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

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Date:   Fri, 13 Apr 2018 09:25:37 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
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 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.

Thanks,

> 
>> Thanks,
> 
> .
>