Unprivileged syslog and encrypted connections

The rsyslog daemon can be used in a privileged or an unprivileged mode. In a privileged mode the daemon is run on the root account, has access to all required files, sockets, etc. In the unprivileged mode, rsyslog daemon is started in a privileged mode first, opens required sockets/ports and then drops all of its privileges and supplementary UNIX groups.

The debops.rsyslog role allows you to select which mode is used by configuring the rsyslog__unprivileged boolean variable. By default, to preserve original configuration, the role enables unprivileged mode on Ubuntu hosts, leaving the configuration privileged on Debian hosts.

The unprivileged operation places certain restrictions on the system configuration. In particular, the rsyslog process only uses its primary system group, dropping any additional groups the user is in. This means, that using TLS with the default configuration maintained by debops.pki role becomes problematic - unprivileged rsyslog process uses only its own primary group, so it cannot access private keys to allow encrypted connections.

There are multiple solutions to this problem, which you can use. Each one has pros and cons, and you should evaluate the selected method in a development environment before implementing it in production to avoid issues.

Run the daemon in privileged mode

This method is the default on Debian hosts. Ubuntu hosts use the unprivileged mode by default, and reverting to the privileged mode should work, but that hasn't been evaluated yet.

The daemon will be run with the root permissions, and there shouldn't be any issues with file access. Enabling TLS connections should work out of the box. On the downside, an externally accessible service is running with root permissions, so you should be careful what hosts have access to it, this is controlled using the firewall.

To enable this mode, set the following in the Ansible inventory:

rsyslog__unprivileged: False

This will enforce the privileged operation.

Grant access to private keys by additional groups

The debops.pki role that maintains the DebOps X.509 infrastructure, allows you to specify additional system groups, which should have access to the private keys. This should be configured before the role creates ths private keys, because the permissions are not enforced afterwards - this means that you will need to recreate the private keys and certificates, or update the permissions manually. Additional permissions are granted using the filesystem ACL support.

To enable rsyslog to get access to the private keys in unprivileged mode by the syslog system groups, configure in the Ansible inventory:

# Ensure that needed system group is present
pki_private_groups_present:
  - name: 'syslog'
    system: True

# Add custom ACL groups to private files and directories for all PKI realms
pki_private_dir_acl_groups:  [ 'syslog' ]
pki_private_file_acl_groups: [ 'syslog' ]

# Or, add custom ACL groups to private files only in default PKI realm
pki_default_realms:
  - name: 'domain'
    acme: False
    private_dir_acl_groups:  [ 'syslog' ]
    private_file_acl_groups: [ 'syslog' ]

After the PKI realm is recreated, you can check the result using command:

root@logs:~# getfacl /etc/pki/realms/domain/private
root@logs:~# getfacl /etc/pki/realms/domain/private/key.pem

You should see the syslog entry on the list of groups that can access the respective files and directories. When the rsyslog process is restarted, it should be able to access the private keys without issues. To enable the unprivileged mode on Debian hosts, you might want to enforce it through the Ansible inventory. Here it is, with example log forwarding to remote host with TCP over TLS:

# Enable unprivileged operation
rsyslog__unprivileged: True

# Enable TLS support
rsyslog__capabilities: [ 'tls' ]

# Forward logs over encrypted TCP connection
rsyslog__forward: [ '*.* @@logs.{{ ansible_domain }}:6514' ]

Create custom PKI realm for syslog

The debops.pki role allows you to create multiple PKI realms with different purposes and configuration. If you don't want to modify and existing infrastructure in place, creating a separate internal realm just for syslog might be an easy alternative.

To create new PKI realm, add this to the Ansible inventory for all involved hosts:

# Ensure that needed system group is present
pki_private_groups_present:
  - name: 'syslog'
    system: True

# Create custom realm for syslog
pki_realms:
  - name: 'syslog'
    acme: False
    private_dir_group:  'syslog'
    private_file_group: 'syslog'

When the new PKI realm is created, the private directory and files inside should be owned by the syslog group. This should ensure that the rsyslog daemon in the unprivileged mode, running as syslog user, should have access to them. The certificates should be signed by existing debops.pki Certificate Authority, so they should be trusted by all hosts in the cluster.

When the new PKI realm is ready, you can tell debops.rsyslog role to use it:

# Enable unprivileged operation
rsyslog__unprivileged: True

# Enable TLS support
rsyslog__capabilities: [ 'tls' ]

# Change the default PKI realm used by rsyslog
rsyslog__pki_realm: 'syslog'

# Forward logs over encrypted TCP connection
rsyslog__forward: [ '*.* @@logs.{{ ansible_domain }}:6514' ]

When the new configuration is applied, you should see in the rsyslog configuration files that the daemon is using the correct private key and certificate.

Testing encrypted connections

To make sure that the logs are sent over an encrypted connection, you can check the traffic using the tshark command. On the receiving server, run the command:

root@logs:~# tshark -i eth0 -f "dst port 514 or dst port 6514" \
             -d tcp.port==514,syslog -d tcp.port==6514,syslog

This will output packets that are sent to TCP ports 514 (plaintext traffic) and 6514 (TLS traffic). Afterwards, on remote hosts try sending some test log messages:

user@host:~$ logger Test log message, please ignore

If the connection is not encrypted, you should see something similar to this (notice the unencrypted contents of the packet):

9 132.751792 192.0.2.2 -> 192.0.2.1 Syslog 133 USER.NOTICE: May 16 14:06:05 host user: Test log message, please ignore\n

If the connection is encrypted, output should look similar to this:

9 132.751792 192.0.2.2 -> 192.0.2.1 Syslog 164 \027\003\003\000]\000\000\000\000\000\000\000\037\257\301,\030\365\311\324\023qR9\b\352\203\256\306\260T\023\022\016g\271\220\325\031\250\326\323\0045\3549\270\277>\205\301\256\325\234\246\tzt\333\255\002\006K"\254\334\021wB1\353\f\356,u\344\220\207d\024o\305\234\b\201\003Js[\2533\261\207\231?k\230J

Of course, the contents of the logs should appear normally in the log files, for example in /var/log/remote/hosts/host/syslog you should see:

May 16 14:06:05 host user: Test log message, please ignore