Index: Lib/test/test_subprocess.py
===================================================================
--- Lib/test/test_subprocess.py	(revision 79884)
+++ Lib/test/test_subprocess.py	(working copy)
@@ -914,7 +914,51 @@
             if dir is not None:
                 os.rmdir(dir)
 
+# The following test covers #6610, handling child pipes when the standard
+#  fds (0, 1, 2) are closed, i.e., in a daemon process
+# This test case backs up and closes the standard fds, restoring them later
+@unittest.skipUnless(os.name == 'posix', "only relevant for UNIX")
+class NoStandardFdsTest(BaseTestCase):
+    def setUp(self):
+        # acquire/release 16 fds to make sure fds are (a) high (b) available
+        dummy_fds = [os.open('/dev/null', os.O_RDONLY) for i in range(16)]
+        for dummy_fd in dummy_fds:
+            os.close(dummy_fd)
+        # duplicate standard fds to the highest available fds
+        for std_fd, dup_fd in enumerate(dummy_fds[-3:]):
+            os.dup2(std_fd, dup_fd)
+        self._dup_fds = dummy_fds[-3:]
+        ProcessTestCase.setUp(self)
 
+    def test_coprocess(self):
+        # coprocess: see Advanced Programming in the UNIX env., 2nd ed, 15.4
+        with _NoStandardFds(self._dup_fds):
+            b = b'teolicy was here'
+            p = subprocess.Popen('/bin/cat',
+                                 stdin=subprocess.PIPE,
+                                 stdout=subprocess.PIPE,
+                                 stderr=subprocess.PIPE)
+            p.stdin.write(b)
+            p.stdin.close()
+            self.assertEqual(p.stdout.read(), b)
+            p.wait()
+
+    def tearDown(self):
+        for dup_fd in self._dup_fds:
+            os.close(dup_fd)
+        ProcessTestCase.tearDown(self)
+
+# context manager that receives backups of the standard file descriptors,
+#  closes them on enter and restores them on exit
+class _NoStandardFds(object):
+    def __init__(self, dup_fds):
+        self.dup_fds = dup_fds
+    def __enter__(self):
+        os.closerange(0, 3)
+    def __exit__(self, error_type, error_value, traceback):
+        for stdfd, dupfd in enumerate(self.dup_fds):
+            os.dup2(dupfd, stdfd)
+
 @unittest.skipUnless(getattr(subprocess, '_has_poll', False),
                      "poll system call not supported")
 class ProcessTestCaseNoPoll(ProcessTestCase):
@@ -967,7 +1011,8 @@
                   ProcessTestCasePOSIXPurePython,
                   CommandTests,
                   ProcessTestCaseNoPoll,
-                  HelperFunctionTests)
+                  HelperFunctionTests,
+                  NoStandardFdsTest)
 
     support.run_unittest(*unit_tests)
     support.reap_children()