xmlsecurity: some Distinguished Names are less equal than others

It turns out that the 2 backends NSS and MS CryptoAPI generate different
string representations of the same Distinguished Name in at least one
corner case, when a value contains a quote " U+0022.

The CryptoAPI function to generate the strings is:
CertNameToStr(..., CERT_X500_NAME_STR | CERT_NAME_STR_REVERSE_FLAG, ...)

This is documented on MSDN:
https://docs.microsoft.com/en-us/windows/win32/api/wincrypt/nf-wincrypt-certnametostra#CERT_X500_NAME_STR

NSS appears to implement RFC 1485, at least that's what the internal
function is named after, or perhaps one of its several successor RFCs
(not clear currently if there's a relevant difference).

This is now causing trouble if a certificate with such a DN is used in a
signature, created on WNT but then verified on another platform, because
commit 5af5ea893bcb8a8eb472ac11133da10e5a604e66
introduced consistency checks that compare the DNs that occur as strings
in META-INF/documentsignatures.xml:

xmlsecurity/source/helper/xmlsignaturehelper.cxx:672: X509Data cannot be parsed

The reason is that in XSecController::setX509Data() the value read from
the X509IssuerSerial element (a string generated by CryptoAPI) doesn't
match the value generated by NSS from the certificate parsed from the
X509Certificate element, so these are erroneously interpreted as 2
distinct certificates.

Try to make the EqualDistinguishedNames() more flexible so that it can
try also a converted variant of the DN.

(libxmlsec's NSS backend also complains that it cannot parse the DN:
 x509vfy.c:607: xmlSecNssX509NameRead() '' '' 12 'invalid data for 'char': actual=34 and expected comma ',''
 but it manages to validate the signature despite this.)

Reviewed-on: https://gerrit.libreoffice.org/c/core/+/124287
Tested-by: Jenkins
Reviewed-by: Michael Stahl <michael.stahl@allotropia.de>
(cherry picked from commit e63611fabd38c757809b510fbb71c077880b1081)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/124196
Reviewed-by: Thorsten Behrens <thorsten.behrens@allotropia.de>
(cherry picked from commit 3dfe381032fc61ea31106f103dee9db8277d4d25)

Change-Id: I4f72900738d1f5313146bbda7320a8f44319ebc8
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/124420
Tested-by: Michael Stahl <michael.stahl@allotropia.de>
Reviewed-by: Michael Stahl <michael.stahl@allotropia.de>

8 files changed, 208 insertions, 20 deletions

diff --git a/xmlsecurity/CppunitTest_xmlsecurity_signing.mk b/xmlsecurity/CppunitTest_xmlsecurity_signing.mk
index bdac7bda71e5..9709b49e2b19 100644
--- a/xmlsecurity/CppunitTest_xmlsecurity_signing.mk
+++ b/xmlsecurity/CppunitTest_xmlsecurity_signing.mk
@@ -28,6 +28,7 @@ $(eval $(call gb_CppunitTest_use_libraries,xmlsecurity_signing, \
 	unotest \
 	utl \
 	xmlsecurity \
+	xsec_xmlsec \
 ))
 
 $(eval $(call gb_CppunitTest_use_externals,xmlsecurity_signing,\
diff --git a/xmlsecurity/inc/biginteger.hxx b/xmlsecurity/inc/biginteger.hxx
index 8b4d8a9143b5..1e6b3f4a876e 100644
--- a/xmlsecurity/inc/biginteger.hxx
+++ b/xmlsecurity/inc/biginteger.hxx
@@ -32,8 +32,17 @@ namespace xmlsecurity
 XSECXMLSEC_DLLPUBLIC OUString bigIntegerToNumericString( const css::uno::Sequence< sal_Int8 >& serial );
 XSECXMLSEC_DLLPUBLIC css::uno::Sequence< sal_Int8 > numericStringToBigInteger ( const OUString& serialNumber );
 
+// DNs read as strings from XML files may need to be mangled for compatibility
+// as NSS and MS CryptoAPI have different string serialisations; if the DN is
+// from an XCertificate it's "native" already and doesn't need to be mangled.
+enum EqualMode
+{
+    NOCOMPAT,
+    COMPAT_2ND,
+    COMPAT_BOTH
+};
 XSECXMLSEC_DLLPUBLIC bool EqualDistinguishedNames(OUString const& rName1,
-                                                  OUString const& rName2);
+                                                  OUString const& rName2, EqualMode eMode);
 }
 
 #endif
diff --git a/xmlsecurity/qa/unit/signing/signing.cxx b/xmlsecurity/qa/unit/signing/signing.cxx
index d696c2b5128f..96d233ad9027 100644
--- a/xmlsecurity/qa/unit/signing/signing.cxx
+++ b/xmlsecurity/qa/unit/signing/signing.cxx
@@ -50,6 +50,7 @@
 #include <documentsignaturehelper.hxx>
 #include <xmlsignaturehelper.hxx>
 #include <documentsignaturemanager.hxx>
+#include <biginteger.hxx>
 #include <certificate.hxx>
 #include <xsecctl.hxx>
 #include <sfx2/docfile.hxx>
@@ -706,6 +707,21 @@ CPPUNIT_TEST_FIXTURE(SigningTest, testODFDoubleX509Certificate)
     CPPUNIT_ASSERT(!infos[0].Signer.is());
 }
 
+CPPUNIT_TEST_FIXTURE(SigningTest, testDNCompatibility)
+{
+    OUString const msDN("CN=\"\"\"ABC\"\".\", O=\"Enterprise \"\"ABC\"\"\"");
+    OUString const nssDN("CN=\\\"ABC\\\".,O=Enterprise \\\"ABC\\\"");
+    // this is just the status quo, possibly either NSS or CryptoAPI might change
+    CPPUNIT_ASSERT(!xmlsecurity::EqualDistinguishedNames(msDN, nssDN, xmlsecurity::NOCOMPAT));
+    CPPUNIT_ASSERT(!xmlsecurity::EqualDistinguishedNames(nssDN, msDN, xmlsecurity::NOCOMPAT));
+    // with compat flag it should work, with the string one 2nd and the native one 1st
+#ifdef _WIN32
+    CPPUNIT_ASSERT(xmlsecurity::EqualDistinguishedNames(msDN, nssDN, xmlsecurity::COMPAT_2ND));
+#else
+    CPPUNIT_ASSERT(xmlsecurity::EqualDistinguishedNames(nssDN, msDN, xmlsecurity::COMPAT_2ND));
+#endif
+}
+
 /// Test a typical OOXML where a number of (but not all) streams are signed.
 CPPUNIT_TEST_FIXTURE(SigningTest, testOOXMLPartial)
 {
diff --git a/xmlsecurity/source/component/documentdigitalsignatures.cxx b/xmlsecurity/source/component/documentdigitalsignatures.cxx
index 8a5bf37a0432..52705860e053 100644
--- a/xmlsecurity/source/component/documentdigitalsignatures.cxx
+++ b/xmlsecurity/source/component/documentdigitalsignatures.cxx
@@ -637,7 +637,7 @@ sal_Bool DocumentDigitalSignatures::isAuthorTrusted(
 
     return std::any_of(aTrustedAuthors.begin(), aTrustedAuthors.end(),
         [&xAuthor, &sSerialNum](const SvtSecurityOptions::Certificate& rAuthor) {
-            return xmlsecurity::EqualDistinguishedNames(rAuthor[0], xAuthor->getIssuerName())
+            return xmlsecurity::EqualDistinguishedNames(rAuthor[0], xAuthor->getIssuerName(), xmlsecurity::NOCOMPAT)
                 && ( rAuthor[1] == sSerialNum );
         });
 }
diff --git a/xmlsecurity/source/helper/xmlsignaturehelper.cxx b/xmlsecurity/source/helper/xmlsignaturehelper.cxx
index bcb79039e342..cdf7d802664d 100644
--- a/xmlsecurity/source/helper/xmlsignaturehelper.cxx
+++ b/xmlsecurity/source/helper/xmlsignaturehelper.cxx
@@ -44,6 +44,7 @@
 #include <comphelper/ofopxmlhelper.hxx>
 #include <comphelper/sequence.hxx>
 #include <tools/diagnose_ex.h>
+#include <rtl/ustrbuf.hxx>
 #include <sal/log.hxx>
 
 #include <optional>
@@ -605,7 +606,7 @@ static auto CheckX509Data(
                 start = i; // issuer isn't in the list
                 break;
             }
-            if (xmlsecurity::EqualDistinguishedNames(certs[i]->getIssuerName(), certs[j]->getSubjectName()))
+            if (xmlsecurity::EqualDistinguishedNames(certs[i]->getIssuerName(), certs[j]->getSubjectName(), xmlsecurity::NOCOMPAT))
             {
                 if (i == j) // self signed
                 {
@@ -638,7 +639,7 @@ static auto CheckX509Data(
             if (chain[i] != j)
             {
                 if (xmlsecurity::EqualDistinguishedNames(
-                        certs[chain[i]]->getSubjectName(), certs[j]->getIssuerName()))
+                        certs[chain[i]]->getSubjectName(), certs[j]->getIssuerName(), xmlsecurity::NOCOMPAT))
                 {
                     if (chain.size() != i + 1) // already found issuee?
                     {
diff --git a/xmlsecurity/source/helper/xsecverify.cxx b/xmlsecurity/source/helper/xsecverify.cxx
index 89141ed1dfd4..1b34afef6c2a 100644
--- a/xmlsecurity/source/helper/xsecverify.cxx
+++ b/xmlsecurity/source/helper/xsecverify.cxx
@@ -271,7 +271,7 @@ void XSecController::setX509Data(
             OUString const serialNumber(xmlsecurity::bigIntegerToNumericString(xCert->getSerialNumber()));
             auto const iter = std::find_if(rX509IssuerSerials.begin(), rX509IssuerSerials.end(),
                 [&](auto const& rX509IssuerSerial) {
-                    return xmlsecurity::EqualDistinguishedNames(issuerName, rX509IssuerSerial.first)
+                    return xmlsecurity::EqualDistinguishedNames(issuerName, rX509IssuerSerial.first, xmlsecurity::COMPAT_2ND)
                         && serialNumber == rX509IssuerSerial.second;
                 });
             if (iter != rX509IssuerSerials.end())
@@ -418,7 +418,7 @@ void XSecController::setX509CertDigest(
     {
         for (auto & it : rData)
         {
-            if (xmlsecurity::EqualDistinguishedNames(it.X509IssuerName, rX509IssuerName)
+            if (xmlsecurity::EqualDistinguishedNames(it.X509IssuerName, rX509IssuerName, xmlsecurity::COMPAT_BOTH)
                 && it.X509SerialNumber == rX509SerialNumber)
             {
                 it.CertDigest = rCertDigest;
@@ -441,7 +441,7 @@ void XSecController::setX509CertDigest(
                     {
                         SAL_INFO("xmlsecurity.helper", "cannot parse X509Certificate");
                     }
-                    else if (xmlsecurity::EqualDistinguishedNames(xCert->getIssuerName(),rX509IssuerName)
+                    else if (xmlsecurity::EqualDistinguishedNames(xCert->getIssuerName(), rX509IssuerName, xmlsecurity::COMPAT_2ND)
                         && xmlsecurity::bigIntegerToNumericString(xCert->getSerialNumber()) == rX509SerialNumber)
                     {
                         it.CertDigest = rCertDigest;
diff --git a/xmlsecurity/source/xmlsec/mscrypt/x509certificate_mscryptimpl.cxx b/xmlsecurity/source/xmlsec/mscrypt/x509certificate_mscryptimpl.cxx
index 244cd46ac564..da64b6c7e4c2 100644
--- a/xmlsecurity/source/xmlsec/mscrypt/x509certificate_mscryptimpl.cxx
+++ b/xmlsecurity/source/xmlsec/mscrypt/x509certificate_mscryptimpl.cxx
@@ -32,6 +32,7 @@
 #include "oid.hxx"
 
 #include <rtl/locale.h>
+#include <rtl/ustrbuf.hxx>
 #include <osl/nlsupport.h>
 #include <osl/process.h>
 #include <o3tl/char16_t2wchar_t.hxx>
@@ -652,6 +653,67 @@ Sequence<OUString> SAL_CALL X509Certificate_MSCryptImpl::getSupportedServiceName
 
 namespace xmlsecurity {
 
+// based on some guesswork and:
+// https://datatracker.ietf.org/doc/html/rfc1485
+// https://docs.microsoft.com/en-us/windows/win32/api/wincrypt/nf-wincrypt-certnametostra#CERT_X500_NAME_STR
+// the main problem appears to be that in values NSS uses \ escapes but CryptoAPI requires " quotes around value
+static OUString CompatDNNSS(OUString const& rDN)
+{
+    OUStringBuffer buf(rDN.getLength());
+    enum { DEFAULT, INVALUE, INQUOTE } state(DEFAULT);
+    for (sal_Int32 i = 0; i < rDN.getLength(); ++i)
+    {
+        if (state == DEFAULT)
+        {
+            buf.append(rDN[i]);
+            if (rDN[i] == '=')
+            {
+                if (rDN.getLength() == i+1)
+                {
+                    break; // invalid?
+                }
+                else
+                {
+                    buf.append('"');
+                    state = INVALUE;
+                }
+            }
+        }
+        else if (state == INVALUE)
+        {
+            if (rDN[i] == '+' || rDN[i] == ',' || rDN[i] == ';')
+            {
+                buf.append('"');
+                buf.append(rDN[i]);
+                state = DEFAULT;
+            }
+            else if (rDN[i] == '\\')
+            {
+                if (rDN.getLength() == i+1)
+                {
+                    break; // invalid?
+                }
+                if (rDN[i+1] == '"')
+                {
+                    buf.append('"');
+                }
+                buf.append(rDN[i+1]);
+                ++i;
+            }
+            else
+            {
+                buf.append(rDN[i]);
+            }
+            if (i+1 == rDN.getLength())
+            {
+                buf.append('"');
+                state = DEFAULT;
+            }
+        }
+    }
+    return buf.makeStringAndClear();
+}
+
 static bool EncodeDistinguishedName(OUString const& rName, CERT_NAME_BLOB & rBlob)
 {
     LPCWSTR pszError;
@@ -674,22 +736,38 @@ static bool EncodeDistinguishedName(OUString const& rName, CERT_NAME_BLOB & rBlo
 }
 
 bool EqualDistinguishedNames(
-        OUString const& rName1, OUString const& rName2)
+        OUString const& rName1, OUString const& rName2,
+        EqualMode const eMode)
 {
+    if (eMode == COMPAT_BOTH && !rName1.isEmpty() && rName1 == rName2)
+    {   // handle case where both need to be converted
+        return true;
+    }
     CERT_NAME_BLOB blob1;
     if (!EncodeDistinguishedName(rName1, blob1))
     {
         return false;
     }
     CERT_NAME_BLOB blob2;
-    if (!EncodeDistinguishedName(rName2, blob2))
+    bool ret(false);
+    if (!!EncodeDistinguishedName(rName2, blob2))
     {
-        delete[] blob1.pbData;
-        return false;
+        ret = CertCompareCertificateName(X509_ASN_ENCODING,
+            &blob1, &blob2) == TRUE;
+        delete[] blob2.pbData;
+    }
+    if (!ret && eMode == COMPAT_2ND)
+    {
+        CERT_NAME_BLOB blob2compat;
+        if (!EncodeDistinguishedName(CompatDNNSS(rName2), blob2compat))
+        {
+            delete[] blob1.pbData;
+            return false;
+        }
+        ret = CertCompareCertificateName(X509_ASN_ENCODING,
+            &blob1, &blob2compat) == TRUE;
+        delete[] blob2compat.pbData;
     }
-    bool const ret(CertCompareCertificateName(X509_ASN_ENCODING,
-            &blob1, &blob2) == TRUE);
-    delete[] blob2.pbData;
     delete[] blob1.pbData;
     return ret;
 }
diff --git a/xmlsecurity/source/xmlsec/nss/x509certificate_nssimpl.cxx b/xmlsecurity/source/xmlsec/nss/x509certificate_nssimpl.cxx
index d6143a81883c..39d4b4ee87eb 100644
--- a/xmlsecurity/source/xmlsec/nss/x509certificate_nssimpl.cxx
+++ b/xmlsecurity/source/xmlsec/nss/x509certificate_nssimpl.cxx
@@ -29,6 +29,8 @@
 #include <comphelper/servicehelper.hxx>
 #include <cppuhelper/supportsservice.hxx>
 #include <rtl/ref.hxx>
+#include <rtl/ustrbuf.hxx>
+#include <sal/log.hxx>
 #include "x509certificate_nssimpl.hxx"
 
 #include <biginteger.hxx>
@@ -536,22 +538,103 @@ Sequence<OUString> SAL_CALL X509Certificate_NssImpl::getSupportedServiceNames()
 
 namespace xmlsecurity {
 
+// based on some guesswork and:
+// https://datatracker.ietf.org/doc/html/rfc1485
+// https://docs.microsoft.com/en-us/windows/win32/api/wincrypt/nf-wincrypt-certnametostra#CERT_X500_NAME_STR
+// the main problem appears to be that in values " is escaped as "" vs. \"
+static OUString CompatDNCryptoAPI(OUString const& rDN)
+{
+    OUStringBuffer buf(rDN.getLength());
+    enum { DEFAULT, INVALUE, INQUOTE } state(DEFAULT);
+    for (sal_Int32 i = 0; i < rDN.getLength(); ++i)
+    {
+        if (state == DEFAULT)
+        {
+            buf.append(rDN[i]);
+            if (rDN[i] == '=')
+            {
+                if (rDN.getLength() == i+1)
+                {
+                    break; // invalid?
+                }
+                else if (rDN[i+1] == '"')
+                {
+                    buf.append(rDN[i+1]);
+                    ++i;
+                    state = INQUOTE;
+                }
+                else
+                {
+                    state = INVALUE;
+                }
+            }
+        }
+        else if (state == INVALUE)
+        {
+            if (rDN[i] == '+' || rDN[i] == ',' || rDN[i] == ';')
+            {
+                state = DEFAULT;
+            }
+            buf.append(rDN[i]);
+        }
+        else
+        {
+            assert(state == INQUOTE);
+            if (rDN[i] == '"')
+            {
+                if (rDN.getLength() != i+1 && rDN[i+1] == '"')
+                {
+                    buf.append('\\');
+                    buf.append(rDN[i+1]);
+                    ++i;
+                }
+                else
+                {
+                    buf.append(rDN[i]);
+                    state = DEFAULT;
+                }
+            }
+            else
+            {
+                buf.append(rDN[i]);
+            }
+        }
+    }
+    return buf.makeStringAndClear();
+}
+
 bool EqualDistinguishedNames(
-        OUString const& rName1, OUString const& rName2)
+        OUString const& rName1, OUString const& rName2,
+        EqualMode const eMode)
 {
+    if (eMode == COMPAT_BOTH && !rName1.isEmpty() && rName1 == rName2)
+    {   // handle case where both need to be converted
+        return true;
+    }
     CERTName *const pName1(CERT_AsciiToName(OUStringToOString(rName1, RTL_TEXTENCODING_UTF8).getStr()));
     if (pName1 == nullptr)
     {
         return false;
     }
     CERTName *const pName2(CERT_AsciiToName(OUStringToOString(rName2, RTL_TEXTENCODING_UTF8).getStr()));
-    if (pName2 == nullptr)
+    bool ret(false);
+    if (pName2)
     {
-        CERT_DestroyName(pName1);
-        return false;
+        ret = (CERT_CompareName(pName1, pName2) == SECEqual);
+        CERT_DestroyName(pName2);
+    }
+    if (!ret && eMode == COMPAT_2ND)
+    {
+        CERTName *const pName2Compat(CERT_AsciiToName(OUStringToOString(
+            CompatDNCryptoAPI(rName2), RTL_TEXTENCODING_UTF8).getStr()));
+        if (pName2Compat == nullptr)
+        {
+            CERT_DestroyName(pName1);
+            return false;
+        }
+        ret = CERT_CompareName(pName1, pName2Compat) == SECEqual;
+        CERT_DestroyName(pName2Compat);
     }
-    bool const ret(CERT_CompareName(pName1, pName2) == SECEqual);
-    CERT_DestroyName(pName2);
     CERT_DestroyName(pName1);
     return ret;
 }