From 22748a83d927d3da1beaed771be30887c42b2500 Mon Sep 17 00:00:00 2001
From: Artem Bulgakov <ArtemSBulgakov@ya.ru>
Date: Mon, 7 Sep 2020 19:46:33 +0300
Subject: [PATCH] bpo-41316: Make tarfile follow specs for FNAME (GH-21511)

tarfile writes full path to FNAME field of GZIP format instead of just basename if user specified absolute path. Some archive viewers may process file incorrectly. Also it creates security issue because anyone can know structure of directories on system and know username or other personal information.

RFC1952 says about FNAME:
This is the original name of the file being compressed, with any directory components removed.

So tarfile must remove directory names from FNAME and write only basename of file.

Automerge-Triggered-By: @jaraco
---
 Lib/tarfile.py                                     |  2 ++
 Lib/test/test_tarfile.py                           | 14 +++++++++++++-
 Misc/ACKS                                          |  1 +
 .../2020-07-28-12-08-58.bpo-41316.bSCbK4.rst       |  1 +
 4 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2020-07-28-12-08-58.bpo-41316.bSCbK4.rst

diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index 6769066cabd..1fae29430fe 100755
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -420,6 +420,8 @@ def _init_write_gz(self):
         self.__write(b"\037\213\010\010" + timestamp + b"\002\377")
         if self.name.endswith(".gz"):
             self.name = self.name[:-3]
+        # Honor "directory components removed" from RFC1952
+        self.name = os.path.basename(self.name)
         # RFC1952 says we must use ISO-8859-1 for the FNAME field.
         self.__write(self.name.encode("iso-8859-1", "replace") + NUL)
 
diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py
index 4ef20db0971..7b34d53d216 100644
--- a/Lib/test/test_tarfile.py
+++ b/Lib/test/test_tarfile.py
@@ -1417,12 +1417,15 @@ def write(self, data):
                                    pax_headers={'non': 'empty'})
             self.assertFalse(f.closed)
 
+
 class GzipWriteTest(GzipTest, WriteTest):
     pass
 
+
 class Bz2WriteTest(Bz2Test, WriteTest):
     pass
 
+
 class LzmaWriteTest(LzmaTest, WriteTest):
     pass
 
@@ -1465,8 +1468,17 @@ def test_file_mode(self):
         finally:
             os.umask(original_umask)
 
+
 class GzipStreamWriteTest(GzipTest, StreamWriteTest):
-    pass
+    def test_source_directory_not_leaked(self):
+        """
+        Ensure the source directory is not included in the tar header
+        per bpo-41316.
+        """
+        tarfile.open(tmpname, self.mode).close()
+        payload = pathlib.Path(tmpname).read_text(encoding='latin-1')
+        assert os.path.dirname(tmpname) not in payload
+
 
 class Bz2StreamWriteTest(Bz2Test, StreamWriteTest):
     decompressor = bz2.BZ2Decompressor if bz2 else None
diff --git a/Misc/ACKS b/Misc/ACKS
index a2cdeb85040..8b0d7a45da1 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -242,6 +242,7 @@ Colm Buckley
 Erik de Bueger
 Jan-Hein Bührman
 Lars Buitinck
+Artem Bulgakov
 Dick Bulterman
 Bill Bumgarner
 Jimmy Burgett
diff --git a/Misc/NEWS.d/next/Library/2020-07-28-12-08-58.bpo-41316.bSCbK4.rst b/Misc/NEWS.d/next/Library/2020-07-28-12-08-58.bpo-41316.bSCbK4.rst
new file mode 100644
index 00000000000..139a170866e
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-07-28-12-08-58.bpo-41316.bSCbK4.rst
@@ -0,0 +1 @@
+Fix the :mod:`tarfile` module to write only basename of TAR file to GZIP compression header.
\ No newline at end of file