Index of Section 8 Manual Pages
|Interix / SUA||smrsh.8||Interix / SUA
smrsh - restricted shell for sendmail
smrsh -c command
The smrsh program is intended as a replacement for sh for
use in the ``prog'' mailer in sendmail(8) configuration
files. It sharply limits the commands that can be run
using the ``|program'' syntax of sendmail in order to
improve the over all security of your system. Briefly,
even if a ``bad guy'' can get sendmail to run a program
without going through an alias or forward file, smrsh lim-
its the set of programs that he or she can execute.
Briefly, smrsh limits programs to be in a single direc-
tory, by default /usr/adm/sm.bin, allowing the system
administrator to choose the set of acceptable commands,
and to the shell builtin commands ``exec'', ``exit'', and
``echo''. It also rejects any commands with the charac-
ters ``', `<', `>', `;', `$', `(', `)', `\r' (carriage
return), or `\n' (newline) on the command line to prevent
``end run'' attacks. It allows ``||'' and ``&&'' to
enable commands like: ``"|exec /usr/local/bin/filter ||
Initial pathnames on programs are stripped, so forwarding
to ``/usr/ucb/vacation'', ``/usr/bin/vacation'',
``/home/server/mydir/bin/vacation'', and ``vacation'' all
actually forward to ``/usr/adm/sm.bin/vacation''.
System administrators should be conservative about popu-
lating the sm.bin directory. For example, a reasonable
additions is vacation(1), and the like. No matter how
brow-beaten you may be, never include any shell or shell-
like program (such as perl(1)) in the sm.bin directory.
Note that this does not restrict the use of shell or perl
scripts in the sm.bin directory (using the ``#!'' syntax);
it simply disallows execution of arbitrary programs.
Also, including mail filtering programs such as proc-
mail(1) is a very bad idea. procmail(1) allows users to
run arbitrary programs in their procmailrc(5).
Compilation should be trivial on most systems. You may
need to use -DSMRSH_PATH=\"path\" to adjust the default
search path (defaults to ``/bin:/usr/bin:/usr/ucb'')
and/or -DSMRSH_CMDDIR=\"dir\" to change the default pro-
gram directory (defaults to ``/usr/adm/sm.bin'').
/usr/adm/sm.bin - default directory for restricted pro-
grams on most OSs
/var/adm/sm.bin - directory for restricted programs on HP
UX and Solaris
/usr/libexec/sm.bin - directory for restricted programs on
FreeBSD (>= 3.3) and DragonFly BSD
$Date: 2004/08/06 03:55:35 $ SMRSH(8)