kit: fix UB in ChildSession::disconnect()

Finally unit-copy-paste passes under sanitizers with this. Details:

==8988==ERROR: AddressSanitizer: heap-use-after-free on address 0x60d0005e6de0 at pc 0x000000988e85 bp 0x7fff753316d0 sp 0x7fff753316c8
READ of size 4 at 0x60d0005e6de0 thread T0 (loolkit)
    #0 0x988e84 in std::pair<int const, UserInfo>::pair(std::pair<int const, UserInfo> const&) /home/vmiklos/git/libreoffice/lode/opt_private/gcc-7.3.0/lib64/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0/bits/stl_pair.h:292:17
...
    #12 0x9322af in Document::notifyViewInfo() /home/vmiklos/git/libreoffice/online-san/kit/Kit.cpp:1600:53
    #13 0x9303f9 in Document::onUnload(ChildSession const&) /home/vmiklos/git/libreoffice/online-san/kit/Kit.cpp:1566:13
    #14 0x616dcd in ChildSession::disconnect() /home/vmiklos/git/libreoffice/online-san/kit/ChildSession.cpp:96:25
    #15 0x616535 in ChildSession::~ChildSession() /home/vmiklos/git/libreoffice/online-san/kit/ChildSession.cpp:85:5

freed by thread T0 (loolkit) here:
    #0 0x60f9b0 in operator delete(void*) _asan_rtl_:0
...
    #8 0x939292 in Document::~Document() /home/vmiklos/git/libreoffice/online-san/kit/Kit.cpp:913:5

I.e. when the Document dtor clears Document::_sessions, the ChildSession
dtor may be called. But ChildSession expected that it has a valid
Document during its lifetime, which is not a promise we can hold, see
the above trace.

Fix the problem by having a pointer (and not a reference) to a Document
in ChildSession and then:

1) Clear that Document pointer in ChildSessions at the end of the
Document dtor using a new resetDocManager()

2) Check if the Document is nullptr in ChildSession::disconnect()
instead of dereferencing it unconditionally.

Change-Id: I19d3d6bfe9e142a52c199f49aaa347d1a2edbf87

kit/ChildSession.cpp

@@ -70,7 +70,7 @@ ChildSession::ChildSession(const std::string& id,
                            DocumentManagerInterface& docManager) :
     Session("ToMaster-" + id, id, false),
     _jailId(jailId),
-    _docManager(docManager),
+    _docManager(&docManager),
     _viewId(-1),
     _isDocLoaded(false),
     _copyToClipboard(false)
@@ -93,7 +93,10 @@ void ChildSession::disconnect()
 
         if (_viewId >= 0)
         {
-            _docManager.onUnload(*this);
+            if (_docManager)
+            {
+                _docManager->onUnload(*this);
+            }
         }
         else
         {
@@ -132,7 +135,7 @@ bool ChildSession::_handleInput(const char *buffer, int length)
             curPart = getLOKitDocument()->getPart();
 
         // Notify all views about updated view info
-        _docManager.notifyViewInfo();
+        _docManager->notifyViewInfo();
 
         if (getLOKitDocument()->getDocumentType() != LOK_DOCTYPE_TEXT)
         {
@@ -565,7 +568,7 @@ bool ChildSession::loadDocument(const char * /*buffer*/, int /*length*/, const s
 
     std::unique_lock<std::recursive_mutex> lock(Mutex);
 
-    const bool loaded = _docManager.onLoad(getId(), getJailedFilePath(), getJailedFilePathAnonym(),
+    const bool loaded = _docManager->onLoad(getId(), getJailedFilePath(), getJailedFilePathAnonym(),
                                            getUserName(), getUserNameAnonym(),
                                            getDocPassword(), renderOpts, getHaveDocPassword(),
                                            getLang(), getWatermarkText(), doctemplate);
@@ -607,8 +610,8 @@ bool ChildSession::loadDocument(const char * /*buffer*/, int /*length*/, const s
     }
 
     // Inform everyone (including this one) about updated view info
-    _docManager.notifyViewInfo();
-    sendTextFrame("editor: " + std::to_string(_docManager.getEditorId()));
+    _docManager->notifyViewInfo();
+    sendTextFrame("editor: " + std::to_string(_docManager->getEditorId()));
 
 
     LOG_INF("Loaded session " << getId());
@@ -750,7 +753,7 @@ bool ChildSession::getCommandValues(const char* /*buffer*/, int /*length*/, cons
                                         std::string(values == nullptr ? "" : values),
                                         std::string(undo == nullptr ? "" : undo));
         // json only contains view IDs, insert matching user names.
-        std::map<int, UserInfo> viewInfo = _docManager.getViewInfo();
+        std::map<int, UserInfo> viewInfo = _docManager->getViewInfo();
         insertUserNames(viewInfo, json);
         success = sendTextFrame("commandvalues: " + json);
         std::free(values);
@@ -848,7 +851,7 @@ bool ChildSession::downloadAs(const char* /*buffer*/, int /*length*/, const std:
     }
 
     // Obfuscate the new name.
-    Util::mapAnonymized(Util::getFilenameFromURL(name), _docManager.getObfuscatedFileId());
+    Util::mapAnonymized(Util::getFilenameFromURL(name), _docManager->getObfuscatedFileId());
 
     getTokenString(tokens[3], "format", format);
 
@@ -1654,7 +1657,7 @@ bool ChildSession::exportSignAndUploadDocument(const char* buffer, int length, c
         std::vector<unsigned char> binaryCertificate = decodeBase64(extractCertificate(x509Certificate));
         std::vector<unsigned char> binaryPrivateKey = decodeBase64(extractPrivateKey(privateKey));
 
-        bResult = _docManager.getLOKit()->signDocument(aTempDocumentURL.c_str(),
+        bResult = _docManager->getLOKit()->signDocument(aTempDocumentURL.c_str(),
                         binaryCertificate.data(), binaryCertificate.size(),
                         binaryPrivateKey.data(), binaryPrivateKey.size());
 
@@ -2046,7 +2049,7 @@ void ChildSession::updateSpeed() {
         _cursorInvalidatedEvent.pop();
     }
     _cursorInvalidatedEvent.push(now);
-    _docManager.updateEditorSpeeds(_viewId, _cursorInvalidatedEvent.size());
+    _docManager->updateEditorSpeeds(_viewId, _cursorInvalidatedEvent.size());
 }
 
 int ChildSession::getSpeed() {

kit/ChildSession.hpp

@@ -221,20 +221,25 @@ public:
     {
         const auto msg = "client-" + getId() + ' ' + std::string(buffer, length);
         const std::unique_lock<std::mutex> lock = getLock();
-        return _docManager.sendFrame(msg.data(), msg.size(), WSOpCode::Text);
+        return _docManager->sendFrame(msg.data(), msg.size(), WSOpCode::Text);
     }
 
     bool sendBinaryFrame(const char* buffer, int length) override
     {
         const auto msg = "client-" + getId() + ' ' + std::string(buffer, length);
         const std::unique_lock<std::mutex> lock = getLock();
-        return _docManager.sendFrame(msg.data(), msg.size(), WSOpCode::Binary);
+        return _docManager->sendFrame(msg.data(), msg.size(), WSOpCode::Binary);
     }
 
     using Session::sendTextFrame;
 
     bool getClipboard(const char* buffer, int length, const std::vector<std::string>& tokens);
 
+    void resetDocManager()
+    {
+        _docManager = nullptr;
+    }
+
 private:
     bool loadDocument(const char* buffer, int length, const std::vector<std::string>& tokens);
 
@@ -278,12 +283,12 @@ private:
 
     std::shared_ptr<lok::Document> getLOKitDocument()
     {
-        return _docManager.getLOKitDocument();
+        return _docManager->getLOKitDocument();
     }
 
     std::string getLOKitLastError()
     {
-        char *lastErr = _docManager.getLOKit()->getError();
+        char *lastErr = _docManager->getLOKit()->getError();
         std::string ret;
         if (lastErr)
         {
@@ -295,7 +300,7 @@ private:
 
 private:
     const std::string _jailId;
-    DocumentManagerInterface& _docManager;
+    DocumentManagerInterface* _docManager;
 
     std::queue<std::chrono::steady_clock::time_point> _cursorInvalidatedEvent;
     const unsigned _eventStorageIntervalMs = 15*1000;

kit/Kit.cpp

@@ -910,6 +910,11 @@ public:
         _stop = true;
 
         _tileQueue->put("eof");
+
+        for (const auto& session : _sessions)
+        {
+            session.second->resetDocManager();
+        }
     }
 
     const std::string& getUrl() const { return _url; }