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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 the directory |
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| 24 | /usr/adm/sm.bin, allowing the system administrator to |
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| 25 | choose the set of acceptable commands. It also rejects |
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| 26 | any commands with the characters ``', `<', `>', `|', `;', |
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| 27 | `&', `$', `(', `)', `\r' (carriage return), or `\n' (new- |
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| 28 | line) on the command line to prevent ``end run'' attacks. |
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| 29 | |
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| 30 | Initial pathnames on programs are stripped, so forwarding |
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| 31 | to ``/usr/ucb/vacation'', ``/usr/bin/vacation'', |
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| 32 | ``/home/server/mydir/bin/vacation'', and ``vacation'' all |
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| 33 | actually forward to ``/usr/adm/sm.bin/vacation''. |
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| 34 | |
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| 35 | System administrators should be conservative about popu- |
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| 36 | lating /usr/adm/sm.bin. Reasonable additions are _v_a_c_a_- |
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| 37 | _t_i_o_n(1), _p_r_o_c_m_a_i_l(1), and the like. No matter how brow- |
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| 38 | beaten you may be, never include any shell or shell-like |
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| 39 | program (such as _p_e_r_l(1)) in the sm.bin directory. Note |
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| 40 | that this does not restrict the use of shell or perl |
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| 41 | scripts in the sm.bin directory (using the ``#!'' syntax); |
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| 42 | it simply disallows execution of arbitrary programs. |
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| 43 | |
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| 44 | CCOOMMPPIILLAATTIIOONN |
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| 45 | Compilation should be trivial on most systems. You may |
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| 46 | need to use -DPATH=\"_p_a_t_h\" to adjust the default search |
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| 47 | path (defaults to ``/bin:/usr/bin:/usr/ucb'') and/or |
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| 48 | -DCMDBIN=\"_d_i_r\" to change the default program directory |
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| 49 | (defaults to ``/usr/adm/sm.bin''). |
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| 50 | |
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| 51 | FFIILLEESS |
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| 52 | /usr/adm/sm.bin - directory for restricted programs |
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| 53 | |
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| 54 | SSEEEE AALLSSOO |
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| 55 | sendmail(8) |
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| 64 | 11/02/93 1 |
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