Re: [PATCH] killswitch: add per-function short-circuit mitigation primitive

[Sasha Levin]

On Thu, May 07, 2026 at 09:21:15AM -0600, Jonathan Corbet wrote:
> Sasha Levin <sashal@xxxxxxxxxx> writes:
>
> > When a (security) issue goes public, fleets stay exposed until a patched kernel
> > is built, distributed, and rebooted into.
> >
> > For many such issues the simplest mitigation is to stop calling the buggy
> > function. Killswitch provides that. An admin writes:
> >
> >     echo "engage af_alg_sendmsg -1" \
> >         > /sys/kernel/security/killswitch/control
> >
> > After this, af_alg_sendmsg() returns -EPERM on every call without
> > running its body. The mitigation takes effect immediately, and is dropped on
> > the next reboot.
>
> A quick look suggests that you're not checking lockdown status.  I don't
> doubt for a second that this thing could be used to bypass lockdown - by
> shorting out security_locked_down() if nothing else.  I'm guessing that
> might not prove entirely popular.

Hmm... Good point. I'll respin a v2 adressing this and Greg's comments.

--
Thanks,
Sasha