Kerberos ticket

[kandolfp]

Would it be possible to not go for username and password but to use a Kerberos ticket for the mount instead?

It would be the equivalent of a mount on the host as:
//server/share /mnt cifs multiuser,sec=krb5,user 0 0

Users will have access to it after a kinit to get a kerberos ticket. Equivalently the pod would need a kerberos ticket but that could be provided by an init script.

[andyzhangx]

so what's the mount options in this case?

[kandolfp]

the options above are multiuser,sec=krb5,user this way the mount uses kerberos and it separate per user. So if the drive is mounted but your users has no kerberos ticket you will not be able to access it.

get a ticket with kinit and you can access it.

It just exchanges user, passwd with a kerberos ticket. the ticket would be generated in the pod.

[avishefi]

Working with Kerberos also solves working under FIPS since NTLM-based SMB requires hmac-md5.

[shaunrampersad]

@kandolfp did you manage to get this to work with Kerberos? If so, how did you do it?

My issue is as @avishefi states, the cluster is installed with FIPS enabled so NTLM wont work.

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[yrro]

the options above are multiuser,sec=krb5,user this way the mount uses kerberos and it separate per user. So if the drive is mounted but your users has no kerberos ticket you will not be able to access it.

Not sure what user means here. Isn't it the option used to specify username? It's probably just redundant when multiuser is specified.

In this mode, when a process tries to access a share, the kernel makes a cifs.spnego upcall to request encryption keys.

It's not clear how this can work when the process triggering the upcall is running in a container. I found a linux-security-module mailing list thread proposing changes to make it work smoothly but I don't know if it was adopted.

[andyzhangx]

for Kerberos ticket support, it requires agent node domain join first, here is one example:
https://learn.microsoft.com/en-us/azure/azure-netapp-files/configure-nfs-clients#ubuntu-configuration

[andyzhangx]

since this feature is already implemented by this driver, when the kerberos ticket is expired, how does this driver handle this issue? do we need to unmount the pv and mount again?

[yrro]

I think the existing Kerberos support is a little bit incomplete. As a user I would like to put a keytab into a secret and have that be used to authenticate the mount; I don't want to have to manage a directory of credentials cache files on every node...

[avishefi]

@yrro take a look at: https://github.com/kubernetes-csi/csi-driver-smb/blob/master/docs/driver-parameters.md#pass-kerberos-ticket-in-kubernetes-secret

[yrro]

"To pass a ticket through secret, it needs to be acquired" - there's the problem. The tickets in a credential cache expire within a few hours.

What I'd like as a user is to have csi-driver-smb handle obtaining the ticket automatically. To do this, a long term secret (in the form of the user's Kerberos keys stored in a keytab file) are required. I'd like to provide the keytab file to csi-driver-smb via a secret object. The mount performed by csi-driver-smb would use the sec=krb5i option.

The difficultly comes when the kernel makes the cifs.spengo upcall in order to obtain Kerberos keys. csi-driver-smb would have to service this upcall, and at that point it would need to use the keytab to obtain a TGT, and then use the TGT to obtain a ST and return that back to the kernel (I'm handwaving here, but hopefully that makes sense to someone who knows how kerberos-authenticated SMB mounts on Linux is implemented).

[cccsss01]

I'd like this feature as well

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[yrro]

/remove-lifecycle rotten