subprocess: pull in a few fixes from Python 2.7.3

gevent/subprocess.py

@@ -504,7 +504,7 @@ class Popen(object):
             if stdin is None:
                 pass
             elif stdin == PIPE:
-                p2cread, p2cwrite = os.pipe()
+                p2cread, p2cwrite = self.pipe_cloexec()
             elif isinstance(stdin, int):
                 p2cread = stdin
             else:
@@ -514,7 +514,7 @@ class Popen(object):
             if stdout is None:
                 pass
             elif stdout == PIPE:
-                c2pread, c2pwrite = os.pipe()
+                c2pread, c2pwrite = self.pipe_cloexec()
             elif isinstance(stdout, int):
                 c2pwrite = stdout
             else:
@@ -524,7 +524,7 @@ class Popen(object):
             if stderr is None:
                 pass
             elif stderr == PIPE:
-                errread, errwrite = os.pipe()
+                errread, errwrite = self.pipe_cloexec()
             elif stderr == STDOUT:
                 errwrite = c2pwrite
             elif isinstance(stderr, int):
@@ -549,6 +549,17 @@ class Popen(object):
             else:
                 fcntl.fcntl(fd, fcntl.F_SETFD, old & ~cloexec_flag)
 
+        def pipe_cloexec(self):
+            """Create a pipe with FDs set CLOEXEC."""
+            # Pipes' FDs are set CLOEXEC by default because we don't want them
+            # to be inherited by other subprocesses: the CLOEXEC flag is removed
+            # from the child's FDs by _dup2(), between fork() and exec().
+            # This is not atomic: we would need the pipe2() syscall for that.
+            r, w = os.pipe()
+            self._set_cloexec_flag(r)
+            self._set_cloexec_flag(w)
+            return r, w
+
         def _close_fds(self, but):
             if hasattr(os, 'closerange'):
                 os.closerange(3, but)
@@ -586,11 +597,9 @@ class Popen(object):
             # For transferring possible exec failure from child to parent
             # The first char specifies the exception type: 0 means
             # OSError, 1 means some other error.
-            errpipe_read, errpipe_write = os.pipe()
+            errpipe_read, errpipe_write = self.pipe_cloexec()
             try:
                 try:
-                    self._set_cloexec_flag(errpipe_write)
-
                     gc_was_enabled = gc.isenabled()
                     # Disable gc to avoid bug where gc -> file_dealloc ->
                     # write to stderr -> hang.  http://bugs.python.org/issue1336
@@ -613,6 +622,14 @@ class Popen(object):
                                 os.close(errread)
                             os.close(errpipe_read)
 
+                            # When duping fds, if there arises a situation
+                            # where one of the fds is either 0, 1 or 2, it
+                            # is possible that it is overwritten (#12607).
+                            if c2pwrite == 0:
+                                c2pwrite = os.dup(c2pwrite)
+                            if errwrite == 0 or errwrite == 1:
+                                errwrite = os.dup(errwrite)
+
                             # Dup fds for child
                             def _dup2(a, b):
                                 # dup2() removes the CLOEXEC flag but