password-agent

Name

password-agent — Run Mandos client as a systemd password agent.

Synopsis

password-agent [--agent-directory=DIRECTORY]
[--helper-directory=DIRECTORY]
[--user=USERID]
[--group=GROUPID]
[--] [ MANDOS_CLIENT [ OPTIONS ...] ]

password-agent --test

password-agent { --help | -? }

password-agent --usage

password-agent { --version | -V }

DESCRIPTION

password-agent is a program which is meant to be a systemd(1) “Password Agent” (See Password Agents). The aim of this program is therefore to acquire and then send a password to some other program which will use the password to unlock the encrypted root disk.

This program is not meant to be invoked directly, but can be in order to test it.

PURPOSE

The purpose of this is to enable remote and unattended rebooting of client host computer with an encrypted root file system. See the section called “OVERVIEW” for details.

OPTIONS

--agent-directory DIRECTORY: Specify a different agent directory. The default is “/run/systemd/ask-password” as per the Password Agents specification.
--helper-directory DIRECTORY: Specify a different helper directory. The default is “/lib/mandos/plugin-helpers”, which will exist in the initial RAM disk environment. (This will simply be passed to the MANDOS_CLIENT program via the MANDOSPLUGINHELPERDIR environment variable. See mandos-client(8mandos).)
--user USERID: Change real user ID to USERID when running MANDOS_CLIENT. The default is 65534. Note: This must be a number, not a name.
--group GROUPID: Change real group ID to GROUPID when running MANDOS_CLIENT. The default is 65534. Note: This must be a number, not a name.
MANDOS_CLIENT: This specifies the file name for mandos-client(8mandos). If the “--” option is given, any following options are passed to the MANDOS_CLIENT program. The default is “/lib/mandos/plugins.d/mandos-client” (which is the correct location for the initial RAM disk environment) without any options.
--help, -?: Gives a help message about options and their meanings.
--test: Ignore normal operation; instead only run self-tests. Adding the --help option may show more options possible in combination with --test.
--usage: Gives a short usage message.
--version, -V: Prints the program version.

OVERVIEW

This is part of the Mandos system for allowing computers to have encrypted root file systems and at the same time be capable of remote and/or unattended reboots. The computers run a small client program in the initial RAM disk environment which will communicate with a server over a network. All network communication is encrypted using TLS. The clients are identified by the server using a TLS key; each client has one unique to it. The server sends the clients an encrypted password. The encrypted password is decrypted by the clients using a separate OpenPGP key, and the password is then used to unlock the root file system, whereupon the computers can continue booting normally.

This program, password-agent, will run on the client side in the initial RAM disk environment, and is responsible for getting a password from the Mandos client program itself, and to send that password to whatever is currently asking for a password using the systemd Password Agents mechanism.

To accomplish this, password-agent runs the mandos-client program (which is the actual client program communicating with the Mandos server) or, alternatively, any executable file specified as MANDOS_CLIENT, and, as soon as a password is acquired from the MANDOS_CLIENT program, sends that password (as per the Password Agents specification) to all currently unanswered password questions.

This program should be started (normally as a systemd service, which in turn is normally started by a systemd.path(5) file) as a reaction to files named “ask.xxxx” appearing in the agent directory “/run/systemd/ask-password” (or the directory specified by --agent-directory).

EXIT STATUS

Exit status of this program is zero if no errors were encountered, and otherwise not.

ENVIRONMENT

This program does not use any environment variables itself, it only passes on its environment to MANDOS_CLIENT. Also, the --helper-directory option will affect the environment variable MANDOSPLUGINHELPERDIR for MANDOS_CLIENT.

FILES

/run/systemd/ask-password: The default directory to watch for password questions as per the Password Agents specification; can be changed by the --agent-directory option.
/lib/mandos/plugin-helpers: The helper directory as supplied to MANDOS_CLIENT via the MANDOSPLUGINHELPERDIR environment variable; can be changed by the --helper-directory option.

BUGS

Please report bugs to the Mandos development mailing list: <mandos-dev@recompile.se> (subscription required). Note that this list is public. The developers can be reached privately at <mandos@recompile.se> (OpenPGP key fingerprint 153A 37F1 0BBA 0435 987F 2C4A 7223 2973 CA34 C2C4 for encrypted mail).

EXAMPLE

Normal invocation needs no options:

password-agent

Run an alternative MANDOS_CLIENT program::

password-agent /usr/local/sbin/alternate

Use alternative locations for the helper directory and the Mandos client, and add extra options suitable for running in the normal file system:

password-agent --helper-directory=/usr/lib/x86_64-linux-gnu/mandos/plugin-helpers -- /usr/lib/x86_64-linux-gnu/mandos/plugins.d/mandos-client --pubkey=/etc/keys/mandos/pubkey.txt --seckey=/etc/keys/mandos/seckey.txt --tls-pubkey=/etc/keys/mandos/tls-pubkey.pem --tls-privkey=/etc/keys/mandos/tls-privkey.pem

Use the default location for mandos-client(8mandos), but add many options to it:

password-agent -- /lib/mandos/plugins.d/mandos-client --pubkey=/etc/mandos/keys/pubkey.txt --seckey=/etc/mandos/keys/seckey.txt --tls-pubkey=/etc/mandos/keys/tls-pubkey.pem --tls-privkey=/etc/mandos/keys/tls-privkey.pem

Only run the self-tests:

password-agent --test

SECURITY

This program will need to run as the root user in order to read the agent directory and the “ask.xxxx” files there, and will, when starting the Mandos client program, require the ability to set the “real” user and group ids to another user, by default user and group 65534, which are assumed to be non-privileged. This is done in order to match the expectations of mandos-client(8mandos), which assumes that its executable file is owned by the root user and also has the set-user-ID bit set (see execve(2)).