Issue #6274. Fixed a potential FD leak in subprocess.py.

Lib/subprocess.py

@@ -1034,6 +1034,8 @@ class Popen(object):
             # The first char specifies the exception type: 0 means
             # OSError, 1 means some other error.
             errpipe_read, errpipe_write = os.pipe()
+            try:
+                try:
                     self._set_cloexec_flag(errpipe_write)
 
                     gc_was_enabled = gc.isenabled()
@@ -1067,11 +1069,12 @@ class Popen(object):
                             if errwrite is not None:
                                 os.dup2(errwrite, 2)
 
-                    # Close pipe fds.  Make sure we don't close the same
-                    # fd more than once, or standard fds.
+                            # Close pipe fds.  Make sure we don't close the
+                            # same fd more than once, or standard fds.
                             if p2cread is not None and p2cread not in (0,):
                                 os.close(p2cread)
-                    if c2pwrite is not None and c2pwrite not in (p2cread, 1):
+                            if c2pwrite is not None and \
+                                                c2pwrite not in (p2cread, 1):
                                 os.close(c2pwrite)
                             if (errwrite is not None and
                                 errwrite not in (p2cread, c2pwrite, 2)):
@@ -1094,21 +1097,25 @@ class Popen(object):
 
                         except:
                             exc_type, exc_value, tb = sys.exc_info()
-                    # Save the traceback and attach it to the exception object
+                            # Save the traceback and attach it to the exception
+                            # object
                             exc_lines = traceback.format_exception(exc_type,
                                                                    exc_value,
                                                                    tb)
                             exc_value.child_traceback = ''.join(exc_lines)
                             os.write(errpipe_write, pickle.dumps(exc_value))
 
-                # This exitcode won't be reported to applications, so it
-                # really doesn't matter what we return.
+                        # This exitcode won't be reported to applications, so
+                        # it really doesn't matter what we return.
                         os._exit(255)
 
                     # Parent
                     if gc_was_enabled:
                         gc.enable()
+                finally:
+                    # be sure the FD is closed no matter what
                     os.close(errpipe_write)
+
                 if p2cread is not None and p2cwrite is not None:
                     os.close(p2cread)
                 if c2pwrite is not None and c2pread is not None:
@@ -1116,9 +1123,13 @@ class Popen(object):
                 if errwrite is not None and errread is not None:
                     os.close(errwrite)
 
-            # Wait for exec to fail or succeed; possibly raising exception
-            data = os.read(errpipe_read, 1048576) # Exceptions limited to 1 MB
+                # Wait for exec to fail or succeed; possibly raising an
+                # exception (limited to 1 MB)
+                data = os.read(errpipe_read, 1048576)
+            finally:
+                # be sure the FD is closed no matter what
                 os.close(errpipe_read)
+
             if data:
                 os.waitpid(self.pid, 0)
                 child_exception = pickle.loads(data)

Misc/NEWS

@@ -15,6 +15,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #6274: Fixed possible file descriptors leak in subprocess.py
+
 - Accessing io.StringIO.buffer now raises an AttributeError instead of
   io.UnsupportedOperation.