Chrooter des comptes SSH
The OpenSSH version (4.8p1 for the GNU/Linux port) features a new configuration option : ChrootDirectory.
This has been made possible by a new SFTP subsystem statically linked to sshd.
This makes it easy to replace a basic FTP service without the hassle of configuring encryption and/or bothering with FTP passive and active modes when operating through a NAT router. This is also simpler than packages such as rssh, scponly or other patches because it does not require setting up and maintaining (i.e. security updates) a chroot environment.
To enable it, you obviously need the new version 4.8p1. I personaly use the cvs version and the debian/ directory of the sid package to build a well integrated Debian package 4.8p1~cvs-1.
In /etc/ssh/sshd_config :
You need to configure OpenSSH to use its internal SFTP subsystem.
Subsystem sftp internal-sftp
Then, I configured chroot()ing in a match rule.
Match group sftponly ChrootDirectory /home/%u X11Forwarding no AllowTcpForwarding no ForceCommand internal-sftp
The directory in which to chroot() must be owned by root. After the call to chroot(), sshd changes directory to the home directory relative to the new root directory. That is why I use / as home directory.
chown root.root /home/user usermod -d / user adduser user sftponly
This seems to work as expected :
The only thing I miss is file transfers logging, but I did not investigate this at all. More on this whenever I find some time to do so.