keep track of available data

Change-Id: Idc54cdef0f3a4355a7e26f25cdc5b50d65d9d583
Reviewed-on: https://gerrit.libreoffice.org/45353Reviewed-by: Michael Stahl <mstahl@redhat.com>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

package/source/zipapi/MemoryByteGrabber.hxx

@@ -36,6 +36,8 @@ public:
     }
     const sal_Int8 * getCurrentPos () { return mpBuffer + mnCurrent; }
 
+    sal_Int32 remainingSize() const { return mnEnd - mnCurrent; }
+
     // XInputStream chained
 
     /// @throws css::io::NotConnectedException

package/source/zipapi/ZipFile.cxx

@@ -934,6 +934,9 @@ sal_Int32 ZipFile::readCEN()
             if ( aEntry.nExtraLen < 0 )
                 throw ZipException("unexpected extra header info length" );
 
+            if (aEntry.nPathLen > aMemGrabber.remainingSize())
+                throw ZipException("name too long");
+
             // read always in UTF8, some tools seem not to set UTF8 bit
             aEntry.sPath = OUString::intern ( reinterpret_cast<char const *>(aMemGrabber.getCurrentPos()),
                                                    aEntry.nPathLen,