Re: [PATCH v3 29/30] luo: allow preserving memfd

[Pratyush Yadav]

On Wed, Aug 13 2025, Greg KH wrote:

> On Wed, Aug 13, 2025 at 09:41:40AM -0300, Jason Gunthorpe wrote:
[...]
>> Use the warn ons. Make sure they can't be triggered by userspace. Use
>> them to detect corruption/malfunction in the kernel.
>> 
>> In this case if kho_unpreserve_folio() fails in this call chain it
>> means some error unwind is wrongly happening out of sequence, and we
>> are now forced to leak memory. Unwind is not something that userspace
>> should be controlling, so of course we want a WARN_ON here.
>
> "should be" is the key here.  And it's not obvious from this patch if
> that's true or not, which is why I mentioned it.
>
> I will keep bringing this up, given the HUGE number of CVEs I keep
> assigning each week for when userspace hits WARN_ON() calls until that
> flow starts to die out either because we don't keep adding new calls, OR
> we finally fix them all.  Both would be good...

Out of curiosity, why is hitting a WARN_ON() considered a vulnerability?
I'd guess one reason is overwhelming system console which can cause a
denial of service, but what about WARN_ON_ONCE() or WARN_RATELIMIT()?

-- 
Regards,
Pratyush Yadav