175 lines
6.6 KiB
Groff
175 lines
6.6 KiB
Groff
.\" $NetBSD: hosts_options.5,v 1.2 1998/01/05 23:54:05 perry Exp $
|
|
.\"
|
|
.TH HOSTS_OPTIONS 5
|
|
.SH NAME
|
|
hosts_options \- host access control language extensions
|
|
.SH DESCRIPTION
|
|
This document describes optional extensions to the language described
|
|
in the hosts_access(5) document. The extensions are enabled at program
|
|
build time. For example, by editing the Makefile and turning on the
|
|
PROCESS_OPTIONS compile-time option.
|
|
.PP
|
|
The extensible language uses the following format:
|
|
.sp
|
|
.ti +3
|
|
daemon_list : client_list : option : option ...
|
|
.PP
|
|
The first two fields are described in the hosts_access(5) manual page.
|
|
The remainder of the rules is a list of zero or more options. Any ":"
|
|
characters within options should be protected with a backslash.
|
|
.PP
|
|
An option is of the form "keyword" or "keyword value". Options are
|
|
processed in the specified order. Some options are subjected to
|
|
%<letter> substitutions. For the sake of backwards compatibility with
|
|
earlier versions, an "=" is permitted between keyword and value.
|
|
.SH LOGGING
|
|
.IP "severity mail.info"
|
|
.IP "severity notice"
|
|
Change the severity level at which the event will be logged. Facility
|
|
names (such as mail) are optional, and are not supported on systems
|
|
with older syslog implementations. The severity option can be used
|
|
to emphasize or to ignore specific events.
|
|
.SH ACCESS CONTROL
|
|
.IP "allow"
|
|
.IP "deny"
|
|
Grant (deny) service. These options must appear at the end of a rule.
|
|
.PP
|
|
The \fIallow\fR and \fIdeny\fR keywords make it possible to keep all
|
|
access control rules within a single file, for example in the
|
|
\fIhosts.allow\fR file.
|
|
.sp
|
|
To permit access from specific hosts only:
|
|
.sp
|
|
.ne 2
|
|
.ti +3
|
|
ALL: .friendly.domain: ALLOW
|
|
.ti +3
|
|
ALL: ALL: DENY
|
|
.sp
|
|
To permit access from all hosts except a few trouble makers:
|
|
.sp
|
|
.ne 2
|
|
.ti +3
|
|
ALL: .bad.domain: DENY
|
|
.ti +3
|
|
ALL: ALL: ALLOW
|
|
.sp
|
|
Notice the leading dot on the domain name patterns.
|
|
.SH RUNNING OTHER COMMANDS
|
|
.IP "spawn shell_command"
|
|
Execute, in a child process, the specified shell command, after
|
|
performing the %<letter> expansions described in the hosts_access(5)
|
|
manual page. The command is executed with stdin, stdout and stderr
|
|
connected to the null device, so that it won\'t mess up the
|
|
conversation with the client host. Example:
|
|
.sp
|
|
.nf
|
|
.ti +3
|
|
spawn (/some/where/safe_finger -l @%h | /usr/ucb/mail root) &
|
|
.fi
|
|
.sp
|
|
executes, in a background child process, the shell command "safe_finger
|
|
-l @%h | mail root" after replacing %h by the name or address of the
|
|
remote host.
|
|
.sp
|
|
The example uses the "safe_finger" command instead of the regular
|
|
"finger" command, to limit possible damage from data sent by the finger
|
|
server. The "safe_finger" command is part of the daemon wrapper
|
|
package; it is a wrapper around the regular finger command that filters
|
|
the data sent by the remote host.
|
|
.IP "twist shell_command"
|
|
Replace the current process by an instance of the specified shell
|
|
command, after performing the %<letter> expansions described in the
|
|
hosts_access(5) manual page. Stdin, stdout and stderr are connected to
|
|
the client process. This option must appear at the end of a rule.
|
|
.sp
|
|
To send a customized bounce message to the client instead of
|
|
running the real ftp daemon:
|
|
.sp
|
|
.nf
|
|
.ti +3
|
|
in.ftpd : ... : twist /bin/echo 421 Some bounce message
|
|
.fi
|
|
.sp
|
|
For an alternative way to talk to client processes, see the
|
|
\fIbanners\fR option below.
|
|
.sp
|
|
To run /some/other/in.telnetd without polluting its command-line
|
|
array or its process environment:
|
|
.sp
|
|
.nf
|
|
.ti +3
|
|
in.telnetd : ... : twist PATH=/some/other; exec in.telnetd
|
|
.fi
|
|
.sp
|
|
Warning: in case of UDP services, do not twist to commands that use
|
|
the standard I/O or the read(2)/write(2) routines to communicate with
|
|
the client process; UDP requires other I/O primitives.
|
|
.SH NETWORK OPTIONS
|
|
.IP "keepalive"
|
|
Causes the server to periodically send a message to the client. The
|
|
connection is considered broken when the client does not respond. The
|
|
keepalive option can be useful when users turn off their machine while
|
|
it is still connected to a server. The keepalive option is not useful
|
|
for datagram (UDP) services.
|
|
.IP "linger number_of_seconds"
|
|
Specifies how long the kernel will try to deliver not-yet delivered
|
|
data after the server process closes a connection.
|
|
.SH USERNAME LOOKUP
|
|
.IP "rfc931 [ timeout_in_seconds ]"
|
|
Look up the client user name with the RFC 931 (TAP, IDENT, RFC 1413)
|
|
protocol. This option is silently ignored in case of services based on
|
|
transports other than TCP. It requires that the client system runs an
|
|
RFC 931 (IDENT, etc.) -compliant daemon, and may cause noticeable
|
|
delays with connections from non-UNIX clients. The timeout period is
|
|
optional. If no timeout is specified a compile-time defined default
|
|
value is taken.
|
|
.SH MISCELLANEOUS
|
|
.IP "banners /some/directory"
|
|
Look for a file in `/some/directory' with the same name as the daemon
|
|
process (for example in.telnetd for the telnet service), and copy its
|
|
contents to the client. Newline characters are replaced by
|
|
carriage-return newline, and %<letter> sequences are expanded (see
|
|
the hosts_access(5) manual page).
|
|
.sp
|
|
The tcp wrappers source code distribution provides a sample makefile
|
|
(Banners.Makefile) for convenient banner maintenance.
|
|
.sp
|
|
Warning: banners are supported for connection-oriented (TCP) network
|
|
services only.
|
|
.IP "nice [ number ]"
|
|
Change the nice value of the process (default 10). Specify a positive
|
|
value to spend more CPU resources on other processes.
|
|
.IP "setenv name value"
|
|
Place a (name, value) pair into the process environment. The value is
|
|
subjected to %<letter> expansions and may contain whitespace (but
|
|
leading and trailing blanks are stripped off).
|
|
.sp
|
|
Warning: many network daemons reset their environment before spawning a
|
|
login or shell process.
|
|
.IP "umask 022"
|
|
Like the umask command that is built into the shell. An umask of 022
|
|
prevents the creation of files with group and world write permission.
|
|
The umask argument should be an octal number.
|
|
.IP "user nobody"
|
|
.IP "user nobody.kmem"
|
|
Assume the privileges of the "nobody" userid (or user "nobody", group
|
|
"kmem"). The first form is useful with inetd implementations that run
|
|
all services with root privilege. The second form is useful for
|
|
services that need special group privileges only.
|
|
.SH DIAGNOSTICS
|
|
When a syntax error is found in an access control rule, the error
|
|
is reported to the syslog daemon; further options will be ignored,
|
|
and service is denied.
|
|
.SH SEE ALSO
|
|
hosts_access(5), the default access control language
|
|
.SH AUTHOR
|
|
.na
|
|
.nf
|
|
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_options.5 1.10 94/12/28 17:42:28
|