Fixes Issue #15798 - subprocess.Popen() no longer fails if file

descriptor 0, 1 or 2 is closed.

2 files changed, 25 insertions, 1 deletions

diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 88355ad..f717c82 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -1361,7 +1361,10 @@ class Popen(object):
                         executable_list = tuple(
                             os.path.join(os.fsencode(dir), executable)
                             for dir in os.get_exec_path(env))
-                    fds_to_keep = set(pass_fds)
+                    # Never close stdin, stdout and stderr for the child.
+                    fds_to_keep = {0,1,2}
+                    fds_to_keep.update(pass_fds)
+                    # Our child uses this one to signal error before exec().
                     fds_to_keep.add(errpipe_write)
                     self.pid = _posixsubprocess.fork_exec(
                             args, executable_list,
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 54f6482..46e012d 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -1559,6 +1559,27 @@ class POSIXProcessTestCase(BaseTestCase):
         # all standard fds closed.
         self.check_close_std_fds([0, 1, 2])
 
+    def test_small_errpipe_write_fd(self):
+        """Issue #15798: Popen should work when stdio fds are available."""
+        new_stdin = os.dup(0)
+        new_stdout = os.dup(1)
+        try:
+            os.close(0)
+            os.close(1)
+
+            # Side test: if errpipe_write fails to have its CLOEXEC
+            # flag set this should cause the parent to think the exec
+            # failed.  Extremely unlikely: everyone supports CLOEXEC.
+            subprocess.Popen([
+                    sys.executable, "-c",
+                    "print('AssertionError:0:CLOEXEC failure.')"]).wait()
+        finally:
+            # Restore original stdin and stdout
+            os.dup2(new_stdin, 0)
+            os.dup2(new_stdout, 1)
+            os.close(new_stdin)
+            os.close(new_stdout)
+
     def test_remapping_std_fds(self):
         # open up some temporary files
         temps = [mkstemp() for i in range(3)]