linux-kernel - Re: [PATCH] f2fs: read page index before freeing

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Date:   Tue, 27 Nov 2018 08:22:47 +0800
From:   PanBian <bianpan2016@....com>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     Jaegeuk Kim <jaegeuk@...nel.org>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: read page index before freeing

On Mon, Nov 26, 2018 at 07:07:08PM +0800, Chao Yu wrote:
> On 2018/11/26 18:28, PanBian wrote:
> > On Mon, Nov 26, 2018 at 05:13:53PM +0800, Chao Yu wrote:
> >> Hi Pan,
> >>
> >> On 2018/11/22 18:58, Pan Bian wrote:
> >>> The function truncate_node frees the page with f2fs_put_page. However,
> >>> the page index is read after that. So, the patch reads the index before
> >>> freeing the page.
> >>
> >> I notice that you found another use-after-free bug in ext4, out of
> >> curiosity, I'd like to ask how do you find those bugs? by tool or code review?
> > 
> > I found such bugs by the aid of a tool I wrote recently. I designed a method 
> > to automatically find paired alloc/free functions. With such functions, I
> > wrote two checkers, one to check mismatched alloc/free bugs, the other to
> > check use-after-free and double-free bugs.
> 
> Excellent! Do you have any plan to open its source or announce it w/ binary
> to linux kernel developers, I think w/ it we can help to improve kernel's
> code quality efficiently.

Yes. I am now writing a paper about the method. I will open the source code
as soon as I complete the paper and some optimizations.

Best,
Pan