jsonwriter: ensure correct number of bytes is available

In some functions author forgot that addCommaBeforeField()
can add additional two characters.

I didn't change cases where more bytes than needed are requested.

Additional change is that in debug mode there is a marker at the
end of allocated buffer - we check that after every write to
detect overflow. No need to request more space for a marker as
we always allocate "needed size * 2".

Change-Id: I28066797b0ba833e408b0a731abc01b7fd989da3
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/126535
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com>

2 files changed, 59 insertions, 2 deletions

diff --git a/include/tools/json_writer.hxx b/include/tools/json_writer.hxx
index 2e50670c5b26..318faef70fee 100644
--- a/include/tools/json_writer.hxx
+++ b/include/tools/json_writer.hxx
@@ -91,9 +91,29 @@ private:
     {
         assert(mpBuffer && "already extracted data");
         int currentUsed = mPos - mpBuffer;
+
+#ifndef NDEBUG
+        currentUsed++; // validation marker
+#endif
+
         if (currentUsed + noMoreBytesRequired >= mSpaceAllocated)
             reallocBuffer(noMoreBytesRequired);
     }
+
+    // overflow validation in debug mode
+    static constexpr char JSON_WRITER_DEBUG_MARKER = 0xde;
+
+    inline void addValidationMark()
+    {
+#ifndef NDEBUG
+        *(mpBuffer + mSpaceAllocated - 1) = JSON_WRITER_DEBUG_MARKER;
+#endif
+    }
+
+    inline void validate()
+    {
+        assert(*(mpBuffer + mSpaceAllocated - 1) == JSON_WRITER_DEBUG_MARKER);
+    }
 };
 
 /**
diff --git a/tools/source/misc/json_writer.cxx b/tools/source/misc/json_writer.cxx
index 0bcbbddc606d..0072e57f1eb6 100644
--- a/tools/source/misc/json_writer.cxx
+++ b/tools/source/misc/json_writer.cxx
@@ -31,6 +31,8 @@ JsonWriter::JsonWriter()
     ++mPos;
     *mPos = ' ';
     ++mPos;
+
+    addValidationMark();
 }
 
 JsonWriter::~JsonWriter()
@@ -42,7 +44,7 @@ JsonWriter::~JsonWriter()
 ScopedJsonWriterNode JsonWriter::startNode(const char* pNodeName)
 {
     auto len = strlen(pNodeName);
-    ensureSpace(len + 6);
+    ensureSpace(len + 8);
 
     addCommaBeforeField();
 
@@ -54,6 +56,9 @@ ScopedJsonWriterNode JsonWriter::startNode(const char* pNodeName)
     mPos += 5;
     mStartNodeCount++;
     mbFirstFieldInNode = true;
+
+    validate();
+
     return ScopedJsonWriterNode(*this);
 }
 
@@ -65,12 +70,14 @@ void JsonWriter::endNode()
     *mPos = '}';
     ++mPos;
     mbFirstFieldInNode = false;
+
+    validate();
 }
 
 ScopedJsonWriterArray JsonWriter::startArray(const char* pNodeName)
 {
     auto len = strlen(pNodeName);
-    ensureSpace(len + 6);
+    ensureSpace(len + 8);
 
     addCommaBeforeField();
 
@@ -82,6 +89,9 @@ ScopedJsonWriterArray JsonWriter::startArray(const char* pNodeName)
     mPos += 5;
     mStartNodeCount++;
     mbFirstFieldInNode = true;
+
+    validate();
+
     return ScopedJsonWriterArray(*this);
 }
 
@@ -93,6 +103,8 @@ void JsonWriter::endArray()
     *mPos = ']';
     ++mPos;
     mbFirstFieldInNode = false;
+
+    validate();
 }
 
 ScopedJsonWriterStruct JsonWriter::startStruct()
@@ -107,6 +119,9 @@ ScopedJsonWriterStruct JsonWriter::startStruct()
     ++mPos;
     mStartNodeCount++;
     mbFirstFieldInNode = true;
+
+    validate();
+
     return ScopedJsonWriterStruct(*this);
 }
 
@@ -118,6 +133,8 @@ void JsonWriter::endStruct()
     *mPos = '}';
     ++mPos;
     mbFirstFieldInNode = false;
+
+    validate();
 }
 
 void JsonWriter::writeEscapedOUString(const OUString& rPropVal)
@@ -195,6 +212,8 @@ void JsonWriter::writeEscapedOUString(const OUString& rPropVal)
             ++mPos;
         }
     }
+
+    validate();
 }
 
 void JsonWriter::put(const char* pPropName, const OUString& rPropVal)
@@ -219,6 +238,8 @@ void JsonWriter::put(const char* pPropName, const OUString& rPropVal)
 
     *mPos = '"';
     ++mPos;
+
+    validate();
 }
 
 void JsonWriter::put(const char* pPropName, const OString& rPropVal)
@@ -265,6 +286,8 @@ void JsonWriter::put(const char* pPropName, const OString& rPropVal)
 
     *mPos = '"';
     ++mPos;
+
+    validate();
 }
 
 void JsonWriter::put(const char* pPropName, const char* pPropVal)
@@ -313,6 +336,8 @@ void JsonWriter::put(const char* pPropName, const char* pPropVal)
 
     *mPos = '"';
     ++mPos;
+
+    validate();
 }
 
 void JsonWriter::put(const char* pPropName, sal_Int64 nPropVal)
@@ -331,6 +356,8 @@ void JsonWriter::put(const char* pPropName, sal_Int64 nPropVal)
     mPos += 3;
 
     mPos += sprintf(mPos, "%" SAL_PRIdINT64, nPropVal);
+
+    validate();
 }
 
 void JsonWriter::put(const char* pPropName, double fPropVal)
@@ -350,6 +377,8 @@ void JsonWriter::put(const char* pPropName, double fPropVal)
 
     memcpy(mPos, sPropVal.getStr(), sPropVal.getLength());
     mPos += sPropVal.getLength();
+
+    validate();
 }
 
 void JsonWriter::put(const char* pPropName, bool nPropVal)
@@ -373,6 +402,8 @@ void JsonWriter::put(const char* pPropName, bool nPropVal)
         pVal = "false";
     memcpy(mPos, pVal, strlen(pVal));
     mPos += strlen(pVal);
+
+    validate();
 }
 
 void JsonWriter::putSimpleValue(const OUString& rPropVal)
@@ -389,6 +420,8 @@ void JsonWriter::putSimpleValue(const OUString& rPropVal)
 
     *mPos = '"';
     ++mPos;
+
+    validate();
 }
 
 void JsonWriter::putRaw(const rtl::OStringBuffer& rRawBuf)
@@ -399,6 +432,8 @@ void JsonWriter::putRaw(const rtl::OStringBuffer& rRawBuf)
 
     memcpy(mPos, rRawBuf.getStr(), rRawBuf.getLength());
     mPos += rRawBuf.getLength();
+
+    validate();
 }
 
 void JsonWriter::addCommaBeforeField()
@@ -424,6 +459,8 @@ void JsonWriter::reallocBuffer(int noMoreBytesRequired)
     mpBuffer = pNew;
     mPos = mpBuffer + currentUsed;
     mSpaceAllocated = newSize;
+
+    addValidationMark();
 }
 
 /** Hands ownership of the underlying storage buffer to the caller,