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[Debian-Sarge] Tunneling NFS over SSH


Welcome

The goal of this howto is building a NFS server that works on a SSH tunnel. This way all traffic between your hosts and the file server is encrypted and thus more secure 🙂
Normally you should enter a password every time you try to establish a SSH connection but since we could be mounting at bootup we will use ssh-keygen to create a keypair so we can login without entering a password. We will, however, limit that login session to executing just 1 command 😉
We will use a new clean Debian Sarge install to begin with.

In this howto I will use the fictional domain “linux.lan”.


Installing Software

We will start with the NFS server.

apt-get -y install nfs-kernel-server

First configure it to run on fixed ports, this will make building a firewall much easier but equally important it aids in simpler client mounts.

echo “STATDOPTS=–port 2231” > /etc/default/nfs-common
echo “options lockd nlm_udpport=2232 nlm_tcpport=2232” >> /etc/modules.conf
echo “RPCNFSDCOUNT=8 RPCMOUNTDOPTS=’-p 2233′” > /etc/default/nfs-kernel-server

Thats it, now we can use port 2233 later on when we mount the shares 🙂 check if it worked with rpcinfo -p. If nlockmgr still uses random ports it is a compiled in setting. Configure this in grub/lilo as kernel parameters:
“lockd.udpport=2232 lockd.tcpport=2232”.

Create a new user called sleeper to use for setting up the ssh tunnel from other hosts. We will generate a key for this account so you can login with a keyfile instead of typing your password everytime. The account will also be restricted to execute ‘sleep’ trough this way. Other commands will simply fail.

adduser sleeper
su sleeper

Now switch over to a client that will use our fileserver.
First we need a key:

ssh-keygen -t rsa -b 2048

(use defaults and NO passphrase!)

Now copy the .pub file to the homedir of sleeper on the server:

scp -P 12345 ~/.ssh/id_rsa.pub sleeper@10.0.0.241:~/

Now back to the server: As the ‘sleeper’ user we need to configure/install the key:

mkdir ~/.ssh
cd ~/.ssh
mv ../id_rsa.pub ./id_rsa.pub
cat id_rsa.pub >> authorized_keys
chmod 600 authorized_keys

Add this to the beginning of authorized_keys (before ssh-rsa […]):

client="client.linux.lan",command="/bin/sleep 600d"

substitute “client” with the correct hostname of your client, or use ip numbers.
(but make sure every entry stays on 1 line!)

Every client that needs access to the fileserver needs to store his security data (from the id_rsa.pub file) in the authorized_keys file, so you should repeat this for every host.

Mounting NFS over SSH on your clients

Issue these commands to start the tunnels for nfs and mountd:
(syntax: ssh -f -c encyption -L localport:nfsserver:nfsport -l username nfsserver remotecommand)
Also note that the portnumber for mountd is different with every restart of the NFS server… Keep that in mind.

ssh -f -i /root/.ssh/id_rsa -c blowfish -L 61001:10.0.0.241:2049 -l sleeper 10.0.0.241 sleep 600d
ssh -f -i /root/.ssh/id_rsa -c blowfish -L 62001:10.0.0.241:2233 -l sleeper 10.0.0.241 sleep 600d

This creates a connection that will stay alive for almost 2 years… 🙂
Now edit your fstab and mount:

echo “localhost:/export/data /mnt nfs

tcp,rsize=8192,wsize=8192,intr,rw,bg,nosuid,port=61001,mountport=62001,noauto” >> /etc/fstab mount /mnt

Ofcourse we need some mountable folders (shares) defined on the NFS server:

mkdir /export
mkdir /export/data
mkdir /export/www-virtual
mkdir /export/www-conf
mkdir /export/mail-virtual
mkdir /export/mail-conf

Add them to /etc/exports:

/home/export/data 10.0.0.241(rw,root_squash,sync)

Notice the ip address is the nfs server itself? Its because youll mount them from localhost when you have established the ssh tunnel.

Some security settings since we dont want anyone from outside our network to access the server:

echo “portmap: ALL” > /etc/hosts.deny
echo “portmap: 10.0.0.0/255.255.255.0” > /etc/hosts.allow

Restart NFS:

/etc/init.d/nfs-kernel-server restart

Thats it ! You can now mount the filesystem on your clients without the need to supply a password. And ofcourse all traffic will be encrypted 🙂

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