linux-kernel - Re: [syzbot] [mm?] WARNING in __folio_rmap_sanity

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Message-ID: <51de00af-9860-4617-80d4-8c9818bcce3d@redhat.com>
Date: Fri, 10 Jan 2025 17:31:37 +0100
From: David Hildenbrand <david@...hat.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: syzbot <syzbot+c0673e1f1f054fac28c2@...kaller.appspotmail.com>,
 akpm@...ux-foundation.org, hdanton@...a.com, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, syzkaller-bugs@...glegroups.com,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Subject: Re: [syzbot] [mm?] WARNING in __folio_rmap_sanity_checks (2)

On 10.01.25 17:27, Matthew Wilcox wrote:
> On Fri, Jan 10, 2025 at 05:19:54PM +0100, David Hildenbrand wrote:
>> On 10.01.25 17:14, Matthew Wilcox wrote:
>>> On Fri, Jan 10, 2025 at 04:48:03PM +0100, David Hildenbrand wrote:
>>>> If I would have to guess, I would assume that we have a refcount issue such
>>>> that we succeed in splitting a folio while concurrently mapping it.
>>>
>>> That would seem hard to accomplish, because both hold the folio lock,
>>> so it wouldn't be just a refcount bug but also a locking bug.  Not sure
>>> what this is though.
>>
>> Yeah, but we also have
>>
>> https://lkml.kernel.org/r/6774bf44.050a0220.25abdd.098a.GAE@google.com
> 
> That one is a UAF on the vma, so it's either a different issue, or the
> problem is with the VMA refcount/lookup/..., not the folio refcount.
> cc'ing the relevant maintainers.

Agreed, it's all a bit confusing.

-- 
Cheers,

David / dhildenb