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

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Date:   Fri, 9 Oct 2020 10:37:01 +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 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?

Thanks,

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