Credit to OSS-Fuzz: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=37363

Do some basic XML validation before running the xmpsdk library to avoid bugs in xmpsdk.

src/CMakeLists.txt

@@ -173,6 +173,9 @@ target_include_directories(exiv2lib SYSTEM PRIVATE
     $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/xmpsdk/include>
 )
 
+target_include_directories(exiv2lib PRIVATE ${EXPAT_INCLUDE_DIR})
+target_link_libraries(exiv2lib PRIVATE EXPAT::EXPAT)
+
 if (EXIV2_ENABLE_XMP)
     target_link_libraries(exiv2lib PRIVATE exiv2-xmp)
 elseif(EXIV2_ENABLE_EXTERNAL_XMP)

src/xmp.cpp

@@ -30,6 +30,7 @@
 #include <algorithm>
 #include <cassert>
 #include <string>
+#include <expat.h>
 
 // Adobe XMP Toolkit
 #ifdef   EXV_HAVE_XMP_TOOLKIT
@@ -42,6 +43,168 @@
 # include <XMP.incl_cpp>
 #endif // EXV_HAVE_XMP_TOOLKIT
 
+// This anonymous namespace contains a class named XMLValidator, which uses
+// libexpat to do a basic validation check on an XML document. This is to
+// reduce the chance of hitting a bug in the (third-party) xmpsdk
+// library. For example, it is easy to a trigger a stack overflow in xmpsdk
+// with a deeply nested tree.
+namespace {
+    using namespace Exiv2;
+
+    class XMLValidator {
+        size_t element_depth_ = 0;
+        size_t namespace_depth_ = 0;
+
+        // These fields are used to record whether an error occurred during
+        // parsing. Why do we need to store the error for later, rather
+        // than throw an exception immediately? Because expat is a C
+        // library, so it isn't designed to be able to handle exceptions
+        // thrown by the callback functions. Throwing exceptions during
+        // parsing is an example of one of the things that xmpsdk does
+        // wrong, leading to problems like https://github.com/Exiv2/exiv2/issues/1821.
+        bool haserror_ = false;
+        std::string errmsg_;
+        XML_Size errlinenum_ = 0;
+        XML_Size errcolnum_ = 0;
+
+        // Very deeply nested XML trees can cause a stack overflow in
+        // xmpsdk.  They are also very unlikely to be valid XMP, so we
+        // error out if the depth exceeds this limit.
+        static const size_t max_recursion_limit_ = 1000;
+
+        const XML_Parser parser_;
+
+    public:
+        // Runs an XML parser on `buf`. Throws an exception if the XML is invalid.
+        static void check(const char* buf, size_t buflen) {
+            XMLValidator validator;
+            validator.check_internal(buf, buflen);
+        }
+
+    private:
+        // Private constructor, because this class is only constructed by
+        // the (static) check method.
+        XMLValidator() : parser_(XML_ParserCreateNS(0, '@')) {
+            if (!parser_) {
+                throw Error(kerXMPToolkitError, "Could not create expat parser");
+            }
+        }
+
+        ~XMLValidator() {
+            XML_ParserFree(parser_);
+        }
+
+        void setError(const char* msg) {
+            const XML_Size errlinenum = XML_GetCurrentLineNumber(parser_);
+            const XML_Size errcolnum = XML_GetCurrentColumnNumber(parser_);
+#ifndef SUPPRESS_WARNINGS
+            EXV_INFO << "Invalid XML at line " << errlinenum
+                     << ", column " << errcolnum
+                     << ": " << msg << "\n";
+#endif
+            // If this is the first error, then save it.
+            if (!haserror_) {
+                haserror_ = true;
+                errmsg_ = msg;
+                errlinenum_ = errlinenum;
+                errcolnum_ = errcolnum;
+            }
+        }
+
+        void check_internal(const char* buf, size_t buflen) {
+            if (buflen > static_cast<size_t>(std::numeric_limits<int>::max())) {
+                throw Error(kerXMPToolkitError, "Buffer length is greater than INT_MAX");
+            }
+
+            XML_SetUserData(parser_, this);
+            XML_SetElementHandler(parser_, startElement_cb, endElement_cb);
+            XML_SetNamespaceDeclHandler(parser_, startNamespace_cb, endNamespace_cb);
+            XML_SetStartDoctypeDeclHandler(parser_, startDTD_cb);
+
+            const XML_Status result = XML_Parse(parser_, buf, static_cast<int>(buflen), true);
+            if (result == XML_STATUS_ERROR) {
+                setError(XML_ErrorString(XML_GetErrorCode(parser_)));
+            }
+
+            if (haserror_) {
+                throw XMP_Error(kXMPErr_BadXML, "Error in XMLValidator");
+            }
+        }
+
+        void startElement(const XML_Char*, const XML_Char**) noexcept {
+            if (element_depth_ > max_recursion_limit_) {
+                setError("Too deeply nested");
+            }
+            ++element_depth_;
+        }
+
+        void endElement(const XML_Char*) noexcept {
+            if (element_depth_ > 0) {
+                --element_depth_;
+            } else {
+                setError("Negative depth");
+            }
+        }
+
+        void startNamespace(const XML_Char*, const XML_Char*) noexcept {
+            if (namespace_depth_ > max_recursion_limit_) {
+                setError("Too deeply nested");
+            }
+            ++namespace_depth_;
+        }
+
+        void endNamespace(const XML_Char*) noexcept {
+            if (namespace_depth_ > 0) {
+                --namespace_depth_;
+            } else {
+                setError("Negative depth");
+            }
+        }
+
+        void startDTD(const XML_Char*, const XML_Char*, const XML_Char*, int) noexcept {
+            // DOCTYPE is used for XXE attacks.
+            setError("DOCTYPE not supported");
+        }
+
+        // This callback function is called by libexpat. It's a static wrapper
+        // around startElement().
+        static void XMLCALL startElement_cb(
+            void* userData, const XML_Char* name, const XML_Char* *attrs
+        ) noexcept {
+            static_cast<XMLValidator*>(userData)->startElement(name, attrs);
+        }
+
+        // This callback function is called by libexpat. It's a static wrapper
+        // around endElement().
+        static void XMLCALL endElement_cb(void* userData, const XML_Char* name) noexcept {
+            static_cast<XMLValidator*>(userData)->endElement(name);
+        }
+
+        // This callback function is called by libexpat. It's a static wrapper
+        // around startNamespace().
+        static void XMLCALL startNamespace_cb(
+            void* userData, const XML_Char* prefix, const XML_Char* uri
+        ) noexcept {
+            static_cast<XMLValidator*>(userData)->startNamespace(prefix, uri);
+        }
+
+        // This callback function is called by libexpat. It's a static wrapper
+        // around endNamespace().
+        static void XMLCALL endNamespace_cb(void* userData, const XML_Char* prefix) noexcept {
+            static_cast<XMLValidator*>(userData)->endNamespace(prefix);
+        }
+
+        static void XMLCALL startDTD_cb(
+            void *userData, const XML_Char *doctypeName, const XML_Char *sysid,
+            const XML_Char *pubid, int has_internal_subset
+        ) noexcept {
+            static_cast<XMLValidator*>(userData)->startDTD(
+                doctypeName, sysid, pubid, has_internal_subset);
+        }
+    };
+}  // namespace
+
+
 // *****************************************************************************
 // local declarations
 namespace {
@@ -601,6 +764,7 @@ namespace Exiv2 {
             return 2;
         }
 
+        XMLValidator::check(xmpPacket.data(), xmpPacket.size());
         SXMPMeta meta(xmpPacket.data(), static_cast<XMP_StringLen>(xmpPacket.size()));
         SXMPIterator iter(meta);
         std::string schemaNs, propPath, propValue;

tests/bugfixes/github/test_CVE_2017_14857.py

@@ -52,7 +52,7 @@ Warning: Directory Image, entry 0x0111: Strip 9 is outside of the data area; ign
 Error: Offset of directory Image, entry 0x0132 is out of bounds: Offset = 0x30003030; truncating the entry
 Error: Directory Image, entry 0x8649 has invalid size 4294967295*1; skipping entry.
 Error: Directory Image, entry 0x8769 Sub-IFD pointer 0 is out of bounds; ignoring it.
-Error: XMP Toolkit error 201: XML parsing failure
+Error: XMP Toolkit error 201: Error in XMLValidator
 Warning: Failed to decode XMP metadata.
 """
     ]

tests/bugfixes/github/test_CVE_2017_14858.py

@@ -42,7 +42,7 @@ Exif comment    :
 Warning: Directory Image, entry 0x0111: Strip 17 is outside of the data area; ignored.
 Error: Directory Photo with 8224 entries considered invalid; not read.
 Warning: Removing 913 characters from the beginning of the XMP packet
-Error: XMP Toolkit error 201: XML parsing failure
+Error: XMP Toolkit error 201: Error in XMLValidator
 Warning: Failed to decode XMP metadata.
 """
     ]

tests/bugfixes/github/test_coverage_xmpsidecar_isXmpType.py

@@ -11,7 +11,7 @@ class coverage_xmpsidecar_isXmpType(metaclass=CaseMeta):
 
     filename = path("$data_path/coverage_xmpsidecar_isXmpType.xmp")
     commands = ["$exiv2 $filename"]
-    stderr = ["""Error: XMP Toolkit error 201: XML parsing failure
+    stderr = ["""Error: XMP Toolkit error 201: Error in XMLValidator
 Warning: Failed to decode XMP metadata.
 $filename: No Exif data found in the file
 """]

tests/bugfixes/github/test_issue_1713.py

@@ -14,12 +14,11 @@ class InvalidDateXMP(metaclass=CaseMeta):
     commands = ["$exiv2 -Ph $filename"]
 
     stderr = [
-"""Warning: Failed to convert Xmp.xmp.CreateDate to Exif.Photo.DateTimeDigitized (Day is out of range)
+"""Error: XMP Toolkit error 201: Error in XMLValidator
-Exiv2 exception in print action for file $filename:
+Warning: Failed to decode XMP metadata.
-Xmpdatum::copy: Not supported
 """
 ]
-    retval = [1]
+    retval = [0]
 
     def compare_stdout(self, i, command, got_stdout, expected_stdout):
         """ We don't care about the stdout, just don't crash """

tests/bugfixes/github/test_issue_1819.py

@@ -15,27 +15,7 @@ class EmptyStringXmpTextValueRead(metaclass=CaseMeta):
 File size       : 1088 Bytes
 MIME type       : application/rdf+xml
 Image size      : 0 x 0
-Thumbnail       : None
-Camera make     : 
-Camera model    : 
-Image timestamp : 
-File number     : 
-Exposure time   : 
-Aperture        : 
-Exposure bias   : 
-Flash           : 
-Flash bias      : 
-Focal length    : 
-Subject distance: 
-ISO speed       : 
-Exposure mode   : 
-Metering mode   : 
-Macro mode      : 
-Image quality   : 
-White balance   : 
-Copyright       : 
-Exif comment    : 
-
 """]
-    stderr = [""]
+    stderr = ["""$filename: No Exif data found in the file
-    retval = [0]
+"""]
+    retval = [253]

tests/bugfixes/github/test_issue_428.py

@@ -29,7 +29,7 @@ class PngReadRawProfile(metaclass=system_tests.CaseMeta):
     stderr.append("""$exiv2_exception_message """ + filenames[5] + """:
 $kerInputDataReadFailed
 """)
-    stderr.append("""Error: XMP Toolkit error 201: XML parsing failure
+    stderr.append("""Error: XMP Toolkit error 201: Error in XMLValidator
 Warning: Failed to decode XMP metadata.
 """ + stderr_exception(filenames[6]))
     stderr.append("""Warning: Failed to decode Exif metadata.

tests/bugfixes/github/test_issue_851.py

@@ -24,8 +24,8 @@ MIME type       : application/rdf+xml
 Image size      : 0 x 0
 """
 ]
-    stderr = [
+    stderr = ["""Error: XMP Toolkit error 201: Error in XMLValidator
-        """Warning: Failed to convert Xmp.xmp.CreateDate to Exif.Photo.DateTimeDigitized (Day is out of range)
+Warning: Failed to decode XMP metadata.
 $filename: No Exif data found in the file
 """]
     retval = [253]

tests/bugfixes/github/test_issue_ghsa_8949_hhfh_j7rj.py

@@ -15,7 +15,7 @@ class Jp2ImageEncodeJp2HeaderOutOfBoundsRead(metaclass=CaseMeta):
     commands = ["$exiv2 in $filename1"]
     stdout = [""]
     stderr = [
-"""Error: XMP Toolkit error 201: XML parsing failure
+"""Error: XMP Toolkit error 201: Error in XMLValidator
 Warning: Failed to decode XMP metadata.
 """]
     retval = [0]

tests/bugfixes/github/test_issue_ghsa_v5g7_46xf_h728.py

@@ -16,6 +16,8 @@ File size       : 276 Bytes
 MIME type       : application/rdf+xml
 Image size      : 0 x 0
 """]
-    stderr = ["""$filename: No Exif data found in the file
+    stderr = ["""Error: XMP Toolkit error 201: Error in XMLValidator
+Warning: Failed to decode XMP metadata.
+$filename: No Exif data found in the file
 """]
     retval = [253]