udp, util: Break out send_nak function

[secnet] / secnet.8

.TH secnet 8

.SH NAME
secnet \- VPN router daemon

.SH SYNOPSIS
\fBsecnet\fR [\fIOPTIONS\fR]

.SH DESCRIPTION
\fBsecnet\fR allows virtual private networks to be constructed
spanning multiple separate sites.

.SH OPTIONS
.TP
.B --verbose\fR, \fB-v
Enable extra diagnostics.
.TP
.B --nowarnings\fR, \fB-w
Suppress warnings.
.TP
.B --help
Display usage message.
.TP
.B --version
Display version string.
.TP
.B --nodetach\fR, \fB-n
Don't go into background.
The default behaviour is to become a daemon during startup.
.TP
.B --silent\fR, \fB--quiet\fR, \fB-f
Suppress error messages.
.TP
.B --debug\fR, \fB-d
Enable debug messages.
.TP
.B --config\fR, \fB-c \fIPATH
Specify configuration file.
The default is \fI/etc/secnet/secnet.conf\fR.
.TP
.B --just-check-config\fR, \fB-j
Check configuration and exit.
.TP
.B --sites-key\fR, \fB-s \fIKEY
Configuration file key defining active sites.
The default is \fBsites\fR.

.SH "CONFIGURATION FILE"
.SS Overview
The default configuration file is \fI/etc/secnet/secnet.conf\fR.
This can be overridden with the \fB--config\fR option.
.PP
The configuration file defines a dictionary (a mapping from keys to
values) of configuration information for secnet.
It is recursive in nature, i.e. values may themselves include dictionaries.
Any node in the nested structure thus defined can be identified by a
\fIpath\fR, which is the sequence of keys necessary to reach it from
the root, separated by "/" characters.
See \fBPaths\fR below for how this is used.
.PP
Furthermore, when a key is looked up in a dictionary, if it cannot be
found, it is sought in the parent dictionary, and so on back to the
root.
For instance, each \fIsite\fR must contain the \fBresolver\fR key, but
in a typical configuration there is no value in having different
resolvers for each site.
Therefore \fBresolver\fR is defined at the root and thus automatically
incorporated into all sites.
.SS Whitespace
Whitespace, including newlines, is ignored except to the extent that
it bounds other symbols.
.PP
Comment begin with "#" and continues to the end of the line.
Comments are ignored.
.SS Inclusion
A file may be recursively included into the configuration file using a
line of the form:
.IP
\fBinclude \fIPATH
.PP
This is handled at a higher level than the main parser and so
precludes the possibility of using the string \fBinclude\fR for any
other purpose.
.\" check if this is true.  it's probably a bug!
.SS Assignments
The configuration file contains one or more assigments.
Each assignment is written:
.IP
\fIkey\fR [\fB=\fR] \fIlist\fR\fB;\fR
.PP
i.e. the equals sign is optional.
The semicolon is mandatory in all contexts.
.PP
Keys start with a letter or "_" and continue with any numbers of
letters, digits, "_" and "-".
.PP
Each \fIkey\fR is a list of one or more \fIvalues\fR, separated by commas.
Possible values types are \fIboolean\fR, \fIstring\fR, \fInumber\fR,
\fIdictionary\fR, \fIpath\fR and \fIclosure evaluation\fR.
.\" This man page draws a distinction between a closure (the thing
.\" evaluated) and a closure evaluation (the closure plus is
.\" arguments).
.SS "Strings"
Strings are contained within "double quotes".
There is (currently) no escape syntax and no way to include quotes
inside strings.
.PP
Example:
.nf
        filename "/var/log/secnet";
.fi
.SS "Numbers"
Numbers are encoded in decimal and do not include a sign.
Numbers must lie in the range 0 to 4294967295.
.PP
Example:
.nf
        mtu 1400;
.fi
.SS "Dictionaries"
.\" In conffile.y dictionaries can be preceded by a search path, but
.\" this is not implemented elsewhere, so not documented here.
Dictionaries consist of one or more assignments, in the same syntax as
given above, enclosed in "{" and "}".
.PP
Example:
.nf
        system {
                userid "secnet";
                pidfile "/var/run/secnet.pid";
        };
.fi
.SS "Paths"
Paths allow a key already defined in the configuration to be aliased.
.PP
Paths consist of a sequence of keys separated by "/".
If the path starts with a "/" then it is an \fIabsolute path\fR and
the search starts at the root of the configuration.
Otherwise it is a \fIrelative path\fR and starts in the containing
dictionary or in any of its parents, down to and including the root.
If there is more than one match, the one furthest from the root "wins".
.PP
The value of a path is the list assigned to the key it refers to.
Lists are flattened; for example if a key is defined as a list of two
paths, and each of those refers to a list of two integers, the
original key is therefore defined to be a list of four integers, not
a list consisting of two lists.
.PP
It is not possible to refer to a \fIlater\fR key using a path.
.PP
Example:
.nf
        vpn {
          test {
            kakajou vpn-data/test/kakajou/kakajou;
            araminta vpn-data/test/araminta/araminta;
            deodand vpn-data/test/deodand/deodand;
            all-sites kakajou,araminta,deodand;
          };
        };
        all-sites vpn/test/all-sites;
.fi
.PP
Here, each of \fBvpn/test/kakajou\fR, \fBvpn/test/araminta\fR and
\fBvpn/test/deodand\fR are defined as aliases to values defined
elsewhere.
\fBvpn/tests/all-sites\fR is defined as the list of all three of those
values, and \fBall-sites\fR is then defined to be an alias for that.
.SS "Booleans"
The (single-element) paths \fBfalse\fR, \fBno\fR and \fBnowise\fR are
predefined and refer to a boolean false value.
Similarly \fBtrue\fR, \fByes\fR and \fBverily\fR point at a boolean
true value.
.PP
In all six cases, variants with just the first letter capitalized, and
with all letters capitalized, are also provided.
.PP
Example:
.nf
        random randomfile("/dev/urandom",no);
.fi
.SS "Closure Evaluation"
Closure evaluation uses the following syntax:
.IP
\fICLOSURE \fB( \fIARGUMENTS \fB)
.PP
\fICLOSURE\fR may be a path referring to a closure, or may itself be a
closure evaluation.
.PP
\fIARGUMENTS\fR is a list of zero or more values, separated by commas.
As a shortcut, if the arguments consist of a single dictionary, the
parentheses may be ommitted:
.IP
\fICLOSURE \fB{ \fR... \fB}
.PP
Example:
.nf
        sites map(site, vpn/test/all-sites);
.fi
.PP
When a closure is evaluated it returns a value (a list, much as above)
and may also have side effects (which may be immediate or may be
deferred to some later phase of execution).
A list of built-in closures is given below.
.SS "Mandatory Keys"
Two keys are mandatory.
\fBsystem\fR must be a dictionary in which the following keys can be
looked up:
.TP
.B log
A \fIlog closure\fR; see the \fBlogfile\fR documentation below.
The destination for log messages.
Mandatory.
.TP
.B userid
A string.
The userid to run as after dropping privilege.
Optional.
.TP
.B pidfile
A string.
The path to write a pidfile.
Optional.
.PP
\fBsites\fR should be a list of \fIsite closures\fR; see the \fBsite\fR documentation below.
This defines the collection of tunnel endpoints that \fBsecnet\fR will
communicate with.
.PP
Recall the recursive lookup logic described in \fBOverview\fR above:
if (for instance) \fBlog\fR is defined in the top level dictionary but
not in \fBsystem\fR, it will nevertheless be found when looked up in
the latter.

.SH CLOSURES
\fBsecnet\fR contains a collection of built-in closures
with names (i.e. single-element paths) given below.
.PP
Most of them return anonymous closures of various types,
which are described contextually.

.SS adns
\fBadns(\fIDICT\fB)\fR => \fIresolver closure\fR
.TP
.I DICT
This either be empty or contain the single key \fBconfig\fR, with a
string value giving configuration to supply to ADNS.
This might be read from a file using \fBreadfile\fR.
.PP
A \fIresolver closure\fR is a means of converting hostnames into
network addresses.

.SS diffie-hellman
.PP
\fBdiffie-hellman(\fIMODULUS\fB, \fIGENERATOR\fR[\fB, \fICHECK\fR]\fB)\fR => \fIdh closure\fR
.TP
.I MODULUS
String.
The prime modulus \fIp\fR in hex.
.TP
.I GENERATOR
String.
The generator \fIg\fR in hex.
.TP
.I CHECK
Boolean.
If \fBtrue\fR (the default) then check if \fIp\fR is prime.
.PP
A \fIdh closure\fR defines a group to be used for key exchange.
The same group must be used by all sites in the VPN.

.SS logfile
\fBlogfile(\fIDICT\fB)\fR => \fIlog closure\fR
.PP
Valid keys in the \fIDICT\fR argument are:
.TP
.B filename
The path to log to.
.TP
.B class
A list of strings defining which classes of message to log.
The possible message classes are \fBdebug-config\fR,
\fBdebug-phase\fR, \fBdebug\fR, \fBinfo\fR, \fBnotice\fR,
\fBwarning\fR, \fBerror\fR, \fBsecurity\fR and \fBfatal\fR.
.IP
\fBall-debug\fR is the union of all the \fBdebug\fR... classes.
\fBdefault\fR is equivalent to \fBwarning, error, security, fatal\fR.
\fBverbose\fR is equivalent to \fBinfo, notice, warning, error,
security, fatal\fR.
\fBquiet\fR is equivalent to \fBfatal\fR.
.PP
A \fIlog closure\fR is a means of saving log messages.
See also \fBsyslog\fR below.

.SS makelist
\fBmakelist(\fIDICT\fB)\fR => \fILIST\fR
.PP
Returns the (flattened) list of values from the dictionary, discarding
the keys.

.SS map
\fBmap(\fICLOSURE\fB, \fIINPUT\fR...\fB)\fR => \fILIST\fR
.PP
Applies \fICLOSURE\fR to all its additional input arguments and
returns the resulting list.

.SS md5
\fBmd5\fR is a \fIhash closure\fR implementing the MD5 algorithm.

.SS null-netlink
\fBnull-netlink(\fIDICT\fB)\fR => \fInetlink closure\fR
.br
\fBnull-netlink(\fIDICT\fB)\fR => \fIpure closure\fR
.\" TODO pure closure is what it's called internally but this is a
.\" very opaque name to use in docs
.PP
Valid keys in the \fIDICT\fR argument are:
.TP
.B name
String.
The name for the netlink device.
The default is \fBnull-netlink\fR.
.TP
.B networks
List of strings.
The networks on the host side of the netlink device.
.TP
.B remote-networks
List of strings.
Networks that may be claimed by remote sites using this netlink device.
.TP
.B secnet-address
String.
IP address of this netlink.
Incompatible with \fBptp-address\fR.
.TP
.B ptp-address
String.
IP address of the other end of a point-to-point link.
Incompatible with \fBsecnet-address\fR.
.TP
.B mtu
Number.
The MTU of the netlink device.
The default is 1000.
.PP
If \fBptp-address\fR is used then the result is a \fInetlink closure\fR.
This can be used directly with the \fBlink\fR key in the \fBsites\fR
closure (see below).
.PP
If \fBsecnet-address\fR is used then the result is a \fIpure
closure\fR.
This must be evaluated to yield a \fInetlink closure\fR, using a
dictionary argument with the following keys:
.TP
.B routes
String list.
networks reachable via this tunnel, in \fIaddress\fB/\fIbits\fR format.
.TP
.B options
String list.
A list of options:
.RS
.TP
.B allow-route
Allow packets received via this tunnel to be routed down other tunnels
(without this option only packets from the host will be routed).
.TP
.B soft
Remove these routes from the host routing table when the link quality
is 0.
.RE
.TP
.B mtu
Number.
Default MTU over this link.
The default is inherited from the \fIpure closure\fR.
.TP
.B priority
Number.
The priority of this link.
Higher values beat lower values.
The default is 0.

.\" TODO ptp-address turns up in sites.conf, but why?  I think this
.\" is a bug in make-secnet-sites; it is not used by
 \" netlink_inst_create.

.PP
A \fInetlink closure\fR is a virtual IP link, and is supplied to the
\fBlink\fR key of a \fIsite\fR closure.
.PP
The netlink created by \fBnull-netlink\fR has no connection to the
host.
See \fBtun\fR and \fBuserv-ipif\fR below for more useful alternatives.



.SS randomfile
\fBrandomfile(\fIFILENAME\fR[\fB, \fIBLOCKING\fR]\fB)\fR => \fIrandomsource closure\fR
.TP
.I FILENAME
String.
Path to random device, e.g. \fI/dev/urandom\fR.
.TP
.I BLOCKING
Boolean.
\fBTrue\fR if this is a blocking device and \fBfalse\fR otherwise (the default).
Blocking device support is not implemented so this must always be
\fBFalse\fR or absent.
.PP
A \fIrandomsource closure\fR is a source of random numbers.

.SS readfile
\fBreadfile(\fIPATH\fB)\fR => \fISTRING\fR
.PP
Read the contents of the file \fIPATH\fR (a string) and return it as a string.

.SS eax-serpent
\eax-fBserpent(\fIDICT\fB)\fR => \fItransform closure\fR
.PP
Valid keys in the \fIDICT\fR argument are:
.TP
.B max-sequence-skew
The maximum acceptable difference between the sequence number in a
received, decrypted message and the previous one.
The default is 10.
It may be necessary to increase this is if connectivity is poor.
.TP
.B tag-length-bytes
The length of the message authentication tag.  The default is 16,
for a 128-bit tag length.  It must be no longer than the Serpent
blocksize, 16.  Must be have the same value at both ends.
.TP
.B padding-rounding
Messages are padded to a multiple of this many bytes.  This
serves to obscure the exact length of messages.  The default is 16,
.PP
A \fItransform closure\fR is a reversible means of transforming
messages for transmission over a (presumably) insecure network.
It is responsible for both confidentiality and integrity.

.SS serpent256-cbc
\fBserpent256-cbc(\fIDICT\fB)\fR => \fItransform closure\fR
.PP
Valid keys in the \fIDICT\fR argument are:
.TP
.B max-sequence-skew
As above.
.PP
Note that this uses a big-endian variant of the Serpent block cipher
(which is not compatible with most other Serpent implementations).
.SS rsa-private
\fBrsa-private(\fIPATH\fB\fR[, \fICHECK\fR]\fB)\fR => \fIrsaprivkey closure\fR
.TP
.I PATH
String.
The path to a file containing an RSA private key in SSH format
(version 1).
There must be no passphrase.
.TP
.I CHECK
Boolean.
If \fBtrue\fR (the default) then check that the key is valid.

.SS rsa-public
\fBrsa-public(\fIKEY\fB, \fIMODULUS\fB)\fR => \fIrsapubkey closure\fR
.TP
.I KEY
String.
The public key exponent (\fIe\fR), in decimal.
.TP
.I MODULUS
String.
The modulus (\fIn\fR), in decimal.

.SS sha1
\fBsha1\fR is a \fIhash closure\fR implementing the SHA-1 algorithm.

.SS site
\fBsite(\fIDICT\fB)\fR => \fIsite closure\fR
.PP
Valid keys in the \fIDICT\fR argument are:
.TP
.B local-name
String.
The site's name for itself.
.TP
.B name
String.
The name of the site's peer.
.TP
.B link
A \fInetlink closure\fR.
.TP
.B comm
A \fIcomm closure\fR.
.TP
.B resolver
A \fIresolver closure\fR.
.TP
.B random
A \fIrandomsource closure\fR.
.TP
.B local-key
An \fIrsaprivkey closure\fR.
The key used to prove our identity to the peer.
.TP
.B address
String.
The DNS name of the peer.
Optional, but if it is missing then it will not be possible to
initiate new connections to the peer.
.TP
.B port
Number.
The port to contact the peer.
.TP
.B key
An \fIrsapubkey closure\fR.
The key used to verify the peer's identity.
.TP
.B transform
A \fItransform closure\fR.
Used to protect packets exchanged with the peer.
.TP
.B dh
A \fIdh closure\fR.
The group to use in key exchange.
.TP
.B hash
The hash function used during setup.
.\" TODO clarify what we actually use it for!
.TP
.B key-lifetime
Number.
The maximum lifetime of a session key in milliseconds.
The default is one hour.
.TP
.B setup-retries
Number.
The maximum number of times a key negotiation packet will be
transmitted before giving up.
The default is 5.
.TP
.B setup-timeout
Number.
The time between retransmissions of key negotiation packets, in milliseconds.
The default is one second.
.TP
.B wait-time
Number.
The time to wait after a failed key setup before making another
attempt, in milliseconds.
The default is 20s.
.TP
.B renegotiate-time
Number.
The time after which a new session key will be negotiated, \fIif\fR
there is traffic on the link, in milliseconds.
It must not be greater than the \fBkey-lifetime\fR.
The default 5 minutes less than the key lifetime, unless the lifetime
is less than 10 minutes in which case the default is half the
lifetime.
.TP
.B keepalive
Boolean.
If \fBtrue\fR then attempt to always maintain a live session key.
Not implemented.
.TP
.B log-events
String list.
Types of event to log for this site.
.RS
.TP
.B unexpected
Unexpected key setup packets (including late retransmissions).
.TP
.B setup-init
Start of attempt to setup a session key.
.TP
.B setup-timeout
Failure of attempt to setup a session key, through timeout.
.TP
.B activate-key
Activation of a new session key.
.TP
.B timeout-key
Deletion of current session key through age.
.TP
.B security
Anything potentially suspicious.
.TP
.B state-change
Steps in the key setup protocol.
.TP
.B packet-drop
Whenever we throw away an outgoing packet.
.TP
.B dump-packets
Every key setup packet we see.
.TP
.B errors
Failure of name resolution, internal errors.
.TP
.B all
Everything (too much!)
.RE
.PP
A \fIsite closure\fR defines one site to communicate with.
\fBsecnet\fR expects the (root) key \fBsite\fR to be a list of site
closures.

.SS sysbuffer
\fBsysbuffer(\fR[\fISIZE\fR[\fB, \fIOPTIONS\fR]]\fB)\fR => \fIbuffer closure\fR
.TP
.I SIZE
Number.
The size of the buffer in bytes.
This must be between 64 and 131072.
The default is 4096.
.TP
.I OPTIONS
Dictionary.
Optional and presently unused.
.\" lockdown is accepted but ignored.
.PP
A \fIbuffer closure\fR is a means of buffering packets to send or that
have been received.

.SS syslog
\fBsyslog(\fIDICT\fB)\fR => \fIlog closure\fR
.PP
Valid keys in the \fIDICT\fR argument are:
.TP
.B ident
String.
The ident string to pass to \fBopenlog\fR(3); this value will appear
in each message.
.TP
.B facility
String.
The facility to log as.
The possible values are \fBauthpriv\fR, \fBcron\fR, \fBdaemon\fR,
\fBkern\fR, \fBlocal0\fR-\fB7\fR, \fBlpr\fR, \fBmail\fR, \fBnews\fR,
\fBsyslog\fR, \fBuser\fR and \fBuucp\fR.
.PP
See also \fBlogfile\fR above.

.SS tun
\fBtun(\fIDICT\fB)\fR => \fInetlink closure\fR
.br
\fBtun(\fIDICT\fB)\fR => \fIpure closure\fR
.PP
Valid keys in the \fIDICT\fR argument are those documented for
\fBnull-netlink\fR above, plus:
.TP
.B flavour
String.
The type of TUN interface to use.
Possible values are \fBlinux\fR, \fBbsd\fR, \fBstreams\fR and \fBguess\fR.
The default is \fBguess\fR.
.TP
.B device
String.
The path to the TUN/TAP device file.
The default is \fI/dev/net/tun\fR for the \fBlinux\fR flavour and
\fI/dev/tun\fR for the others.
.TP
.B interface
String.
The interface to use.
The default is to pick one automatically.
This cannot be used with the \fBstreams\fR flavour.
.TP
.B local-address
String.
IP address of the host's tunnel interface.
.\" README says this belongs to netlink-null but actually it's
 \" duplicated between slip & tun
.TP
.B ifconfig-path
String.
The name of the \fBifconfig\fR command.
The default is simply "ifconfig".
.TP
.B route-path
String.
The name of the \fBroute\fR command.
The default is simply "route".
.TP
.B ifconfig-type
String.
The syntax expected by the \fBifconfig\fR command.
Possible values are \fBlinux\fR, \fBbsd\fR, \fBioctl\fR,
\fBsolaris-2.5\fR and \fBguess\fR.
The default is \fBguess\fR.
.TP
.B route-type
String.
The syntax expected by the \fBifconfig\fR command.
Possible values are \fBlinux\fR, \fBbsd\fR, \fBioctl\fR,
\fBsolaris-2.5\fR and \fBguess\fR.
The default is \fBguess\fR.
.TP
.B buffer
A \fIbuffer closure\fR to use for packets transferred from the host to secnet.
The buffer size must be at least 60 greater than the MTU.
.\" TODO rumour has is that buffers are sometimes shareable between
.\" netlink devices - document that if the conditions are reasonable
.\" ones.
.PP
The \fBifconfig-type\fR and \fBroute-type\fR values determine how
those commands are executed.
If they are set to \fBioctl\fR then low-level system calls are used
directly instead of invoking the commands.
.PP
The netlink created by \fBtun\fR uses the \fBtun\fR device to
communicate with the host kernel.

.SS udp
\fBudp(\fIDICT\fB)\fR => \fIcomm closure\fR
.PP
Valid keys in the \fIDICT\fR argument are:
.TP
.B address
String.
The IP address to bind on.
The default is 0.0.0.0, i.e. "any".
.TP
.B port
Number.
The port number to bind to.
The default is 0, i.e. the OS will choose one.
It is suggested that any given VPN agree a common port number.
.TP
.B buffer
A \fIbuffer closure\fR.
See the \fBsysbuffer\fR closure above.
.TP
.B authbind
String.
The path to a helper program to bind the socket.
Optional.
.IP
The program will be invoked with the address and port number as its
arguments, and with the socket to bind as file descriptor 0.
It should either bind the socket as requested, or exit with nonzero
status.
.PP
A \fIcomm closure\fR is a means of sending and receiving messages via
a network.
It does not provide confidentiality, reliablity or availability.

.SS userv-ipif
\fBuserv-ipif(\fIDICT\fB)\fR => \fInetlink closure\fR
.br
\fBuserv-ipif(\fIDICT\fB)\fR => \fIpure closure\fR
.PP
Valid keys in the \fIDICT\fR argument are those documented for
\fBnull-netlink\fR above, plus:
.TP
.B local-address
String.
IP address of the host's SLIP interface.
.\" README says this belongs to netlink-null but actually it's
 \" duplicated between SLIP & tun
.TP
.B userv-path
String.
Where to find \fBuserv\fR(1).
The default is \fB"userv"\fR.
.TP
.B service-user
String.
The name of the user that owns the service.
The default is \fB"root"\fR.
.TP
.B service-name
String.
The name of the service to request.
The default is \fB"ipif"\fR.
.TP
.B buffer
A \fIbuffer closure\fR to use for packets transferred from the host to secnet.
.PP
The netlink created by \fBuserv-ipif\fR invokes the specified \fBuserv\fR service with pipes connected to its standard input and output.
It uses SLIP to communicate with the host kernel via these pipes.

.SH FILES
.TP
.I /etc/secnet/secnet.conf
Configuration file.

.SH "SEE ALSO"
\fBuserv\fR(1)