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99 lines
3.0 KiB
Groff
99 lines
3.0 KiB
Groff
.\" Copyright (c) 1998-2004 Sendmail, Inc. and its suppliers.
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.\" All rights reserved.
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.\" Copyright (c) 1993 Eric P. Allman. All rights reserved.
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.\" Copyright (c) 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" By using this file, you agree to the terms and conditions set
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.\" forth in the LICENSE file which can be found at the top level of
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.\" the sendmail distribution.
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.\"
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.\"
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.\" $Id: smrsh.8,v 8.22 2004/08/06 03:55:35 gshapiro Exp $
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.\"
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.TH SMRSH 8 "$Date: 2004/08/06 03:55:35 $"
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.SH NAME
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smrsh \- restricted shell for sendmail
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.SH SYNOPSIS
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.B smrsh
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.B \-c
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command
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.SH DESCRIPTION
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The
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.I smrsh
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program is intended as a replacement for
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.I sh
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for use in the ``prog'' mailer in
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.IR sendmail (8)
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configuration files.
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It sharply limits the commands that can be run using the
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``|program'' syntax of
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.I sendmail
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in order to improve the over all security of your system.
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Briefly, even if a ``bad guy'' can get sendmail to run a program
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without going through an alias or forward file,
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.I smrsh
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limits the set of programs that he or she can execute.
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.PP
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Briefly,
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.I smrsh
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limits programs to be in a single directory,
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by default
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/usr/libexec/sm.bin,
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allowing the system administrator to choose the set of acceptable commands,
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and to the shell builtin commands ``exec'', ``exit'', and ``echo''.
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It also rejects any commands with the characters
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`\`', `<', `>', `;', `$', `(', `)', `\er' (carriage return),
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or `\en' (newline)
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on the command line to prevent ``end run'' attacks.
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It allows ``||'' and ``&&'' to enable commands like:
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``"|exec /usr/local/bin/filter || exit 75"''
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.PP
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Initial pathnames on programs are stripped,
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so forwarding to ``/usr/bin/vacation'',
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``/home/server/mydir/bin/vacation'',
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and
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``vacation''
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all actually forward to
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``/usr/libexec/sm.bin/vacation''.
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.PP
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System administrators should be conservative about populating
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the sm.bin directory.
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For example, a reasonable additions is
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.IR vacation (1),
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and the like.
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No matter how brow-beaten you may be,
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never include any shell or shell-like program
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(such as
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.IR perl (1))
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in the
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sm.bin
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directory.
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Note that this does not restrict the use of shell or perl scripts
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in the sm.bin directory (using the ``#!'' syntax);
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it simply disallows execution of arbitrary programs.
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Also, including mail filtering programs such as
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.IR procmail (1)
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is a very bad idea.
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.IR procmail (1)
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allows users to run arbitrary programs in their
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.IR procmailrc (5).
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.SH COMPILATION
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Compilation should be trivial on most systems.
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You may need to use \-DSMRSH_PATH=\e"\fIpath\fP\e"
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to adjust the default search path
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(defaults to ``/bin:/usr/bin'')
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and/or \-DSMRSH_CMDDIR=\e"\fIdir\fP\e"
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to change the default program directory
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(defaults to ``/usr/libexec/sm.bin'').
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.SH FILES
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/usr/adm/sm.bin \- default directory for restricted programs on most OSs
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.PP
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/var/adm/sm.bin \- directory for restricted programs on HP UX and Solaris
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.PP
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/usr/libexec/sm.bin \- directory for restricted programs on FreeBSD (>= 3.3) and DragonFly BSD
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.SH SEE ALSO
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sendmail(8)
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.\" $FreeBSD$
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