ntptfs & passthrough - error when accessing exFAT and FAT32 volumes

Bug Report

Used ntptfs to mount an exFAT and FAT32 volume. Mounting succeeded for both file systems as the mount point shows up in Windows Explorer, but trying to access it fails with the following error:

ProcMon shows that IRP_MJ_QUERY_INFORMATION with info type of QueryAttributeTagFile is failing with STATUS_INVALID_PARAMETER on the original volume:

This happens even with the passthrough sample.

Problem is with the following call in GetSecurityByName():

https://github.com/winfsp/winfsp/blob/624f28545224c242087688359b4a4be878320510/tst/ntptfs/ptfs.c#L107-L112

Somehow it's failing with STATUS_INVALID_PARAMETER. Changing the info type to FileBasicInformation eliminated the failure and fixed the issue.

I suspect the reason could be FAT-type volumes not supporting FileAttributeTagInformation, but I couldn't find any documentation on this.

How to Reproduce

1. Format a local or removable drive as exFAT or FAT32.
2. Run the following command to mount the local folder (assuming the FAT volume is mounted as H:):
   复制

   ntptfs -p H: -m Y:

3. Via Windows Explorer, open the volume.

Behaviors

Step 3 should succeed, but it fails with the error in the 1st screenshot.

Environment

• OS version and build: Win10 1809 17763.2458
• WinFsp version and build: 2.1.25156