Re: [RFC 3/3] ima: make the integrity inode cache per namespace

[Christian Brauner <christian.brauner@ubuntu.com>]

On Mon, Nov 29, 2021 at 09:10:29AM -0500, James Bottomley wrote:
> On Mon, 2021-11-29 at 08:53 -0500, Stefan Berger wrote:
> > On 11/29/21 07:50, James Bottomley wrote:
> > > On Sun, 2021-11-28 at 22:58 -0600, Serge E. Hallyn wrote:
> > > > On Sat, Nov 27, 2021 at 04:45:49PM +0000, James Bottomley wrote:
> > > > > Currently we get one entry in the IMA log per unique file
> > > > > event.  So, if you have a measurement policy and it measures a
> > > > > particular binary it will not get measured again if it is
> > > > > subsequently executed. For Namespaced IMA, the correct
> > > > > behaviour
> > > > > seems to be to log once per inode per namespace (so every
> > > > > unique
> > > > > execution in a namespace gets a separate log entry).  Since
> > > > > logging
> > > > > once per inode per namespace is
> > > > I suspect I'll need to do a more in depth reading of the existing
> > > > code, but I'll ask the lazy question anyway (since you say "the
> > > > correct behavior seems to be") - is it actually important that
> > > > files which were appraised under a parent namespace's policy
> > > > already
> > > > should be logged again?
> > > I think so.  For a couple of reasons, assuming the namespace
> > > eventually
> > > gets its own log entries, which the next incremental patch proposed
> > > to
> > > do by virtualizing the securityfs entries.  If you don't do this:
> > 
> > To avoid duplicate efforts, an implementation of a virtualized 
> > securityfs is in this series here:
> > 
> > https://github.com/stefanberger/linux-ima-namespaces/commits/v5.15%2Bimans.20211119.v3
> > 
> > It starts with 'securityfs: Prefix global variables with secruityfs_'
> 
> That's quite a big patch series.  I already actually implemented this
> as part of the RFC for getting the per namespace measurement log.  The
> attached is basically what I did.
> 
> Most of the time we don't require namespacing the actual virtualfs
> file, because it's world readable.  IMA has a special requirement in
> this regard because the IMA files should be readable (and writeable
> when we get around to policy updates) by the admin of the namespace but
> their protection is 0640 or 0440.  I thought the simplest solution
> would be to make an additional flag that coped with the permissions and
> a per-inode flag way of making the file as "accessible by userns
> admin".  Doing something simple like this gives a much smaller
> diffstat:

That's a NAK from me. Stefan's series might be bigger but it does things
correctly. I appreciate the keep it simple attitude but no. I won't
speciale-case securityfs or similar stuff in core vfs helpers.

Christian