Re: [PATCH v7 0/8] iov_iter: Improve page extraction (ref, pin or just list)

[David Hildenbrand]

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@xxxxxxxxxxxxx> 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