[3.10] gh-151987: Pass filter_function to TarFile._extract_one() during .extract() (GH-151988) (#152613)

* gh-151987: Pass filter_function to TarFile._extract_one() during .extract() (GH-151988)

(cherry picked from commit 7ccdbab)

Co-authored-by: Petr Viktorin <encukou@gmail.com>
Co-authored-by: Seth Michael Larson <seth@python.org>

* Remove newer test helpers

3.11+ has more granular platform support, mostly for WASI.
Use the 3.10 idioms instead:

- @symlink_test is a no-op on non-WASI platforms
- can_chmod is approximated by "not win32" elsewhere in test_tarfile

---------

Co-authored-by: Petr Viktorin <encukou@gmail.com>
Co-authored-by: Seth Michael Larson <seth@python.org>

Author: 3 people

Lib/tarfile.py

@@ -2401,7 +2401,8 @@ def extract(self, member, path="", set_attrs=True, *, numeric_owner=False,
         tarinfo, unfiltered = self._get_extract_tarinfo(
             member, filter_function, path)
         if tarinfo is not None:
-            self._extract_one(tarinfo, path, set_attrs, numeric_owner)
+            self._extract_one(tarinfo, path, set_attrs, numeric_owner,
+                              filter_function=filter_function)
 
     def _get_extract_tarinfo(self, member, filter_function, path):
         """Get (filtered, unfiltered) TarInfos from *member*

Lib/test/test_tarfile.py

@@ -4040,6 +4040,96 @@ def test_chmod_outside_dir(self):
                     st_mode = cc.outerdir.stat().st_mode
                     self.assertNotEqual(st_mode & 0o777, 0o777)
 
+    @unittest.skipUnless(hasattr(os, 'chown'), "missing os.chown")
+    @unittest.skipUnless(hasattr(os, 'lchown'), "missing os.lchown")
+    @unittest.skipUnless(hasattr(os, 'geteuid'), "missing os.geteuid")
+    @support.subTests('link_type', (tarfile.SYMTYPE, tarfile.LNKTYPE))
+    def test_chown_links_on_extract(self, link_type):
+        with ArchiveMaker() as arc:
+            arc.add("test.txt",
+                    uid=1337, gid=1337, uname="", gname="", mode='-rwxr-xr-x')
+            arc.add("link",
+                    type=link_type,
+                    linkname='test.txt',
+                    uid=1337, gid=1337, uname="", gname="", mode='-rwxr-xr-x')
+
+        with (
+            os_helper.temp_dir() as tmpdir,
+            arc.open() as tar,
+            unittest.mock.patch("os.chown") as mock_chown,
+            unittest.mock.patch("os.lchown") as mock_lchown,
+            unittest.mock.patch("os.geteuid") as mock_geteuid,
+        ):
+            # Set UID to 0 so chown() is attempted.
+            mock_geteuid.return_value = 0
+            tar.extract("link", path=tmpdir, filter='data')
+            extract_path = os.path.join(tmpdir, "link")
+
+            if link_type == tarfile.SYMTYPE:
+                mock_chown.assert_not_called()
+                mock_lchown.assert_called_once_with(extract_path, -1, -1)
+            else:
+                mock_chown.assert_has_calls([
+                    unittest.mock.call(extract_path, -1, -1),
+                    unittest.mock.call(extract_path, -1, -1)
+                ])
+                mock_lchown.assert_not_called()
+
+    @unittest.skipUnless(hasattr(os, 'chown'), "missing os.chown")
+    @unittest.skipUnless(hasattr(os, 'lchown'), "missing os.lchown")
+    @unittest.skipUnless(hasattr(os, 'geteuid'), "missing os.geteuid")
+    @support.subTests('link_type', (tarfile.SYMTYPE, tarfile.LNKTYPE))
+    def test_chown_links_on_extractall(self, link_type):
+        with ArchiveMaker() as arc:
+            arc.add("test.txt",
+                    uid=1337, gid=1337, uname="", gname="", mode='-rwxr-xr-x')
+            arc.add("link",
+                    type=link_type,
+                    linkname='test.txt',
+                    uid=1337, gid=1337, uname="", gname="", mode='-rwxr-xr-x')
+
+        with (
+            os_helper.temp_dir() as tmpdir,
+            arc.open() as tar,
+            unittest.mock.patch("os.chown") as mock_chown,
+            unittest.mock.patch("os.lchown") as mock_lchown,
+            unittest.mock.patch("os.geteuid") as mock_geteuid,
+        ):
+            # Set UID to 0 so chown() is attempted.
+            mock_geteuid.return_value = 0
+            tar.extractall(path=tmpdir, filter='data')
+            extract_link_path = os.path.join(tmpdir, "link")
+            extract_file_path = os.path.join(tmpdir, "test.txt")
+
+            if link_type == tarfile.SYMTYPE:
+                mock_chown.assert_called_once_with(extract_file_path, -1, -1)
+                mock_lchown.assert_called_once_with(extract_link_path, -1, -1)
+            else:
+                mock_chown.assert_has_calls([
+                    unittest.mock.call(extract_file_path, -1, -1),
+                    unittest.mock.call(extract_link_path, -1, -1)
+                ])
+                mock_lchown.assert_not_called()
+
+    def test_extract_filters_target(self):
+        # Test that when extract() falls back to extracting (rather than
+        # linking) a hardlink target, it filters the target.
+        with ArchiveMaker() as arc:
+            arc.add("target")
+            arc.add("link", hardlink_to="target")
+        def testing_filter(member, path):
+            if member.name == 'target':
+                # target: set read-only
+                return member.replace(mode=stat.S_IRUSR)
+            # link: don't overwrite the mode
+            return member.replace(mode=None)
+        tempdir = pathlib.Path(TEMPDIR) / 'extract'
+        with os_helper.temp_dir(tempdir), arc.open() as tar:
+            tar.extract("link", path=tempdir, filter=testing_filter)
+            path = tempdir / 'link'
+            if sys.platform != 'win32':
+                self.assertFalse(path.stat().st_mode & stat.S_IWUSR)
+
     def test_link_fallback_normalizes(self):
         # Make sure hardlink fallbacks work for non-normalized paths for all
         # filters

Misc/NEWS.d/next/Security/2026-06-23-14-19-30.gh-issue-151987.8mNIMf.rst

@@ -0,0 +1,2 @@
+The :meth:`tarfile.TarFile.extract` method now applies the given filter when
+it extracts a link target from the archive as a fallback.