** Changed in: cloud-init
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1845552
Title:
ssh_util: fails to parse sshd_config when config contains an entry
missing a value
Status in cloud-init:
Fix Released
Bug description:
# Overview
If the sshd_config contains keys with no values, cloud-init fails to
parse the config. This results in a system that is inaccessible over
ssh using pubkey authentication.
# Steps to reproduce:
1. Append the following content to /etc/ssh/sshd_config in a pristine
Ubuntu cloud image:
AllowUsers ubuntu
AllowGroups ubuntu
DenyUsers
DenyGroups
2. Boot the image with a cloud-config that injects an ssh key for the
ubuntu user.
3. Note the following error in the boot output:
util.py[WARNING]: Applying ssh credentials failed!
4. Attempt to login over ssh, note the pubkey authentication failure.
# Cause of the issue
In cloudinit/ssh_util.py, in parse_ssh_config_lines(), we attempt to
parse each line of sshd_config. This function expects each line to be
one of the following forms:
# comment
key value
key=value
If the line does not match one of these forms, we throw a ValueError.
Instead, we could ignore the offending line:
diff --git a/cloudinit/ssh_util.py b/cloudinit/ssh_util.py
index 3f99b58c..ec5ef9fb 100644
--- a/cloudinit/ssh_util.py
+++ b/cloudinit/ssh_util.py
@@ -304,7 +304,10 @@ def parse_ssh_config_lines(lines):
try:
key, val = line.split(None, 1)
except ValueError:
- key, val = line.split('=', 1)
+ try:
+ key, val = line.split('=', 1)
+ except ValueError:
+ continue
ret.append(SshdConfigLine(line, key, val))
return ret
# Notes about debugging
This issue was somewhat difficult to debug because the error message
produced by cloud-init was not very useful. To dig in and find the
actual issue, I modified cloudinit/config/cc_ssh.py to print the
traceback:
diff --git a/cloudinit/config/cc_ssh.py b/cloudinit/config/cc_ssh.py
index fdd8f4d3..2b356a4c 100755
--- a/cloudinit/config/cc_ssh.py
+++ b/cloudinit/config/cc_ssh.py
@@ -99,6 +99,7 @@ public keys.
import glob
import os
import sys
+import traceback
from cloudinit.distros import ug_util
from cloudinit import ssh_util
@@ -213,8 +214,9 @@ def handle(_name, cfg, cloud, log, _args):
keys.extend(cfgkeys)
apply_credentials(keys, user, disable_root, disable_root_opts)
- except Exception:
- util.logexc(log, "Applying ssh credentials failed!")
+ except Exception as err:
+ util.logexc(log, "Applying ssh credentials failed: {}".format(err))
+ traceback.print_exc()
def apply_credentials(keys, user, disable_root, disable_root_opts):
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