From 30e769382dfb67a68fe8e6bfe8509addb4aa9514 Mon Sep 17 00:00:00 2001 From: "Miss Islington (bot)" <31488909+miss-islington@users.noreply.github.com> Date: Tue, 4 Feb 2020 13:41:55 -0800 Subject: closes bpo-39510: Fix use-after-free in BufferedReader.readinto() (GH-18295) When called on a closed object, readinto() segfaults on account of a write to a freed buffer: ==220553== Process terminating with default action of signal 11 (SIGSEGV): dumping core ==220553== Access not within mapped region at address 0x2A ==220553== at 0x48408A0: memmove (vg_replace_strmem.c:1272) ==220553== by 0x58DB0C: _buffered_readinto_generic (bufferedio.c:972) ==220553== by 0x58DCBA: _io__Buffered_readinto_impl (bufferedio.c:1053) ==220553== by 0x58DCBA: _io__Buffered_readinto (bufferedio.c.h:253) Reproducer: reader = open ("/dev/zero", "rb") _void = reader.read (42) reader.close () reader.readinto (bytearray (42)) GH-GH-GH- BANG! The problem exists since 2012 when commit dc469454ec added code to free the read buffer on close(). Signed-off-by: Philipp Gesang (cherry picked from commit cb1c0746f277052e45a60d6c436a765e34722821) Co-authored-by: Philipp Gesang --- Lib/test/test_io.py | 5 +++++ .../next/Core and Builtins/2020-02-04-10-27-41.bpo-39510.PMIh-f.rst | 1 + Modules/_io/bufferedio.c | 1 + 3 files changed, 7 insertions(+) create mode 100644 Misc/NEWS.d/next/Core and Builtins/2020-02-04-10-27-41.bpo-39510.PMIh-f.rst diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py index 50459e0..bea4342 100644 --- a/Lib/test/test_io.py +++ b/Lib/test/test_io.py @@ -735,6 +735,11 @@ class IOTest(unittest.TestCase): file.seek(0) file.close() self.assertRaises(ValueError, file.read) + with self.open(support.TESTFN, "rb") as f: + file = self.open(f.fileno(), "rb", closefd=False) + self.assertEqual(file.read()[:3], b"egg") + file.close() + self.assertRaises(ValueError, file.readinto, bytearray(1)) def test_no_closefd_with_filename(self): # can't use closefd in combination with a file name diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-02-04-10-27-41.bpo-39510.PMIh-f.rst b/Misc/NEWS.d/next/Core and Builtins/2020-02-04-10-27-41.bpo-39510.PMIh-f.rst new file mode 100644 index 0000000..9a38e4a --- /dev/null +++ b/Misc/NEWS.d/next/Core and Builtins/2020-02-04-10-27-41.bpo-39510.PMIh-f.rst @@ -0,0 +1 @@ +Fix segfault in ``readinto()`` method on closed BufferedReader. diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c index 8e8ff97..ad7a8c9 100644 --- a/Modules/_io/bufferedio.c +++ b/Modules/_io/bufferedio.c @@ -965,6 +965,7 @@ _buffered_readinto_generic(buffered *self, Py_buffer *buffer, char readinto1) PyObject *res = NULL; CHECK_INITIALIZED(self) + CHECK_CLOSED(self, "readinto of closed file") n = Py_SAFE_DOWNCAST(READAHEAD(self), Py_off_t, Py_ssize_t); if (n > 0) { -- cgit v0.12