tdf#140606 make PDF parsing more lenient and prevent a crash

If the external document can't be opened, it tried to continue
with the export anyway, which eventually lead to a crash. This
is fixed by handling this situation and prevent a crash, however
the part of the document in this case isn't exported.

The document couldn't be opened because of a parsing error - there
was a unexpected null character instead of a whitespace, which
made the parser panic. Fix this by making the parser more lenient
in such a situation when there is an unexpected null and try to
continue parsing.

Bug document seems to be created with a buggy PDF writer, but other
PDF readers don't complain when parsing the document so it looks to
be a valid. qpdf --check doesn't complain either.

Change-Id: I61eb281e821ccd195ef006d778556e25d1c7f5e3
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/111820
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>
(cherry picked from commit 2c1ed5a5dad827cde032f27a4348e81be15889bc)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/111857
Reviewed-by: Adolfo Jayme Barrientos <fitojb@ubuntu.com>

3 files changed, 26 insertions, 10 deletions

diff --git a/vcl/inc/pdf/ExternalPDFStreams.hxx b/vcl/inc/pdf/ExternalPDFStreams.hxx
index ab3d057bd83c..0a1997fe7dc7 100644
--- a/vcl/inc/pdf/ExternalPDFStreams.hxx
+++ b/vcl/inc/pdf/ExternalPDFStreams.hxx
@@ -33,21 +33,25 @@ struct VCL_DLLPUBLIC ExternalPDFStream
 
     std::map<sal_Int32, sal_Int32>& getCopiedResources() { return maCopiedResources; }
 
-    filter::PDFDocument& getPDFDocument()
+    std::shared_ptr<filter::PDFDocument>& getPDFDocument()
     {
         if (!mpPDFDocument)
         {
             SvMemoryStream aPDFStream;
             aPDFStream.WriteBytes(maData.data(), maData.size());
             aPDFStream.Seek(0);
-            mpPDFDocument = std::make_shared<filter::PDFDocument>();
-            if (!mpPDFDocument->Read(aPDFStream))
+            auto pPDFDocument = std::make_shared<filter::PDFDocument>();
+            if (!pPDFDocument->Read(aPDFStream))
             {
                 SAL_WARN("vcl.pdfwriter",
                          "PDFWriterImpl::writeReferenceXObject: reading the PDF document failed");
             }
+            else
+            {
+                mpPDFDocument = pPDFDocument;
+            }
         }
-        return *mpPDFDocument;
+        return mpPDFDocument;
     }
 };
 
diff --git a/vcl/source/filter/ipdf/pdfdocument.cxx b/vcl/source/filter/ipdf/pdfdocument.cxx
index 41c44bd01b57..804713abaf10 100644
--- a/vcl/source/filter/ipdf/pdfdocument.cxx
+++ b/vcl/source/filter/ipdf/pdfdocument.cxx
@@ -1441,12 +1441,18 @@ bool PDFDocument::Tokenize(SvStream& rStream, TokenizeMode eMode,
                 }
                 else
                 {
-                    if (!rtl::isAsciiWhiteSpace(static_cast<unsigned char>(ch)))
+                    auto uChar = static_cast<unsigned char>(ch);
+                    // Be more lenient and allow unexpected null char
+                    if (!rtl::isAsciiWhiteSpace(uChar) && uChar != 0)
                     {
-                        SAL_WARN("vcl.filter", "PDFDocument::Tokenize: unexpected character: "
-                                                   << ch << " at byte position " << rStream.Tell());
+                        SAL_WARN("vcl.filter",
+                                 "PDFDocument::Tokenize: unexpected character with code "
+                                     << sal_Int32(ch) << " at byte position " << rStream.Tell());
                         return false;
                     }
+                    SAL_WARN_IF(uChar == 0, "vcl.filter",
+                                "PDFDocument::Tokenize: unexpected null character at "
+                                    << rStream.Tell() << " - ignoring");
                 }
                 break;
             }
diff --git a/vcl/source/gdi/pdfwriter_impl.cxx b/vcl/source/gdi/pdfwriter_impl.cxx
index 951cda0f29da..eeeb4305a181 100644
--- a/vcl/source/gdi/pdfwriter_impl.cxx
+++ b/vcl/source/gdi/pdfwriter_impl.cxx
@@ -8459,10 +8459,16 @@ void PDFWriterImpl::writeReferenceXObject(ReferenceXObjectEmit& rEmit)
         // object.
         if (rEmit.m_nExternalPDFDataIndex < 0)
             return;
-        auto & rExternalPDFStream = m_aExternalPDFStreams.get(rEmit.m_nExternalPDFDataIndex);
-        auto & rPDFDocument = rExternalPDFStream.getPDFDocument();
+        auto& rExternalPDFStream = m_aExternalPDFStreams.get(rEmit.m_nExternalPDFDataIndex);
+        auto& pPDFDocument = rExternalPDFStream.getPDFDocument();
+        if (!pPDFDocument)
+        {
+            // Couldn't parse the document and can't continue
+            SAL_WARN("vcl.pdfwriter", "PDFWriterImpl::writeReferenceXObject: failed to parse the document");
+            return;
+        }
 
-        std::vector<filter::PDFObjectElement*> aPages = rPDFDocument.GetPages();
+        std::vector<filter::PDFObjectElement*> aPages = pPDFDocument->GetPages();
         if (aPages.empty())
         {
             SAL_WARN("vcl.pdfwriter", "PDFWriterImpl::writeReferenceXObject: no pages");