Fixes issue #16140: The subprocess module no longer double closes its

child subprocess.PIPE parent file descriptors on child error prior to
exec().

This would lead to race conditions in multithreaded programs where
another thread opened a file reusing the fd which was then closed out
from beneath it by the errant second close.

diff --cc Lib/subprocess.py
index 0fff36fa5d67763f395ee12b983c0faf6828dcac,d3d90ca2cec8cd279a77316ea5cb17b36e79b8b0..c0151046ec5e911615cd283e4517cfeaba0c25fd
--- 1/Lib/subprocess.py
--- 2/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@@ -1418,10 -1418,7 +1418,7 @@@ class Popen(object)
                                 repr(errpipe_data))
                  child_exception_type = getattr(
                          builtins, exception_name.decode('ascii'),
 -                        RuntimeError)
 +                        SubprocessError)
-                 for fd in (p2cwrite, c2pread, errread):
-                     if fd != -1:
-                         os.close(fd)
                  err_msg = err_msg.decode(errors="surrogatepass")
                  if issubclass(child_exception_type, OSError) and hex_errno:
                      errno_num = int(hex_errno, 16)

diff --cc Lib/test/test_subprocess.py
index 8978b31fb5f36bbf74a2f8436b484be18fbeb006,da7045cb5f57aa69b4d08a868f9d3ff6ae71d107..e502618219fcfc17d745e485b90fd7865ed79c0d
--- 1/Lib/test/test_subprocess.py
--- 2/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@@ -1189,6 -1189,44 +1189,45 @@@ class POSIXProcessTestCase(BaseTestCase
              self.fail("Exception raised by preexec_fn did not make it "
                        "to the parent process.")
  
 -            raise RuntimeError("force the _execute_child() errpipe_data path.")
+     @unittest.skipIf(not os.path.exists("/dev/zero"), "/dev/zero required.")
+     def test_preexec_errpipe_does_not_double_close_pipes(self):
+         """Issue16140: Don't double close pipes on preexec error."""
+         class SafeConstructorPopen(subprocess.Popen):
+             def __init__(self):
+                 pass  # Do nothing so we can modify the instance for testing.
+             def RealPopen(self, *args, **kwargs):
+                 subprocess.Popen.__init__(self, *args, **kwargs)
+         def raise_it():
 -        with self.assertRaises(RuntimeError):
++            raise subprocess.SubprocessError(
++                    "force the _execute_child() errpipe_data path.")
+ 
+         p = SafeConstructorPopen()
+ 
+         def _test_fds_execute_child_wrapper(*args, **kwargs):
+             try:
+                 subprocess.Popen._execute_child(p, *args, **kwargs)
+             finally:
+                 # Open a bunch of file descriptors and verify that
+                 # none of them are the same as the ones the Popen
+                 # instance is using for stdin/stdout/stderr.
+                 devzero_fds = [os.open("/dev/zero", os.O_RDONLY)
+                                for _ in range(8)]
+                 try:
+                     for fd in devzero_fds:
+                         self.assertNotIn(fd, (
+                                 p.stdin.fileno(), p.stdout.fileno(),
+                                 p.stderr.fileno()),
+                                 msg="At least one fd was closed early.")
+                 finally:
+                     map(os.close, devzero_fds)
+ 
+         p._execute_child = _test_fds_execute_child_wrapper
+ 
++        with self.assertRaises(subprocess.SubprocessError):
+             p.RealPopen([sys.executable, "-c", "pass"],
+                         stdin=subprocess.PIPE, stdout=subprocess.PIPE,
+                         stderr=subprocess.PIPE, preexec_fn=raise_it)
+ 
      def test_preexec_gc_module_failure(self):
          # This tests the code that disables garbage collection if the child
          # process will execute any Python.

diff --cc Misc/NEWS
Simple merge