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Monica For CEO
Asked: 2013-10-05 00:42:51 +0800 CST

How to use `rsync` to securely push to a mirror?

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I am using rsync --rsh "ssh" to push to a mirror. Setting the necessary file system permissions on the mirror requires rsync to run with root privileges on the mirror. However, the mirrored files are under a single hierarchy and I would like to allow rsync to access only that hierarchy and nothing else on the mirror.

How would I allow rsync to set permissions while also limiting access?

Is there possibly some combination of rsync --rsh "???" and the command="???" option in authorized_keys that might do the trick? The rsync command is already using a dedicated key in authorized_keys.

Or is there a way for rsync to connect as an unprivileged user, be jailed, and then gain access to set file system permissions? Jailing the process is easy, but allowing the remote rsync to gain privileges seems difficult, and allowing a jailed process to gain any permissions seems risky. (Of course, right now the process has root and any degree of restriction would be an improvement, even if only to mitigate accidents.)

security

3 Answers

  1. To rsync a remote location to a local location:

    rsync -avze ssh user@source:/dir destination

    To rsync a local location to a remote location:

    rsync -avz source -e ssh user@destination:/dir

    From the manpage (http://linux.die.net/man/1/rsync):

    -a archive mode; e.g. copies permissions
-v verbose; in case you want to log what gets copied
-z compress during transfer
-e specify the remote shell to use; let's you use ssh

    To get rsync to work without prompting for a password, you'll need to configure a trust between the source and destination servers by generating rsa-keys and entering them into their respective authorized keys. Here's a good tutorial:

    http://troy.jdmz.net/rsync/index.html

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  2. Best Answer

    You should be running rsync from your mirror with your original as the source.

    Depending on your use case you should either run it as a cronjob (periodic) or an sshkey command (push initiated pull, effectively a push).

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  3. The solution in my particular case is to use rsync --rsh "ssh" to connect as the user who should own the files being mirrored and to use the ssh configuration to chroot that user to the proper hierarchy.

    Recipe something like this, on destination server:

    useradd user
mkdir /home/user/srv/service
chown -R root:root /home/user

Grant user write permission to /srv/service

nano /etc/fstab

/srv/service /home/user/srv/service none bind 0 0

mount /srv/service

nano /etc/ssh/sshd_config

Match User user
ChrootDirectory %h

service ssh reload

nano /home/user/.ssh/authorized_keys

Add public key for remote user.

    Finally, from remote system, as unprivileged user, push data to mirror:

    rsync --archive --rsh "ssh" --compress /srv/service/ user@server:/srv/service/
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