[ale] Permission hell question

[Stephan Uphoff]

Geoffrey wrote:
> Dow Hurst wrote:
> > The underlying mount point permissions are very important to match up 
> > with what your filesystem has that will be mounted.  You can't see those 
> > permissions on the mount point unless the filesystem isn't mounted yet 
> > on that mount point.
> 
> This isn't accurate either, sorry Dow. :)
> 
> /mnt/memstick on my box was 755 and I can mount it and created/delete 
> files or directories.  As root, I changed the perms of /mnt/memstick to 
> 700.  I'm still able to mount the filesystem as well as create/delete 
> files and directories.

The permissions of the covered mount point usually only come into play
when accessing ".." from the root of the mounted fs.

This is true for Unix and BSD ... but I have never looked at this part 
of the Linux sources.

As a normal user try to
	cd /mnt/memstick  #OK
	pwd               #Fails unless cached by shell
	ls ..             #Should fail

with /mnt/memstick permission set to 700 and user root.

It is not really necessary to have matching permissions - but the wrong set
of permissions can cause interesting problems in a production environment.

	Stephan