NFS Howto Submissions nfs krb5

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Revision as of 16:20, 11 April 2006

Kerberos and NFS

Kerberos can be used to provide both mutual authentication (validating both the client and server prior to transmitting data) and encryption for data sent via NFS. This is implemented with the RPCSEC_GSS security flavor of ONC RPC protocol, defined by RFC 1831 and RFC 2203. This subsection of NFS Howto: Security attempts to provide a complete and accurate cookbook configuration guide for how to get Kerberos validation / authentication working with NFSv3/NFSv4 mount points.

Requirements

• A working Kerberos realm for all of your NFS clients and server to authenticate against.
• A working NTP configuration on all hosts participating in your Kerberos realm. This will insure that the system clocks on your machines are set to matching times.
• /etc/services should have entries in it for port 2049 for both TCP and UDP NFS. This should be present in virtually every modern version of Linux, but it warrants mentioning.
• Proper forward/reverse name FQDN/IP resolution must be working in DNS, or, at a minimum, the /etc/hosts file must contain this information. The machine's hostname must also not be included on the localhost line, aka:

[cmsmith@client ~]$ cat /etc/hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1               localhost.localdomain localhost
10.161.131.10       client.netapp.com client

Is ok. Whereas this:

[cmsmith@broken ~]$ cat /etc/hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1               localhost.localdomain broken localhost 

is not.

The system clocks on your machines must be set to the correct time; install ntp to make sure this is the case. The /etc/hosts file must list the fully-qualified domain name as the first entry on the line with the machine's IP address, and the machine's name must not be include on the localhost line. The /etc/services file must list the nfs service (port 2049). Something like the following: nfs 2049/tcp nfsd # Network File System nfs 2049/udp nfsd # Network File System

Kerberos Configuration

Verify that the client has a working Kerberos configuration
Generate NFS Machine Credentials for the Kerberos Client
Add the NFS Machine Credentials to both the Kerberos Client and Server

NFSv3 Specifics

NFSv4 Specifics

The following is only necessary if you wish to use Kerberos 5 (krb5). (Which is a good idea.) We assume you have a Kerberos KDC installed somewhere and have configured Kerberos on your client and server. Create machine credentials for the client. This means creating a Kerberos V5 principal/instance name of the form nfs/dns.name.of.client@REALM, and either adding a key for this principal to an existing /etc/krb5.keytab or creating an /etc/krb5.keytab. Note: only the encryption type of des-cbc-crc is functional so far in the kernel, so add only this type of key.

kadmin: addprinc -randkey nfs/myclient.mydomain kadmin: ktadd -e des-cbc-crc:normal -k /tmp/keytab nfs/myclient.mydomain Now copy the new keytab /tmp/keytab to /etc/krb5.keytab on the client. Repeat steps 2 and 3 for the server, this time adding a key for nfs/dns.name.of.server@REALM to the keytab on the server. Things to be aware of when using Kerberos:

SPKM and NFS