Avoid integer overflow.

tests/bugfixes/github/test_issue_843.py

@@ -0,0 +1,22 @@
+# -*- coding: utf-8 -*-
+
+from system_tests import CaseMeta, path
+
+
+class IntegerOverflowInCiffDirectoryReadDirectory(metaclass=CaseMeta):
+    """
+    Regression test for the bug described in:
+    https://github.com/Exiv2/exiv2/issues/843
+
+    An integer overflow causes an out-of-bounds read.
+    """
+    url = "https://github.com/Exiv2/exiv2/issues/843"
+
+    filename = path("$data_path/issue_843_poc.crw")
+    commands = ["$exiv2 $filename"]
+    stdout = [""]
+    stderr = [
+        """$exiv2_exception_message $filename:
+$kerCorruptedMetadata
+"""]
+    retval = [1]