How can I restrict incoming root rsync over ssh to specified command?

From: mjcsfo (mjcsfo_at_yahoo.com)
Date: 02/04/04

  • Next message: Tim Haynes: "Re: How can I restrict incoming root rsync over ssh to specified command?" 
    Date: 4 Feb 2004 14:50:50 -0800

    I'm trying to setup a centralized backup server on RHEL 3.0, which
    will use rsync over ssh to pull certain directories from the ssh
    server/rsync source
    to the ssh client/rsync destination. Here's an example of the command,
    in a
    script run via cron as root:

    rsync --rsh="ssh -i /root/.ssh/rsync-id_rsa" \
          -avR --stats --delete --max-delete=100 \
          $HOST:/etc/ $CURR_DIR

    $HOST would be static but $CURR_DIR would vary on each call - it
    basically
    contains a path containing the date and time, such as:

    HOST=myserver
    CURR_DIR=/var/spool/backups/$HOST/2004-02-04.18

    for a backup run on Feb 4, 2004 at 6pm.

    I've setup a non-password protected private key as noted above to
    allow
    non-interactive complete access to all files I want to backup. I'm
    currently
    using "PermitRootLogin without-password" in sshd_config and the
    from="myclient", no-port-forwarding, no-X11-forwarding,
    no-agent-forwarding,
    no-pty options in authorized_keys to restrict how this key can be
    used. But
    this method would allow anyone who managed to obtain the private key
    non-
    password protected root access to all servers which are being backed
    up with
    this approach - hopfully without a terminal, but I don't know what
    risks
    there are in this technique.

    I was hoping to use the command="command" option, but from the
    description
    in the man pages it seems like this wouldn't work, since it seems like
    the
    command must be static, any command I send is ignored, and I'm not
    sure of
    which command I'd run on the other end to implement the rsync
    technique I
    want to do in any case.

    I did think potentially the remote command could use environment
    variables
    which I could set remotely via "PermitUserEnvironment yes" in
    sshd_config,
    hopefully thereby allowing the remote command to be static, but I
    don't see
    how this would work with rsync using ssh as an underlying transport.

    Questions:
    1. Does anyone think that the technique I'm using today is simply too
       insecure? Even with the server locked up in a room with no user
       access and running no daemons?

    2. Is there a way to implement what I'm trying to do with rsync using
       some variant of the command="" option to prevent any other use of
       this non-password protected key?

    Thanks in advance!

    Mike

    P.S. Please, no spam even though I'm posting through Google and can't
    hide
    my email address!

  • Next message: Tim Haynes: "Re: How can I restrict incoming root rsync over ssh to specified command?"

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