xmlsecurity: fold pdfio into pdfsignaturehelper

Most of the initial pdfio was moved to vcl as vcl::filter::PDFDocument.
A small part was left here, because it depended on NSS.  Then later the
NSS bits were moved to svl::crypto::Signing.  The rest is just a small
amount of code, keeping that separate from PDFSignatureHelper, which is
its only user makes little sense.

With this, vcl::filter::PDFDocument is an implementation detail of
PDFSignatureHelper during signature verification.

Change-Id: I6230f9e46deeff7159970f88dbb3bd2de0e9ce7d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/103350
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>

1 files changed, 310 insertions, 3 deletions

diff --git a/xmlsecurity/source/helper/pdfsignaturehelper.cxx b/xmlsecurity/source/helper/pdfsignaturehelper.cxx
index b49cdd3e449f..f9bb5342c626 100644
--- a/xmlsecurity/source/helper/pdfsignaturehelper.cxx
+++ b/xmlsecurity/source/helper/pdfsignaturehelper.cxx
@@ -30,8 +30,11 @@
 #include <unotools/streamwrap.hxx>
 #include <unotools/ucbstreamhelper.hxx>
 #include <vcl/filter/pdfdocument.hxx>
-
-#include <pdfio/pdfdocument.hxx>
+#include <vcl/checksum.hxx>
+#include <rtl/ustrbuf.hxx>
+#include <svl/cryptosign.hxx>
+#include <config_features.h>
+#include <vcl/filter/PDFiumLibrary.hxx>
 
 using namespace ::com::sun::star;
 
@@ -112,6 +115,310 @@ void GetSignatureLineShape(const uno::Reference<frame::XModel>& xModel, sal_Int3
     rSignatureLineShape = std::vector<sal_Int8>(aStream.GetSize());
     aStream.ReadBytes(rSignatureLineShape.data(), rSignatureLineShape.size());
 }
+
+/// Turns an array of floats into offset + length pairs.
+bool GetByteRangesFromPDF(vcl::filter::PDFArrayElement& rArray,
+                          std::vector<std::pair<size_t, size_t>>& rByteRanges)
+{
+    size_t nByteRangeOffset = 0;
+    const std::vector<vcl::filter::PDFElement*>& rByteRangeElements = rArray.GetElements();
+    for (size_t i = 0; i < rByteRangeElements.size(); ++i)
+    {
+        auto pNumber = dynamic_cast<vcl::filter::PDFNumberElement*>(rByteRangeElements[i]);
+        if (!pNumber)
+        {
+            SAL_WARN("xmlsecurity.helper",
+                     "ValidateSignature: signature offset and length has to be a number");
+            return false;
+        }
+
+        if (i % 2 == 0)
+        {
+            nByteRangeOffset = pNumber->GetValue();
+            continue;
+        }
+        size_t nByteRangeLength = pNumber->GetValue();
+        rByteRanges.emplace_back(nByteRangeOffset, nByteRangeLength);
+    }
+
+    return true;
+}
+
+/// Determines the last position that is covered by a signature.
+bool GetEOFOfSignature(vcl::filter::PDFObjectElement* pSignature, size_t& rEOF)
+{
+    vcl::filter::PDFObjectElement* pValue = pSignature->LookupObject("V");
+    if (!pValue)
+    {
+        return false;
+    }
+
+    auto pByteRange = dynamic_cast<vcl::filter::PDFArrayElement*>(pValue->Lookup("ByteRange"));
+    if (!pByteRange || pByteRange->GetElements().size() < 2)
+    {
+        return false;
+    }
+
+    std::vector<std::pair<size_t, size_t>> aByteRanges;
+    if (!GetByteRangesFromPDF(*pByteRange, aByteRanges))
+    {
+        return false;
+    }
+
+    rEOF = aByteRanges[1].first + aByteRanges[1].second;
+    return true;
+}
+
+/// Checks if there are unsigned incremental updates between the signatures or after the last one.
+bool IsCompleteSignature(SvStream& rStream, vcl::filter::PDFDocument& rDocument,
+                         vcl::filter::PDFObjectElement* pSignature)
+{
+    std::set<size_t> aSignedEOFs;
+    for (const auto& i : rDocument.GetSignatureWidgets())
+    {
+        size_t nEOF = 0;
+        if (!GetEOFOfSignature(i, nEOF))
+        {
+            return false;
+        }
+
+        aSignedEOFs.insert(nEOF);
+    }
+
+    size_t nSignatureEOF = 0;
+    if (!GetEOFOfSignature(pSignature, nSignatureEOF))
+    {
+        return false;
+    }
+
+    const std::vector<size_t>& rAllEOFs = rDocument.GetEOFs();
+    bool bFoundOwn = false;
+    for (const auto& rEOF : rAllEOFs)
+    {
+        if (rEOF == nSignatureEOF)
+        {
+            bFoundOwn = true;
+            continue;
+        }
+
+        if (!bFoundOwn)
+        {
+            continue;
+        }
+
+        if (aSignedEOFs.find(rEOF) == aSignedEOFs.end())
+        {
+            // Unsigned incremental update found.
+            return false;
+        }
+    }
+
+    // Make sure we find the incremental update of the signature itself.
+    if (!bFoundOwn)
+    {
+        return false;
+    }
+
+    // No additional content after the last incremental update.
+    rStream.Seek(STREAM_SEEK_TO_END);
+    size_t nFileEnd = rStream.Tell();
+    return std::find(rAllEOFs.begin(), rAllEOFs.end(), nFileEnd) != rAllEOFs.end();
+}
+
+#if HAVE_FEATURE_PDFIUM
+/// Collects the checksum of each page of one version of the PDF.
+void AnalyizeSignatureStream(SvMemoryStream& rStream, std::vector<BitmapChecksum>& rPageChecksums)
+{
+    auto pPdfium = vcl::pdf::PDFiumLibrary::get();
+    vcl::pdf::PDFiumDocument aPdfDocument(
+        FPDF_LoadMemDocument(rStream.GetData(), rStream.GetSize(), /*password=*/nullptr));
+
+    int nPageCount = aPdfDocument.getPageCount();
+    for (int nPage = 0; nPage < nPageCount; ++nPage)
+    {
+        std::unique_ptr<vcl::pdf::PDFiumPage> pPdfPage(aPdfDocument.openPage(nPage));
+        if (!pPdfPage)
+        {
+            return;
+        }
+
+        BitmapChecksum nPageChecksum = pPdfPage->getChecksum();
+        rPageChecksums.push_back(nPageChecksum);
+    }
+}
+#endif
+
+/**
+ * Checks if incremental updates after singing performed valid modifications only.
+ * Annotations/commenting is OK, other changes are not.
+ */
+bool IsValidSignature(SvStream& rStream, vcl::filter::PDFObjectElement* pSignature)
+{
+    size_t nSignatureEOF = 0;
+    if (!GetEOFOfSignature(pSignature, nSignatureEOF))
+    {
+        return false;
+    }
+
+#if HAVE_FEATURE_PDFIUM
+    SvMemoryStream aSignatureStream;
+    sal_uInt64 nPos = rStream.Tell();
+    rStream.Seek(0);
+    aSignatureStream.WriteStream(rStream, nSignatureEOF);
+    rStream.Seek(nPos);
+    aSignatureStream.Seek(0);
+    std::vector<BitmapChecksum> aSignedPages;
+    AnalyizeSignatureStream(aSignatureStream, aSignedPages);
+
+    SvMemoryStream aFullStream;
+    nPos = rStream.Tell();
+    rStream.Seek(0);
+    aFullStream.WriteStream(rStream);
+    rStream.Seek(nPos);
+    aFullStream.Seek(0);
+    std::vector<BitmapChecksum> aAllPages;
+    AnalyizeSignatureStream(aFullStream, aAllPages);
+
+    // Fail if any page looks different after signing and at the end. Annotations/commenting doesn't
+    // count, though.
+    return aSignedPages == aAllPages;
+#else
+    (void)rStream;
+    return true;
+#endif
+}
+
+/**
+ * @param rInformation The actual result.
+ * @param rDocument the parsed document to see if the signature is partial.
+ * @return If we can determinate a result.
+ */
+bool ValidateSignature(SvStream& rStream, vcl::filter::PDFObjectElement* pSignature,
+                       SignatureInformation& rInformation, vcl::filter::PDFDocument& rDocument)
+{
+    vcl::filter::PDFObjectElement* pValue = pSignature->LookupObject("V");
+    if (!pValue)
+    {
+        SAL_WARN("xmlsecurity.helper", "ValidateSignature: no value");
+        return false;
+    }
+
+    auto pContents = dynamic_cast<vcl::filter::PDFHexStringElement*>(pValue->Lookup("Contents"));
+    if (!pContents)
+    {
+        SAL_WARN("xmlsecurity.helper", "ValidateSignature: no contents");
+        return false;
+    }
+
+    auto pByteRange = dynamic_cast<vcl::filter::PDFArrayElement*>(pValue->Lookup("ByteRange"));
+    if (!pByteRange || pByteRange->GetElements().size() < 2)
+    {
+        SAL_WARN("xmlsecurity.helper", "ValidateSignature: no byte range or too few elements");
+        return false;
+    }
+
+    auto pSubFilter = dynamic_cast<vcl::filter::PDFNameElement*>(pValue->Lookup("SubFilter"));
+    const bool bNonDetached = pSubFilter && pSubFilter->GetValue() == "adbe.pkcs7.sha1";
+    if (!pSubFilter
+        || (pSubFilter->GetValue() != "adbe.pkcs7.detached" && !bNonDetached
+            && pSubFilter->GetValue() != "ETSI.CAdES.detached"))
+    {
+        if (!pSubFilter)
+            SAL_WARN("xmlsecurity.helper", "ValidateSignature: missing sub-filter");
+        else
+            SAL_WARN("xmlsecurity.helper", "ValidateSignature: unsupported sub-filter: '"
+                                               << pSubFilter->GetValue() << "'");
+        return false;
+    }
+
+    // Reason / comment / description is optional.
+    auto pReason = dynamic_cast<vcl::filter::PDFHexStringElement*>(pValue->Lookup("Reason"));
+    if (pReason)
+    {
+        // See appendUnicodeTextString() for the export equivalent of this.
+        std::vector<unsigned char> aReason = vcl::filter::PDFDocument::DecodeHexString(pReason);
+        OUStringBuffer aBuffer;
+        sal_uInt16 nByte = 0;
+        for (size_t i = 0; i < aReason.size(); ++i)
+        {
+            if (i % 2 == 0)
+                nByte = aReason[i];
+            else
+            {
+                sal_Unicode nUnicode;
+                nUnicode = (nByte << 8);
+                nUnicode |= aReason[i];
+                aBuffer.append(nUnicode);
+            }
+        }
+
+        if (!aBuffer.isEmpty())
+            rInformation.ouDescription = aBuffer.makeStringAndClear();
+    }
+
+    // Date: used only when the time of signing is not available in the
+    // signature.
+    auto pM = dynamic_cast<vcl::filter::PDFLiteralStringElement*>(pValue->Lookup("M"));
+    if (pM)
+    {
+        // Example: "D:20161027100104".
+        const OString& rM = pM->GetValue();
+        if (rM.startsWith("D:") && rM.getLength() >= 16)
+        {
+            rInformation.stDateTime.Year = rM.copy(2, 4).toInt32();
+            rInformation.stDateTime.Month = rM.copy(6, 2).toInt32();
+            rInformation.stDateTime.Day = rM.copy(8, 2).toInt32();
+            rInformation.stDateTime.Hours = rM.copy(10, 2).toInt32();
+            rInformation.stDateTime.Minutes = rM.copy(12, 2).toInt32();
+            rInformation.stDateTime.Seconds = rM.copy(14, 2).toInt32();
+        }
+    }
+
+    // Build a list of offset-length pairs, representing the signed bytes.
+    std::vector<std::pair<size_t, size_t>> aByteRanges;
+    if (!GetByteRangesFromPDF(*pByteRange, aByteRanges))
+    {
+        return false;
+    }
+
+    // Detect if the byte ranges don't cover everything, but the signature itself.
+    if (aByteRanges.size() < 2)
+    {
+        SAL_WARN("xmlsecurity.helper", "ValidateSignature: expected 2 byte ranges");
+        return false;
+    }
+    if (aByteRanges[0].first != 0)
+    {
+        SAL_WARN("xmlsecurity.helper", "ValidateSignature: first range start is not 0");
+        return false;
+    }
+    // 2 is the leading "<" and the trailing ">" around the hex string.
+    size_t nSignatureLength = static_cast<size_t>(pContents->GetValue().getLength()) + 2;
+    if (aByteRanges[1].first != (aByteRanges[0].second + nSignatureLength))
+    {
+        SAL_WARN("xmlsecurity.helper",
+                 "ValidateSignature: second range start is not the end of the signature");
+        return false;
+    }
+    rInformation.bPartialDocumentSignature = !IsCompleteSignature(rStream, rDocument, pSignature);
+    if (!IsValidSignature(rStream, pSignature))
+    {
+        SAL_WARN("xmlsecurity.helper", "ValidateSignature: invalid incremental update detected");
+        return false;
+    }
+
+    // At this point there is no obviously missing info to validate the
+    // signature.
+    std::vector<unsigned char> aSignature = vcl::filter::PDFDocument::DecodeHexString(pContents);
+    if (aSignature.empty())
+    {
+        SAL_WARN("xmlsecurity.helper", "ValidateSignature: empty contents");
+        return false;
+    }
+
+    return svl::crypto::Signing::Verify(rStream, aByteRanges, bNonDetached, aSignature,
+                                        rInformation);
+}
 }
 
 PDFSignatureHelper::PDFSignatureHelper() = default;
@@ -148,7 +455,7 @@ bool PDFSignatureHelper::ReadAndVerifySignatureSvStream(SvStream& rStream)
     {
         SignatureInformation aInfo(i);
 
-        if (!xmlsecurity::pdfio::ValidateSignature(rStream, aSignatures[i], aInfo, aDocument))
+        if (!ValidateSignature(rStream, aSignatures[i], aInfo, aDocument))
             SAL_WARN("xmlsecurity.helper", "failed to determine digest match");
 
         m_aSignatureInfos.push_back(aInfo);