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.

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 paramenter 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 they're 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.

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.

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.

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.

For any connection from a host that matches that wildmat expression or netblock, <res-program> (the program given with the res: parameter, if present) is run to determine the identity of the user just from the connection information. If it fails, 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 is passed to <auth-program>, the value of the auth: parameter (if present). If this 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.

When matching auth groups, the last auth group in the file that matches a given connection or 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 that 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 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 checked. 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.

Also note in the above 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.

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
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 does not exist. A command line for a user resolver. The program executed must be located in pathbin/auth/resolv. 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, a username and password aren't used). An examples of a resolver would be a program that gets the username 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 in and the results of the first successful one will be used. A command line for a user authenticator. The program executed must be located in pathbin/auth/passwd. 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. 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: is appended after an "@" if set, or a full identity string containing an "@", in which case it will be used verbatim. 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.) If this parameter is present, any connection matching this auth group will have its privileges determined only by access groups containing a matching key parameter.

ACCESS GROUP PARAMETERS
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: *"). Users that match this access group are allowed to read and post to all newsgroups matching this comma-separated list of wildmat patterns. Like the newsgroups: parameter, but the client is only given permission to read the matching newsgroups. This parameter is often used with post: (below) and cannot be used in the same access group with a newsgroups: parameter. 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. A set of letters specifying the permissions granted to the client. The letters are chosen from the following set:
    The client may read articles. The client may post articles. The client may post articles with Approved: headers (in other words, may approve articles for moderated newsgroups). By default, this is not allowed. The client may use the NEWNEWS command, overriding the global setting. The client may post to newsgroups that are set to disallow local posting (mode "n" in the active(5) file).

    Note that if this parameter is given, allownewnews in inn.conf(5) 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.)
If this parameter is present, this access group is only considered when finding privileges for users matching auth groups with this same key: parameter. If a Date: header is not included in a posted article, nnrpd(8) normally adds a new Date: header in UTC. If this is set to true, the Date: header will be formatted in local time instead. This is a boolean value and the default is false. Used as the contact address in the help message returned by nnrpd(8) if the virtualhost: parameter is set to true. 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. 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. 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. If set to true, nnrpd(8) will behave as if it's running on a server with a different name. This affects the Path:, Message-ID:, and X-Trace: headers of posted articles, as well as the apparent Path: and Xref: headers of all articles read by the client. One of pathhost: or domain: must be set in the same access group if this parameter is set to true, and nnrpd(8) will act as if the server name is the value of pathhost:, or domain: if pathhost: isn't set or is set to the same value as in inn.conf(5). One of these parameters must be set to something different than that set in inn.conf.

In addition, all of the following parameters are valid in access groups and override the global setting in inn.conf(5). See inn.conf(5) for the descriptions of these parameters: addnntppostingdate, addnntppostinghost, 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, and 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 IP address are eliminated. Each remaining auth group is 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 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, all auth groups with auth: lines are then checked from the bottom up and the first one that returns a valid user is kept as the default auth group. Regardless of how an auth group is established, as soon as one is, the user permissions are granted by scanning the access groups from bottom up and finding the first match.

EXAMPLES
Here is 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 from anywhere else:

    auth example.com {
        hosts: "*.example.com, example.com"
        default: <LOCAL>
    }
    access full {
        newsgroups: *
    }
Note that the access realm has no users: key and therefore applies to any user identity. The only available auth realm only matches hosts in the example.com domain, though, so 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, and those users 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 is first checked against an external database of usernames and passwords, and then against the system shadow password file:

    auth all {
        auth: "ckpasswd -d /usr/local/news/db/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 ckpasswd may have to be setgid to a shadow group to use this option). If both of those fail, the user will continue to have no identity; otherwise, they will acquire some other identity string (whatever username they specified, since the password was valid) and the access group will match, giving them full access.

Finally, 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 have to use 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.

    auth default {
        auth: "ckpasswd -f /usr/local/news/db/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: *
        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 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 (or AUTHINFO SIMPLE) and 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.

HISTORY
Written by Aidan Cully <aidan@panix.com> for InterNetNews. Substantially expanded by Russ Allbery <rra@stanford.edu>.

$Id: readers.conf.5,v 1.5.2.8 2001/03/03 07:57:56 rra Exp $

SEE ALSO
inn.conf(5), innd(8), newsfeeds(5), nnrpd(8), wildmat(3).