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Message-ID: <2pro6x6xdvfhaypqhddzlmitx2vo6h7ro5mcqcf5tc7ssvzdls@cge4oegdkf5t>
Date: Thu, 23 Oct 2025 22:15:51 +0300
From: "Nikola Z. Ivanov" <zlatistiv@...il.com>
To: Chao Yu <chao@...nel.org>
Cc: jaegeuk@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org, skhan@...uxfoundation.org, david.hunter.linux@...il.com,
linux-kernel-mentees@...ts.linuxfoundation.org, khalid@...nel.org,
syzbot+c07d47c7bc68f47b9083@...kaller.appspotmail.com
Subject: Re: [PATCH] f2fs: Perform sanity check before unlinking directory
inode
On Wed, Oct 15, 2025 at 03:55:40PM +0300, Nikola Z. Ivanov wrote:
> On Wed, Oct 15, 2025 at 02:41:53PM +0800, Chao Yu wrote:
> > On 10/14/25 20:17, Nikola Z. Ivanov wrote:
> > > On Mon, Oct 13, 2025 at 08:53:04PM +0800, Chao Yu wrote:
> > >> On 10/13/25 05:19, Nikola Z. Ivanov wrote:
> > >>> On Thu, Oct 09, 2025 at 10:54:40AM +0800, Chao Yu wrote:
> > >>>> On 10/3/2025 9:47 PM, Nikola Z. Ivanov wrote:
> > >>>>> Current i_nlink corruption check does not take into account
> > >>>>> directory inodes which have one additional i_nlink for their "." entry.
> > >>>>>
> > >>>>> Add additional check and a common corruption path.
> > >>>>>
> > >>>>> Reported-by: syzbot+c07d47c7bc68f47b9083@...kaller.appspotmail.com
> > >>>>> Closes: https://syzkaller.appspot.com/bug?extid=c07d47c7bc68f47b9083
> > >>>>> Fixes: 81edb983b3f5 ("f2fs: add check for deleted inode")
> > >>>>> Signed-off-by: Nikola Z. Ivanov <zlatistiv@...il.com>
> > >>>>> ---
> > >>>>> fs/f2fs/namei.c | 28 ++++++++++++++++++++--------
> > >>>>> 1 file changed, 20 insertions(+), 8 deletions(-)
> > >>>>>
> > >>>>> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
> > >>>>> index b882771e4699..68b33e8089b0 100644
> > >>>>> --- a/fs/f2fs/namei.c
> > >>>>> +++ b/fs/f2fs/namei.c
> > >>>>> @@ -502,12 +502,14 @@ static struct dentry *f2fs_lookup(struct inode *dir, struct dentry *dentry,
> > >>>>> goto out;
> > >>>>> }
> > >>>>> - if (inode->i_nlink == 0) {
> > >>>>> + if (unlikely(inode->i_nlink == 0)) {
> > >>>>> f2fs_warn(F2FS_I_SB(inode), "%s: inode (ino=%lx) has zero i_nlink",
> > >>>>> __func__, inode->i_ino);
> > >>>>> - err = -EFSCORRUPTED;
> > >>>>> - set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
> > >>>>> - goto out_iput;
> > >>>>> + goto corrupted;
> > >>>>> + } else if (unlikely(S_ISDIR(inode->i_mode) && inode->i_nlink == 1)) {
> > >>>>> + f2fs_warn(F2FS_I_SB(inode), "%s: directory inode (ino=%lx) has a single i_nlink",
> > >>>>> + __func__, inode->i_ino);
> > >>>>> + goto corrupted;
> > >>>>
> > >>>> Can we detect such corruption in sanity_check_inode() as well? So that if
> > >>>> f2fs internal flow calls f2fs_iget() on corrupted inode, we can set SBI_NEED_FSCK
> > >>>> flag and then triggering fsck repairment later.
> > >>>>
> > >>>> Thanks,
> > >>>>
> > >>>>> }
> > >>>>> if (IS_ENCRYPTED(dir) &&
> > >>>>> @@ -533,6 +535,9 @@ static struct dentry *f2fs_lookup(struct inode *dir, struct dentry *dentry,
> > >>>>> trace_f2fs_lookup_end(dir, !IS_ERR_OR_NULL(new) ? new : dentry,
> > >>>>> ino, IS_ERR(new) ? PTR_ERR(new) : err);
> > >>>>> return new;
> > >>>>> +corrupted:
> > >>>>> + err = -EFSCORRUPTED;
> > >>>>> + set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
> > >>>>> out_iput:
> > >>>>> iput(inode);
> > >>>>> out:
> > >>>>> @@ -572,10 +577,11 @@ static int f2fs_unlink(struct inode *dir, struct dentry *dentry)
> > >>>>> if (unlikely(inode->i_nlink == 0)) {
> > >>>>> f2fs_warn(F2FS_I_SB(inode), "%s: inode (ino=%lx) has zero i_nlink",
> > >>>>> __func__, inode->i_ino);
> > >>>>> - err = -EFSCORRUPTED;
> > >>>>> - set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
> > >>>>> - f2fs_folio_put(folio, false);
> > >>>>> - goto fail;
> > >>>>> + goto corrupted;
> > >>>>> + } else if (unlikely(S_ISDIR(inode->i_mode) && inode->i_nlink == 1)) {
> > >>>>> + f2fs_warn(F2FS_I_SB(inode), "%s: directory inode (ino=%lx) has a single i_nlink",
> > >>>>> + __func__, inode->i_ino);
> > >>>>> + goto corrupted;
> > >>>>> }
> > >>>>> f2fs_balance_fs(sbi, true);
> > >>>>> @@ -601,6 +607,12 @@ static int f2fs_unlink(struct inode *dir, struct dentry *dentry)
> > >>>>> if (IS_DIRSYNC(dir))
> > >>>>> f2fs_sync_fs(sbi->sb, 1);
> > >>>>> +
> > >>>>> + goto fail;
> > >>>>> +corrupted:
> > >>>>> + err = -EFSCORRUPTED;
> > >>>>> + set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
> > >>>>> + f2fs_folio_put(folio, false);
> > >>>>> fail:
> > >>>>> trace_f2fs_unlink_exit(inode, err);
> > >>>>> return err;
> > >>>>
> > >>>
> > >>> Hi Chao,
> > >>>
> > >>> Thank you for the suggestion.
> > >>> I will add this to sanity_check_inode and remove it
> > >>> from f2fs_lookup as it becomes redundant since f2fs_lookup
> > >>> obtains the inode through f2fs_iget. For f2fs_unlink I will
> > >>> move the i_nlink == 1 check to f2fs_rmdir.
> > >>
> > >> Hi Nikola,
> > >>
> > >> I meant we can move the i_nlink == 1 check from both f2fs_lookup() and
> > >> f2fs_unlink() to sanity_check_inode(), because before we create in-memory
> > >> inode, we will always call sanity_check_inode().
> > >>
> > >> Let me know if you have other concerns.
> > >>
> > >> Thanks,
> > >>
> > >
> > > The issue here is that sanity_check_inode will be called only when
> > > we initially read the inode off disk, not when it's already in the cache
> > >
> > > The syzkaller repro does something like this:
> > > Creates a directory structure /dir1/dir2 where dir1 has
> > > i_nlink == 2, which is one less than it should. It then does
> > > rmdir(/dir1/dir2) followed by rmdir(/dir1) which leads to the warning.
> >
> > Oh, I missed this case.
> >
> > >
> > > In such case what would you say should happen, should the second rmdir
> > > fail and report the corruption, or do we close our eyes and just drop
> > > i_nlink to 0 and possibly log a message that something isn't quite right?
> >
> > I agreed that we should keep i_nlink == 1 check in f2fs_unlink().
> >
> > Thanks,
> >
>
> Hi Chao,
>
> Just to make sure we're on the same page, do you mean to keep the check
> in f2fs_unlink as well as sanity_check_inode, or only do it in f2fs_unlink?
>
Hello,
Kindly sending a reminder here, could you please
provide input when you have the chance?
Thank you!
> > >
> > > Thank you,
> > >
> > >>>
> > >>> I will send v2 as soon as I do some more testing.
> > >>
> >
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