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

From: Chao Yu
Date: Mon Nov 26 2018 - 22:12:46 EST

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. :)


> Best,
> Pan
> .