On Dienstag, 28. Juli 2020 15:08:59 CEST Greg Kurz wrote: > On Tue, 28 Jul 2020 11:55:03 +0100 > > "Dr. David Alan Gilbert" <dgilbert@xxxxxxxxxx> wrote: > > Hi, > > > > Are there any standards for mapping xattr names/classes when > > > > a restricted view of the filesystem needs to think it's root? > > > > e.g. VMs that mount host filesystems, remote filesystems etc and the > > client kernel tries to set a trusted. or security. xattr and you want > > to store that on an underlying normal filesystem, but your > > VM system doesn't want to have CAP_SYS_ADMIN and/or doesn't want to > > interfere with the real hosts security. > > > > I can see some existing examples: > > 9p in qemu > > > > maps system.posix_acl_* to user.virtfs.system.posix_acl_* > > > > stops the guest accessing any user.virtfs.* Not that they were remapped, but the 'local' 9pfs fs driver also actively interprets: user.virtfs.uid user.virtfs.gid user.virtfs.mode user.virtfs.rdev > > overlayfs > > > > uses trusted.overlay.* on upper layer and blocks that from > > > > clients > > > > fuse-overlayfs > > > > uses trusted.overlay.* for compatibiltiy if it has perms, > > otherwise falls back to user.fuseoverlayfs.* > > > > crosvm's virtiofs > > > > maps "security.sehash" to "user.virtiofs.security.sehash" > > and blocks the guest from accessing user.virtiofs.* > > > > Does anyone know of any others? Well, depends on how large you draw the scope here. For instance Samba has a bunch VFS modules which also uses and hence prohibits certain xattrs. For instance for supporting (NTFS) alternate data streams (a.k.a. resource forks) of Windows clients it uses user.DosStream.*: https://www.samba.org/samba/docs/current/man-html/vfs_streams_xattr.8.html as well as "user.DOSATTRIB". And as macOS heavily relies on resource forks (i.e. macOS doesn't work without them), there are a bunch of xattr remappings in the dedicated Apple VFS module, like "aapl_*": https://www.samba.org/samba/docs/current/man-html/vfs_fruit.8.html https://github.com/samba-team/samba/blob/master/source3/modules/vfs_fruit.c Best regards, Christian Schoenebeck
