From e280f2f7b07e249d116c8b1cd63670044e602119 Mon Sep 17 00:00:00 2001
From: Brian Coca <bcoca@users.noreply.github.com>
Date: Thu, 14 Mar 2019 11:04:56 -0400
Subject: [PATCH] Try to get correct buffer size to avoid races (#53547)

* Try to get correct buffer size to avoid races

  fixes #51393

* fix test, mock buffer function since all is mocked
---
 changelogs/fragments/avoid_race.yml           |  2 +
 lib/ansible/module_utils/basic.py             | 38 +++++++++++++------
 .../module_utils/basic/test_run_command.py    |  1 +
 3 files changed, 30 insertions(+), 11 deletions(-)
 create mode 100644 changelogs/fragments/avoid_race.yml

diff --git a/changelogs/fragments/avoid_race.yml b/changelogs/fragments/avoid_race.yml
new file mode 100644
index 00000000000..6ad9b4c51ca
--- /dev/null
+++ b/changelogs/fragments/avoid_race.yml
@@ -0,0 +1,2 @@
+bugfixes:
+    - Attempt to avoid race condition based on incorrect buffer size assumptions
diff --git a/lib/ansible/module_utils/basic.py b/lib/ansible/module_utils/basic.py
index d63b61bfe36..f98a0b7fd4d 100644
--- a/lib/ansible/module_utils/basic.py
+++ b/lib/ansible/module_utils/basic.py
@@ -47,25 +47,27 @@ PASS_BOOLS = ('no_log', 'debug', 'diff')
 
 import __main__
 import atexit
+import errno
+import datetime
+import grp
+import fcntl
 import locale
 import os
+import pwd
+import platform
 import re
+import select
 import shlex
+import shutil
 import signal
+import stat
 import subprocess
 import sys
-import types
-import time
-import select
-import shutil
-import stat
 import tempfile
+import time
 import traceback
-import grp
-import pwd
-import platform
-import errno
-import datetime
+import types
+
 from collections import deque
 from itertools import chain, repeat
 
@@ -2584,7 +2586,7 @@ class AnsibleModule(object):
     def _read_from_pipes(self, rpipes, rfds, file_descriptor):
         data = b('')
         if file_descriptor in rfds:
-            data = os.read(file_descriptor.fileno(), 9000)
+            data = os.read(file_descriptor.fileno(), self.get_buffer_size(file_descriptor))
             if data == b(''):
                 rpipes.remove(file_descriptor)
 
@@ -2905,6 +2907,20 @@ class AnsibleModule(object):
     # In 2.0, moved from inside the module to the toplevel
     is_executable = is_executable
 
+    @staticmethod
+    def get_buffer_size(fd):
+        try:
+            # 1032 == FZ_GETPIPE_SZ
+            buffer_size = fcntl.fcntl(fd, 1032)
+        except Exception:
+            try:
+                # not as exact as above, but should be good enough for most platforms that fail the previous call
+                buffer_size = select.PIPE_BUF
+            except Exception:
+                buffer_size = 9000  # use sane default JIC
+
+        return buffer_size
+
 
 def get_module_path():
     return os.path.dirname(os.path.realpath(__file__))
diff --git a/test/units/module_utils/basic/test_run_command.py b/test/units/module_utils/basic/test_run_command.py
index cd1971d3f36..607f3f47dad 100644
--- a/test/units/module_utils/basic/test_run_command.py
+++ b/test/units/module_utils/basic/test_run_command.py
@@ -83,6 +83,7 @@ def rc_am(mocker, am, mock_os, mock_subprocess):
     am.fail_json = mocker.MagicMock(side_effect=SystemExit)
     am._os = mock_os
     am._subprocess = mock_subprocess
+    am.get_buffer_size = mocker.MagicMock(return_value=900)
     yield am