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

[Florian Weimer <fweimer@redhat.com>]

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