CSI NFS driver does not follow NFSv4 referrals inside PVC volumes

[karamav]

Hello,
I have the following problem using the csi-driver-nfs driver 4.11.

PVC provisioning with the CSI NFS driver succeeds and the pod can read/write under /data.
However, directories that are NFSv4 referral junctions under the exported root (e.g. /data/nfs1, /data/nfs2) cannot be entered from inside the pod and return: No such file or directory.

The same export mounted natively on a Linux host using mount -t nfs4 correctly follows the referrals (entering /mnt/nfs/nfs1 and /mnt/nfs/nfs2 redirects to the backend servers and works).

What you expected to happen
When a volume is mounted by the CSI NFS driver from an NFSv4 proxy export, referral junctions under that export should be traversable from inside the pod just like they are with a native mount.nfs4.

How to reproduce it
There is one NFS proxy server (Linux kernel NFS server) which exports /nfs as the NFSv4 root export.
This proxy does not store data itself, but instead uses NFSv4 referrals to redirect clients to two backend NFS servers.

• NFS Proxy export (Linux kernel NFS server):

/nfs *(rw,fsid=0,no_subtree_check,no_root_squash,sec=sys)

• Create referrals:

nfsref add /nfs/nfs1 10.164.0.14 /nfs1
nfsref add /nfs/nfs2 10.164.0.15 /nfs2

• Sanity check on a VM (works):

mount -t nfs4 10.164.0.16:/ /mnt/nfs
ls /mnt/nfs/nfs1     # OK, redirected to backend 1
ls /mnt/nfs/nfs2     # OK, redirected to backend 2

Environment

• CSI Driver version: 4.11
• Kubernetes version: v1.30.14
• OS: Ubuntu 24.04