Re: [PATCH v3 0/7] File Sealing & memfd_create()

[Florian Weimer]

On 06/17/2014 12:01 PM, David Herrmann wrote:

> > I don't think this is what potential users expect because mlock requires
> > capabilities which are not available to them.
> >
> > A couple of weeks ago, sealing was to be applied to anonymous shared memory.
> > Has this changed?  Why should *reading* it trigger OOM?
>
> The file might have holes, therefore, you'd have to allocate backing
> pages. This might hit a soft-limit and fail. To avoid this, use
> fallocate() to allocate pages prior to mmap()

This does not work because the consuming side does not know how the 
descriptor was set up if sealing does not imply that.

> or mlock() to make the kernel lock them in memory.

See above for why that does not work.

I think you should eliminate the holes on sealing and report ENOMEM 
there if necessary.

--
Florian Weimer / Red Hat Product Security Team
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