bionic (8) mandos.8.gz

Provided by: mandos_1.7.19-1_all bug

NAME

       mandos - Gives encrypted passwords to authenticated Mandos clients

SYNOPSIS

       mandos [--interface NAME | -i NAME]
              [--address ADDRESS | -a ADDRESS]
              [--port PORT | -p PORT]
              [--priority PRIORITY]
              [--servicename NAME]
              [--configdir DIRECTORY]
              [--debug]
              [--debuglevel LEVEL]
              [--no-dbus]
              [--no-ipv6]
              [--no-restore]
              [--statedir DIRECTORY]
              [--socket FD]
              [--foreground]
              [--no-zeroconf]

       mandos {--help | -h}

       mandos --version

       mandos --check

DESCRIPTION

       mandos is a server daemon which handles incoming request for passwords for a pre-defined list of client
       host computers. For an introduction, see intro(8mandos). The Mandos server uses Zeroconf to announce
       itself on the local network, and uses TLS to communicate securely with and to authenticate the clients.
       The Mandos server uses IPv6 to allow Mandos clients to use IPv6 link-local addresses, since the clients
       will probably not have any other addresses configured (see the section called “OVERVIEW”). Any
       authenticated client is then given the stored pre-encrypted password for that specific client.

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

       --help, -h
           Show a help message and exit

       --interface NAME, -i NAME
           If this is specified, the server will only announce the service and listen to requests on the
           specified network interface. Default is to use all available interfaces.  Note: a failure to bind to
           the specified interface is not considered critical, and the server will not exit, but instead
           continue normally.

       --address ADDRESS, -a ADDRESS
           If this option is used, the server will only listen to the specified IPv6 address. If a link-local
           address is specified, an interface should be set, since a link-local address is only valid on a
           single interface. By default, the server will listen to all available addresses. If set, this must
           normally be an IPv6 address; an IPv4 address can only be specified using IPv4-mapped IPv6 address
           syntax: “::FFFF:192.0.2.3”. (Only if IPv6 usage is disabled (see below) must this be an IPv4
           address.)

       --port PORT, -p PORT
           If this option is used, the server will bind to that port. By default, the server will listen to an
           arbitrary port given by the operating system.

       --check
           Run the server’s self-tests. This includes any unit tests, etc.

       --debug
           If the server is run in debug mode, it will run in the foreground and print a lot of debugging
           information. The default is to not run in debug mode.

       --debuglevel LEVEL
           Set the debugging log level.  LEVEL is a string, one of “CRITICAL”, “ERROR”, “WARNING”, “INFO”, or
           “DEBUG”, in order of increasing verbosity. The default level is “WARNING”.

       --priority  PRIORITY
           GnuTLS priority string for the TLS handshake. The default is
           “SECURE256:!CTYPE-X.509:+CTYPE-OPENPGP:!RSA :+SIGN-DSA-SHA256”. See gnutls_priority_init(3) for the
           syntax.  Warning: changing this may make the TLS handshake fail, making server-client communication
           impossible. Changing this option may also make the network traffic decryptable by an attacker.

       --servicename NAME
           Zeroconf service name. The default is “Mandos”. This only needs to be changed if for some reason is
           would be necessary to run more than one server on the same host. This would not normally be useful.
           If there are name collisions on the same network, the newer server will automatically rename itself
           to “Mandos #2”, and so on; therefore, this option is not needed in that case.

       --configdir DIRECTORY
           Directory to search for configuration files. Default is “/etc/mandos”. See mandos.conf(5) and mandos-
           clients.conf(5).

       --version
           Prints the program version and exit.

       --no-dbus
           This option controls whether the server will provide a D-Bus system bus interface. The default is to
           provide such an interface.

           See also the section called “D-BUS INTERFACE”.

       --no-ipv6
           This option controls whether the server will use IPv6 sockets and addresses. The default is to use
           IPv6. This option should never normally be turned off, even in IPv4-only environments. This is
           because mandos-client(8mandos) will normally use IPv6 link-local addresses, and will not be able to
           find or connect to the server if this option is turned off.  Only advanced users should consider
           changing this option.

       --no-restore
           This option controls whether the server will restore its state from the last time it ran. Default is
           to restore last state.

           See also the section called “PERSISTENT STATE”.

       --statedir DIRECTORY
           Directory to save (and restore) state in. Default is “/var/lib/mandos”.

       --socket FD
           If this option is used, the server will not create a new network socket, but will instead use the
           supplied file descriptor. By default, the server will create a new network socket.

       --foreground
           This option will make the server run in the foreground and not write a PID file. The default is to
           not run in the foreground, except in debug mode, which implies this option.

       --no-zeroconf
           This option controls whether the server will announce its existence using Zeroconf. Default is to use
           Zeroconf. If Zeroconf is not used, a port number or a socket is required.

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 an OpenPGP 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 the same OpenPGP key, and the password is then used to unlock the root
       file system, whereupon the computers can continue booting normally.

       This program is the server part. It is a normal server program and will run in a normal system
       environment, not in an initial RAM disk environment.

NETWORK PROTOCOL

       The Mandos server announces itself as a Zeroconf service of type “_mandos._tcp”. The Mandos client
       connects to the announced address and port, and sends a line of text where the first whitespace-separated
       field is the protocol version, which currently is “1”. The client and server then start a TLS protocol
       handshake with a slight quirk: the Mandos server program acts as a TLS “client” while the connecting
       Mandos client acts as a TLS “server”. The Mandos client must supply an OpenPGP certificate, and the
       fingerprint of this certificate is used by the Mandos server to look up (in a list read from clients.conf
       at start time) which binary blob to give the client. No other authentication or authorization is done by
       the server.

       Table 1. Mandos Protocol (Version 1)
       ┌────────────────────────────┬───────────┬──────────────────────────┐
       │Mandos ClientDirectionMandos Server            │
       ├────────────────────────────┼───────────┼──────────────────────────┤
       │Connect                     │ ->        │                          │
       ├────────────────────────────┼───────────┼──────────────────────────┤
       │“1\r\n”                     │ ->        │                          │
       ├────────────────────────────┼───────────┼──────────────────────────┤
       │TLS handshake as TLS        │ <->       │ TLS handshake as TLS     │
       │“server”                    │           │ “client”                 │
       ├────────────────────────────┼───────────┼──────────────────────────┤
       │OpenPGP public key (part of │ ->        │                          │
       │TLS handshake)              │           │                          │
       ├────────────────────────────┼───────────┼──────────────────────────┤
       │                            │ <-        │ Binary blob (client will │
       │                            │           │ assume OpenPGP data)     │
       ├────────────────────────────┼───────────┼──────────────────────────┤
       │                            │ <-        │ Close                    │
       └────────────────────────────┴───────────┴──────────────────────────┘

CHECKING

       The server will, by default, continually check that the clients are still up. If a client has not been
       confirmed as being up for some time, the client is assumed to be compromised and is no longer eligible to
       receive the encrypted password. (Manual intervention is required to re-enable a client.) The timeout,
       extended timeout, checker program, and interval between checks can be configured both globally and per
       client; see mandos-clients.conf(5).

APPROVAL

       The server can be configured to require manual approval for a client before it is sent its secret. The
       delay to wait for such approval and the default action (approve or deny) can be configured both globally
       and per client; see mandos-clients.conf(5). By default all clients will be approved immediately without
       delay.

       This can be used to deny a client its secret if not manually approved within a specified time. It can
       also be used to make the server delay before giving a client its secret, allowing optional manual denying
       of this specific client.

LOGGING

       The server will send log message with various severity levels to /dev/log. With the --debug option, it
       will log even more messages, and also show them on the console.

PERSISTENT STATE

       Client settings, initially read from clients.conf, are persistent across restarts, and run-time changes
       will override settings in clients.conf. However, if a setting is changed (or a client added, or removed)
       in clients.conf, this will take precedence.

D-BUS INTERFACE

       The server will by default provide a D-Bus system bus interface. This interface will only be accessible
       by the root user or a Mandos-specific user, if such a user exists. For documentation of the D-Bus API,
       see the file DBUS-API.

EXIT STATUS

       The server will exit with a non-zero exit status only when a critical error is encountered.

ENVIRONMENT

       PATH
           To start the configured checker (see the section called “CHECKING”), the server uses /bin/sh, which
           in turn uses PATH to search for matching commands if an absolute path is not given. See sh(1).

FILES

       Use the --configdir option to change where mandos looks for its configurations files. The default file
       names are listed here.

       /etc/mandos/mandos.conf
           Server-global settings. See mandos.conf(5) for details.

       /etc/mandos/clients.conf
           List of clients and client-specific settings. See mandos-clients.conf(5) for details.

       /run/mandos.pid
           The file containing the process id of the mandos process started last.  Note: If the /run directory
           does not exist, /var/run/mandos.pid will be used instead.

       /var/lib/mandos
           Directory where persistent state will be saved. Change this with the --statedir option. See also the
           --no-restore option.

       /dev/log
           The Unix domain socket to where local syslog messages are sent.

       /bin/sh
           This is used to start the configured checker command for each client. See mandos-clients.conf(5) for
           details.

BUGS

       This server might, on especially fatal errors, emit a Python backtrace. This could be considered a
       feature.

       There is no fine-grained control over logging and debug output.

       This server does not check the expire time of clients’ OpenPGP keys.

       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:

       mandos

       Run the server in debug mode, read configuration files from the ~/mandos directory, and use the Zeroconf
       service name “Test” to not collide with any other official Mandos server on this host:

       mandos --debug --configdir ~/mandos --servicename Test

       Run the server normally, but only listen to one interface and only on the link-local address on that
       interface:

       mandos --interface eth7 --address fe80::aede:48ff:fe71:f6f2

SECURITY

   SERVER
       Running this mandos server program should not in itself present any security risk to the host computer
       running it. The program switches to a non-root user soon after startup.

   CLIENTS
       The server only gives out its stored data to clients which does have the OpenPGP key of the stored
       fingerprint. This is guaranteed by the fact that the client sends its OpenPGP public key in the TLS
       handshake; this ensures it to be genuine. The server computes the fingerprint of the key itself and looks
       up the fingerprint in its list of clients. The clients.conf file (see mandos-clients.conf(5)) must be
       made non-readable by anyone except the user starting the server (usually root).

       As detailed in the section called “CHECKING”, the status of all client computers will continually be
       checked and be assumed compromised if they are gone for too long.

       For more details on client-side security, see mandos-client(8mandos).

SEE ALSO

       intro(8mandos), mandos-clients.conf(5), mandos.conf(5), mandos-client(8mandos), sh(1)

       Zeroconf[1]
           Zeroconf is the network protocol standard used by clients for finding this Mandos server on the local
           network.

       Avahi[2]
           Avahi is the library this server calls to implement Zeroconf service announcements.

       GnuTLS[3]
           GnuTLS is the library this server uses to implement TLS for communicating securely with the client,
           and at the same time confidently get the client’s public OpenPGP key.

       RFC 4291: IP Version 6 Addressing Architecture

           Section 2.2: Text Representation of Addresses

           Section 2.5.5.2: IPv4-Mapped IPv6 Address

           Section 2.5.6, Link-Local IPv6 Unicast Addresses
               The clients use IPv6 link-local addresses, which are immediately usable since a link-local
               addresses is automatically assigned to a network interfaces when it is brought up.

       RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2
           TLS 1.2 is the protocol implemented by GnuTLS.

       RFC 4880: OpenPGP Message Format
           The data sent to clients is binary encrypted OpenPGP data.

       RFC 6091: Using OpenPGP Keys for Transport Layer Security (TLS) Authentication
           This is implemented by GnuTLS and used by this server so that OpenPGP keys can be used.

       Copyright © 2008-2018 Teddy Hogeborn, Björn Påhlsson

       This manual page is part of Mandos.

       Mandos is free software: you can redistribute it and/or modify it under the terms of the GNU General
       Public License as published by the Free Software Foundation, either version 3 of the License, or (at your
       option) any later version.

       Mandos is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the
       implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
       License for more details.

       You should have received a copy of the GNU General Public License along with Mandos. If not, see
       http://www.gnu.org/licenses/.

NOTES

        1. Zeroconf
           http://www.zeroconf.org/

        2. Avahi
           http://www.avahi.org/

        3. GnuTLS
           https://gnutls.org/