linux-kernel - Re: [PATCH] f2fs: set deadline to drop expired inmem pages

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Date:   Thu, 12 Apr 2018 21:05:25 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH] f2fs: set deadline to drop expired inmem pages

On 04/13, Chao Yu wrote:
> On 2018/4/13 9:04, Jaegeuk Kim wrote:
> > On 04/10, Chao Yu wrote:
> >> Hi Jaegeuk,
> >>
> >> On 2018/4/8 16:13, Chao Yu wrote:
> >>> f2fs doesn't allow abuse on atomic write class interface, so except
> >>> limiting in-mem pages' total memory usage capacity, we need to limit
> >>> start-commit time as well, otherwise we may run into infinite loop
> >>> during foreground GC because target blocks in victim segment are
> >>> belong to atomic opened file for long time.
> >>>
> >>> Now, we will check the condition with f2fs_balance_fs_bg in
> >>> background threads, once if user doesn't commit data exceeding 30
> >>> seconds, we will drop all cached data, so I expect it can keep our
> >>> system running safely to prevent Dos attack.
> >>
> >> Is it worth to add this patch to avoid abuse on atomic write interface by user?
> > 
> > Hmm, hope to see a real problem first in this case.
> 
> I think this can be a more critical security leak instead of a potential issue
> which we can wait for someone reporting that can be too late.
> 
> For example, user can simply write a huge file whose data spread in all f2fs
> segments, once user open that file as atomic, foreground GC will suffer
> deadloop, causing denying any further service of f2fs.

How can you guarantee it won't happen within 30sec? If you want to avoid that,
you have to take a look at foreground gc.

> 
> Thanks,
> 
> > 
> >> Thanks,
> > 
> > .
> >