readers.conf(5)
NAME
readers.conf - Access control and configuration for nnrpd
DESCRIPTION
readers.conf in pathetc specifies access control for nnrpd(8). It controls who is allowed to connect as a news reader and what they're allowed to do after they connect. nnrpd reads this file when it starts up. This generally means that any changes take effect immediately on all subsequent connections, but nnrpd may have to be restarted if you use the -D option. (The location pathetc/readers.conf is only the default; the same format applies to any file specified with "nnrpd -c".) There are two types of entries in readers.conf: parameter/value pairs and configuration groups. Blank lines and anything after a number sign ("#") are ignored, unless the character "#" is escaped with "\". The maximum number of characters on each line is 8,191. Parameter/value pairs consist of a keyword immediately followed by a colon, at least one whitespace character, and a value. The case of the parameter is significant (parameter should generally be in all lowercase), and a parameter may contain any characters except colon, "#", and whitespace. An example: hosts: *.example.com Values that contain whitespace should be quoted with double quotes, as in: hosts: "*.example.com, *.example.net" If the parameter does not contain whitespace, such as: hosts: *.example.com,*.example.net it's not necessary to quote it, although you may wish to anyway for clarity. There is no way to continue a line on the next line, and therefore no way to have a single parameter with a value longer than about 8,180 characters. Many parameters take a boolean value. For all such parameters, the value may be specified as "true", "yes", or "on" to turn it on and may be any of "false", "no", or "off" to turn it off. The case of these values is not significant. There are two basic types of configuration groups, auth and access. The auth group provides mechanisms to establish the identity of the user, who they are. The access group determines, given the user's identity, what that user is permitted to do. Writing a readers.conf file for your setup is a two-step process: first assigning an identity to each incoming connection using auth groups, and then giving each identity appropriate privileges with access group. We recommend not intermingling auth groups and access groups in the config file; it is often more sensible (in the absence of the key parameter) to put all of the auth groups first, and all of the access groups below. A user identity, as established by an auth group, looks like an e-mail address; in other words, it's in the form "<username>@<domain>" (or sometimes just "<username>" if no domain is specified. If nnrpdauthsender is set in inn.conf, the user identity is also put into the Sender: header of posts made by that user. See the documentation of that option in inn.conf(5) for more details. An auth group definition looks like: auth <name> { hosts: <host-wildmat> auth: <auth-program> res: <res-program> default: <defuser> default-domain: <defdomain> # ...possibly other settings } The <name> is used as a label for the group and is only for documentation purposes. (If your syslog configuration records the "news.debug" facility, the <name> will appear in the debugging output of nnrpd. Examining that output can be very helpful in understanding why your configuration doesn't do what you expect it to.) A given auth group applies only to hosts whose name or IP address matches the wildmat expression given with the hosts: parameter (comma- separated wildmat expressions allowed, but "@" is not supported). Rather than wildmat expressions, you may also use CIDR notation to match any IP address in a netblock; for example, "10.10.10.0/24" will match any IP address between 10.10.10.0 and 10.10.10.255 inclusive. If compiled against the TLS/SSL or SASL libraries, an auth group with the require_ssl parameter set to true only applies if the incoming connection is using an encryption layer, either from the beginning if the -S flag was passed to nnrpd, or after a successful use of STARTTLS, or after a successful authentication using a SASL mechanism which negotiates an encryption layer. For any connection from a host that matches that wildmat expression or netblock, each <res-program> (multiple res: lines may be present in a block; they are run in sequence until one succeeds), if any, is run to determine the identity of the user just from the connection information. If all the resolvers fail, or if the res: parameter isn't present, the user is assigned an identity of "<defuser>@<defdomain>"; in other words, the values of the default: and default-domain: parameters are used. If <res-program> only returns a username, <defdomain> is used as the domain. If the user later authenticates via the AUTHINFO USER/PASS commands, the provided username and password are passed to each <auth-program> (multiple auth, perl_auth, or python_auth lines may be present in a block; they are run in sequence until one succeeds), if any. If one succeeds and returns a different identity than the one assigned at the time of the connection, it is matched against the available access groups again and the actions the user is authorized to do may change. The most common <auth-program> to use is ckpasswd, which supports several ways of checking passwords including using PAM. See the ckpasswd(8) man page for more details. When matching auth groups, the last auth group in the file that matches a given connection and username/password combination is used. An access group definition usually looks like: access <name> { users: <identity-wildmat> newsgroups: <group-wildmat> # ...possibly other settings } Again, <name> is just for documentation purposes. This says that all users whose identity matches <identity-wildmat> can read and post to all newsgroups matching <group-wildmat> (as before, comma-separated wildmat expressions are allowed, but "@" is not supported). Alternately, you can use the form: access <name> { users: <identity-wildmat> read: <read-wildmat> post: <post-wildmat> } and matching users will be able to read any group that matches <read-wildmat> and post to any group that matches <post-wildmat>. You can also set several other things in the access group as well as override various inn.conf(5) parameters for just a particular group of users. Just like with auth groups, when matching access groups the last matching one in the file is used to determine the user's permissions. There is an exception to this rule: if the auth group which matched the client contains a perl_access: or python_access: parameter, then the script given as argument is used to dynamically generate an access group. This new access group is then used to determine the access rights of the client; the access groups in the file are ignored. There is one additional special case to be aware of. When forming particularly complex authentication and authorization rules, it is sometimes useful for the identities provided by a given auth group to only apply to particular access groups; in other words, rather than checking the identity against the users: parameter of every access group, it's checked against the users: parameter of only some specific access groups. This is done with the key: parameter. For example: auth example { key: special hosts: *.example.com default: <SPECIAL> } access example { key: special users: <SPECIAL> newsgroups: * } In this case, the two key: parameters bind this auth group with this access group. For any incoming connection matching "*.example.com" (assuming there isn't any later auth group that also matches such hosts), no access group that doesn't have "key: special" will even be considered. Similarly, the above access group will only be checked if the user was authenticated with an auth group containing "key: special". This mechanism normally isn't useful; there is almost always a better way to achieve the same result. Also note in the example that there's no default-domain: parameter, which means that no domain is appended to the default username and the identity for such connections is just "<SPECIAL>". Note that some additional add-ons to INN may prefer that authenticated identities always return a full e-mail address (including a domain), so you may want to set up your system that way. Configuration files can be included in other configuration files via the syntax: include <filename> The file named <filename> is then included. This syntax is allowed only at top-level. Below is the full list of allowable parameters for auth groups and access groups, and after that are some examples that may make this somewhat clearer.
AUTH GROUP PARAMETERS
An auth group without at least one of the res:, auth:, perl_auth:,
python_auth:, or default: parameters makes no sense (and in practice
will just be ignored).
hosts:
A comma-separated list of remote hosts, wildmat patterns matching
either hostnames or IP addresses, or IP netblocks specified in CIDR
notation. If a user connects from a host that doesn't match this
parameter, this auth group will not match the connection and is
ignored.
Note that if you have a large number of patterns that can't be
merged into broader patterns (such as a large number of individual
systems scattered around the net that should have access), the
hosts: parameter may exceed the maximum line length of 8,192
characters. In that case, you'll need to break that auth group
into multiple auth groups, each with a portion of the hosts listed
in its hosts: parameter, and each assigning the same user identity.
All hosts match if this parameter is not given.
localaddress:
A comma-separated list of local host or address patterns with the
same syntax as the same as with the hosts: parameter. If this
parameter is specified, its auth group will only match connections
made to a matching local interface. (Obviously, this is only
useful for servers with multiple interfaces.)
All local addresses match if this parameter is not given.
res:
A simple command line for a user resolver (shell metacharacters are
not supported). If a full path is not given, the program executed
must be in the pathbin/auth/resolv directory. A resolver is an
authentication program which attempts to figure out the identity of
the connecting user using nothing but the connection information
(in other words, the user has not provided a username and
password). An examples of a resolver would be a program that
assigns an identity from an ident callback or from the user's
hostname.
One auth group can have multiple res: parameters, and they will be
tried in the order they're listed. The results of the first
successful one will be used.
Alternatively, a res block can be used instead of a res: paramater.
The recognized parameters in such res blocks are:
log:
A string to log in pathlog/news.notice (with "res also-log:"
prepended) before the resolver is tried. One res group can have
multiple log: parameters, and they will be logged in the order
they're listed.
program:
This parameter is mandatory in a res block. Its meaning is the
same as the res: parameter used directly in an auth block.
auth <auth-name> {
res: <res-program>
}
is therefore equivalent to:
auth <auth-name> {
res <res-name> {
program: <res-program>
}
}
auth:
A simple command line for a user authenticator (shell
metacharacters are not supported). If a full path is not given,
the program executed must be located in the pathbin/auth/passwd
directory. An authenticator is a program used to handle a user-
supplied username and password, via a mechanism such as AUTHINFO
USER/PASS. Like with res:, one auth group can have multiple auth:
parameters; they will be tried in order and the results of the
first successful one will be used. See also perl_auth: below.
The most common authenticator to use is ckpasswd(8); see its man
page for more information.
perl_auth:
A path to a perl script for authentication. The perl_auth:
parameter works exactly like auth:, except that it calls the named
script using the perl hook rather then an external program.
Multiple/mixed use of the auth, perl_auth, and python_auth
parameters is permitted within any auth group; each line is tried
in the order it appears. perl_auth: has more power than auth: in
that it provides the authentication program with additional
information about the client and the ability to return an error
string and a username. This parameter is only valid if INN is
compiled with Perl support (--with-perl passed to configure). More
information may be found in doc/hook-perl.
python_auth:
A Python script for authentication. The python_auth parameter
works exactly like auth, except that it calls the named script
(without its ".py" extension) using the Python hook rather then an
external program. Multiple/mixed use of the auth, perl_auth, and
python_auth parameters is permitted within any auth group; each
line is tried in the order it appears. python_auth has more power
than auth in that it provides the authentication program with
additional information about the client and the ability to return
an error string and a username. This parameter is only valid if
INN is compiled with Python support (--with-python passed to
configure). More information may be found in doc/hook-python.
default:
The default username for connections matching this auth group.
This is the username assigned to the user at connection time if all
resolvers fail or if there are no res: parameters. Note that it
can be either a bare username, in which case default-domain: (if
present) is appended after an "@", or a full identity string
containing an "@", in which case it will be used verbatim.
default-domain:
The default domain string for this auth group. If a user resolver
or authenticator doesn't provide a domain, or if the default
username is used and it doesn't contain a "@", this domain is used
to form the user identity. (Note that for a lot of setups, it's
not really necessary for user identities to be qualified with a
domain name, in which case there's no need to use this parameter.)
key:
If this parameter is present, any connection matching this auth
group will have its privileges determined only by the subset of
access groups containing a matching key parameter.
require_ssl:
If set to true, an incoming connection only matches this auth group
if it is encrypted, either from the beginning if the -S flag was
passed to nnrpd, or after a successful use of STARTTLS, or after a
successful authentication using a SASL mechanism which negotiates
an encrypted layer. This parameter is only valid if INN is
compiled with TLS/SSL or SASL support (by default if the OpenSSL
SSL and crypto libraries or the Cyrus SASL library are found at
configure time, otherwise see the --with-openssl and --with-sasl
flags passed to configure).
perl_access:
A path to a perl script for dynamically generating an access group.
If an auth group matches successfully and contains a perl_access
parameter, then the argument perl script will be used to create an
access group. This group will then determine the access rights of
the client, overriding any access groups in readers.conf. If and
only if a sucessful auth group contains the perl_access parameter,
readers.conf access groups are ignored and the client's rights are
instead determined dynamically. This parameter is only valid if
INN is compiled with Perl support (--with-perl passed to
configure). More information may be found in the file
doc/hook-perl.
python_access:
A Python script for dynamically generating an access group. If an
auth group matches successfully and contains a python_access
parameter, then the argument script (without its ".py" extension)
will be used to create an access group. This group will then
determine the access rights of the client, overriding any access
groups in readers.conf. If and only if a successful auth group
contains the python_access parameter, readers.conf access groups
are ignored and the client's rights are instead determined
dynamically. This parameter is only valid if INN is compiled with
Python support (--with-python passed to configure). More
information may be found in the file doc/hook-python.
python_dynamic:
A Python script for applying access control dynamically on a per
newsgroup basis. If an auth group matches successfully and
contains a python_dynamic parameter, then the argument script
(without its ".py" extension) will be used to determine the clients
rights each time the user attempts to view a newsgroup, or read or
post an article. Access rights as determined by python_dynamic
override the values of access group parameters such as newsgroups,
read and post. This parameter is only valid if INN is compiled
with Python support (--with-python passed to configure). More
information may be found in the file doc/hook-python.
ACCESS GROUP PARAMETERS
users:
The privileges given by this access group apply to any user
identity which matches this comma-separated list of wildmat
patterns. If this parameter isn't given, the access group applies
to all users (and is essentially equivalent to "users: *").
newsgroups:
Users that match this access group are allowed to read and post to
all newsgroups matching this comma-separated list of wildmat
patterns. The empty string is equivalent to "newsgroups: *"; if
this parameter is missing, the connection will be rejected (unless
read: and/or post: are used instead, see below).
read:
Like the newsgroups: parameter, but the client is only given
permission to read the matching newsgroups. This parameter is
often used with post: (below) to specify some read-only groups; it
cannot be used in the same access group with a newsgroups:
parameter. (If read: is used and post: is missing, the client will
have only read-only access.)
post:
Like the newsgroups: parameter, but the client is only given
permission to post to the matching newsgroups. This parameter is
often used with read: (above) to define the patterns for reading
and posting separately (usually to give the user permission to read
more newsgroups than they're permitted to post to). It cannot be
used in the same access group with a newsgroups: parameter.
access:
A set of letters specifying the permissions granted to the client.
The letters are chosen from the following set:
R The client may read articles.
P The client may post articles.
I The client may inject articles with IHAVE. Note that in order
to inject articles with the IHAVE command, the user must also
have POST permission (the "P" option). Articles injected with
IHAVE are treated as though they were injected with POST, that
is to say such articles must not have been previously injected
(they must not contain headers like Injection-Info:).
A The client may post articles with Approved: headers (in other
words, may approve articles for moderated newsgroups). By
default, this is not allowed.
N The client may use the NEWNEWS command, overriding the global
setting.
L The client may post to newsgroups that are set to disallow local
posting (status fields "j", "n" and "x" in the active(5) file).
Note that if this parameter is given, allownewnews in inn.conf is
ignored for connections matching this access group and the ability
of the client to use NEWNEWS is entirely determined by the presence
of "N" in the access string. If you want to support NEWNEWS, make
sure to include "N" in the access string when you use this
parameter.
Note that if this parameter is given and "R" isn't present in the
access string, the client cannot read regardless of newsgroups: or
read: parameters. Similarly, if this parameter is given and "P"
isn't present, the client cannot post. This use of access: is
deprecated and confusing; it's strongly recommended that if the
access: parameter is used, "R" and "P" always be included in the
access string and newsgroups:, read:, and post: be used to control
access. (To grant read access but no posting access, one can have
just a read: parameter and no post: parameter.)
key:
If this parameter is present, this access group is only considered
when finding privileges for users matching auth groups with this
same key: parameter.
reject_with:
If this parameter is present, a client matching this block will be
disconnected with a "Permission denied" message containing the
contents (a "reason" string) of this parameter. Some newsreaders
will then display the reason to the user.
max_rate:
If this parameter is present (and nonzero), it is used for nnrpd's
rate-limiting code. The client will only be able to download at
this speed (in bytes/second). Note that if an encryption layer is
being used, limiting is applied to the pre-encryption datastream.
localtime:
If a Date: or an Injection-Date: header field is not included in a
posted article, nnrpd(8) normally adds these header fields in UTC.
If this is set to true, the Date: header field will be formatted in
local time instead. (The Injection-Date: header field will remain
in UTC, though.) This is a boolean value and the default is false.
This parameter permits to handle a relatively unusual corner case.
It is mostly a tool for people who want to disclose their local
time zone (it can be useful information in certain types of
discussions), but whose clients don't for some reason, and who can
arrange for the server to be in the same time zone as the client.
newsmaster:
Used as the contact address in the help message returned by
nnrpd(8), if the virtualhost: parameter is set to true.
strippath:
If set to true, any Path: header provided by a user in a post is
stripped rather than used as the beginning of the Path: header of
the article. This is a boolean value and the default is false.
perlfilter:
If set to false, posts made by these users do not pass through the
Perl filter even if it is otherwise enabled. This is a boolean
value and the default is true.
pythonfilter:
If set to false, posts made by these users do not pass through the
Python filter even if it is otherwise enabled. This is a boolean
value and the default is true.
virtualhost:
Set this parameter to true in order to make nnrpd behave as if it
is running on a server with a different name than it actually is.
If you set this parameter to true, you must also set either
pathhost: or domain: in the relevant access group in readers.conf
to something different than is set in inn.conf. All articles
displayed to clients will then have their Path: and Xref: headers
altered to appear to be from the server named in pathhost: or
domain: (whichever is set), and posted articles will use that
server name in the Path:, Message-ID:, and Injection-Info: headers.
Note that setting this parameter requires the server modify all
posts before presenting them to the client and therefore may
decrease performance slightly.
In addition, all of the following parameters are valid in access groups
and override the global setting in inn.conf. See inn.conf(5) for the
descriptions of these parameters:
addinjectiondate, addinjectionpostingaccount, addinjectionpostinghost,
backoff_auth, backoff_db, backoff_k, backoff_postfast, backoff_postslow,
backoff_trigger, checkincludedtext, clienttimeout, complaints, domain,
fromhost, localmaxartsize, moderatormailer, nnrpdauthsender, nnrpdcheckart,
nnrpdoverstats, nnrpdposthost, nnrpdpostport, organization, pathhost,
readertrack, spoolfirst, strippostcc.
SUMMARY
Here's a basic summary of what happens when a client connects:
* All auth groups are scanned and the ones that don't match the client
(due to hosts, localaddress, require_ssl, etc.) are eliminated.
* The remaining auth groups are scanned from the last to the first, and
an attempt is made to apply it to the current connection. This means
running res: programs, if any, and otherwise applying default:. The
first auth group (starting from the bottom) to return a valid user is
kept as the active auth group.
* If no auth groups yield a valid user (none have default: parameters
or successful res: programs) but some of the auth groups have auth:
lines (indicating a possibility that the user can authenticate and
then obtain permissions), the connection is considered to have no
valid auth group (which means that the access groups are ignored
completely) but the connection isn't closed. Instead, 480 is
returned for everything until the user authenticates.
* When the user authenticates, the auth groups are rescanned, and only
the matching ones which contain at least one auth, perl_auth, or
python_auth line are considered. These auth groups are scanned from
the last to the first, running auth: programs and perl_auth: or
python_auth: scripts. The first auth group (starting from the
bottom) to return a valid user is kept as the active auth group.
* Regardless of how an auth group is established, as soon as one is,
that auth group is used to assign a user identity by taking the
result of the successful res, auth, perl_auth, or python_auth line
(or the default: if necessary), and appending the default-domain if
necessary. (If the perl_access: or python_access: parameter is
present, see below.)
* Finally, an access group is selected by scanning the access groups
from bottom up and finding the first match. (If the established auth
group contained a perl_access: or python_access line, the dynamically
generated access group returned by the script is used instead.) User
permissions are granted based on the established access group.
EXAMPLES
Probably the simplest useful example of a complete readers.conf, this
gives permissions to read and post to all groups to any connections
from the "example.com" domain, and no privileges for anyone connecting
elsewhere:
auth example.com {
hosts: "*.example.com, example.com"
default: "<EXAMPLE>"
}
access full {
users: "<EXAMPLE>"
newsgroups: *
}
Note that the above access realm could also be written without the
users: key, in which case it applies to any user identity (though in
this example, the user identity that will be assigned to all matching
connections is "<EXAMPLE>"). It is however recommended to keep an
explicit users: key so as to better view to whom the access block
applies.
As the only available auth realm only matches hosts in the
"example.com" domain, any connections from other hosts will be rejected
immediately.
If you have some systems that should only have read-only access to the
server, you can modify the example above slightly by adding an
additional auth and access group:
auth lab {
hosts: "*.lab.example.com"
default: <LAB>
}
access lab {
users: <LAB>
read: *
}
If those are put in the file after the above example, they'll take
precedence (because they're later in the file) for any user coming from
a machine in the lab.example.com domain, everyone will only have read
access, not posting access.
Here's a similar example for a news server that accepts connections
from anywhere but requires the user to specify a username and password.
The username and password are first checked against an external
database of usernames and passwords, and then against the system shadow
password file:
auth all {
auth: "ckpasswd -d <pathdb in inn.conf>/newsusers"
auth: "ckpasswd -s"
}
access full {
users: *
newsgroups: *
}
When the user first connects, there are no res: keys and no default, so
they don't receive any valid identity and the connection won't match
any access groups (even ones with "users: *"). Such users receive
nothing but authentication-required responses from nnrpd until they
authenticate.
If they then later authenticate, the username and password are checked
first by running ckpasswd with the -d option for an external dbm file
of encrypted passwords, and then with the -s option to check the shadow
password database (note that this option may require ckpasswd to be
setgid to a shadow group, and there are security considerations; see
ckpasswd(8) for details). If both of those fail, the user will
continue to have no identity; otherwise, an identity will be assigned
(usually the supplied username, perhaps with a domain appended,
although an authenticator technically can provide a completely
different username for the identity), and the access group will match,
giving full access.
It may be educational to consider how to combine the above examples;
general groups always go first. The order of the auth groups actually
doesn't matter, since the "hosts: example.com" one only matches
connections before username/password is sent, and the "auth: ckpasswd"
one only matches after; order would matter if either group applied to
both cases. The order of the access groups in this case does matter,
provided the newsgroups: lines differ; the access group with no users:
line needs to be first, with the "users: <LOCAL>" group after.
Here's an example of another common case: a server that only allows
connections from a local domain and has an additional hierarchy that's
password-restricted.
auth "example.com" {
hosts: "*.example.com"
auth: "ckpasswd -d <pathdb in inn.conf>/newsusers"
default: "anonymous"
}
access regular {
newsgroups: "*,!example.restricted.*"
}
access full {
users: "*,!anonymous"
newsgroups: *
}
In this example, unauthenticated users get the identity "anonymous",
which matches only the first access group and hence doesn't get access
to the example.restricted.* hierarchy. Anyone who authenticates using
a password in the newsusers file gets full access to all groups.
However, note that the only authentication block is limited to
hostnames in the example.com domain; connections outside of that domain
will never be allowed access or an opportunity to authenticate.
Here's a very complicated example. This is for an organization that
has an internal hierarchy "example.*" only available to local shell
users, who are on machines where identd can be trusted. Dialup users
must provide a username and password, which is then checked against
RADIUS. Remote users have to use a username and password that's
checked against a database on the news server. Finally, the admin
staff (users "joe" and "jane") can post anywhere (including the
"example.admin.*" groups that are read-only for everyone else), and are
exempted from the Perl filter. For an additional twist, posts from
dialup users have their Sender: header replaced by their authenticated
identity.
Since this organization has some internal moderated newsgroups, the
admin staff can also post messages with Approved: headers, but other
users cannot.
auth default {
auth: "ckpasswd -f <pathdb in inn.conf>/newsusers"
default: <FAIL>
default-domain: example.com
}
auth shell {
hosts: *.shell.example.com
res: ident
auth: "ckpasswd -s"
default: <FAIL>
default-domain: shell.example.com
}
auth dialup {
hosts: *.dialup.example.com
auth: radius
default: <FAIL>
default-domain: dialup.example.com
}
access shell {
users: *@shell.example.com
read: *
post: "*, !example.admin.*"
}
access dialup {
users: *@dialup.example.com
newsgroups: *,!example.*
nnrpdauthsender: true
}
access other {
users: "*@example.com, !<FAIL>@example.com"
newsgroups: *,!example.*
}
access fail {
users: "<FAIL>@*"
newsgroups: !*
}
access admin {
users: "joe@*,jane@*"
newsgroups: *
access: "RPA"
perlfilter: false
}
Note the use of different domains to separate dialup from shell users
easily. Another way to do that would be with key: parameters, but this
way provides slightly more intuitive identity strings. Note also that
the fail access group catches not only failing connections from
external users but also failed authentication of shell and dialup users
and dialup users before they've authenticated. The identity string
given for, say, dialup users before RADIUS authentication has been
attempted matches both the dialup access group and the fail access
group, since it's "<FAIL>@dialup.example.com", but the fail group is
last so it takes precedence.
The shell auth group has an auth: parameter so that users joe and jane
can, if they choose, use username and password authentication to gain
their special privileges even if they're logged on as a different user
on the shell machines (or if ident isn't working). When they first
connect, they'd have the default access for that user, but they could
then send AUTHINFO USER and AUTHINFO PASS in order to get their
extended access.
Also note that if the users joe and jane are using their own accounts,
they get their special privileges regardless of how they connect,
whether the dialups, the shell machines, or even externally with a
username and password.
Finally, here's a very simple example of a configuration for a public
server for a particular hierarchy.
auth default {
hosts: *
default: <PUBLIC>
}
access default {
users: <PUBLIC>
newsgroups: example.*
}
Notice that clients aren't allowed to read any other groups; this keeps
them from getting access to administrative groups or reading control
messages, just as a precaution. When running a public server like
this, be aware that many public hierarchies will later be pulled down
and reinjected into the main Usenet, so it's highly recommended that
you also run a Perl or Python filter to reject any messages crossposted
out of your local hierarchy and any messages containing a Supersedes:
header. This will keep messages posted to your public hierarchy from
hurting any of the rest of Usenet if they leak out.
SECURITY CONSIDERATIONS
In general, separate passwords should be used for NNTP wherever
possible; the NNTP protocol itself does not protect passwords from
casual interception, and many implementations (including this one) do
not "lock out" accounts or otherwise discourage password-guessing
attacks. So it is best to ensure that a compromised password has
minimal effects.
Authentication using the AUTHINFO USER/PASS commands passes unencrypted
over the network. Extreme caution should therefore be used especially
with system passwords (e.g. "auth: ckpasswd -s"). Passwords can be
protected by using NNTP over TLS/SSL or through ssh tunnels, and this
usage can be enforced by a well-considered server configuration that
only permits certain auth groups to be applied in certain cases. One
can also authenticate using a strong SASL mechanism. Here are some
ideas:
* To restrict connections on the standard NNTP port (119) to use an
encryption layer for some (or all) of the auth groups to match, use
the require_ssl parameter. Note that a client can use STARTTLS to
negotiate an encrypted TLS connection. A secure layer can also be
negotiated during authentication via AUTHINFO SASL.
* If you consider your local network (but not the internet) secure,
have some auth groups with a restrictive hosts: parameter; they
would go above, with ones having global applicability below.
* Consider running nnrpd with the -S flag (either also with -D, or
out of "super-server" like inetd) on the NNTPS port (563) for
clients that support TLS/SSL. See nnrpd(8) for more details about
how to configure that. You can use the require_ssl parameter or
the -c flag to specify an alternate readers.conf file if you want a
substantially different configuration for this case.
* If you want to restrict an auth group to only match loopback
connections (for users running newsreaders on localhost or
connecting via an ssh tunnel), use the localaddress: parameter.
HISTORY
Written by Aidan Cully <aidan@panix.com> for InterNetNews. Substantially expanded by Russ Allbery <eagle@eyrie.org>. $Id: readers.conf.pod 9977 2015-12-10 20:49:04Z iulius $
SEE ALSO
auth_krb5(8), ckpasswd(8), inn.conf(5), innd(8), newsfeeds(5), nnrpd(8), uwildmat(3).
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