[3.6] bpo-30121: Fix debug assert in subprocess on Windows (#1224) (#3173)

* bpo-30121: Fix debug assert in subprocess on Windows (#1224)

* bpo-30121: Fix debug assert in subprocess on Windows

This is caused by closing HANDLEs using os.close which is for CRT file
descriptors and not for HANDLEs.

* bpo-30121: Suppress debug assertion in test_subprocess when ran directly

(cherry picked from commit 4d385172)

* Add test_subprocess.test_nonexisting_with_pipes() (#3133)

bpo-30121: Test the Popen failure when Popen was created with pipes.
Create also NONEXISTING_CMD variable in test_subprocess.py.
(cherry picked from commit 9a83f651)

Lib/subprocess.py

@@ -725,7 +725,10 @@ class Popen(object):
                     to_close.append(self._devnull)
                 for fd in to_close:
                     try:
-                        os.close(fd)
+                        if _mswindows and isinstance(fd, Handle):
+                            fd.Close()
+                        else:
+                            os.close(fd)
                     except OSError:
                         pass
 
@@ -1005,6 +1008,9 @@ class Popen(object):
                     errwrite.Close()
                 if hasattr(self, '_devnull'):
                     os.close(self._devnull)
+                # Prevent a double close of these handles/fds from __init__
+                # on error.
+                self._closed_child_pipe_fds = True
 
             # Retain the process handle, but close the thread handle
             self._child_created = True

Lib/test/test_subprocess.py

@@ -49,6 +49,8 @@ if mswindows:
 else:
     SETBINARY = ''
 
+NONEXISTING_CMD = ('nonexisting_i_hope',)
+
 
 class BaseTestCase(unittest.TestCase):
     def setUp(self):
@@ -1120,10 +1122,11 @@ class ProcessTestCase(BaseTestCase):
             p.stdin.write(line) # expect that it flushes the line in text mode
             os.close(p.stdin.fileno()) # close it without flushing the buffer
             read_line = p.stdout.readline()
-            try:
-                p.stdin.close()
-            except OSError:
-                pass
+            with support.SuppressCrashReport():
+                try:
+                    p.stdin.close()
+                except OSError:
+                    pass
             p.stdin = None
         self.assertEqual(p.returncode, 0)
         self.assertEqual(read_line, expected)
@@ -1148,13 +1151,54 @@ class ProcessTestCase(BaseTestCase):
         # 1024 times (each call leaked two fds).
         for i in range(1024):
             with self.assertRaises(OSError) as c:
-                subprocess.Popen(['nonexisting_i_hope'],
+                subprocess.Popen(NONEXISTING_CMD,
                                  stdout=subprocess.PIPE,
                                  stderr=subprocess.PIPE)
             # ignore errors that indicate the command was not found
             if c.exception.errno not in (errno.ENOENT, errno.EACCES):
                 raise c.exception
 
+    def test_nonexisting_with_pipes(self):
+        # bpo-30121: Popen with pipes must close properly pipes on error.
+        # Previously, os.close() was called with a Windows handle which is not
+        # a valid file descriptor.
+        #
+        # Run the test in a subprocess to control how the CRT reports errors
+        # and to get stderr content.
+        try:
+            import msvcrt
+            msvcrt.CrtSetReportMode
+        except (AttributeError, ImportError):
+            self.skipTest("need msvcrt.CrtSetReportMode")
+
+        code = textwrap.dedent(f"""
+            import msvcrt
+            import subprocess
+
+            cmd = {NONEXISTING_CMD!r}
+
+            for report_type in [msvcrt.CRT_WARN,
+                                msvcrt.CRT_ERROR,
+                                msvcrt.CRT_ASSERT]:
+                msvcrt.CrtSetReportMode(report_type, msvcrt.CRTDBG_MODE_FILE)
+                msvcrt.CrtSetReportFile(report_type, msvcrt.CRTDBG_FILE_STDERR)
+
+            try:
+                subprocess.Popen([cmd],
+                                 stdout=subprocess.PIPE,
+                                 stderr=subprocess.PIPE)
+            except OSError:
+                pass
+        """)
+        cmd = [sys.executable, "-c", code]
+        proc = subprocess.Popen(cmd,
+                                stderr=subprocess.PIPE,
+                                universal_newlines=True)
+        with proc:
+            stderr = proc.communicate()[1]
+        self.assertEqual(stderr, "")
+        self.assertEqual(proc.returncode, 0)
+
     @unittest.skipIf(threading is None, "threading required")
     def test_double_close_on_error(self):
         # Issue #18851
@@ -1167,7 +1211,7 @@ class ProcessTestCase(BaseTestCase):
         t.start()
         try:
             with self.assertRaises(EnvironmentError):
-                subprocess.Popen(['nonexisting_i_hope'],
+                subprocess.Popen(NONEXISTING_CMD,
                                  stdin=subprocess.PIPE,
                                  stdout=subprocess.PIPE,
                                  stderr=subprocess.PIPE)
@@ -2433,7 +2477,7 @@ class POSIXProcessTestCase(BaseTestCase):
         # should trigger the wait() of p
         time.sleep(0.2)
         with self.assertRaises(OSError) as c:
-            with subprocess.Popen(['nonexisting_i_hope'],
+            with subprocess.Popen(NONEXISTING_CMD,
                                   stdout=subprocess.PIPE,
                                   stderr=subprocess.PIPE) as proc:
                 pass
@@ -2863,7 +2907,7 @@ class ContextManagerTests(BaseTestCase):
 
     def test_invalid_args(self):
         with self.assertRaises((FileNotFoundError, PermissionError)) as c:
-            with subprocess.Popen(['nonexisting_i_hope'],
+            with subprocess.Popen(NONEXISTING_CMD,
                                   stdout=subprocess.PIPE,
                                   stderr=subprocess.PIPE) as proc:
                 pass