Not working with DFS Targets

[ShyBilly]

We're using the csi-driver-smb to connect to several Windows shares from a K8s cluster comprised of Linux nodes. We are switching to DFS and we are able to connect to the DFS Root folder, but cannot access any DFS link targets. We're getting the error: Interrupted system call

I saw an issue which seems like similar behavior for Windows nodes - microsoft/Windows-Containers#299

Does the csi-driver-smb not support this or could it be a configuration issue on our end?

We've tried this using csi-driver-smb version 1.13.0 and 1.16.0

[dbuzatto]

DFS root working but failing on DFS link targets with Interrupted system call strongly suggests a DFS referral handling issue rather than a simple credential problem.

The SMB CSI driver itself does not implement DFS — it relies on the underlying Linux CIFS client (mount.cifs / kernel cifs.ko). If DFS targets fail, the most common causes are:

• Kernel CIFS client without proper DFS support
• Missing mfsymlinks or DFS-related mount options
• Network/firewall blocking access to the referral target server
• DNS resolution issues for the DFS target hostnames
• SMB protocol negotiation issues (vers mismatch)

Things to verify:

1. Confirm the Linux node kernel supports DFS:

   modinfo cifs | grep dfs
   

   Also check:

   cat /proc/fs/cifs/DebugData
   

2. Test manual mount directly on the node (outside Kubernetes):

   mount -t cifs //dfs-root/share /mnt/test \
     -o username=...,password=...,vers=3.0
   

   Then try accessing a DFS link target inside /mnt/test.
   If this fails, the issue is at the OS/kernel level, not the CSI driver.

3. Try explicitly setting mount options in your StorageClass:

   • vers=3.0 (or 3.1.1)
   • mfsymlinks
   • serverino
   • Avoid very old SMB versions

4. Ensure the node can directly reach the DFS target servers:

   smbclient -L //<dfs-target>
   

Important: csi-driver-smb does not add special DFS logic. If the Linux CIFS client cannot follow referrals correctly, the driver will also fail.

If manual mounting on the node works but CSI does not, please share:

• Your StorageClass YAML
• The mountOptions being used
• Kernel version of the node (uname -r)
• Full error from the node plugin logs

In most DFS cases on Linux, the root cause is kernel CIFS configuration or missing DFS support rather than a driver limitation.

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