From 71589491ad0da27f57789b97354f6094a91e2eb3 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Mon, 17 Jun 2019 01:45:04 -0700
Subject: bpo-37267: Do not check for FILE_TYPE_CHAR in os.dup() on Windows
 (GH-14051) (GH-14141)

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 +++++++++
 .../Windows/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 fd9f70e30d..a917050400 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -3240,6 +3240,15 @@ 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 0000000000..a4dcfcde35
--- /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 5e71d37526..868fbf9103 100644
--- a/Python/fileutils.c
+++ b/Python/fileutils.c
@@ -1659,7 +1659,6 @@ _Py_dup(int fd)
 {
 #ifdef MS_WINDOWS
     HANDLE handle;
-    DWORD ftype;
 #endif
 
     assert(PyGILState_Check());
@@ -1673,9 +1672,6 @@ _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);
@@ -1686,14 +1682,11 @@ _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
-- 
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