linux-kernel - Re: [FYI] tux3: Core changes

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Date:	Tue, 26 May 2015 14:33:20 +0200
From:	Jan Kara <jack@...e.cz>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	Daniel Phillips <daniel@...nq.net>, Jan Kara <jack@...e.cz>,
	David Lang <david@...g.hm>, Rik van Riel <riel@...hat.com>,
	linux-fsdevel@...r.kernel.org, tux3@...3.org,
	linux-kernel@...r.kernel.org,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: [FYI] tux3: Core changes

On Tue 26-05-15 19:22:39, Sergey Senozhatsky wrote:
> On (05/26/15 01:08), Daniel Phillips wrote:
> > On Tuesday, May 26, 2015 12:09:10 AM PDT, Jan Kara wrote:
> > >  E.g. video drivers (or infiniband or direct IO for that matter) which
> > >have buffers in user memory (may be mmapped file), grab references to pages
> > >and hand out PFNs of those pages to the hardware to store data in them...
> > >If you fork a page after the driver has handed PFNs to the hardware, you've
> > >just lost all the writes hardware will do.
> > 
> > Hi Jan,
> > 
> > The page forked because somebody wrote to it with write(2) or mmap write at
> > the same time as a video driver (or infiniband or direct IO) was doing io to
> > it. Isn't the application trying hard to lose data in that case? It would
> > not need page fork to lose data that way.
> > 
> 
> Hello,
> 
> is it possible to page-fork-bomb the system by some 'malicious' app?
  Well, you can have only two copies of each page - the one under writeout
and the one in page cache. Furthermore you are limited by dirty throttling
so I don't think this would allow any out-of-ordinary DOS vector...

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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