be shifted, it can provide
+     *   its shifting policy by overriding GetNewSessionHandlingPolicy in SessionDelegate. For example SessionHolders inside
+     *   ExchangeContext and PairingSession are not eligible for auto-shifting.
+     *
      * Note: the default implementation orders shifting to the new session, it should be fine for all users, unless the
-     * SessionHolder object is expected to be sticky to a specified session.
+     *       SessionHolder object is expected to be sticky to a specified session.
+     *
+     * Note: the implementation MUST NOT modify the session pool or the state of session holders (eg, adding new session, removing
+     *       old session) from inside this callback.
      */
     virtual NewSessionHandlingPolicy GetNewSessionHandlingPolicy() { return NewSessionHandlingPolicy::kShiftToNewSession; }
 

src/transport/SessionHolder.h

@@ -28,19 +28,23 @@ namespace chip {
  *    released when the underlying session is released. One must verify it is available before use. The object can be
  *    created using SessionHandle.Grab()
  */
-class SessionHolder : public SessionDelegate, public IntrusiveListNodeBase<>
+class SessionHolder : public IntrusiveListNodeBase<>
 {
 public:
     SessionHolder() {}
-    ~SessionHolder() override;
+    virtual ~SessionHolder();
 
     SessionHolder(const SessionHolder &);
     SessionHolder(SessionHolder && that);
     SessionHolder & operator=(const SessionHolder &);
     SessionHolder & operator=(SessionHolder && that);
 
-    // Implement SessionDelegate
-    void OnSessionReleased() override { Release(); }
+    virtual void SessionReleased() { Release(); }
+    virtual void ShiftToSession(const SessionHandle & session)
+    {
+        Release();
+        Grab(session);
+    }
 
     bool Contains(const SessionHandle & session) const
     {
@@ -51,7 +55,7 @@ class SessionHolder : public SessionDelegate, public IntrusiveListNodeBase<>
     bool Grab(const SessionHandle & session);
     void Release();
 
-    operator bool() const { return mSession.HasValue(); }
+    explicit operator bool() const { return mSession.HasValue(); }
     Optional<SessionHandle> Get() const
     {
         //
@@ -81,14 +85,20 @@ class SessionHolderWithDelegate : public SessionHolder
     SessionHolderWithDelegate(const SessionHandle & handle, SessionDelegate & delegate) : mDelegate(delegate) { Grab(handle); }
     operator bool() const { return SessionHolder::operator bool(); }
 
-    void OnSessionReleased() override
+    void SessionReleased() override
     {
         Release();
 
         // Note, the session is already cleared during mDelegate.OnSessionReleased
         mDelegate.OnSessionReleased();
     }
 
+    void ShiftToSession(const SessionHandle & session) override
+    {
+        if (mDelegate.GetNewSessionHandlingPolicy() == SessionDelegate::NewSessionHandlingPolicy::kShiftToNewSession)
+            SessionHolder::ShiftToSession(session);
+    }
+
     void DispatchSessionEvent(SessionDelegate::Event event) override { (mDelegate.*event)(); }
 
 private:

src/transport/SessionManager.cpp

@@ -412,6 +412,27 @@ CHIP_ERROR SessionManager::InjectPaseSessionWithTestKey(SessionHolder & sessionH
     return CHIP_NO_ERROR;
 }
 
+CHIP_ERROR SessionManager::InjectCaseSessionWithTestKey(SessionHolder & sessionHolder, uint16_t localSessionId,
+                                                        uint16_t peerSessionId, NodeId localNodeId, NodeId peerNodeId,
+                                                        FabricIndex fabric, const Transport::PeerAddress & peerAddress,
+                                                        CryptoContext::SessionRole role, const CATValues & cats)
+{
+    Optional<SessionHandle> session =
+        mSecureSessions.CreateNewSecureSessionForTest(chip::Transport::SecureSession::Type::kCASE, localSessionId, localNodeId,
+                                                      peerNodeId, cats, peerSessionId, fabric, GetLocalMRPConfig());
+    VerifyOrReturnError(session.HasValue(), CHIP_ERROR_NO_MEMORY);
+    SecureSession * secureSession = session.Value()->AsSecureSession();
+    secureSession->SetPeerAddress(peerAddress);
+
+    size_t secretLen = strlen(CHIP_CONFIG_TEST_SHARED_SECRET_VALUE);
+    ByteSpan secret(reinterpret_cast<const uint8_t *>(CHIP_CONFIG_TEST_SHARED_SECRET_VALUE), secretLen);
+    ReturnErrorOnFailure(secureSession->GetCryptoContext().InitFromSecret(
+        secret, ByteSpan(nullptr, 0), CryptoContext::SessionInfoType::kSessionEstablishment, role));
+    secureSession->GetSessionMessageCounter().GetPeerMessageCounter().SetCounter(Transport::PeerMessageCounter::kInitialSyncValue);
+    sessionHolder.Grab(session.Value());
+    return CHIP_NO_ERROR;
+}
+
 void SessionManager::OnMessageReceived(const PeerAddress & peerAddress, System::PacketBufferHandle && msg)
 {
     CHIP_TRACE_PREPARED_MESSAGE_RECEIVED(&peerAddress, &msg);

src/transport/SessionManager.h

@@ -154,6 +154,10 @@ class DLL_EXPORT SessionManager : public TransportMgrDelegate
     CHIP_ERROR InjectPaseSessionWithTestKey(SessionHolder & sessionHolder, uint16_t localSessionId, NodeId peerNodeId,
                                             uint16_t peerSessionId, FabricIndex fabricIndex,
                                             const Transport::PeerAddress & peerAddress, CryptoContext::SessionRole role);
+    CHIP_ERROR InjectCaseSessionWithTestKey(SessionHolder & sessionHolder, uint16_t localSessionId, uint16_t peerSessionId,
+                                            NodeId localNodeId, NodeId peerNodeId, FabricIndex fabric,
+                                            const Transport::PeerAddress & peerAddress, CryptoContext::SessionRole role,
+                                            const CATValues & cats = CATValues{});
 
     /**
      * @brief
@@ -210,6 +214,7 @@ class DLL_EXPORT SessionManager : public TransportMgrDelegate
     void FabricRemoved(FabricIndex fabricIndex);
 
     TransportMgrBase * GetTransportManager() const { return mTransportMgr; }
+    Transport::SecureSessionTable & GetSecureSessions() { return mSecureSessions; }
 
     /**
      * @brief