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.
(cherry picked from commit 0e7144b064a19493a146af94175a087b3888c37b)
Co-authored-by: Alexey Izbyshev <izbyshev@users.noreply.github.com>
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index ddee3b9..2a766d7 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -6,6 +6,7 @@
import platform
import signal
import io
+import itertools
import os
import errno
import tempfile
@@ -2134,6 +2135,55 @@
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")