linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Hugh Dickins <hughd@google.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Christian Koenig <christian.koenig@amd.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: Possible deny of service with memfd_create()
Date: Thu, 4 Feb 2021 16:32:38 -0800 (PST)	[thread overview]
Message-ID: <alpine.LSU.2.11.2102041627040.2796@eggly.anvils> (raw)
In-Reply-To: <YBwrGNS+Q4JMpuom@dhcp22.suse.cz>

On Thu, 4 Feb 2021, Michal Hocko wrote:
> On Thu 04-02-21 17:32:20, Christian Koenig wrote:
> > Hi Michal,
> > 
> > as requested in the other mail thread the following sample code gets my test
> > system down within seconds.
> > 
> > The issue is that the memory allocated for the file descriptor is not
> > accounted to the process allocating it, so the OOM killer pics whatever
> > process it things is good but never my small test program.
> > 
> > Since memfd_create() doesn't need any special permission this is a rather
> > nice deny of service and as far as I can see also works with a standard
> > Ubuntu 5.4.0-65-generic kernel.
> 
> Thanks for following up. This is really nasty but now that I am looking
> at it more closely, this is not really different from tmpfs in general.
> You are free to create files and eat the memory without being accounted
> for that memory because that is not seen as your memory from the sysstem
> POV. You would have to map that memory to be part of your rss.
> 
> The only existing protection right now is to use memoery cgroup
> controller because the tmpfs memory is accounted to the process which
> faults the memory in (or write to the file).
> 
> I am not sure there is a good way to handle this in general
> unfortunatelly. Shmem is is just tricky (e.g. how to you deal with left
> overs after the fd is closed?). Maybe memfd_create can be more clever
> and account memory to all owners of the fd but even that sounds far from
> trivial from the accounting POV. It is true that tmpfs can at least
> control who can write to it which is not the case for memfd but then we
> hit the backward compatibility wall.

Yes, no solution satisfactory, and memcg best, but don't forget
echo 2 >/proc/sys/vm/overcommit_memory

Hugh

  reply	other threads:[~2021-02-05  0:33 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-04 16:32 Possible deny of service with memfd_create() Christian König
2021-02-04 17:12 ` Michal Hocko
2021-02-05  0:32   ` Hugh Dickins [this message]
2021-02-05  7:54     ` Christian König
2021-02-05 10:50       ` Michal Hocko
2021-02-05 10:57         ` Christian König
2021-02-05 12:26           ` Michal Hocko

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=alpine.LSU.2.11.2102041627040.2796@eggly.anvils \
    --to=hughd@google.com \
    --cc=christian.koenig@amd.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mhocko@suse.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).