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

[Luke Kenneth Casson Leighton]

On Wed, 5 Jan 2000, Cole, Timothy D. wrote:

> > -----Original Message-----
> > From:	Luke Kenneth Casson Leighton [SMTP:lkcl at samba.org]
> > Sent:	Tuesday, January 04, 2000 20:49
> > To:	Multiple recipients of list SAMBA-TECHNICAL
> > Subject:	RE: Security Identifier (SID) to User Identifier (uid)
> > Resolution  System
> > 
> > On Tue, 4 Jan 2000, Steve Langasek wrote:
> > 
> > > On Wed, 5 Jan 2000, Luke Kenneth Casson Leighton wrote:
> > > 
> > > > > 	Well, I said what I did under the assumption that there
> > would be no
> > > > > mapping from -2 back to any SID (i.e. the mapping function would
> > fail).
> > > 
> > > > the mapping from SID to unknowwn uid MUST fail.  the mapping from uid
> > to
> > > > unknown SID MUST fail.
> > > 
> > > Wouldn't this be a cosmetic issue?  If the driver only allows access to
> > the
> > > resource if it can successfully map a uid/gid to an SID, and it's
> > explicit
> > > that the 'nobody' uid will *not* map to an SID, then it will only
> > *appear*
> > > that user 'nobody' has read/write/whatever access.  That, IMHO, is a lot
> > > better than returning -1 from stat() and having to invent a new errno
> > for the
> > > occasion.  Returning a uid that no one on the system is supposed to be
> > > using should be relatively harmless, as long as it doesn't mean that
> > POSIX uid
> > > isn't *really* granted illegitimate access to the file.
> > 
> > hum, don't know exactly what's going on, here.  like i keep mentioning,
> > i'm not a unix expert.
> > 
> > as long as you're not telling me that you want to use nobody(-2) as an NT
> > user, i think that's ok, but i don't quite get why.
> > 
> > .. how does not mapping to a uid make a user "appear" to have rwx/
> > acccess?  what kind of acess?  and are you referring to "user "appearing""
> > as an nt user or a unix user?
> > 
> 	this is basically about stat() -- it's a single system call used to
> fill out a structure with all the following information about a given file,
> and is the only POSIX way to get the following information about a file:
> 
> 	 - block device the filesystem is on
> 	 - the file's inode number
> 	 - the filesystem type (not in all Unices)
> 	 - the file's permissions set (rwx) and type
> (directory/file/char/block/fifo/symlink/socket)
> 	 - number of links (directory entries referencing the file)
> 	 - the uid of the file's owner
> 	 - the gid of the file's owning group
> 	 - device id (for char and block devices only)
> 	 - the file size
> 	 - last access time
> 	 - last modification time
> 	 - last attribute change time
> 
> 	If stat() fails, then it is impossible to determine any of this
> information.  Many, many things rely on being able to stat() a file (under
> normal circumstances, assuming the object exists, the only reason stat()
> would fail is if the user did not have search(execute) permission on the
> object's container).
> 
> 	Consequently, we need SOMETHING to put in the st_uid and st_gid
> fields if the SID is unknown.
>

AH!  you're talking about a _kernel_ level implemntation that uses this
stuff, not samba.

ok...  having created a uid / gid, it's permanent, so it's ok.  ither
representations are then nothing to do with this.  it's _external_
representiations that, say, samba or winbind use, that sid/uid converion
becomes imprtant.