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NAME

snazzer-send-wrapper - ssh forced command wrapper for snazzer-receive

SYNOPSIS

SSH_ORIGINAL_COMMAND="sudo -n snazzer --list-snapshots '--all'" \
  ./snazzer-send-wrapper

SSH_ORIGINAL_COMMAND="sudo -n grep -srl \
  'sendinghost1' '/some/.snapshotz/.measurements/'" snazzer-send-wrapper

SSH_ORIGINAL_COMMAND="sudo -n btrfs send \
  '/some/.snapshotz/2015-04-01T000000Z'" snazzer-send-wrapper

SSH_ORIGINAL_COMMAND="sudo -n cat \
  '/some/.snapshotz/.measurements/2015-04-01T000000Z'" snazzer-send-wrapper

OPTIONS

  • --help: Brief help message

  • --version: Print version

  • --man: Full documentation

  • --man-roff: Full documentation as *roff output, Eg:

      snazzer --man-roff | nroff -man

  • --man-markdown: Full documentation as markdown output, Eg:

      snazzer --man-markdown > snazzer-manpage.md

DESCRIPTION

This is a wrapper script to be used in place of a real login shell (Eg. as an ssh(1) forced command) in order to restrict the commands available to the user account used by snazzer-receive to run btrfs send. It may be utilized by adding an entry in the ~/.ssh/authorized_keys file on the sending host (Eg. sendinghost1) under the user account used by snazzer-receive to run btrfs send. ~/.ssh/authorized_keys:

command="/usr/bin/snazzer-send-wrapper",no-port-forwarding, \
    no-X11-forwarding,no-pty ssh-rsa AAAA...snip...== my key

And then (as an example) receive btrfs snapshots from this sendinghost1:

snazzer-receive sendinghost1 --all

ENVIRONMENT

  • SSH_ORIGINAL_COMMAND

    This variable holds the original remote ssh command to be acted upon.

BUGS AND LIMITATIONS

  • This script tries too hard to parse normal shell commands

    A better design would be custom command tokens issued with more easily parsed string and argument delimeters. This would require some changes to snazzer-receive.

    A mitigating factor is that all commands are executed in the form of:

      foo "$@"

    Rather than any variant of the more exciting:

      foo $BAREWORD_ARGUMENTS

    or

      eval "$SSH_ORIGINAL_COMMAND"

    This wrapper script is also sanity-checked with bats regression tests which check that only the correct number of arguments, valid arguments, switches, path patterns and escape characters are dealt with - anything else is rejected.

EXIT STATUS

snazzer-send-wrapper will abort with an error message printed to STDERR and non-zero exit status under the following conditions:

    1. the command string was not recognized
    1. the command string was recognized but the arguments were not safe
    1. the command string was recognized and an attempt was made to parse/re-pack the arguments however the argument string had dangling quotes or otherwise confused the parser/"$@" unpacker

SEE ALSO

snazzer-receive

AUTHOR

Snazzer Authors are listed in the AUTHORS.md file in the root of this distribution. See https://github.com/csirac2/snazzer for more information. NOTE: Please extend that file, not this notice.

LICENSE AND COPYRIGHT

Copyright (C) 2015-2016, Snazzer Authors All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.