Re: [PATCH] f2fs: read page index before freeing

From: PanBian
Date: Mon Nov 26 2018 - 19:23:03 EST

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.