Re: [PATCH 1/9] integrity: Prepare for having "ima" and "evm" available in "integrity" LSM

Mickaël Salaün
2022-10-17T09:32:59Z

On 14/10/2022 19:59, Kees Cook wrote:
> On Fri, Oct 14, 2022 at 04:40:01PM +0200, Mickaël Salaün wrote:
>> This is not backward compatible
>
> Why? Nothing will be running LSM hooks until init finishes, at which
> point the integrity inode cache will be allocated. And ima and evm don't
> start up until lateinit.
>
>> , but can easily be fixed thanks to
>> DEFINE_LSM().order
>
> That forces the LSM to be enabled, which may not be desired?

This is not backward compatible because currently IMA is enabled
independently of the "lsm=" cmdline, which means that for all installed
systems using IMA and also with a custom "lsm=" cmdline, updating the
kernel with this patch will (silently) disable IMA. Using ".order =
LSM_ORDER_FIRST," should keep this behavior.

BTW, I think we should set such order (but maybe rename it) for LSMs
that do nothing unless configured (e.g. Yama, Landlock).

>
>> Side node: I proposed an alternative to that but it was Nacked:
>> https://lore.kernel.org/all/20210222150608.808146-1-mic@digikod.net/
>
> Yeah, for the reasons pointed out -- that can't work. The point is to
> not have The Default LSM. I do think Casey's NAK was rather prickly,
> though. ;)

I don't agree, there is no "the default LSM", and this new behavior is
under an LSM_AUTO configuration option.