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

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Mon, 2021-11-29 at 09:30 -0500, Stefan Berger wrote:
> On 11/29/21 09:10, 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.
> 
> I know it's big. I tried to avoid having to bind-mount the system-
> wide single securityfs into the container and inherit all the other
> security subsystems' files and directories (evm, TPM, safesetid,
> apparmor, tomoyo  [ 
> https://elixir.bootlin.com/linux/latest/C/ident/securityfs_create_dir
>  
> ]) and instead have a  'view' that is a bit more restricted to those 
> subsystems that are namespaced. The securityfs_ns I created can be 
> mounted into each user namespace individually and only shows what
> you're supposed to see without other filesystem tricks to hide files
> or so. It should be future-extensible for other subsystem to register
> themselves there if they have something to show to the user.

Using F_USER_NS for this is certainly what it was designed for.  I
don't think size is a problem as long as it's right sized to perform
the required function.  I usually find it easier to oversimplify and
work up, but that's certainly not the only approach.

James