NAME

       restricted-ssh-commands - Restrict SSH users to a predefined set of commands

SYNOPSIS

       /usr/lib/restricted-ssh-commands [config]

DESCRIPTION

       restricted-ssh-commands is intended to be called by SSH to restrict a user to only run
       specific commands. A list of allowed regular expressions can be configured in
       /etc/restricted-ssh-commands/. The requested command has to match at least one regular
       expression.  Otherwise it will be rejected.

       restricted-ssh-commands is useful to grant restricted access via SSH to do only certain
       task. For example, it could allow a user to upload a Debian packages via scp and run
       reprepro processincoming.

       The optional config parameter is the name of the configuration inside
       /etc/restricted-ssh-commands/ that should be used. If config is omitted, the user name
       will be used.

USAGE

       Create a configuration file in /etc/restricted-ssh-commands/$config and add following line
       to ~/.ssh/authorized_keys to use it

           command="/usr/lib/restricted-ssh-commands",no-port-forwarding,\
           no-X11-forwarding,no-agent-forwarding,no-pty ssh-rsa [...]

       To enable debug output, set the RSC_VERBOSE environment variable to a nonzero value, e.g.
       by adding it to authorized_keys:

           command="RSC_VERBOSE=1 /usr/lib/restricted-ssh-commands"

EXIT STATUS

       restricted-ssh-commands will exit with the exit status from the called command if the
       command is allowed and therefore executed. If the command is rejected, restricted-ssh-
       commands will exit with one of the following exit codes.

       124     A configuration file was found and contains at least one regular expression, but
               the requested command does not match any of those regular expressions.

       125     The configuration file is missing or does not contain any regular expressions.
               Thus all commands are rejected.

EXAMPLES

       Imagine you have a Debian package repository on a host using reprepro and you want to
       allow package upload to it. Assuming the user is reprepro and the package configuration is
       stored in /srv/reprepro, you would create the configuration file
       /etc/restricted-ssh-commands/reprepro containing these three regular expressions:

           ^scp -p( -d)? -t( --)? /srv/reprepro/incoming(/[-a-z0-9+~_.]*[-a-z0-9+~_])?$
           ^chmod 0644( /srv/reprepro/incoming/[-a-z0-9+~_.]*[-a-z0-9+~_])+$
           ^reprepro ( -V)? -b /srv/reprepro processincoming foobar$

SECURITY NOTES

       It is dangerous and not recommended to use negative bracket expressions (like [^ /]).
       Characters like CR LF $ & ; ( ) and so on can be abused to execute arbitrary commands. For
       example, the rule

           ^echo [^ /]$

       can be abused to execute these commands

           echo foo&echo owned
           echo foo&rm -rf $(printf "\x2f")

       where a TAB is used instead of spaces after the first ampersand. Therefore only use
       positive bracked expressions (like [a-z]).

FILES

       The configuration files are placed in /etc/restricted-ssh-commands/. Each line in the
       configuration file represents one POSIX extended regular expression (ERE). Lines starting
       with # are considered as comments and are ignored. Empty lines (containing only
       whitespaces) are ignored, too.

SEE ALSO

       Regular expressions on http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_04_01.html

       Section 9.4 Extended Regular Expressions (ERE) on
       http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html

AUTHOR

       restricted-ssh-commands and this manpage have been written by Benjamin Drung
       <benjamin.drung@profitbricks.com>.