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

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Message-ID: <20201009145626.GA2186792@google.com>
Date:   Fri, 9 Oct 2020 07:56:26 -0700
From:   jaegeuk@...nel.org
To:     Chao Yu <yuchao0@...wei.com>
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 10/09, Chao Yu wrote:
> 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?

We may need another option to deal with this. At least, however, it's literally
_nofail function which should guarantee no error, instead of hiding the error
with zero'ed page.

> 
> 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
> > > > > > .
> > > > > > 
> > > > .
> > > > 
> > .
> >