sudo_logsrvd - Man Page

The I/O log data sent to sudo_logsrvd may contain sensitive information such as passwords and should be secured using Transport Layer Security (TLS). Doing so requires having a signed certificate on the server and, if tls_checkpeer is enabled in sudo_logsrvd.conf(5), a signed certificate on the client as well.

The certificates can either be signed by a well-known Certificate Authority (CA), or a private CA can be used. Instructions for creating a private CA are included below in the Examples section.

sudo_logsrvd supports a flexible debugging framework that is configured via Debug lines in the sudo.conf(5) file.

For more information on configuring sudo.conf(5), refer to its manual.

Unless you are using certificates signed by a well-known Certificate Authority (or a local enterprise CA), you will need to create your own CA that can sign the certificates used by sudo_logsrvd, sudo_sendlog, and the sudoers plugin. The following steps use the openssl(1) command to create keys and certificates.

First, we need to create a directory structure to store the files for the CA. We'll create a new directory hierarchy in /etc/ssl/sudo for this purpose.

# mkdir /etc/ssl/sudo
# cd /etc/ssl/sudo
# mkdir certs csr newcerts private
# chmod 700 private
# touch index.txt
# echo 1000 > serial

The serial and index.txt files are used to keep track of signed certificates.

Next, we need to make a copy of the openssl.conf file and customize it for our new CA. The path to openssl.cnf is system-dependent but /etc/ssl/openssl.cnf is the most common location. You will need to adjust the example below if it has a different location on your system.

# cp /etc/ssl/openssl.cnf .

Now edit the openssl.cnf file in the current directory and make sure it contains “ca”, “CA_default”, “v3_ca”, and “usr_cert” sections. Those sections should include at least the following settings:

[ ca ]
default_ca              = CA_default

[ CA_default ]
dir                     = /etc/ssl/sudo
certs                   = $dir/certs
database                = $dir/index.txt
certificate             = $dir/cacert.pem
serial                  = $dir/serial

[ v3_ca ]
subjectKeyIdentifier    = hash
authorityKeyIdentifier  = keyid:always,issuer
basicConstraints        = critical,CA:true
keyUsage                = cRLSign, keyCertSign

[ usr_cert ]
basicConstraints        = CA:FALSE
keyUsage                = nonRepudiation, digitalSignature, \
                          keyEncipherment
subjectKeyIdentifier    = hash
authorityKeyIdentifier  = keyid,issuer

If your openssl.conf file already has a “CA_default” section, you may only need to modify the “dir” setting and enable the “keyUsage” settings if they are commented out.

In order to create and sign our own certificates, we need to create a private key and a certificate for the root of the CA. First, create the private key and protect it with a pass phrase:

# openssl genrsa -aes256 -out private/cakey.pem 4096
# chmod 400 private/cakey.pem

Next, generate the root certificate, using appropriate values for the site-specific fields:

# openssl req -config openssl.cnf -key private/cakey.pem \
    -new -x509 -days 7300 -sha256 -extensions v3_ca \
    -out cacert.pem

Enter pass phrase for private/cakey.pem:
You are about to be asked to enter information that will be
incorporated into your certificate request.
What you are about to enter is what is called a Distinguished Name
or a DN.
There are quite a few fields but you can leave some blank.
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:US
State or Province Name (full name) [Some-State]:Colorado
Locality Name (eg, city) []:
Organization Name (eg, company) [Internet Widgits Pty Ltd]:sudo
Organizational Unit Name (eg, section) []:sudo Certificate Authority
Common Name (e.g., server FQDN or YOUR name) []:sudo Root CA
Email Address []:

# chmod 444 cacert.pem

Finally, verify the root certificate:

# openssl x509 -noout -text -in cacert.pem

The server and client certificates will be signed by the previously created root CA. Usually, the root CA is not used to sign server/client certificates directly. Instead, intermediate certificates are created and signed with the root CA and the intermediate certs are used to sign CSRs (Certificate Signing Request). In this example we'll skip this part for simplicity's sake and sign the CSRs with the root CA.

First, generate the private key without a pass phrase.

# openssl genrsa -out private/logsrvd_key.pem 2048
# chmod 400 private/logsrvd_key.pem

Next, create a certificate signing request (CSR) for the server's certificate. The organization name must match the name given in the root certificate. The common name should be either the server's IP address or a fully qualified domain name.

# openssl req -config openssl.cnf -key private/logsrvd_key.pem -new \
    -sha256 -out csr/logsrvd_csr.pem

Enter pass phrase for private/logsrvd_key.pem:
You are about to be asked to enter information that will be
incorporated into your certificate request.
What you are about to enter is what is called a Distinguished Name
or a DN.
There are quite a few fields but you can leave some blank.
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:US
State or Province Name (full name) [Some-State]:Colorado
Locality Name (eg, city) []:
Organization Name (eg, company) [Internet Widgits Pty Ltd]:sudo
Organizational Unit Name (eg, section) []:sudo log server
Common Name (e.g., server FQDN or YOUR name) []:logserver.example.com
Email Address []:

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:

Now sign the CSR that was just created:

# openssl ca -config openssl.cnf -days 375 -notext -md sha256 \
    -in csr/logsrvd_csr.pem -out certs/logsrvd_cert.pem

Using configuration from openssl.cnf
Enter pass phrase for ./private/cakey.pem:
Check that the request matches the signature
Signature ok
Certificate Details:
        Serial Number: 4096 (0x1000)
        Validity
            Not Before: Nov 11 14:05:05 2019 GMT
            Not After : Nov 20 14:05:05 2020 GMT
        Subject:
            countryName               = US
            stateOrProvinceName       = Colorado
            organizationName          = sudo
            organizationalUnitName    = sudo log server
            commonName                = logserve.example.com
        X509v3 extensions:
            X509v3 Basic Constraints:
                CA:FALSE
            X509v3 Key Usage:
                Digital Signature, Non Repudiation, Key Encipherment
            X509v3 Subject Key Identifier:
                4C:50:F9:D0:BE:1A:4C:B2:AC:90:76:56:C7:9E:16:AE:E6:9E:E5:B5
            X509v3 Authority Key Identifier:
                keyid:D7:91:24:16:B1:03:06:65:1A:7A:6E:CF:51:E9:5C:CB:7A:95:3E:0C

Certificate is to be certified until Nov 20 14:05:05 2020 GMT (375 days)
Sign the certificate? [y/n]:y

1 out of 1 certificate requests certified, commit? [y/n]y
Write out database with 1 new entries
Data Base Updated

Finally, verify the new certificate:

# openssl verify -CAfile cacert.pem certs/logsrvd_cert.pem
certs/logsrvd_cert.pem: OK

The /etc/ssl/sudo/certs directory now contains a signed and verified certificate for use with sudo_logsrvd.

To generate a client certificate, repeat the process above using a different file name.

To use TLS for client/server communication, both sudo_logsrvd and the sudoers plugin need to be configured to use TLS. Configuring sudo_logsrvd for TLS requires the following settings, assuming the same path names used earlier:

# Listen on port 30344 for TLS connections to any address.
listen_address = *:30344(tls)

# Path to the certificate authority bundle file in PEM format.
tls_cacert = /etc/ssl/sudo/cacert.pem

# Path to the server's certificate file in PEM format.
tls_cert = /etc/ssl/sudo/certs/logsrvd_cert.pem

# Path to the server's private key file in PEM format.
tls_key = /etc/ssl/sudo/private/logsrvd_key.pem

The root CA cert (cacert.pem) must be installed on the system running sudo_logsrvd. If peer authentication is enabled on the client, a copy of cacert.pem must be present on the client system too.