Duplicate SMB file_ids leading to Windows client cache poisoning

[Christof Schmitt]

On Fri, Dec 10, 2021 at 04:04:09PM -0500, Tom Talpey via samba-technical wrote:
> I believe the EXT, BTRFS, XFS and a few other Linux filesystems support
> retrieving the generation number via ioctl(FS_IOC_GETVERSION). But I'm
> not certain how universal this is. There being hundreds of file systems
> in Linux...
> 
> Could Samba perhaps insert a kernel module, or use the SMB client kmod,
> to fetch this? It'd be ugly and will have security implications, so I
> would not go into it lightly.

I missed FS_IOC_GETVERSION. That might be an option, since that is at
least supported on the most commonly used file systems (ext4, xfs,
btrfs). And if the call fails, we could log a warning, that this setup
might be unreliable for MacOS clients.

Christof