linux-kernel - Re: [f2fs-dev] [f2fs bug] infinite loop in f2fs_get_meta_page

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Date:   Fri, 9 Oct 2020 15:05:25 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     <jaegeuk@...nel.org>
CC:     Eric Biggers <ebiggers@...nel.org>,
        <syzbot+ee250ac8137be41d7b13@...kaller.appspotmail.com>,
        <syzkaller-bugs@...glegroups.com>, <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [f2fs bug] infinite loop in
 f2fs_get_meta_page_nofail()

On 2020/10/9 12:32, jaegeuk@...nel.org wrote:
> On 10/09, Chao Yu wrote:
>> On 2020/10/9 9:50, jaegeuk@...nel.org wrote:
>>> On 10/09, Chao Yu wrote:
>>>> On 2020/10/8 5:53, jaegeuk@...nel.org wrote:
>>>>> On 10/07, Eric Biggers wrote:
>>>>>> [moved linux-fsdevel to Bcc]
>>>>>>
>>>>>> On Wed, Oct 07, 2020 at 02:18:19AM -0700, syzbot wrote:
>>>>>>> Hello,
>>>>>>>
>>>>>>> syzbot found the following issue on:
>>>>>>>
>>>>>>> HEAD commit:    a804ab08 Add linux-next specific files for 20201006
>>>>>>> git tree:       linux-next
>>>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=17fe30bf900000
>>>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=26c1b4cc4a62ccb
>>>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=ee250ac8137be41d7b13
>>>>>>> compiler:       gcc (GCC) 10.1.0-syz 20200507
>>>>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1336413b900000
>>>>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12f7392b900000
>>>>>>>
>>>>>>> The issue was bisected to:
>>>>>>>
>>>>>>> commit eede846af512572b1f30b34f9889d7df64c017d4
>>>>>>> Author: Jaegeuk Kim <jaegeuk@...nel.org>
>>>>>>> Date:   Fri Oct 2 21:17:35 2020 +0000
>>>>>>>
>>>>>>>        f2fs: f2fs_get_meta_page_nofail should not be failed
>>>>>>>
>>>>>>
>>>>>> Jaegeuk, it looks like the loop you added in the above commit doesn't terminate
>>>>>> if the requested page is beyond the end of the device.
>>>>>
>>>>> Yes, that will go infinite loop. Otherwise, it will trigger a panic during
>>>>> the device reboot. Let me think how to avoid that before trying to get the
>>>>> wrong lba access.
>>>>
>>>> Delivering f2fs_get_sum_page()'s return value needs a lot of codes change, I think
>>>> we can just zeroing sum_page in error case, as we have already shutdown f2fs via
>>>> calling f2fs_stop_checkpoint(), then f2fs_cp_error() will stop all updates to
>>>> filesystem data including summary pages.
>>>
>>> That sounds like one solution tho, I'm afraid of getting another panic by
>>> wrong zero'ed summary page.
>>
>> What case do you mean? maybe I missed some corner cases?
> 
> I sent v2 to fix syzbot issue, which fixes wrong use of
> f2fs_get_meta_page_nofail.

I agreed to fix that case, however we may encounter deadloop in other
places where we call f2fs_get_meta_page_nofail()? like the case that
filesystem will always see EIO after we shutdown device via dmflakey?

Thanks,

> 
>>
>> Thanks,
>>
>>>
>>>>
>>>> Thoughts?
>>>>
>>>> Thanks,
>>>>
>>>>>
>>>>>>
>>>>>> - Eric
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Linux-f2fs-devel mailing list
>>>>> Linux-f2fs-devel@...ts.sourceforge.net
>>>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>>>> .
>>>>>
>>> .
>>>
> .
>