samba - Jan 2003 - UNIX/SAMBA file permission interaction

Hi Everyone,

Just prior to christmas I asked a question relating to the interaction
of SAMBA with UNIX permissions. The answer I got back was to set the
sticky bit on the folder in question. I did this and sure enough SAMBA
then followed the behaviour I expected.

Can any one explain to me why?

For those of you baffled, this is what occurs:

Without the sticky bit set on a folder that has rwx set for ogw a file
can be deleted from within this folder (using Windows Explorer)
regardless of whether you are the owner or part of the group that this
file belongs to. (as long as rw is set for the owner) If you use an
application to modify this same file the application behaves as expected
and prohibits you from modifying the file.

If you set the sticky bit on the folder, Windows Explorer then behaves
as it should (as does the application), and if you are not the owner or
part of the group that the file belongs to you can not delete the file.

I'm sorry, I must be missing something as this does not make sense.
Surely I would have expected SAMBA to adhere to the UNIX permissions
without the sticky bit being set on the folder.
-- 
David Beards
Technical Manager Networks and Systems
CFA
8 Lakeside Drive
Burwood East 3151

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On Sat, Jan 18, 2003 at 10:44:35PM +1100, David Beards
wrote:
> Without the sticky bit set on a folder that has rwx set for ogw a file
> can be deleted from within this folder (using Windows Explorer)
> regardless of whether you are the owner or part of the group that this
> file belongs to. (as long as rw is set for the owner) If you use an
> application to modify this same file the application behaves as expected
> and prohibits you from modifying the file.
> 
> If you set the sticky bit on the folder, Windows Explorer then behaves
> as it should (as does the application), and if you are not the owner or
> part of the group that the file belongs to you can not delete the file.
> 
> I'm sorry, I must be missing something as this does not make sense.
> Surely I would have expected SAMBA to adhere to the UNIX permissions
> without the sticky bit being set on the folder.
Samba is adhering to the UNIX permissions, that's how directory
permissions work. rw on the directory means that you (everyone, in your
case) can add/remove directory entries. Deleting a file is nothing more
than removing a directory entry, so you can do it because you're
modifying the directory and not the file. Setting the sticky bit on a
directory changes this behavior to only allow the owner of the file and
the owner of the directory to delete the file.

If you're curious, the sticky bit used to have another meaning (which is
where the name came from). I'm not clear on the details, but it had
something to do with keeping an executable's code segment in memory even
if there wasn't an instance running. I'm not sure if any current variety
of UNIX still implements that behavior, but I think most/all of them do
support sticky bits on directories (it's particularly important for /tmp
and /var/tmp).

-- 
Michael Heironimus