How mode bits are stored in NFS/NTFS/CIFS/SMB3 ACLs

Jeremy Allison jra at
Thu Sep 25 18:09:43 MDT 2014

On Thu, Sep 25, 2014 at 09:02:50AM -0700, Steve French wrote:
> On Thu, Sep 25, 2014 at 3:29 AM, Anton Altaparmakov <aia21 at> wrote:
> > Hi Steve,
> >
> > On 25 Sep 2014, at 07:04, Steve French <smfrench at> wrote:
> >> Did some experiments today to see how mode bits are stored by the
> >> Windows NFS server in the RichACL (CIFS or NFS ACL).   mounted nfsv4.1
> >> to Windows from Linux then created a bunch of files and did chmod of
> >> various combinations of 07777 bits (including sticky, setuid etc.)
> >>
> >> Windows NFS server is storing the user owner bits with SID
> >> S-1-5-88-1 and using SID S-15-88-2 for group owner and S-1-5-88-4 for
> >> the ACE for "other" (this is easy to spot over CIFS/SMB3 etc because
> >> user owner and group owner map to these SIDs in the security
> >> descriptor returned over the wire).
> >>
> >> As expected, for each of the 3 ACEs, it is setting "GENERIC_READ" in
> >> the ACE for '4' (read) and GENERIC_WRITE for '2' (write) and
> >> GENERIC_EXECUTE for '1' (execute).  What is puzzling is where it
> >> stores the setuid and sticky bits (bits 07000) because they are not
> >> visible in the CIFS/NTFS ACL.
> >
> > As far as I know the Windows NFS server user "Services For Unix (SFU)" and those special bits are stored on NTFS in an Extended Attribute (EA) (note this is the $EA attribute not a named stream/named $DATA attribute on NTFS).  I wrote about this 9 years ago on linux-ntfs-dev mailing list.  Archive post is here (read my point "2" in that post for the details):
> >
> >
> >
> > This means that those bits only take effect / have any significance for applications using the Windows POSIX subsystem (e.g. NFS server and Cygwin), i.e. normal Win32 based apps will not be affected by them at all.
> >
> I did a getfattr to list all the windows (os/2) exstended attributes
> (over cifs) and didn't see it, perhaps it is hidden - but I can query
> for SETFILEBITS directly

Try using smbclient's "geteas <filename>" command.

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