Make the destination link check lexical

Author: StanFromIreland

Doc/library/tarfile.rst

@@ -1132,7 +1132,7 @@ reused in custom filters:
     path (after following symlinks) would end up outside the destination.
     This raises :class:`~tarfile.OutsideDestinationError`.
   - :ref:`Refuse <tarfile-extraction-refuse>` to extract links (hard or soft)
-    whose path resolves to the destination directory itself.
+    whose name refers to the destination directory itself.
     This raises :class:`~tarfile.OutsideDestinationError`.
     Note that such files are refused even on platforms that do not support
     symbolic links.

Lib/tarfile.py

@@ -848,10 +848,11 @@ def _get_filtered_attrs(member, dest_path, for_data=True):
                                    strict=os.path.ALLOW_MISSING)
     if os.path.commonpath([target_path, dest_path]) != dest_path:
         raise OutsideDestinationError(member, target_path)
-    # A link member that resolves to the destination directory itself
+    # A link member named after the destination directory itself
     # would replace it with a (sym)link, redirecting the destination
     # for all subsequent members.
-    if (member.islnk() or member.issym()) and target_path == dest_path:
+    if ((member.islnk() or member.issym())
+            and os.path.normpath(name) == os.curdir):
         raise OutsideDestinationError(member, target_path)
     # Limit permissions (no high bits, and go-w)
     mode = member.mode