From 0e7144b064a19493a146af94175a087b3888c37b Mon Sep 17 00:00:00 2001 From: Alexey Izbyshev Date: Mon, 26 Mar 2018 22:49:35 +0300 Subject: [PATCH] bpo-32844: Fix a subprocess misredirection of a low fd (GH5689) bpo-32844: subprocess: Fix a potential misredirection of a low fd to stderr. When redirecting, subprocess attempts to achieve the following state: each fd to be redirected to is less than or equal to the fd it is redirected from, which is necessary because redirection occurs in the ascending order of destination descriptors. It fails to do so in a couple of corner cases, for example, if 1 is redirected to 2 and 0 is closed in the parent. --- Lib/test/test_subprocess.py | 50 +++++++++++++++++++ .../2018-02-28-13-08-00.bpo-32844.u8tnAe.rst | 2 + Modules/_posixsubprocess.c | 2 +- 3 files changed, 53 insertions(+), 1 deletion(-) create mode 100644 Misc/NEWS.d/next/Library/2018-02-28-13-08-00.bpo-32844.u8tnAe.rst diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py index ddee3b94fe..2a766d7c92 100644 --- a/Lib/test/test_subprocess.py +++ b/Lib/test/test_subprocess.py @@ -6,6 +6,7 @@ import sys import platform import signal import io +import itertools import os import errno import tempfile @@ -2134,6 +2135,55 @@ class POSIXProcessTestCase(BaseTestCase): self.check_swap_fds(2, 0, 1) self.check_swap_fds(2, 1, 0) + def _check_swap_std_fds_with_one_closed(self, from_fds, to_fds): + saved_fds = self._save_fds(range(3)) + try: + for from_fd in from_fds: + with tempfile.TemporaryFile() as f: + os.dup2(f.fileno(), from_fd) + + fd_to_close = (set(range(3)) - set(from_fds)).pop() + os.close(fd_to_close) + + arg_names = ['stdin', 'stdout', 'stderr'] + kwargs = {} + for from_fd, to_fd in zip(from_fds, to_fds): + kwargs[arg_names[to_fd]] = from_fd + + code = textwrap.dedent(r''' + import os, sys + skipped_fd = int(sys.argv[1]) + for fd in range(3): + if fd != skipped_fd: + os.write(fd, str(fd).encode('ascii')) + ''') + + skipped_fd = (set(range(3)) - set(to_fds)).pop() + + rc = subprocess.call([sys.executable, '-c', code, str(skipped_fd)], + **kwargs) + self.assertEqual(rc, 0) + + for from_fd, to_fd in zip(from_fds, to_fds): + os.lseek(from_fd, 0, os.SEEK_SET) + read_bytes = os.read(from_fd, 1024) + read_fds = list(map(int, read_bytes.decode('ascii'))) + msg = textwrap.dedent(f""" + When testing {from_fds} to {to_fds} redirection, + parent descriptor {from_fd} got redirected + to descriptor(s) {read_fds} instead of descriptor {to_fd}. + """) + self.assertEqual([to_fd], read_fds, msg) + finally: + self._restore_fds(saved_fds) + + # Check that subprocess can remap std fds correctly even + # if one of them is closed (#32844). + def test_swap_std_fds_with_one_closed(self): + for from_fds in itertools.combinations(range(3), 2): + for to_fds in itertools.permutations(range(3), 2): + self._check_swap_std_fds_with_one_closed(from_fds, to_fds) + def test_surrogates_error_message(self): def prepare(): raise ValueError("surrogate:\uDCff") diff --git a/Misc/NEWS.d/next/Library/2018-02-28-13-08-00.bpo-32844.u8tnAe.rst b/Misc/NEWS.d/next/Library/2018-02-28-13-08-00.bpo-32844.u8tnAe.rst new file mode 100644 index 0000000000..67412fe5ba --- /dev/null +++ b/Misc/NEWS.d/next/Library/2018-02-28-13-08-00.bpo-32844.u8tnAe.rst @@ -0,0 +1,2 @@ +Fix wrong redirection of a low descriptor (0 or 1) to stderr in subprocess +if another low descriptor is closed. diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.c index dc43ffc2e1..0150fcb097 100644 --- a/Modules/_posixsubprocess.c +++ b/Modules/_posixsubprocess.c @@ -424,7 +424,7 @@ child_exec(char *const exec_array[], either 0, 1 or 2, it is possible that it is overwritten (#12607). */ if (c2pwrite == 0) POSIX_CALL(c2pwrite = dup(c2pwrite)); - if (errwrite == 0 || errwrite == 1) + while (errwrite == 0 || errwrite == 1) POSIX_CALL(errwrite = dup(errwrite)); /* Dup fds for child. -- 2.40.0