Security Identifier (SID) to User Identifier (uid) Resolution System

Cole, Timothy D. timothy_d_cole at
Tue Jan 4 21:30:50 GMT 2000

> -----Original Message-----
> From:	Steve Langasek [SMTP:vorlon at]
> Sent:	Tuesday, January 04, 2000 15:04
> To:	Cole, Timothy D.
> Cc:	Multiple recipients of list SAMBA-TECHNICAL
> Subject:	RE: Security Identifier (SID) to User Identifier (uid)
> Resolution  System
> On Wed, 5 Jan 2000, Cole, Timothy D. wrote:
> > 	On another note, although it's not really relevent to Samba, over
> > the holiday I was actually pondering sticking a SURS-like table in a
> hidden
> > inode on an ext2/3 filesystem, mapping between uids/gids on the disk and
> > SIDs.  The kernel patch would also include a SURS-like mapping table
> > in-kernel, which would map between SIDs and "system" uids/gids (which
> might
> > well be different from those on disk).
> > 	The kernel table would be filled out from userspace, having a few
> > initial entries for root and the like hard-coded.   SIDs with no kernel
> > entry would map to uid/gid -2 (nobody), until such time as a mapping
> were
> > added from userspace.  Mapping between fs uids/gids and "system"
> uids/gids
> > would be done by the filesystem driver, so none of the existing
> interfaces
> > would really have to change -- no hits from comparing SIDs everywhere,
> it's
> > still all word-size integers.
> Intriguing.  It's probably not that important for a first implementation,
> but
> would it be possible to make the default 'nobody' SID mapping configurable
> via
> a mount option?
	Hmm, that's a good idea.  Yes, I would think it'd be trivial to do.

	The actual kernel table lookup (which would be independent of the
filesystems) would still return -2, but since the fs driver would be the one
doing the lookup, it could return whatever uid/gid it wanted in that case.

	Or, better, the lookup function could take a parameter for the
uid/gid to fall back on, which would of course be supplied by the caller,
normally fs driver.  Yes, that seems like a better design to me.

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