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

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Date:   Fri, 9 Oct 2020 09:42:02 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     <jaegeuk@...nel.org>, Eric Biggers <ebiggers@...nel.org>
CC:     <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 2020/10/8 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.

Thoughts?

Thanks,

> 
>>
>> - Eric
> 
> 
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