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

On Tue, 2022-01-11 at 20:14 -0500, Mimi Zohar wrote:

On Tue, 2022-01-11 at 21:26 +0000, Eric Snowberg wrote:

quoted

quoted

On Jan 11, 2022, at 11:16 AM, Mimi Zohar [off-list ref] wrote:

On Mon, 2022-01-10 at 23:25 +0000, Eric Snowberg wrote:

quoted

quoted

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