Re: Leaking Path in XFS's ioctl interface(missing LSM check)

On Mon, 1 Oct 2018, Darrick J. Wong wrote:

If we /did/ replace CAP_SYS_ADMIN checking with a pile of LSM hooks,

Not sure we'd need a pile of hooks, what about just "read" and "write" 
storage admin?

Or even two new capabilities along these lines, which we convert existing 
CAP_SYS_ADMIN etc. to?

how do we make sure that we (XFS) avoid breaking existing XFS tools?  I 
guess the default compatibility handler for all of those new hooks would 
be "return capable(CAP_SYS_ADMIN) ? 0 : -EPERM;" and then other LSMs 
could restrict that further if so configured.

Seriously, I don't know that much about how LSMs actually perform
security checks -- it looks like a number of them can be active
simultaneously, and we just call each of them in a chain until one of
them denies permission or we run out of LSMs and allow it?

Correct.

FWIW I didn't have a particular security or threat model in mind when I
made the above list; all I did was break up the existing CAP_SYS_ADMIN
into rough functional areas.  Maybe it makes sense, but maybe I'm
rambling. :)

--D

quoted

You can build that model where for example only an administrative
login from a trusted console may launch processes to do that
management.

Or you could - if things were not going around the LSM hooks.

Alan

-- 
James Morris
[off-list ref]