Security issues when rsyncing directories as root

[Marc Haber]

Hi,

I am using rsync to keep two directores on two servers in sync. Machine
A, the "client" is the one where the rsync process is invoked, which
then logs into Machine B, the "server" as root with ssh and a key. The
key is restricted in /root/.ssh/authorized_keys to a script that checks
wither $SSH_ORIGINAL_COMMAND matches the rsync --server command that I
expect, such as, for example,
rsync --server -re.iLsfxC --delete . /etc/dhcp/synced/

Unfortunately, this is rather restrictive and unflexible.

Things would be easier if rsync would have an option like
--restrict-write, making rsync not write anywhere outside the path given
there. That way, my script would be easier an I would only need to check
server-wise whether the command line being called contains the
--restrict-write option with the correct directory.

Would that make sense? Or am I more in the market for an rsync daemon
with the "path" and "write only" options set? If so, would I need to
have an rsync daemon _running_ on the remote side if I use the rsync
--rsh=ssh /path/to/local/dir host::module syntax?

Greetings
Marc

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