On Tue, Oct 27, 2020 at 6:34 PM Aleksandr Nogikh [off-list ref] wrote:

[...]

quoted

In addition to this global one, what do you think about per-hook fault
injection,
i.e. /sys/kernel/debug/fail_lsm_hooks/<FUNC>/retval ?

I was thinking about this, but decided to begin with a simple version
that could definitely be useful in practice (for syzbot/syzkaller it is just
necessary to have a fault injection capability that will be triggered via
fail-nth). If per-hook fault injection can also be useful to someone, I
can try to add it as well.

Yes, before we add it, it would be useful to have a clear use case
(otherwise we can add an unused thing, or implement it in a way that
slightly misses the use case).
Note that fail-nth allows to fail a single concrete site for testing,
though it's not super convenient for this as one would need to figure
out the right N first. But as a one-off test it should do.

quoted

In this case, we need a fault_attr for each hook. (Maybe, we can use the same
technique that is used to define security_hook_heads).

Yes, that technique should help to implement the feature in a very concise
way. Thanks for the suggestion.