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FWKNOPD(8) | Fwknop Server | FWKNOPD(8) |
NAME¶
fwknopd - Firewall Knock Operator DaemonSYNOPSIS¶
fwknopd [options]DESCRIPTION¶
fwknopd is the server component for the FireWall Knock Operator, and is responsible for monitoring and processing Single Packet Authorization (SPA) packets that are generated by fwknop clients, modifying a firewall or ACL policy to allow the desired access after decrypting a valid SPA packet, and removing access after a configurable timeout.COMMAND-LINE OPTIONS¶
-a, --access-file=<access-file>Specify the location of the access.conf
file. If this option is not given, fwkopd will use the compile-time
default location (typically /etc/fwknop/access.conf.
-c, --config=<config-file>
Specify the location of the
fwknopd.conf file. If this option is not given, fwkopd will use
the default location (typically /etc/fwknop/fwknopd.conf.
-C, --packet-limit=<n>
Specify the number of candidate SPA packets to
process and exit when this limit is reached.
-D, --Dump-config
Dump the configuration values that
fwknopd derives from the fwknop.conf (or override files) and
access.conf on stderr.
-i, --interface=<interface>
Manually specify interface on which to sniff,
e.g. “-i eth0”. This option is not usually needed because the
“PCAP_INTF” keyword in the fwknopd.conf file defines the
sniffing interface.
-f, --foreground
Run fwknopd in the foreground instead
of becoming a daemon. When run in the foreground, message that would go to the
log would instead be sent to stderr. This mode is usually used when testing
and/or debugging.
--fw-list
List all firewall rules that any running
fwknopd daemon has created and then exit.
-K, --Kill
Kill the current fwknopd process. This
provides a quick and easy way to stop fwknopd without having to look in
the process table.
-l, --locale=<locale>
Set/override the system default locale
setting.
-O, --Override-config=<file>
Override config variable values that are
normally read from the fwknop.conf file with values from the specified
file. Multiple override config files can be given as a comma-separated
list.
-R, --Restart
Restart the currently running fwknopd
processes. This option will preserve the command line options that were
supplied to the original fwknopd process but will force fwknopd
to re-read the fwknopd.conf and access.conf files. This will
also force a flush of the current “FWKNOP” Netfilter
chain(s).
--rotate-digest-cache
Rotate the digest cache file by renaming it to
“<name>-old”, and starting a new one. The digest cache file
is typically found in /var/run/fwknop/digest.cache.
-S, --Status
Display the status of any fwknopd
processes that may or not be running.
-v, --verbose
Run fwknopd in verbose mode. This can
option can be specified multiple times to increase the verbosity of the output
to the system log file (or to the screen if running in the foreground).
-h, --help
Display usage information and exit.
-V, --Version
Display version information and exit.
FWKNOPD CONFIG AND ACCESS VARIABLES¶
fwknopd references the fwknopd.conf file for configuration variables that define its operational parameters (what network interface and port to sniff, what features to enable/disable, etc.). The fwknopd.conf file does not define any access control directives.FWKNOPD.CONF VARIABLES¶
This section list the more prominent configuration variables used by fwknopd. It is not a complete list. There are directives for the type of firewall used by fwknopd (i.e. iptables or ipfw). You will want to make sure to check these to make sure they have appropriate values. See the fwknopd.conf file for the full list and corresponding details. PCAP_INTF <interface>Specify the ethernet interface on which
fwknopd will sniff packets.
ENABLE_PCAP_PROMISC <Y/N>
By default fwknopd puts the pcap
interface into promiscuous mode. Set this to “N” to disable that
behavior (non-promiscuous).
PCAP_FILTER <pcap filter spec>
Define the filter used for PCAP modes;
fwknopd defaults to UDP port 62201. However, if an fwknop client
uses the --rand-port option to send the SPA packet over a random port,
then this variable should be updated to something like “udp dst
portrange 10000-65535”.
ENABLE_SPA_PACKET_AGING <Y/N>
This instructs fwknopd to not honor SPA
packets that have an old time stamp. The value for “old” is
defined by the “MAX_SPA_PACKET_AGE” variable. If
“ENABLE_SPA_PACKET_AGING” is set to “N”,
fwknopd will not use the client time stamp at all.
MAX_SPA_PACKET_AGE <seconds>
Defines the maximum age (in seconds) that an
SPA packet will be accepted. This requires that the client system is in
relatively close time synchronization with the fwknopd server system
(NTP is good). The default age is 120 seconds (two minutes).
ENABLE_DIGEST_PERSISTENCE <Y/N>
Track digest sums associated with previous SPA
packets processed by fwknopd. This allows digest sums to remain
persistent across executions of fwknopd. The default is
“Y”. If set to “N”, fwknopd will not check
incoming SPA packet data against any previously save digests. It is a good
idea to leave this feature on to reduce the possibility of being vulnerable to
a replay attack.
ENABLE_IPT_FORWARDING <Y/N>
Allow SPA clients to request access to
services through an iptables firewall instead of just to it (i.e. access
through the FWKNOP_FORWARD chain instead of the INPUT chain).
ENABLE_IPT_LOCAL_NAT >Y/N>
Allow SPA clients to request access to a local
socket via NAT. This still puts an ACCEPT rule into the FWKNOP_INPUT chain,
but a different port is translated via DNAT rules to the real one. So, the
user would do “ssh -p <port>” to access the local service
(see the --NAT-local and --NAT-rand-port on the fwknop
client command line).
ENABLE_IPT_SNAT <Y/N>
Set this to “Y” to enable a
corresponding SNAT rule. By default, if forwarding access is enabled (see the
“ENABLE_IPT_FORWARDING” variable above), then fwknopd
creates DNAT rules for incoming connections, but does not also complement
these rules with SNAT rules at the same time. In some situations, internal
systems may not have a route back out for the source address of the incoming
connection, so it is necessary to also apply SNAT rules so that the internal
systems see the IP of the internal interface where fwknopd is
running.
SNAT_TRANSLATE_IP <ip_address>
Specify the IP address for SNAT. This
functionality is only enabled when “ENABLE_IPT_SNAT” is set to
“Y” and by default SNAT rules are built with the MASQUERADE target
(since then the internal IP does not have to be defined here in the
fwknopd.conf file), but if you want fwknopd to use the SNAT
target, you mus also define an IP address with the
“SNAT_TRANSLATE_IP” variable.
ENABLE_IPT_OUTPUT <Y/N>
Add ACCEPT rules to the FWKNOP_OUTPUT chain.
This is usually only useful if there are no state tracking rules to allow
connection responses out and the OUTPUT chain has a default-drop stance.
MAX_SNIFF_BYTES <bytes>
Specify the the maximum number of bytes to
sniff per frame. 1500 is the default.
FLUSH_IPT_AT_INIT <Y/N>
Flush all existing rules in the fwknop chains
at fwknopd start time. The default is “Y”.
FLUSH_IPT_AT_EXIT <Y/N>
Flush all existing rules in the fwknop chains
when fwknopd is stopped or otherwise exits cleanly. The default is
“Y”.
GPG_HOME_DIR <path>
If GPG keys are used instead of a Rijndael
symmetric key, this is the default GPG keys directory. Note that each access
block in access.conf can specify its own GPG directory to override this
default. If not set here or in an access.conf stanza, then the
$HOME/.gnupg directory of the user running fwknopd (most likely
root).
LOCALE <locale>
Set the locale (via the LC_ALL variable). This
can be set to override the default system locale.
ENABLE_SPA_OVER_HTTP <Y/N>
Allow fwknopd to acquire SPA data from
HTTP requests (generated with the fwknop client in --HTTP mode). Note
that when this is enabled, the “PCAP_FILTER” variable would need
to be updated to sniff traffic over TCP/80 connections and a web server should
be running on the same server as fwknopd.
ENABLE_TCP_SERVER <Y/N>
Enable the fwknopd TCP server. This is a
"dummy" TCP server that will accept TCP connection requests on the
specified TCPSERV_PORT. If set to "Y", fwknopd will fork off a child
process to listen for, and accept incoming TCP request. This server only
accepts the request. It does not otherwise communicate. This is only to allow
the incoming SPA over TCP packet which is detected via PCAP. The connection is
closed after 1 second regardless. Note that fwknopd still only gets its data
via pcap, so the filter defined by PCAP_FILTER needs to be updated to include
this TCP port.
TCPSERV_PORT <port>
Set the port number that the
“dummy” TCP server listens on. This server is only spawned when
“ENABLE_TCP_SERVER” is set to “Y”.
SYSLOG_IDENTITY <identity>
Override syslog identity on message logged by
fwknopd. The defaults are usually ok.
SYSLOG_FACILITY <facility>
Override syslog facility. The
“SYSLOG_FACILITY” variable can be set to
ACCESS.CONF VARIABLES¶
This section describes the access control directives in the access.conf file. Theses directives define encryption keys and level of access that is granted to fwknop clients that have generated the appropriate encrypted message.This defines the source address from which the
SPA packet will be accepted. The string “ANY” is also accepted if
a valid SPA packet should be honored from any source IP. Every authorization
stanza in access.conf definition must start with the
“SOURCE” keyword. Networks should be specified in CIDR notation
(e.g. “192.168.10.0/24”), and individual IP addresses can be
specified as well. Also, multiple IP’s and/or networks can be defined as
a comma separated list (e.g. “192.168.10.0/24,10.1.1.123”)
OPEN_PORTS: <proto/port>,...,<proto/port>
Define a set of ports and protocols (tcp or
udp) that will be opened if a valid knock sequence is seen. If this entry is
not set, fwknopd will attempt to honor any proto/port request specified
in the SPA data (unless of it matches any “RESTRICT_PORTS”
entries). Multiple entries are comma-separated.
RESTRICT_PORTS: <proto/port>,...,<proto/port>
Define a set of ports and protocols (tcp or
udp) that are explicitly not allowed regardless of the validity of the
incoming SPA packet. Multiple entries are comma-separated.
KEY: <password>
Define the key used for decrypting an incoming
SPA packet that is using its built-in (Rijndael) encryption. This variable is
required for all non-GPG-encrypted SPA packets.
FW_ACCESS_TIMEOUT: <seconds>
Define the length of time access will be
granted by fwknopd through the firewall after a valid knock sequence
from a source IP address. If “FW_ACCESS_TIMEOUT” is not set then
the default timeout of 30 seconds will automatically be set.
ENABLE_CMD_EXEC: <Y/N>
This instructs fwknopd to accept
complete commands that are contained within an authorization packet. Any such
command will be executed on the fwknopd server as the user specified by
the “CMD_EXEC_USER” or as the user that started fwknopd if
that is not set.
CMD_EXEC_USER: <username>
This specifies the user that will execute
commands contained within a SPA packet. If not specified, fwknopd will execute
it as the user it is running as (most likely root). Setting this to a non-root
user is highly recommended.
REQUIRE_USERNAME: <username>
Require a specific username from the client
system as encoded in the SPA data. This variable is optional and if not
specified, the username data in the SPA data is ignored.
REQUIRE_SOURCE_ADDRESS: <Y/N>
Force all SPA packets to contain a real IP
address within the encrypted data. This makes it impossible to use the
-s command line argument on the fwknop client command line, so
either -R has to be used to automatically resolve the external address
(if the client behind a NAT) or the client must know the external IP.
GPG_HOME_DIR: <path>
Define the path to the GnuPG directory to be
used by the fwknopd server. If this keyword is not specified within
access.conf then fwknopd will default to using the
/root/.gnupg directory for the server key(s) for incoming SPA packets
handled by the matching access.conf stanza.
GPG_DECRYPT_ID: <keyID>
Define a GnuPG key ID to use for decrypting
SPA messages that have been encrypted by an fwknop client. This keyword
is required for authentication that is based on GPG keys. The GPG key ring on
the client must have imported and signed the fwknopd server key, and
vice versa. It is ok to use a sensitive personal GPG key on the client, but
each fwknopd server should have its own GPG key that is generated
specifically for fwknop communications. The reason for this is that the
decryption password for the server key must be placed within the
access.conf file for fwknopd to function (it has to be able to
decrypt SPA messages that have been encrypted with the server’s public
key). For more information on using fwknop with GnuPG keys, see the following
link: “http://www.cipherdyne.org/fwknop/docs/gpghowto.html”.
GPG DECRYPT_PW: <decrypt password>
Specify the decryption password for the gpg
key defined by the “GPG_DECRYPT_ID” above. This is a required
field for gpg-based authentication.
GPG_REQUIRE_SIG: <Y/N>
With this setting set to Y, fwknopd
check all GPG-encrypted SPA messages for a signature (signed by the
sender’s key). If the incoming message is not signed, the decryption
process will fail. If not set, the default is N.
GPG_IGNORE_SIG_VERIFY_ERROR: <Y/N>
Setting this will allow fwknopd to accept
incoming GPG-encrypted packets that are signed, but the signature did not pass
verification (i.e. the signer key was expired, etc.). This setting only
applies if the GPG_REQUIRE_SIG is also set to Y.
GPG_REMOTE_ID: <keyID,...,keyID>
Define a list of gpg key ID’s that are
required to have signed any incoming SPA message that has been encrypted with
the fwknopd server key. This ensures that the verification of the
remote user is accomplished via a strong cryptographic mechanism. This setting
only applies if the “GPG_REQUIRE_SIG” is set to Y. Separate
multiple entries with a comma.
FILES¶
fwknop.confThe main configuration file for fwknop.
access.conf
Defines all knock sequences and access control
directives.
DEPENDENCIES¶
The fwknopd daemon requires a functioning Netfilter firewall on the underlying operating system.DIAGNOSTICS¶
fwknopd can be run in debug mode by combining the -f, --foreground and the -v, --verbose command line options. This will disable daemon mode execution, and print verbose information to the screen on stderr as packets are received.SEE ALSO¶
fwknop(8), iptables(8), libfko docmentation.AUTHOR¶
Damien Stuart <dstuart@dstuart.org>, Michael Rash <mbr@cipherdyne.org>CREDITS¶
This “C” version of fwknopd was derived from the original Perl-based version on which many people who are active in the open source community have contributed. See the CREDITS file in the fwknop sources, or visit http://www.cipherdyne.org/fwknop/docs/contributors.html to view the online list of contributors.BUGS¶
Send bug reports to dstuart@dstuart.org. Suggestions and/or comments are always welcome as well.DISTRIBUTION¶
fwknopd is distributed under the GNU General Public License (GPL), and the latest version may be downloaded from http://www.cipherdyne.org.08/28/2010 | Fwknop Server |