[OpenAFS] Re: fs setacl and permissions

Christopher D. Clausen cclausen@acm.org
Tue, 30 Jan 2007 10:49:27 -0600

Bob Cook <bobcook@slac.stanford.edu> wrote:
> On Sun, 28 Jan 2007, Juha [UTF-8] JC$ykkC$ wrote:
>>> So what it really comes down to is this: I claim that, if someone
>>> who "owns" a directory (i.e. has "explicit" a privs) defines a
>>> subdirectory and restricts someone else to non-a privs there, it is
>>> really a security breach for that someone else to be able to get
>>> "a" privs anywhere below it.  But that's exactly what this
>>> "implicit a privs for a directory's owner" provides.
>> Good point, but one question immediately arises: why was the other
>> obvious solution discarded? The other one being as follows. Suppose
>> your scenario with a teacher, who owns and has "a" at dir1 plus a
>> bunch of students, who own dir1/student1, dir1/student2 etc and have
>> "a" in their respective directories. Suppose teacher also wants to
>> have "a" on all subdirectories of dir1. Now, your problem can be
>> solved by allowing anyone with "a" access to dir1 to alter the ACLs
>> on all its subdirs. This way, if a student removes the teacher from
>> the ACL of dir1/student1, the teacher can always grant oneself the
>> access again. I fail to see which security holes this would open,
>> although I wouldn't be surprised if it does since the regular unix
>> filesystems and chmod/chown do not seem to allow this either.
> I'm not an expert on this stuff, but two things occur to me.  One is
> that your "obvious solution" doesn't allow me a different scenario.
> Suppose I want to allocate a subdirectory to someone else and turn
> over ALL control
> to that person; i.e., I don't want to be involved any more; I don't
> want to have ANY privileges in the new directory.  With my scenario,
> I can easily remove myself after adding rlidwka for the new "owner".
> But with yours, I can't.
> The other is that your solution doesn't allow me to allocate a
> subdirectory to someone or group with permissions more restricted
> than rlidwk, because the person/group can regain all those
> permissions in the subdirectories they create, and I can't prevent it.

I see a need for both solutions.  Would it be possible to change the 
behaviour on a per-fileserver basis?  That you could allow one scenario 
on volumes on fileserver a and allow the other on fileserver b.

Perhaps a flag to the fileserver on start-up to select which method the 
cell admin would like?