[RFC] inetd(8) changes proposal

[tlaronde%polynum.com@localhost]

After a little reflection, here are the proposed changes to inetd(8):


                        THE CONFIGURATION

There is only one configuration file given by a path---whether on the
command line or defaulting to "/etc/inetd.conf".

The inclusion directive is a dot i.e. a here script: there are not
different configuration files, but only one that may simply be assembled
by dot'ing others.

This means that all definitions have a global scope and that the
feature of the default address, if not specified, is not limited to the
file that is dot'ed there.

The configuration has hence to be wholly correct since any failure may
totally change the meaning of the directives (by changing the default
address).

=> I will disentangle the execution of the directives from the parsing
of the config (at the moment, services are launched once a line is
parsed, ignoring errors). To begin any action, the configuration will
have to be globally accepted.

The consequence will be that it will be possible to check the config
without running and without adding spaghetti code to not
execute if only checking.

For checking, two options will be added:

-c	check a config file (and does not execute). Returns 0 on success and
	ENOENT or EINVAL on error.

-C	as -c plus dump on stdout an explicit normalized config as it has
	been parsed. If the config is invalid, nothing is dumped: no action
	is taken if the config is invalid (there is no security problem if
	inetd is run by a not root user since the user has to have reading
	rights to the whole configuration to obtain any result: nothing is
	revealed that he would not have been able to get without the program.

                         NORMAL BEHAVIOR

	In the normal behavior, an incorrect config is fatal: a message is
	logged via syslog, but the process exits with error (ENOENT or
	EINVAL).

                       RESILIENT BEHAVIOR

Since a config can be rejected and hence nothing serviced, there will be
the addition of another mode:

-r	Resilient. At start, if the config given is invalid, try to load
	instead a fallback config file "/etc/inetd.fallback.conf". If this
	config also fails (maybe inexistent), serves nothing but keep
	running (the program is then still loaded, meaning resilience also
	against an update of the binaries). In this mode, an instruction to 
	reload will try to reload THE config (the one defined at the
	beginning, not the fallback one) and if this new config fails,
	the process will continue to serve the previous config (since
	nothing is done before validating the whole configuration, the
	previous, as it is, continues to be serviced; if it was the no-op,
	it continues to be the no-op: the fallback config is not reloaded.
	But see below.).

Note: resilient does not mean restricted. The fallback conf can be as
convoluted as a "normal" conf file. But one usage (not mandatory) will
probably be a safe minimal file with essential services to ensure in all
cases that the minimum is accessible.

                             CONTROL

Supplementary to SIGHUP:

	SIGUSR1	will instruct to load the fallback conf. This doesn't change
	THE config (a SIGHUP following will try to reload THE config and not
	the fallback), but loads, now, in its stead, the fallback one. This
	is a way to decrease the services serviced without stopping and
	restarting with another config file.

	SIGUSR2 (or SIGINFO?) will instruct to dump the current config via
	syslog. (Rationale: whether for debugging purposes, or because the
	administrator has tampered with its config without knowing anymore
	what worked, offer the possibility to tell what is supposed to work
	now).

                           CONFIG DUMP

	A config dump shall be so that its loading as config will lead to
	exactly the same behavior as the one obtained with the config file
	initially provided to the parser.

           MODIFICATION FROM PRESENT PARSING HANDLING

	A file can be loaded several times as long as there is no loop (in
fact, at the moment, contrary to what is stated in the man page, loops
are not detected: they are prevented by not allowing to load the same
file twice---and due to bugs, this is not guaranteed). The loop
detection will not use realpath(3) but dev/inode.

	A config file has to be a regular file (not a pipe). Its size is
retrieved at opening and not more than its initial size is processed. If
the process succeeds but the size of the file has changed when reaching
the end (of the processing of this file), there is tampering with the
file and the config fails (it does not guarantee against any
tampering but at least it ensures that there will be, by file, a
definite amount of data to process).

	The pathnames list resulting from globing will be sorted
lexicographically. This means that a user, by choosing carefully the
names, can ensure a definite order of inclusion of the files while
having the convenience of using globbing.

                           MONITORING

There are logs with syslog facility if not just checking.

In order to allow scripting the log, the messages will have a
defined format (these are only for global behavior and do not
include messages related to individual services):

[Is there guidelines about them?]

'inetd' SPACE <action> SPACE <arguments> 

<action>:
	'STARTING' SPACE <arg[0] arguments>
	'REJECTING' SPACE <config pathname>
	'SERVICING' SPACE <config pathname>
	'RELOADING' SPACE <config pathname>
	'KEEPING' /* the config is the one parsed; it has no name... */
	'FALLING-BACK' SPACE '/etc/inetd.fallback.conf'
	'DUMPING' SPACE <explicit normalized config directive>
	'EXITING' SPACE <status>
-- 
        Thierry Laronde <tlaronde +AT+ polynum +dot+ com>
                     http://www.kergis.com/
                    http://kertex.kergis.com/
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