&bytes[0] (std::vector) will crash if bytes has zero elements (backport #1789)

src/image.cpp

@@ -467,20 +467,20 @@ namespace Exiv2 {
                             seekOrThrow(io, restore, BasicIo::beg, kerCorruptedMetadata);
                         }
                     } else if ( option == kpsRecursive && tag == 0x83bb /* IPTCNAA */ ) {
+                        if (count > 0) {
+                            if (static_cast<size_t>(Safe::add(count, offset)) > io.size()) {
+                                throw Error(kerCorruptedMetadata);
+                            }
 
-                        if (static_cast<size_t>(Safe::add(count, offset)) > io.size()) {
-                            throw Error(kerCorruptedMetadata);
+                            const long restore = io.tell();
+                            seekOrThrow(io, offset, BasicIo::beg, kerCorruptedMetadata);  // position
+                            std::vector<byte> bytes(count) ;  // allocate memory
+                            // TODO: once we have C++11 use bytes.data()
+                            readOrThrow(io, &bytes[0], count, kerCorruptedMetadata);
+                            seekOrThrow(io, restore, BasicIo::beg, kerCorruptedMetadata);
+                            // TODO: once we have C++11 use bytes.data()
+                            IptcData::printStructure(out, makeSliceUntil(&bytes[0], count), depth);
                         }
-
-                        const long restore = io.tell();
-                        seekOrThrow(io, offset, BasicIo::beg, kerCorruptedMetadata);  // position
-                        std::vector<byte> bytes(count) ;  // allocate memory
-                        // TODO: once we have C++11 use bytes.data()
-                        readOrThrow(io, &bytes[0], count, kerCorruptedMetadata);
-                        seekOrThrow(io, restore, BasicIo::beg, kerCorruptedMetadata);
-                        // TODO: once we have C++11 use bytes.data()
-                        IptcData::printStructure(out, makeSliceUntil(&bytes[0], count), depth);
-
                     }  else if ( option == kpsRecursive && tag == 0x927c /* MakerNote */ && count > 10) {
                         const long restore = io.tell();  // save
 

tests/bugfixes/github/test_issue_g44w_q3vm_gwjq.py

@@ -0,0 +1,22 @@
+# -*- coding: utf-8 -*-
+
+from system_tests import CaseMeta, CopyTmpFiles, path, check_no_ASAN_UBSAN_errors
+import unittest
+
+@unittest.skip("Skipping test using option -pR (only for Debug mode)")
+class ImagePrintIFDStructureZeroCountAssert(metaclass=CaseMeta):
+    """
+    Regression test for the bug described in:
+    https://github.com/Exiv2/exiv2/security/advisories/GHSA-g44w-q3vm-gwjq
+    """
+    url = "https://github.com/Exiv2/exiv2/security/advisories/GHSA-g44w-q3vm-gwjq"
+
+    filename = path("$data_path/issue_ghsa_g44w_q3vm_gwjq_poc.jpg")
+    commands = ["$exiv2 -pR $filename"]
+    stderr = ["""invalid type in tiff structure0
+Exiv2 exception in print action for file $filename:
+$kerInvalidTypeValue
+"""]
+    retval = [1]
+
+    compare_stdout = check_no_ASAN_UBSAN_errors