Re: [RFC 1/3] userns: add uuid field

["Serge E. Hallyn" <serge@hallyn.com>]

On Sun, Nov 28, 2021 at 08:29:21AM -0500, James Bottomley wrote:
> On Sat, 2021-11-27 at 22:45 -0600, Serge E. Hallyn wrote:
> > On Sat, Nov 27, 2021 at 04:45:47PM +0000, James Bottomley wrote:
> > > As a precursor to namespacing IMA a way of uniquely identifying the
> > > namespace to appear in the IMA log is needed.  This log may be
> > > transported away from the running system and may be analyzed even
> > > after the system has been rebooted.  Thus we need a way of
> > > identifying namespaces in the log which is unique.  UUID, being
> > > designed probabilistically never to repeat, fits this bill so add
> > > it to the user_namespace which we'll also use for namespacing IMA.
> > 
> > If the logs run across 5 boots, is it important to you that the
> > uuid be unique across all 5 boots?  Would it suffice to have a
> > per-boot unique count and report that plus some indicator of the
> > current boot (like boot time in jiffies)?
> 
> For the purposes of IMA it's only really important to have the uuid be
> unique within the particular log ... i.e. unique per boot.  However,
> given the prevalence of uuids elsewhere and the fact we have no current
> per-boot unique label for the namespace (the inode number could
> repeat), it seemed reasonable to employ uuids for this rather than
> invent a different identifier.  Plus IMA isn't going to complain if we
> have a globally unique identifier ...

Ok - Note I'm not saying I heavily object, but I'm mildly concerned
about users who happen to spin off a lot of user namespaces for
quick jobs being penalized.  I suspect Eric will also worry about the
namespacing implications - i.e. people *will* want to start restoring
user namespaces with a previously used uuid.

So given that 'unique per boot' is sufficient, what would be the problem
with simply adding a simple ever-increasing unique atomix count to the
struct user_namespace?

-serge