ec2: Fix maybe_perform_dhcp_discovery to use /var/tmp as a tmpdir

/run/cloud-init/tmp is on a filesystem mounted noexec, so running
dchlient in Ec2Local during discovery breaks with 'Permission denied'.
This branch allows us to run from a different tmp dir so we have exec
rights.

LP: #1717627

1 files changed, 15 insertions, 7 deletions

diff --git a/cloudinit/temp_utils.py b/cloudinit/temp_utils.py
index 0355f19d..5d7adf70 100644
--- a/cloudinit/temp_utils.py
+++ b/cloudinit/temp_utils.py
@@ -8,9 +8,10 @@ import tempfile
 
 _TMPDIR = None
 _ROOT_TMPDIR = "/run/cloud-init/tmp"
+_EXE_ROOT_TMPDIR = "/var/tmp/cloud-init"
 
 
-def _tempfile_dir_arg(odir=None):
+def _tempfile_dir_arg(odir=None, needs_exe=False):
     """Return the proper 'dir' argument for tempfile functions.
 
     When root, cloud-init will use /run/cloud-init/tmp to avoid
@@ -20,8 +21,10 @@ def _tempfile_dir_arg(odir=None):
     If the caller of this function (mkdtemp or mkstemp) was provided
     with a 'dir' argument, then that is respected.
 
-    @param odir: original 'dir' arg to 'mkdtemp' or other."""
-
+    @param odir: original 'dir' arg to 'mkdtemp' or other.
+    @param needs_exe: Boolean specifying whether or not exe permissions are
+        needed for tempdir. This is needed because /run is mounted noexec.
+    """
     if odir is not None:
         return odir
 
@@ -29,7 +32,9 @@ def _tempfile_dir_arg(odir=None):
     if _TMPDIR:
         return _TMPDIR
 
-    if os.getuid() == 0:
+    if needs_exe:
+        tdir = _EXE_ROOT_TMPDIR
+    elif os.getuid() == 0:
         tdir = _ROOT_TMPDIR
     else:
         tdir = os.environ.get('TMPDIR', '/tmp')
@@ -42,7 +47,8 @@ def _tempfile_dir_arg(odir=None):
 
 
 def ExtendedTemporaryFile(**kwargs):
-    kwargs['dir'] = _tempfile_dir_arg(kwargs.pop('dir', None))
+    kwargs['dir'] = _tempfile_dir_arg(
+        kwargs.pop('dir', None), kwargs.pop('needs_exe', False))
     fh = tempfile.NamedTemporaryFile(**kwargs)
     # Replace its unlink with a quiet version
     # that does not raise errors when the
@@ -82,12 +88,14 @@ def tempdir(**kwargs):
 
 
 def mkdtemp(**kwargs):
-    kwargs['dir'] = _tempfile_dir_arg(kwargs.pop('dir', None))
+    kwargs['dir'] = _tempfile_dir_arg(
+        kwargs.pop('dir', None), kwargs.pop('needs_exe', False))
     return tempfile.mkdtemp(**kwargs)
 
 
 def mkstemp(**kwargs):
-    kwargs['dir'] = _tempfile_dir_arg(kwargs.pop('dir', None))
+    kwargs['dir'] = _tempfile_dir_arg(
+        kwargs.pop('dir', None), kwargs.pop('needs_exe', False))
     return tempfile.mkstemp(**kwargs)
 
 # vi: ts=4 expandtab