netdev - Re: [Nbd] [PATCH 3/4] treewide: convert PF_MEMALLOC manipulations to new helpers

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 6 Apr 2017 08:38:10 +0200
From:   Wouter Verhelst <w@...r.be>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        nbd-general@...ts.sourceforge.net, Chris Leech <cleech@...hat.com>,
        linux-scsi@...r.kernel.org, Josef Bacik <jbacik@...com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, linux-mm@...ck.org,
        Eric Dumazet <edumazet@...gle.com>,
        Lee Duncan <lduncan@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        open-iscsi@...glegroups.com,
        Mel Gorman <mgorman@...hsingularity.net>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [Nbd] [PATCH 3/4] treewide: convert PF_MEMALLOC manipulations to
 new helpers

On Wed, Apr 05, 2017 at 01:30:31PM +0200, Michal Hocko wrote:
> On Wed 05-04-17 09:46:59, Vlastimil Babka wrote:
> > We now have memalloc_noreclaim_{save,restore} helpers for robust setting and
> > clearing of PF_MEMALLOC. Let's convert the code which was using the generic
> > tsk_restore_flags(). No functional change.
> 
> It would be really great to revisit why those places outside of the mm
> proper really need this flag. I know this is a painful exercise but I
> wouldn't be surprised if there were abusers there.
[...]
> > ---
> >  drivers/block/nbd.c      | 7 ++++---
> >  drivers/scsi/iscsi_tcp.c | 7 ++++---
> >  net/core/dev.c           | 7 ++++---
> >  net/core/sock.c          | 7 ++++---
> >  4 files changed, 16 insertions(+), 12 deletions(-)

These were all done to make swapping over network safe. The idea is that
if a socket has SOCK_MEMALLOC set, incoming packets for that socket can
access PFMEMALLOC reserves (whereas other sockets cannot); this all in
the hope that one packe destined to that socket will contain the TCP ACK
that confirms the swapout was successful and we can now release RAM
pages for other processes.

I don't know whether they need the PF_MEMALLOC flag specifically (not a
kernel hacker), but they do need to interact with it at any rate.

-- 
< ron> I mean, the main *practical* problem with C++, is there's like a dozen
       people in the world who think they really understand all of its rules,
       and pretty much all of them are just lying to themselves too.
 -- #debian-devel, OFTC, 2016-02-12