Re: [PATCH v9 2/8] integrity: Introduce a Linux keyring called machine

[Jarkko Sakkinen <jarkko@kernel.org>]

On Sat, Jan 15, 2022 at 07:12:35PM +0000, Eric Snowberg wrote:
> 
> 
> > On Jan 15, 2022, at 10:11 AM, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> > 
> > On Wed, Jan 12, 2022 at 02:41:47PM -0500, Mimi Zohar wrote:
> >> On Tue, 2022-01-11 at 20:14 -0500, Mimi Zohar wrote:
> >>> On Tue, 2022-01-11 at 21:26 +0000, Eric Snowberg wrote:
> >>>> 
> >>>>> On Jan 11, 2022, at 11:16 AM, Mimi Zohar <zohar@linux.ibm.com> wrote:
> >>>>> 
> >>>>> On Mon, 2022-01-10 at 23:25 +0000, Eric Snowberg wrote:
> >>>>>>> Jarkko, my concern is that once this version of the patch set is
> >>>>>>> upstreamed, would limiting which keys may be loaded onto the .machine
> >>>>>>> keyring be considered a regression?
> >>>>>> 
> >>>>>> 
> >>>>>> Currently certificates built into the kernel do not have a CA restriction on them.  
> >>>>>> IMA will trust anything in this keyring even if the CA bit is not set.  While it would 
> >>>>>> be advisable for a kernel to be built with a CA, nothing currently enforces it. 
> >>>>>> 
> >>>>>> My thinking for the dropped CA restriction patches was to introduce a new Kconfig.  
> >>>>>> This Kconfig would do the CA enforcement on the machine keyring.  However if the 
> >>>>>> Kconfig option was not set for enforcement, it would work as it does in this series, 
> >>>>>> plus it would allow IMA to work with non-CA keys.  This would be done by removing 
> >>>>>> the restriction placed in this patch. Let me know your thoughts on whether this would 
> >>>>>> be an appropriate solution.  I believe this would get around what you are identifying as 
> >>>>>> a possible regression.
> >>>>> 
> >>>>> True the problem currently exists with the builtin keys, but there's a
> >>>>> major difference between trusting the builtin keys and those being
> >>>>> loading via MOK.  This is an integrity gap that needs to be closed and
> >>>>> shouldn't be expanded to keys on the .machine keyring.
> >>>>> 
> >>>>> "plus it would allow IMA to work with non-CA keys" is unacceptable.
> >>>> 
> >>>> Ok, I’ll leave that part out.  Could you clarify the wording I should include in the future 
> >>>> cover letter, which adds IMA support, on why it is unacceptable for the end-user to
> >>>> make this decision?
> >>> 
> >>> The Kconfig IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY
> >>> "help" is very clear:
> >> 
> >> [Reposting the text due to email formatting issues.]
> >> 
> >> help
> >>  Keys may be added to the IMA or IMA blacklist keyrings, if the
> >>  key is validly signed by a CA cert in the system built-in or
> >>  secondary trusted keyrings.
> >> 
> >>  Intermediate keys between those the kernel has compiled in and the 
> >>  IMA keys to be added may be added to the system secondary keyring,
> >>  provided they are validly signed by a key already resident in the
> >>  built-in or secondary trusted keyrings.
> >> 
> >> 
> >> The first paragraph requires "validly signed by a CA cert in the system
> >> built-in or secondary trusted keyrings" for keys to be loaded onto the
> >> IMA keyring.  This Kconfig is limited to just the builtin and secondary
> >> keyrings.  Changing this silently to include the ".machine" keyring
> >> introduces integrity risks that previously did not exist.  A new IMA
> >> Kconfig needs to be defined to allow all three keyrings - builtin,
> >> machine, and secondary.
> >> 
> >> The second paragraph implies that only CA and intermediate CA keys are
> >> on secondary keyring, or as in our case the ".machine" keyring linked
> >> to the secondary keyring.
> >> 
> >> Mimi
> >> 
> > I have also now test environment for this patch set but if there are
> > any possible changes, I'm waiting for a new version, as it is anyway
> > for 5.18 cycle earliest.
> 
> Other than the two sentence changes, I have not seen anything identified 
> code wise requiring a change.  If you’d like me to respin a v10 with the sentence 
> changes let me know.  Or if you want to remove the ima reference, that works 
> too.  Just let me know how you want to handle this.  Thanks.

I'm basically waiting also Mimi to test this as I do not have IMA test
environment.

From my side:

Tested-by: Jarkko Sakkinen <jarkko@kernel.org>

/Jarkko