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

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Message-ID: <mafs01ppfxwe8.fsf@kernel.org>
Date: Wed, 13 Aug 2025 14:02:07 +0200
From: Pratyush Yadav <pratyush@...nel.org>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: Vipin Sharma <vipinsh@...gle.com>,  Pasha Tatashin
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Subject: Re: [PATCH v3 29/30] luo: allow preserving memfd

On Wed, Aug 13 2025, Greg KH wrote:

> On Tue, Aug 12, 2025 at 11:34:37PM -0700, Vipin Sharma wrote:
>> On 2025-08-07 01:44:35, Pasha Tatashin wrote:
>> > From: Pratyush Yadav <ptyadav@...zon.de>
>> > +static void memfd_luo_unpreserve_folios(const struct memfd_luo_preserved_folio *pfolios,
>> > +					unsigned int nr_folios)
>> > +{
>> > +	unsigned int i;
>> > +
>> > +	for (i = 0; i < nr_folios; i++) {
>> > +		const struct memfd_luo_preserved_folio *pfolio = &pfolios[i];
>> > +		struct folio *folio;
>> > +
>> > +		if (!pfolio->foliodesc)
>> > +			continue;
>> > +
>> > +		folio = pfn_folio(PRESERVED_FOLIO_PFN(pfolio->foliodesc));
>> > +
>> > +		kho_unpreserve_folio(folio);
>> 
>> This one is missing WARN_ON_ONCE() similar to the one in
>> memfd_luo_preserve_folios().
>
> So you really want to cause a machine to reboot and get a CVE issued for
> this, if it could be triggered?  That's bold :)
>
> Please don't.  If that can happen, handle the issue and move on, don't
> crash boxes.

Why would a WARN() crash the machine? That is what BUG() does, not
WARN().

-- 
Regards,
Pratyush Yadav