rrsync(1) - Man pages

rrsync(1) User Commands rrsync(1)

NAME
rrsync - a script to setup restricted rsync users via ssh logins

SYNOPSIS
rrsync [-ro|-wo] [-munge] [-no-del] [-no-lock] [-no-overwrite] DIR

The single non-option argument specifies the restricted DIR to use. It
can be relative to the user's home directory or an absolute path.

The online version of this manpage (that includes cross-linking of top-
ics) is available at ]8;;https://download.samba.org/pub/rsync/rrsync.1\https://download.samba.org/pub/rsync/rrsync.1]8;;\.

DESCRIPTION
A user's ssh login can be restricted to only allow the running of an
rsync transfer in one of two easy ways:

o forcing the running of the rrsync script

o forcing the running of an rsync daemon-over-ssh command.

Both of these setups use a feature of ssh that allows a command to be
forced to run instead of an interactive shell. However, if the user's
home shell is bash, please see BASH SECURITY ISSUE for a potential is-
sue.

To use the rrsync script, edit the user's ~/.ssh/authorized_keys file
and add a prefix like one of the following (followed by a space) in
front of each ssh-key line that should be restricted:

command="rrsync DIR"
command="rrsync -ro DIR"
command="rrsync -munge -no-del DIR"

Then, ensure that the rrsync script has your desired option restric-
tions. You may want to copy the script to a local bin dir with a unique
name if you want to have multiple configurations. One or more rrsync op-
tions can be specified prior to the DIR if you want to further restrict
the transfer.

To use an rsync daemon setup, edit the user's ~/.ssh/authorized_keys
file and add a prefix like one of the following (followed by a space) in
front of each ssh-key line that should be restricted:

command="rsync --server --daemon ."
command="rsync --server --daemon --config=/PATH/TO/rsyncd.conf ."

Then, ensure that the rsyncd.conf file is created with one or more mod-
ule names with the appropriate path and option restrictions. If rsync's
--config option is omitted, it defaults to ~/rsyncd.conf. See the
rsyncd.conf(5) manpage for details of how to configure an rsync daemon.

When using rrsync, there can be just one restricted dir per authorized
key. A daemon setup, on the other hand, allows multiple module names
inside the config file, each one with its own path setting.

The remainder of this manpage is dedicated to using the rrsync script.

OPTIONS
-ro Allow only reading from the DIR. Implies -no-del and -no-lock.

-wo Allow only writing to the DIR.

-munge Enable rsync's --munge-links on the server side.

-no-del
Disable rsync's --delete* and --remove* options.

-no-lock
Avoid the single-run (per-user) lock check. Useful with -munge.

-no-overwrite
Enforce --ignore-existing on the server. Prevents overwriting ex-
isting files when the server is the receiver.

-help, -h
Output this help message and exit.

SECURITY RESTRICTIONS
The rrsync script validates the path arguments it is sent to try to re-
strict them to staying within the specified DIR.

The rrsync script rejects rsync's --copy-links option (by default) so
that a copy cannot dereference a symlink within the DIR to get to a file
outside the DIR.

The rrsync script rejects rsync's --protect-args (-s) option because it
would allow options to be sent to the server-side that the script cannot
check. If you want to support --protect-args, use a daemon-over-ssh
setup.

The rrsync script accepts just a subset of rsync's options that the real
rsync uses when running the server command. A few extra convenience op-
tions are also included to help it to interact with BackupPC and accept
some convenient user overrides.

The script (or a copy of it) can be manually edited if you want it to
customize the option handling.

BASH SECURITY ISSUE
If your users have bash set as their home shell, bash may try to be
overly helpful and ensure that the user's login bashrc files are run
prior to executing the forced command. This can be a problem if the
user can somehow update their home bashrc files, perhaps via the re-
stricted copy, a shared home directory, or something similar.

One simple way to avoid the issue is to switch the user to a simpler
shell, such as dash. When choosing the new home shell, make sure that
you're not choosing bash in disguise, as it is unclear if it avoids the
security issue.

Another potential fix is to ensure that the user's home directory is not
a shared mount and that they have no means of copying files outside of
their restricted directories. This may require you to force the en-
abling of symlink munging on the server side.

A future version of openssh may have a change to the handling of forced
commands that allows it to avoid using the user's home shell.

EXAMPLES
The ~/.ssh/authorized_keys file might have lines in it like this:

command="rrsync client/logs" ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAIEAzG...
command="rrsync -ro results" ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAIEAmk...

FILES
~/.ssh/authorized_keys