OpenSolaris_b135/cmd/tcpd/tcpd.8

.TH TCPD 8
.SH NAME
tcpd \- access control facility for internet services
.SH DESCRIPTION
.PP
The \fItcpd\fR program can be set up to monitor incoming requests for
\fItelnet\fR, \fIfinger\fR, \fIftp\fR, \fIexec\fR, \fIrsh\fR,
\fIrlogin\fR, \fItftp\fR, \fItalk\fR, \fIcomsat\fR and other services
that have a one-to-one mapping onto executable files.
.PP
The program supports both 4.3BSD-style sockets and System V.4-style
TLI.  Functionality may be limited when the protocol underneath TLI is
not an internet protocol.
.PP
Operation is as follows: whenever a request for service arrives, the
\fIinetd\fP daemon is tricked into running the \fItcpd\fP program
instead of the desired server. \fItcpd\fP logs the request and does
some additional checks. When all is well, \fItcpd\fP runs the
appropriate server program and goes away.
.PP
Optional features are: pattern-based access control, client username
lookups with the RFC 931 etc. protocol, protection against hosts that
pretend to have someone elses host name, and protection against hosts
that pretend to have someone elses network address.
.SH LOGGING
Connections that are monitored by
.I tcpd
are reported through the \fIsyslog\fR(3) facility. Each record contains
a time stamp, the client host name and the name of the requested
service.  The information can be useful to detect unwanted activities,
especially when logfile information from several hosts is merged.
.PP
In order to find out where your logs are going, examine the syslog
configuration file, usually /etc/syslog.conf.
.SH ACCESS CONTROL
Optionally,
.I tcpd
supports a simple form of access control that is based on pattern
matching.  The access-control software provides hooks for the execution
of shell commands when a pattern fires.  For details, see the
\fIhosts_access\fR(5) manual page.
.SH HOST NAME VERIFICATION
The authentication scheme of some protocols (\fIrlogin, rsh\fR) relies
on host names. Some implementations believe the host name that they get
from any random name server; other implementations are more careful but
use a flawed algorithm.
.PP
.I tcpd
verifies the client host name that is returned by the address->name DNS
server by looking at the host name and address that are returned by the
name->address DNS server.  If any discrepancy is detected,
.I tcpd
concludes that it is dealing with a host that pretends to have someone
elses host name.
.PP
If the sources are compiled with -DPARANOID,
.I tcpd
will drop the connection in case of a host name/address mismatch.
Otherwise, the hostname can be matched with the \fIPARANOID\fR wildcard,
after which suitable action can be taken.
.SH HOST ADDRESS SPOOFING
Optionally,
.I tcpd
disables source-routing socket options on every connection that it
deals with. This will take care of most attacks from hosts that pretend
to have an address that belongs to someone elses network. UDP services
do not benefit from this protection. This feature must be turned on
at compile time.
.SH RFC 931
When RFC 931 etc. lookups are enabled (compile-time option) \fItcpd\fR
will attempt to establish the name of the client user. This will
succeed only if the client host runs an RFC 931-compliant daemon.
Client user name lookups will not work for datagram-oriented
connections, and may cause noticeable delays in the case of connections
from PCs.

.SH EXAMPLE
In order to monitor access to the \fIfinger\fR service, run the following
command to enable the tcp_wrapper :
.nf
.sp
.ti +5
inetadm -m network/finger tcp_wrapper=TRUE
.sp
.fi
.PP
The example assumes that the network/finger service hasn't been removed from
your system.
.PP
Similar changes will be needed for the other services that are to be
covered by \fItcpd\fR. In case a (non-standard) daemon does not exist as a
service already, use \fIsmf(5)\fR to make it a service by creating a manifest,
and then enable tcp_wrappers for that service as shown in the example.

.SH BUGS
Some UDP (and RPC) daemons linger around for a while after they have
finished their work, in case another request comes in.
.PP
The program does not work with RPC services over TCP. The
only non-trivial service that is affected by this limitation is
\fIrexd\fR, which is used by the \fIon(1)\fR command. This is no great
loss.  On most systems, \fIrexd\fR is less secure than a wildcard in
/etc/hosts.equiv.
.PP
RPC broadcast requests (for example: \fIrwall, rup, rusers\fR) always
appear to come from the responding host. What happens is that the
client broadcasts the request to all \fIportmap\fR daemons on its
network; each \fIportmap\fR daemon forwards the request to a local
daemon. As far as the \fIrwall\fR etc.  daemons know, the request comes
from the local host.
.SH FILES
.PP
The default locations of the host access control tables are:
.PP
/etc/hosts.allow
.br
/etc/hosts.deny
.SH SEE ALSO
.na
.nf
hosts_access(5), format of the tcpd access control tables.
syslog.conf(5), format of the syslogd control file.
smf(5), service management facility.
.SH AUTHORS
.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
\" @(#) tcpd.8 1.5 96/02/21 16:39:16