From a83ebdb495a9cbd28a03675acdeda235fade90b3 Mon Sep 17 00:00:00 2001 From: Petr Viktorin Date: Tue, 23 Jun 2026 15:13:30 +0200 Subject: [PATCH] gh-151981: Make tarfile._Stream.seek break at EOF (GH-151982) Co-authored-by: Stan Ulbrych CVE: CVE-2026-11972 Upstream-Status: Backport [https://github.com/python/cpython/commit/f50bf13566189c8d0ce5a814f33eff3d89951896] Signed-off-by: Benjamin Robin --- Lib/tarfile.py | 4 +++- Lib/test/test_tarfile.py | 16 ++++++++++++++++ 2 files changed, 19 insertions(+), 1 deletion(-) diff --git a/Lib/tarfile.py b/Lib/tarfile.py index 83226e907e4b..c0007a78f700 100755 --- a/Lib/tarfile.py +++ b/Lib/tarfile.py @@ -516,7 +516,9 @@ def seek(self, pos=0): if pos - self.pos >= 0: blocks, remainder = divmod(pos - self.pos, self.bufsize) for i in range(blocks): - self.read(self.bufsize) + data = self.read(self.bufsize) + if not data: + break self.read(remainder) else: raise StreamError("seeking backwards is not allowed") diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py index 29719d95b6c1..8aeb2e1b1b9a 100644 --- a/Lib/test/test_tarfile.py +++ b/Lib/test/test_tarfile.py @@ -4480,6 +4480,22 @@ def valueerror_filter(tarinfo, path): with self.check_context(arc.open(errorlevel='boo!'), filtererror_filter): self.expect_exception(TypeError) # errorlevel is not int + @support.subTests('format', [tarfile.GNU_FORMAT, tarfile.PAX_FORMAT]) + def test_getmembers_big_size(self, format): + # gh-151981: A loop in seek() for streaming files tried to read the + # declared number of blocks even at EOF + tinfo = tarfile.TarInfo("huge-file") + tinfo.size = 1 << 64 + bio = io.BytesIO() + # Write header without data + bio.write(tinfo.tobuf(format)) + + # Reset & try to get contents + bio.seek(0) + with tarfile.open(fileobj=bio, mode="r|") as tar: + with self.assertRaises(tarfile.ReadError): + tar.getmembers() + class OverwriteTests(archiver_tests.OverwriteTests, unittest.TestCase): testdir = os.path.join(TEMPDIR, "testoverwrite") -- 2.54.0