About the purpose of client host principals for NFS

Marco Rebhan via Kerberos <[email protected]> Sat, 07 Oct 2023 21:21:23 +0200

Newsgroups	gmane.comp.encryption.kerberos.general
Message-ID	<2245400.ev0DxJNslZ@invader>

Hey list,

I'm currently setting up Kerberos for my home network. The main motivation was 
to get secure NFS, and as such I've looked at various guides on how to set it 
up for that. They (for example, the Arch Wiki[1]) pretty much all tell you to 
create principals for the host and NFS service for both the NFS server and 
clients that want to connect.

However, after setting up the NFS server and my Linux PC like this, I tested 
the whole setup with my MacBook which doesn't have a host principal or any 
other krb5 configuration yet (it can find the KDC due to DNS), and to my 
surprise it can both obtain a TGT for my user and afterwards also mount the 
NFS share.

What purpose does the host principal for clients serve here? I assumed it 
would be either used to authenticate hosts before they're allowed to obtain a 
TGT, or authenticate for mounting NFS shares, but clearly that's not the case 
since it works without. Is it only used so that the network share can be 
mounted without a user TGT?

Thanks,
Marco

[1]: https://wiki.archlinux.org/title/Kerberos#NFS_security

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