[PATCH security-next v5 00/30] LSM: Explict ordering

[Jordan Glover]

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‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Friday, October 12, 2018 3:19 AM, John Johansen <john.johansen at canonical.com> wrote:
>
> It isn't perfect but it manages consistency across distros as best as
> can be achieved atm.
>
> Its just a fact that some LSMs are not going to be built into some
> kernels. The only way to deal with that is direct people to build
> their own kernels.
>
> The other major problem is that the current LSM stacking patches do
> not deal with "extreme" stacking. So doing
>
> lsm=+apparmor
>
> (I am going to stick with the + syntax atm to avoid confusion between
> adding and setting)
>
> assuming apparmor is builtin will not necessarily get you apparmor if
> another major lsm is enabled. Yes your specific proposal would as it
> specifies it overrides the current major, except that ordering
> important so if say landlock registers before apparmor, you may still
> not get apparmor.
>

I think this will be solved with LSM_ORDER_LAST or something like that
Kees proposed.

> You proposal does not provide a means to ensure you have only a
> specific set of LSMs enabled. As an LSM not explicitly listed in lsm=
> lsm=! may still be enabled. So the user is going to have to be aware
> of the initial LSMs list if they are trying to guarentee a specific
> security arrangement.
>

What about special marker like "!!" which will mean "this string is
explicit?

lsm=!!,apparmor

will enable apparmor and disable everything else.

lsm=!!,!apparmor or lsm=!!

will set the string empty and disable everything.

"!!" in "CONFIG_LSM" will take precedence over "!!" in "lsm=" which
will make "lsm=" totally ignored. This way distro could lock specific
lsm set which isn't possible with current approach.

CONFIG_LSM=!!,yama,loadpin,integrity,apparmor

> This violates one of the hard asks, and I will tell you that this will
> just mean there is going to be some distro patching to make sure it
> exists.
>

I think I can quess who will make those patches :)

> The current explicit list is more consistent, and it is amenable to
> being extended with + or ! as selective add/remove so we are not
> locked into only supporting an explicit list.
>

Jordan