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| 4 | SMRSH(8) SMRSH(8) |
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| 6 | |
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| 7 | NNAAMMEE |
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| 8 | smrsh - restricted shell for sendmail |
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| 9 | |
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| 10 | SSYYNNOOPPSSIISS |
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| 11 | ssmmrrsshh --cc command |
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| 12 | |
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| 13 | DDEESSCCRRIIPPTTIIOONN |
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| 14 | The _s_m_r_s_h program is intended as a replacement for _s_h for |
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| 15 | use in the ``prog'' mailer in _s_e_n_d_m_a_i_l(8) configuration |
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| 16 | files. It sharply limits the commands that can be run |
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| 17 | using the ``|program'' syntax of _s_e_n_d_m_a_i_l in order to |
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| 18 | improve the over all security of your system. Briefly, |
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| 19 | even if a ``bad guy'' can get sendmail to run a program |
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| 20 | without going through an alias or forward file, _s_m_r_s_h lim- |
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| 21 | its the set of programs that he or she can execute. |
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| 22 | |
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| 23 | Briefly, _s_m_r_s_h limits programs to be in a single direc- |
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| 24 | tory, by default /usr/adm/sm.bin, allowing the system |
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| 25 | administrator to choose the set of acceptable commands, |
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| 26 | and to the shell builtin commands ``exec'', ``exit'', and |
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| 27 | ``echo''. It also rejects any commands with the charac- |
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| 28 | ters ``', `<', `>', `;', `$', `(', `)', `\r' (carriage |
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| 29 | return), or `\n' (newline) on the command line to prevent |
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| 30 | ``end run'' attacks. It allows ``||'' and ``&&'' to |
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| 31 | enable commands like: ``"|exec /usr/local/bin/procmail -f- |
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| 32 | /etc/procmailrcs/user || exit 75"'' |
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| 33 | |
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| 34 | Initial pathnames on programs are stripped, so forwarding |
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| 35 | to ``/usr/ucb/vacation'', ``/usr/bin/vacation'', |
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| 36 | ``/home/server/mydir/bin/vacation'', and ``vacation'' all |
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| 37 | actually forward to ``/usr/adm/sm.bin/vacation''. |
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| 38 | |
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| 39 | System administrators should be conservative about popu- |
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| 40 | lating the sm.bin directory. Reasonable additions are |
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| 41 | _v_a_c_a_t_i_o_n(1), _p_r_o_c_m_a_i_l(1), and the like. No matter how |
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| 42 | brow-beaten you may be, never include any shell or shell- |
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| 43 | like program (such as _p_e_r_l(1)) in the sm.bin directory. |
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| 44 | Note that this does not restrict the use of shell or perl |
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| 45 | scripts in the sm.bin directory (using the ``#!'' syntax); |
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| 46 | it simply disallows execution of arbitrary programs. |
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| 47 | |
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| 48 | CCOOMMPPIILLAATTIIOONN |
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| 49 | Compilation should be trivial on most systems. You may |
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| 50 | need to use -DSMRSH_PATH=\"_p_a_t_h\" to adjust the default |
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| 51 | search path (defaults to ``/bin:/usr/bin:/usr/ucb'') |
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| 52 | and/or -DSMRSH_CMDDIR=\"_d_i_r\" to change the default pro- |
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| 53 | gram directory (defaults to ``/usr/adm/sm.bin''). |
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| 54 | |
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| 55 | FFIILLEESS |
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| 56 | /usr/adm/sm.bin - directory for restricted programs |
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| 57 | |
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| 58 | SSEEEE AALLSSOO |
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| 59 | sendmail(8) |
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| 64 | $Date: 2003-04-08 15:09:33 $ 1 |
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