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

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Message-ID: <20181126102841.GA94853@bp>
Date:   Mon, 26 Nov 2018 18:28:41 +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 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.

Best regards,
Pan Bian