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SubjectRe: [PATCH v7 0/8] iov_iter: Improve page extraction (ref, pin or just list)
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On 23.01.23 18:25, Jan Kara wrote:
> On Mon 23-01-23 16:42:56, Matthew Wilcox wrote:
>> On Mon, Jan 23, 2023 at 04:38:47PM +0000, David Howells wrote:
>>> Matthew Wilcox <willy@infradead.org> wrote:
>>> Also you only mention DIO read - but what about "start DIO write; fork(); touch
>>> buffer" in the parent - now the write buffer belongs to the child and they can
>>> affect the parent's write.
>>
>> I'm struggling to see the problem here. If the child hasn't exec'd, the
>> parent and child are still in the same security domain. The parent
>> could have modified the buffer before calling fork().
>
> Sadly they are not. Android in particular starts applications by forking
> one big binary (zygote) that has multiple apps linked together and relies
> on the fact the child cannot influence the parent after the fork. We've
> already had CVEs with GUP & COW & fork due to this. David Hildebrand has a
> lot of memories regarding this I believe ;)

:)

Once FOLL_PIN is used most of the issues go away and we don't have to
play any games with VM flags or similar ...

With FOLL_PIN, I consider anon a solved problem and not worth any new
fancy ideas.

--
Thanks,

David / dhildenb

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