linux-kernel - Re: [PATCH] fs: f2fs: remove WARN_ON in f2fs_is_valid

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Message-ID: <CAD-N9QXM_xds692Lh-QZc5aL01uRivLGrNnxJys41hiTUfKE5w@mail.gmail.com>
Date:   Sat, 9 Apr 2022 14:42:29 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     Chao Yu <chao@...nel.org>
Cc:     Dongliang Mu <dzm91@...t.edu.cn>, Jaegeuk Kim <jaegeuk@...nel.org>,
        syzbot+763ae12a2ede1d99d4dc@...kaller.appspotmail.com,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs: f2fs: remove WARN_ON in f2fs_is_valid_blkaddr

On Sat, Apr 9, 2022 at 11:46 AM Chao Yu <chao@...nel.org> wrote:
>
> On 2022/4/9 9:34, Dongliang Mu wrote:
> > On Sat, Apr 9, 2022 at 8:27 AM Chao Yu <chao@...nel.org> wrote:
> >>
> >> On 2022/4/8 13:22, Dongliang Mu wrote:
> >>> From: Dongliang Mu <mudongliangabcd@...il.com>
> >>>
> >>> In f2fs_is_valid_blkaddr, if type is DATA_GENERIC_ENHANCE or
> >>> DATA_GENERIC_ENHANCE_READ, it invokes WARN_ON(1) not matter
> >>> blkaddr is in the range or not.
> >>
> >> If we run into the path where we invoke WARN_ON(1) in f2fs_is_valid_blkaddr(),
> >> It means f2fs image may be broken, or there is a bug in f2fs.
> >>
> >> So, do you suffer any related issue in your environment?
> >
> > related issue? Can you explain a little?
> >
> > If you mean if this warning occurs, any other issues or crash
>
> I mean have you seen any warning info printed in the path of
> f2fs_is_valid_blkaddr() before applying this patch, and if so, w/ what
> reproducer? or you just figure out this patch from perspective of code
> review?

Yes, I have seen both warning information from Syzbot [1] and my local
syzkaller instance.

In f2fs_is_valid_blkaddr, if the following condition is satisfied,
i.e., blkaddr is not in the right range [2], it will directly invoke
one WARN_ON.

if (unlikely(blkaddr >= MAX_BLKADDR(sbi) ||
                 blkaddr < MAIN_BLKADDR(sbi))) {

This is the case on Syzbot.

Otherwise, it will jump into __is_bitmap_valid. And if the following
condition is satisfied [3], it will trigger another WARN_ON.

exist = f2fs_test_bit(offset, se->cur_valid_map);
if (!exist && type == DATA_GENERIC_ENHANCE) {

This appears in my local syzbot instance, but unfortunately it does
not get any reproducer.

[1] https://syzkaller.appspot.com/bug?extid=763ae12a2ede1d99d4dc
[2] https://elixir.bootlin.com/linux/latest/source/fs/f2fs/checkpoint.c#L187
[3] https://elixir.bootlin.com/linux/latest/source/fs/f2fs/checkpoint.c#L135


>
> Thanks,
>
> > behaviors are generated? I tested on the syzbot. After removing the
> > WARN_ON, there is no abnormal issue or crash behaviors followed with
> > the corresponding reproducer.
> >
> >
> >>
> >> Thanks,
> >>
> >>>
> >>> Fix this by removing WARN_ON.
> >>>
> >>> Note that, syzbot patch testing does not incur any further issues
> >>>
> >>> Reported-by: syzbot+763ae12a2ede1d99d4dc@...kaller.appspotmail.com
> >>> Signed-off-by: Dongliang Mu <mudongliangabcd@...il.com>
> >>> ---
> >>>    fs/f2fs/checkpoint.c | 2 --
> >>>    1 file changed, 2 deletions(-)
> >>>
> >>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> >>> index f5366feea82d..521498b2dd8c 100644
> >>> --- a/fs/f2fs/checkpoint.c
> >>> +++ b/fs/f2fs/checkpoint.c
> >>> @@ -158,7 +158,6 @@ static bool __is_bitmap_valid(struct f2fs_sb_info *sbi, block_t blkaddr,
> >>>                f2fs_err(sbi, "Inconsistent error blkaddr:%u, sit bitmap:%d",
> >>>                         blkaddr, exist);
> >>>                set_sbi_flag(sbi, SBI_NEED_FSCK);
> >>> -             WARN_ON(1);
> >>>        }
> >>>        return exist;
> >>>    }
> >>> @@ -196,7 +195,6 @@ bool f2fs_is_valid_blkaddr(struct f2fs_sb_info *sbi,
> >>>                        f2fs_warn(sbi, "access invalid blkaddr:%u",
> >>>                                  blkaddr);
> >>>                        set_sbi_flag(sbi, SBI_NEED_FSCK);
> >>> -                     WARN_ON(1);
> >>>                        return false;
> >>>                } else {
> >>>                        return __is_bitmap_valid(sbi, blkaddr, type);