ksmbd-server: SMB3 file copy fails on Windows 11 with "Invalid signature"

[radekzlato]

Package Name

ksmbd-server

Maintainer

N/A (no PKG_MAINTAINER defined)

OpenWrt Version

25.12.5

OpenWrt Target/Subtarget

mediatek/filogic

Steps to Reproduce

1. Install OpenWrt 25.12.5 with ksmbd-server 3.5.6.

2. Create a writable SMB share on an ext4 filesystem.

3. Connect from Windows 11 24H2 using the default SMB client (SMB signing enabled).

4. Verify that:

   • browsing directories works,
   • opening files works,
   • editing and saving files works.

5. Copy a file using either:

   • Windows Explorer
   • or PowerShell:

Copy-Item "\\<server>\share\test.txt" "C:\Temp\"

6. Observe that the copy fails with "Invalid signature".

7. Force the server to SMB2.1 (server max protocol = SMB2_10), reconnect and repeat the same test.

8. The same copy succeeds without any other changes.

Actual Behaviour

Windows successfully authenticates and establishes a signed SMB session.

The SMB share is fully accessible:

• browsing directories works
• opening files works
• editing and saving files works
• reading files (e.g. Get-Content) works

However, copying a file using Windows Explorer or PowerShell Copy-Item consistently fails with:

Copy-Item : Invalid signature.

The problem is 100% reproducible.

Additional observations:

• SMB 3.1.1: fails
• SMB 3.0.2: fails
• SMB 2.1: works correctly

The following configuration changes were tested and did not change the behaviour:

• server signing = disable
• server signing = auto
• server signing = mandatory
• smb2 leases = no

The hardware crypto accelerator (Safexcel) was also disabled without any effect.

Based on the attached Windows PktMon capture, the failure appears to occur before the first SMB READ request, during the CREATE / QUERY_INFO sequence

PktMon capture, logs and ksmbd configuration can be provided if needed.

Confirmation Checklist

• The package is maintained in this repository.
• I understand that issues related to the base OpenWrt repository or LuCI repository will be closed.
• I am reporting an issue for OpenWrt, not an unsupported fork.