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

[PanBian <bianpan2016@163.com>]

On Tue, Nov 27, 2018 at 11:12:40AM +0800, Chao Yu wrote:
> On 2018/11/27 8:22, PanBian wrote:
> > 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.
> 
> Cool, if there is any progress, please let f2fs guys know, thank you in
> advance. :)

No problem. It's my honor to apply my tool to the Linux kernel.

> 
> Thanks,
>