NAME

       hosts_access, hosts_ctl, request_init, request_set - access control library

SYNOPSIS

       #include <tcpd.h>

       extern int allow_severity;
       extern int deny_severity;

       struct request_info *request_init(request, key, value, ..., 0)
       struct request_info *request;

       struct request_info *request_set(request, key, value, ..., 0)
       struct request_info *request;

       void fromhost(request)
       struct request_info *request;

       int hosts_access(request)
       struct request_info *request;

       int hosts_ctl(daemon, client_name, client_addr, client_user)
       char *daemon;
       char *client_name;
       char *client_addr;
       char *client_user;

DESCRIPTION

       The  routines  described  in this document are part of the libwrap.a library. They implement a rule-based
       access control language with optional shell commands that are executed when a rule fires.

       request_init() initializes a structure with information about a client request. request_set() updates  an
       already  initialized request structure. Both functions take a variable-length list of key-value pairs and
       return their first argument.  The argument lists are terminated with a zero key value. All  string-valued
       arguments are copied. The expected keys (and corresponding value types) are:

       RQ_FILE (int)
              The file descriptor associated with the request.

       RQ_CLIENT_NAME (char *)
              The client host name.

       RQ_CLIENT_ADDR (char *)
              A printable representation of the client network address.

       RQ_CLIENT_SIN (struct sockaddr_in *)
              An  internal representation of the client network address and port.  The contents of the structure
              are not copied.

       RQ_SERVER_NAME (char *)
              The hostname associated with the server endpoint address.

       RQ_SERVER_ADDR (char *)
              A printable representation of the server endpoint address.

       RQ_SERVER_SIN (struct sockaddr_in *)
              An internal representation of the server endpoint address and port.  The contents of the structure
              are not copied.

       RQ_DAEMON (char *)
              The name of the daemon process running on the server host.

       RQ_USER (char *)
              The name of the user on whose behalf the client host makes the request.

       hosts_access()  consults  the  access  control tables described in the hosts_access(5) manual page.  When
       internal endpoint information is available, host names and client user names are  looked  up  on  demand,
       using  the  request  structure  as  a  cache.   hosts_access()  returns  zero if access should be denied.
       fromhost() must be called before hosts_access().

       hosts_ctl() is a wrapper around the request_init()  and  hosts_access()  routines  with  a  perhaps  more
       convenient  interface (though it does not pass on enough information to support automated client username
       lookups).  The client host address, client host name and username arguments should contain valid data  or
       STRING_UNKNOWN.  hosts_ctl() returns zero if access should be denied.

       The  allow_severity  and  deny_severity  variables  determine  how  accepted and rejected requests may be
       logged. They must be provided by the caller and may be modified by rules in the access control tables.

DIAGNOSTICS

       Problems are reported via the syslog daemon.

SEE ALSO

       hosts_access(5), format of the access control tables.  hosts_options(5), optional extensions to the  base
       language.

FILES

       /etc/hosts.allow, /etc/hosts.deny, access control tables.

BUGS

       hosts_access()  uses  the  strtok()  library  function. This may interfere with other code that relies on
       strtok().

AUTHOR

       Wietse Venema (wietse@wzv.win.tue.nl)
       Department of Mathematics and Computing Science
       Eindhoven University of Technology
       Den Dolech 2, P.O. Box 513,
       5600 MB Eindhoven, The Netherlands

                                                                                                 HOSTS_ACCESS(3)