From 693945d45dfe50c843970cab3e3aa1fa3a3eddbe Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Mon, 17 Jun 2019 01:45:26 -0700
Subject: [PATCH] bpo-37267: Do not check for FILE_TYPE_CHAR in os.dup() on
 Windows (GH-14051) (GH-14140)

On Windows, os.dup() no longer creates an inheritable fd when handling a
character file.
(cherry picked from commit 28fca0c422b425a6be43be31add0a5328c16b0b8)

Co-authored-by: Zackery Spytz <zspytz@gmail.com>
---
 Lib/test/test_os.py                             |  9 +++++++++
 .../2019-06-13-04-15-51.bpo-37267.Ygo5ef.rst    |  2 ++
 Python/fileutils.c                              | 17 +++++------------
 3 files changed, 16 insertions(+), 12 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Windows/2019-06-13-04-15-51.bpo-37267.Ygo5ef.rst

diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index a8eae616205..b540fcbd4d7 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -3382,6 +3382,15 @@ class FDInheritanceTests(unittest.TestCase):
         self.addCleanup(os.close, fd2)
         self.assertEqual(os.get_inheritable(fd2), False)
 
+    @unittest.skipUnless(sys.platform == 'win32', 'win32-specific test')
+    def test_dup_nul(self):
+        # os.dup() was creating inheritable fds for character files.
+        fd1 = os.open('NUL', os.O_RDONLY)
+        self.addCleanup(os.close, fd1)
+        fd2 = os.dup(fd1)
+        self.addCleanup(os.close, fd2)
+        self.assertFalse(os.get_inheritable(fd2))
+
     @unittest.skipUnless(hasattr(os, 'dup2'), "need os.dup2()")
     def test_dup2(self):
         fd = os.open(__file__, os.O_RDONLY)
diff --git a/Misc/NEWS.d/next/Windows/2019-06-13-04-15-51.bpo-37267.Ygo5ef.rst b/Misc/NEWS.d/next/Windows/2019-06-13-04-15-51.bpo-37267.Ygo5ef.rst
new file mode 100644
index 00000000000..a4dcfcde35b
--- /dev/null
+++ b/Misc/NEWS.d/next/Windows/2019-06-13-04-15-51.bpo-37267.Ygo5ef.rst
@@ -0,0 +1,2 @@
+On Windows, :func:`os.dup` no longer creates an inheritable fd when handling
+a character file.
diff --git a/Python/fileutils.c b/Python/fileutils.c
index 178e2f1268f..93c093f89b4 100644
--- a/Python/fileutils.c
+++ b/Python/fileutils.c
@@ -1776,7 +1776,6 @@ _Py_dup(int fd)
 {
 #ifdef MS_WINDOWS
     HANDLE handle;
-    DWORD ftype;
 #endif
 
     assert(PyGILState_Check());
@@ -1790,9 +1789,6 @@ _Py_dup(int fd)
         return -1;
     }
 
-    /* get the file type, ignore the error if it failed */
-    ftype = GetFileType(handle);
-
     Py_BEGIN_ALLOW_THREADS
     _Py_BEGIN_SUPPRESS_IPH
     fd = dup(fd);
@@ -1803,14 +1799,11 @@ _Py_dup(int fd)
         return -1;
     }
 
-    /* Character files like console cannot be make non-inheritable */
-    if (ftype != FILE_TYPE_CHAR) {
-        if (_Py_set_inheritable(fd, 0, NULL) < 0) {
-            _Py_BEGIN_SUPPRESS_IPH
-            close(fd);
-            _Py_END_SUPPRESS_IPH
-            return -1;
-        }
+    if (_Py_set_inheritable(fd, 0, NULL) < 0) {
+        _Py_BEGIN_SUPPRESS_IPH
+        close(fd);
+        _Py_END_SUPPRESS_IPH
+        return -1;
     }
 #elif defined(HAVE_FCNTL_H) && defined(F_DUPFD_CLOEXEC)
     Py_BEGIN_ALLOW_THREADS