NAME¶
Sendmail::PMilter - Perl binding of Sendmail Milter protocol
SYNOPSIS¶
use Sendmail::PMilter;
my $milter = new Sendmail::PMilter;
$milter->auto_setconn(NAME);
$milter->register(NAME, { CALLBACKS }, FLAGS);
$milter->main();
DESCRIPTION¶
Sendmail::PMilter is a mail filtering API implementing the Sendmail milter
protocol in pure Perl. This allows Sendmail servers (and perhaps other MTAs
implementing milter) to filter and modify mail in transit during the SMTP
connection, all in Perl.
It should be noted that PMilter 0.90 and later is NOT compatible with scripts
written for PMilter 0.5 and earlier. The API has been reworked significantly,
and the enhanced APIs and rule logic provided by PMilter 0.5 and earlier has
been factored out for inclusion in a separate package to be called
Mail::Milter.
METHODS¶
- get_max_interpreters()
- Returns the maximum number of interpreters passed to
"main()". This is only useful when called from within the
dispatcher, as it is not set before "main()" is called.
- get_max_requests()
- Returns the maximum number of requests per interpreter
passed to "main()". This is only useful when called from within
the dispatcher, as it is not set before "main()" is called.
- main([MAXCHILDREN[, MAXREQ]])
- This is the last method called in the main block of a
milter program. If successful, this call never returns; the protocol
engine is launched and begins accepting connections.
MAXCHILDREN (default 0, meaning unlimited) specifies the maximum number of
connections that may be serviced simultaneously. If a connection arrives
with the number of active connections above this limit, the milter will
immediately return a temporary failure condition and close the connection.
MAXREQ (default 0, meaning unlimited) is the maximum number of requests that
a child may service before being recycled. It is not guaranteed that the
interpreter will service this many requests, only that it will not go over
the limit.
Any callback which "die"s will have its output sent to
"warn", followed by a clean shutdown of the milter connection.
To catch any warnings generated by the callbacks, and any error messages
caused by a "die", set $SIG{__WARN__} to a user-defined
subroutine. (See perlvar.)
- register(NAME, CALLBACKS[, FLAGS])
- Sets up the main milter loop configuration.
NAME is the name of the milter. For compatibility with the official
Sendmail::Milter distribution, this should be the same name as passed to
auto_getconn() or auto_setconn(), but this PMilter
implementation does not enforce this.
CALLBACKS is a hash reference containing one or more callback subroutines.
If a callback is not named in this hashref, the caller's package will be
searched for subroutines named "CALLBACK_callback", where
CALLBACK is the name of the callback function.
FLAGS, if specified, is a bitmask of message modification actions (a bitwise
OR of the SMFIF_* constants, or SMFI_CURR_ACTS to ask for all
capabilities) that are requested by the callback object for use during
message processing. If any bit is not set in this mask, its corresponding
action will not be allowed during message processing.
"register()" must be called successfully exactly once. If called a
second time, the previously registered callbacks will be erased.
Returns a true value on success, undef on failure.
- setconn(DESC)
- Sets up the server socket with connection descriptor DESC.
This is identical to the descriptor syntax used by the "X"
milter configuration lines in sendmail.cf (if using Sendmail). This should
be one of the following:
- local:PATH
- A local ("UNIX") socket on the filesystem, named
PATH. This has some smarts that will auto-delete the pathname if it seems
that the milter is not currently running (but this currently contains a
race condition that may not be fixable; at worst, there could be two
milters running with one never receiving connections).
- inet:PORT[@HOST]
- An IPv4 socket, bound to address HOST (default INADDR_ANY),
on port PORT. It is not recommended to open milter engines to the world,
so the @HOST part should be specified.
- inet6:PORT[@HOST]
- An IPv6 socket, bound to address HOST (default INADDR_ANY),
on port PORT. This requires IPv6 support and the Perl INET6 package to be
installed. It is not recommended to open milter engines to the world, so
the @HOST part should be specified.
Returns a true value on success, undef on failure.
- set_dispatcher(CODEREF)
- Sets the dispatcher used to accept socket connections and
hand them off to the protocol engine. This allows pluggable resource
allocation so that the milter script may use fork, threads, or any other
such means of handling milter connections. See "DISPATCHERS"
below for more information.
The subroutine (code) reference will be called by "main()" when
the listening socket object is prepared and ready to accept connections.
It will be passed the arguments:
MILTER, LSOCKET, HANDLER
MILTER is the milter object currently running. LSOCKET is a listening socket
(an instance of "IO::Socket"), upon which "accept()"
should be called. HANDLER is a subroutine reference which should be
called, passing the socket object returned by
"LSOCKET->accept()".
Note that the dispatcher may also be set from one of the off-the-shelf
dispatchers noted in this document by setting the PMILTER_DISPATCHER
environment variable. See "DISPATCHERS", below.
- set_listen(BACKLOG)
- Set the socket listen backlog to BACKLOG. The default is 5
connections if not set explicitly by this method. Only useful before
calling "main()".
- set_socket(SOCKET)
- Rather than calling "setconn()", this method may
be called explicitly to set the "IO::Socket" instance used to
accept inbound connections.
SENDMAIL-SPECIFIC METHODS¶
The following methods are only useful if Sendmail is the MTA connecting to this
milter. Other MTAs likely don't use Sendmail's configuration file, so these
methods would not be useful with them.
- auto_getconn(NAME[, CONFIG])
- Returns the connection descriptor for milter NAME in
Sendmail configuration file CONFIG (default
"/etc/mail/sendmail.cf" or whatever was set by
"set_sendmail_cf()"). This can then be passed to
setconn(), below.
Returns a true value on success, undef on failure.
- auto_setconn(NAME[, CONFIG])
- Creates the server connection socket for milter NAME in
Sendmail configuration file CONFIG.
Essentially, does:
$milter->setconn($milter->auto_getconn(NAME, CONFIG))
Returns a true value on success, undef on failure.
- get_sendmail_cf()
- Returns the pathname of the Sendmail configuration file set
by "set_sendmail_cf()", else the default of
"/etc/mail/sendmail.cf".
- get_sendmail_class(CLASS[, CONFIG])
- Returns a list containing all members of the Sendmail class
CLASS, in Sendmail configuration file CONFIG (default
"/etc/mail/sendmail.cf" or whatever is set by
"set_sendmail_cf()"). Typically this is used to look up the
entries in class "w", the local hostnames class.
- set_sendmail_cf(FILENAME)
- Set the default filename used by "auto_getconn",
"auto_setconn", and "sendmail_class" to find
Sendmail-specific configuration data. If not explicitly set by this
method, it defaults to "/etc/mail/sendmail.cf".
DISPATCHERS¶
Milter requests may be dispatched to the protocol handler in a pluggable manner
(see the description for the "set_dispatcher()" method above).
"Sendmail::PMilter" offers some off-the-shelf dispatchers that use
different methods of resource allocation.
Each of these is referenced as a non-object function, and return a value that
may be passed directly to "set_dispatcher()".
- Sendmail::PMilter::ithread_dispatcher()
- (environment) PMILTER_DISPATCHER=ithread
- The "ithread" dispatcher spins up a new thread
upon each connection to the milter socket. This provides a thread-based
model that may be more resource efficient than the similar
"postfork" dispatcher. This requires that the Perl interpreter
be compiled with "-Duseithreads", and uses the
"threads" module (available on Perl 5.8 or later only).
- Sendmail::PMilter::prefork_dispatcher([PARAMS])
- (environment) PMILTER_DISPATCHER=prefork
- The "prefork" dispatcher forks the main Perl
process before accepting connections, and uses the main process to monitor
the children. This should be appropriate for steady traffic flow sites.
Note that if MAXINTERP is not set in the call to "main()" or in
PARAMS, an internal default of 10 processes will be used; similarly, if
MAXREQ is not set, 100 requests will be served per child.
Currently the child process pool is fixed-size: discarded children will be
immediately replaced. This may change to use a dynamic sizing method in
the future, more like the Apache webserver's fork-based model.
PARAMS, if specified, is a hash of key-value pairs defining parameters for
the dispatcher. The available parameters that may be set are:
- child_init
- subroutine reference that will be called after each child
process is forked. It will be passed the "MILTER" object.
- child_exit
- subroutine reference that will be called just before each
child process terminates. It will be passed the "MILTER"
object.
- max_children
- Maximum number of child processes active at any time.
Equivalent to the MAXINTERP option to main() -- if not set in the
main() call, this value will be used.
- max_requests_per_child
- Maximum number of requests a child process may service
before being recycled. Equivalent to the MAXREQ option to main() --
if not set in the main() call, this value will be used.
- Sendmail::PMilter::postfork_dispatcher()
- (environment) PMILTER_DISPATCHER=postfork
- In this release, this is the default dispatcher for PMilter
if no explicit dispatcher is set.
The "postfork" dispatcher forks the main Perl process upon each
connection to the milter socket. This is adequate for machines that get
bursty but otherwise mostly idle mail traffic, as the idle-time resource
consumption is very low.
- Sendmail::PMilter::sequential_dispatcher()
- (environment) PMILTER_DISPATCHER=sequential
- The "sequential" dispatcher forces one request to
be served at a time, making other requests wait on the socket for the next
pass through the loop. This is not suitable for most production
installations, but may be quite useful for milter debugging or other
software development purposes.
Note that, because the default socket backlog is 5 connections, it may be
wise to increase this backlog by calling "set_listen()" before
entering "main()" if using this dispatcher.
EXPORTS¶
Each of these symbols may be imported explicitly, imported with tag
":all", or referenced as part of the "Sendmail::PMilter::"
package.
- Callback Return Values
- Of these, SMFIS_CONTINUE will allow the milter to continue
being called for the remainder of the message phases. All others will
terminate processing of the current message and take the noted action.
As a special exception, SMFIS_REJECT and SMFIS_TEMPFAIL in the
"envrcpt" callback will reject only the current recipient,
otherwise continuing message processing as if SMFIS_CONTINUE were
returned.
SMFIS_CONTINUE - continue processing the message
SMFIS_REJECT - reject the message with a 5xx error
SMFIS_DISCARD - accept, but discard the message
SMFIS_ACCEPT - accept the whole message as-is
SMFIS_TEMPFAIL - reject the message with a 4xx error
- Milter Capability Request Flags
- These values are bitmasks passed as the FLAGS argument to
"register()". Some MTAs may choose different methods of resource
allocation, so keeping this list short may help the MTA's memory usage. If
the needed capabilities are not known, however, "SMFI_CURR_ACTS"
should be used.
SMFIF_ADDHDRS - allow $ctx->addheader()
SMFIF_CHGBODY - allow $ctx->replacebody()
SMFIF_MODBODY - (compatibility synonym for SMFIF_CHGBODY)
SMFIF_ADDRCPT - allow $ctx->addrcpt()
SMFIF_DELRCPT - allow $ctx->delrcpt()
SMFIF_CHGHDRS - allow $ctx->chgheader()
SMFIF_QUARANTINE - allow $ctx->quarantine()
(requires Sendmail 8.13; not defined in Sendmail::Milter)
SMFIF_SETSENDER - allow $ctx->setsender()
(requires special Sendmail patch; see below[*])
SMFI_V1_ACTS - SMFIF_ADDHDRS through SMFIF_DELRCPT
(Sendmail 8.11 _FFR_MILTER capabilities)
SMFI_V2_ACTS - SMFIF_ADDHDRS through SMFIF_CHGHDRS
SMFI_CURR_ACTS - (compatibility synonym for SMFI_V2_ACTS)
(Sendmail 8.12 capabilities)
(Currently no combined macro includes SMFIF_QUARANTINE or
SMFIF_SETSENDER.)
[*] NOTE: SMFIF_SETSENDER is not official as of Sendmail 8.13.x. To enable
this flag, Sendmail must be patched with the diff available from:
C<http://www.sourceforge.net/projects/mlfi-setsender>
Additionally, the following statement must appear after the "use"
statements in your milter program; otherwise, setsender() will
always fail when called:
local $Sendmail::PMilter::enable_setsender = 1;
SECURITY CONSIDERATIONS¶
- Running as root
- Running Perl as root is dangerous. Running
"Sendmail::PMilter" as root may well be system-assisted suicide
at this point. So don't do that.
More specifically, though, it is possible to run a milter frontend as root,
in order to gain access to network resources (such as a filesystem socket
in /var/run), and then drop privileges before accepting connections. To do
this, insert drop-privileges code between calls to setconn/auto_setconn
and main; for instance:
$milter->auto_setconn('pmilter');
$> = 65534; # drop root privileges
$milter->main();
The semantics of properly dropping system administrator privileges in Perl
are, unfortunately, somewhat OS-specific, so this process is not described
in detail here.
AUTHOR¶
Todd Vierling, <tv@duh.org> <tv@pobox.com>
Maintenance¶
Since 0.96 Sendmail::Pmilter is no longer maintained on sourceforge.net,
cpan:AVAR took it over in version 0.96 to fix a minor bug and currently owns
the module in PAUSE.
However this module is effectively orphaned and looking for a new maintainer.
The current maintainer doesn't use Sendmail and probably never will again. If
this code is important to you and you find a bug in it or want something new
implemented please:
- •
- Fork it & fix it on GitHub at
<http://github.com/avar/sendmail-pmilter>
- •
- Send AVAR an E-Mail requesting upload permissions so you
can upload the fixed version to the CPAN.
SEE ALSO¶
Sendmail::PMilter::Context for a description of the arguments passed to each
callback function
The project homepage:
http://pmilter.sourceforge.net/
THANKS¶
rob.casey@bluebottle.com - for the prefork mechanism idea