149 lines
4.9 KiB
Groff
149 lines
4.9 KiB
Groff
.\" $NetBSD: rexecd.8,v 1.13 2017/07/03 21:35:49 wiz Exp $
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.\"
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.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" from: @(#)rexecd.8 8.3 (Berkeley) 6/1/94
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.\"
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.Dd June 1, 1994
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.Dt REXECD 8
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.Os
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.Sh NAME
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.Nm rexecd
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.Nd remote execution server
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.Sh SYNOPSIS
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.Nm
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.Sh DESCRIPTION
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.Nm
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is the server for the
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.Xr rexec 3
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routine.
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The server provides remote execution facilities with authentication
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based on user names and passwords.
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.Pp
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.Nm
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listens for service requests at the port indicated in
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the ``exec'' service specification; see
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.Xr services 5 .
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When a service request is received the following protocol
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is initiated:
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.Bl -enum
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.It
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The server reads characters from the socket up to a NUL
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.Pq Ql \e0
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byte.
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The resultant string is interpreted as an
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.Tn ASCII
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number, base 10.
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.It
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If the number received in step 1 is non-zero,
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it is interpreted as the port number of a secondary
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stream to be used for the
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.Em stderr .
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A second connection is then created to the specified
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port on the client's machine.
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.It
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A NUL terminated user name of at most 16 characters
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is retrieved on the initial socket.
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.It
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A NUL terminated, unencrypted password of at most
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16 characters is retrieved on the initial socket.
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.It
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A NUL terminated command to be passed to a
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shell is retrieved on the initial socket.
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The length of the command is limited by the upper bound on the size
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of the system's argument list.
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.It
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.Nm
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then validates the user as is done at login time and, if the
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authentication was successful, changes to the user's home directory,
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and establishes the user and group protections of the user.
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If any of these steps fail the connection is
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aborted with a diagnostic message returned.
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.It
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A NUL byte is returned on the initial socket and the command line
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is passed to the normal login shell of the user.
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The shell inherits the network connections established by
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.Nm .
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.El
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.Sh DIAGNOSTICS
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Except for the last one listed below,
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all diagnostic messages are returned on the initial socket,
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after which any network connections are closed.
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An error is indicated by a leading byte with a value of
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1 (0 is returned in step 7 above upon successful completion
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of all the steps prior to the command execution).
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.Pp
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.Bl -tag -width Ds
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.It Sy username too long
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The name is
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longer than 16 characters.
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.It Sy password too long
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The password is longer than 16 characters.
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.It Sy command too long
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The command line passed exceeds the size of the argument
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list (as configured into the system).
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.It Sy Login incorrect.
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No password file entry for the user name existed.
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.It Sy Password incorrect.
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The wrong password was supplied.
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.It Sy \&No remote directory.
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The
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.Xr chdir 2
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to the home directory failed.
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.It Sy Try again.
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A
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.Xr fork 2
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by the server failed.
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.It Sy <shellname>: ...
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The user's login shell could not be started.
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This message is returned
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on the connection associated with the
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.Em stderr ,
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and is not preceded by a flag byte.
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.El
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.Sh SEE ALSO
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.Xr rexec 3
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.Sh HISTORY
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The
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.Nm
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command appeared in
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.Bx 4.2 .
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.Sh BUGS
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Indicating ``Login incorrect'' as opposed to ``Password incorrect''
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is a security breach which allows people to probe a system for users
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with null passwords.
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.Pp
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A facility to allow all data and password exchanges to be encrypted should be
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present.
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.Sh SECURITY CONSIDERATIONS
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As the passwords exchanged by the client and
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.Nm
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are not encrypted, it is
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.Em strongly
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recommended that this service is not enabled.
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