Issue #10806, issue #9905: Fix subprocess pipes when some of the standard

file descriptors (0, 1, 2) are closed in the parent process.  Initial
patch by Ross Lagerwall.

1 files changed, 27 insertions, 25 deletions

diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index c12898d..7d3f77f 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -393,22 +393,22 @@ else:
     # POSIX defines PIPE_BUF as >= 512.
     _PIPE_BUF = getattr(select, 'PIPE_BUF', 512)
 
+    _FD_CLOEXEC = getattr(fcntl, 'FD_CLOEXEC', 1)
+
+    def _set_cloexec(fd, cloexec):
+        old = fcntl.fcntl(fd, fcntl.F_GETFD)
+        if cloexec:
+            fcntl.fcntl(fd, fcntl.F_SETFD, old | _FD_CLOEXEC)
+        else:
+            fcntl.fcntl(fd, fcntl.F_SETFD, old & ~_FD_CLOEXEC)
+
     if _posixsubprocess:
         _create_pipe = _posixsubprocess.cloexec_pipe
     else:
         def _create_pipe():
-            try:
-                cloexec_flag = fcntl.FD_CLOEXEC
-            except AttributeError:
-                cloexec_flag = 1
-
             fds = os.pipe()
-
-            old = fcntl.fcntl(fds[0], fcntl.F_GETFD)
-            fcntl.fcntl(fds[0], fcntl.F_SETFD, old | cloexec_flag)
-            old = fcntl.fcntl(fds[1], fcntl.F_GETFD)
-            fcntl.fcntl(fds[1], fcntl.F_SETFD, old | cloexec_flag)
-
+            _set_cloexec(fds[0], True)
+            _set_cloexec(fds[1], True)
             return fds
 
 __all__ = ["Popen", "PIPE", "STDOUT", "call", "check_call", "getstatusoutput",
@@ -1194,23 +1194,25 @@ class Popen(object):
                                 os.close(errpipe_read)
 
                                 # Dup fds for child
-                                if p2cread != -1:
-                                    os.dup2(p2cread, 0)
-                                if c2pwrite != -1:
-                                    os.dup2(c2pwrite, 1)
-                                if errwrite != -1:
-                                    os.dup2(errwrite, 2)
+                                def _dup2(a, b):
+                                    # dup2() removes the CLOEXEC flag but
+                                    # we must do it ourselves if dup2()
+                                    # would be a no-op (issue #10806).
+                                    if a == b:
+                                        _set_cloexec(a, False)
+                                    elif a != -1:
+                                        os.dup2(a, b)
+                                _dup2(p2cread, 0)
+                                _dup2(c2pwrite, 1)
+                                _dup2(errwrite, 2)
 
                                 # Close pipe fds.  Make sure we don't close the
                                 # same fd more than once, or standard fds.
-                                if p2cread != -1 and p2cread not in (0,):
-                                    os.close(p2cread)
-                                if (c2pwrite != -1 and
-                                    c2pwrite not in (p2cread, 1)):
-                                    os.close(c2pwrite)
-                                if (errwrite != -1 and
-                                    errwrite not in (p2cread, c2pwrite, 2)):
-                                    os.close(errwrite)
+                                closed = set()
+                                for fd in [p2cread, c2pwrite, errwrite]:
+                                    if fd > 2 and fd not in closed:
+                                        os.close(fd)
+                                        closed.add(fd)
 
                                 # Close all other fds, if asked for
                                 if close_fds: