make stdin read from /dev/null for all cloud-init programs (LP: #903993)

the cloud-init programs are never intended to run interactively.
Some programs were being run via subprocess, and would notice that their
input was attached to a terminal (/dev/console).   As a result, they
they would try to prompt the user for input (apt-add-repository)

This change simply re-opens standard input as /dev/null so any
subprocesses will not end up blocking on input.

ChangeLog

@@ -8,6 +8,7 @@
  - support setting of Acquire::HTTP::Proxy via 'apt_proxy'
  - DataSourceEc2: more resilliant to slow metadata service
    - config change: 'retries' dropped, 'max_wait' added, timeout increased
+ - close stdin in all cloud-init programs that are launched at boot (LP: #903993)
 0.6.2:
  - fix bug where update was not done unless update was explicitly set.
    It would not be run if 'upgrade' or packages were set to be installed

cloud-init-cfg.py

@@ -35,6 +35,8 @@ def main():
     #   read cloud config jobs from config (builtin -> system)
     #   and run all in order
 
+    util.close_stdin()
+
     modename = "config"
     
     if len(sys.argv) < 2:

cloud-init-run-module.py

@@ -25,6 +25,8 @@ def Usage(out = sys.stdout):
     out.write("Usage: cloud-init-run-module freq sem-name mod-name [args]\n")
     
 def main():
+    util.close_stdin()
+
     # expect to be called with
     #   <freq> <semaphore-name> <module-name> args
     if len(sys.argv) < 4:

cloud-init.py

@@ -34,6 +34,8 @@ def warn(wstr):
     sys.stderr.write("WARN:%s" % wstr)
 
 def main():
+    util.close_stdin()
+
     cmds = ( "start", "start-local" )
     deps = { "start" : ( ds.DEP_FILESYSTEM, ds.DEP_NETWORK ),
              "start-local" : ( ds.DEP_FILESYSTEM, ) }

cloudinit/util.py

@@ -26,6 +26,7 @@ import urllib
 import logging
 import re
 import socket
+import sys
 import time
 import traceback
 import urlparse
@@ -523,3 +524,16 @@ def search_for_mirror(candidates):
             raise
 
     return None
+
+def close_stdin():
+   """
+   reopen stdin as /dev/null so even subprocesses or other os level things get
+   /dev/null as input.
+
+   if _CLOUD_INIT_SAVE_STDIN is set in environment to a non empty or '0' value
+   then input will not be closed (only useful potentially for debugging).
+   """
+   if os.environ.get("_CLOUD_INIT_SAVE_STDIN") in ("", "0", False):
+      return
+   with open(os.devnull) as fp:
+       os.dup2(fp.fileno(), sys.stdin.fileno())