linux-kernel - Re: [PATCH v3 0/7] File Sealing & memfd

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Message-ID: <53A012C8.7060109@redhat.com>
Date:	Tue, 17 Jun 2014 12:04:56 +0200
From:	Florian Weimer <fweimer@...hat.com>
To:	David Herrmann <dh.herrmann@...il.com>
CC:	Andy Lutomirski <luto@...capital.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Ryan Lortie <desrt@...rt.ca>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Greg Kroah-Hartman <greg@...ah.com>,
	John Stultz <john.stultz@...aro.org>,
	Lennart Poettering <lennart@...ttering.net>,
	Daniel Mack <zonque@...il.com>, Kay Sievers <kay@...y.org>,
	Hugh Dickins <hughd@...gle.com>,
	Tony Battersby <tonyb@...ernetics.com>
Subject: Re: [PATCH v3 0/7] File Sealing & memfd_create()

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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