linux-kernel - Re: [PATCH v2 2/2] f2fs: Add sanity checks before unlinking and loading inodes

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Message-ID: <pcxf66ac2yjkqyvhb6xgbk6jiihcejuncgbblkewz6rs7i5uzt@m6yjin7t67is>
Date: Mon, 3 Nov 2025 09:55:01 +0200
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 v2 2/2] f2fs: Add sanity checks before unlinking and
 loading inodes

On Mon, Nov 03, 2025 at 10:35:17AM +0800, Chao Yu wrote:
> On 11/1/25 20:56, Nikola Z. Ivanov wrote:
> > Add check for inode->i_nlink == 1 for directories during unlink,
> > as their value is decremented twice, which can trigger a warning in
> > drop_nlink. In such case mark the filesystem as corrupted and return
> > from the function call with the relevant failure return value.
> > 
> > Additionally add the 2 checks for i_nlink == 0 and i_nlink == 1 in
> > sanity_check_inode in order to detect on-disk corruption early.
> > 
> > Reported-by: syzbot+c07d47c7bc68f47b9083@...kaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=c07d47c7bc68f47b9083
> > Tested-by: syzbot+c07d47c7bc68f47b9083@...kaller.appspotmail.com
> > Signed-off-by: Nikola Z. Ivanov <zlatistiv@...il.com>
> > ---
> >  fs/f2fs/inode.c | 10 ++++++++++
> >  fs/f2fs/namei.c | 15 +++++++++++----
> >  2 files changed, 21 insertions(+), 4 deletions(-)
> > 
> > diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> > index 8c4eafe9ffac..089cbf3646f0 100644
> > --- a/fs/f2fs/inode.c
> > +++ b/fs/f2fs/inode.c
> > @@ -294,6 +294,16 @@ static bool sanity_check_inode(struct inode *inode, struct folio *node_folio)
> >  		return false;
> >  	}
> >  
> > +	if (unlikely(inode->i_nlink == 0)) {
> 
> This is a possible case, as an orphan inode may exist in filesystem after sudden
> power-cut.
> 
> Thanks,
> 

Hi Chao,

Do you suggest that it should not be wrapped in unlikely()?

I also now realise that I intended to wrap the "else if" case
as well but I've missed it in the final patch.

Should I resend the patch with both cases wrapped in "unlikely()"
or would you suggest otherwise?


> > +		f2fs_warn(F2FS_I_SB(inode), "%s: inode (ino=%lx) has zero i_nlink",
> > +			  __func__, inode->i_ino);
> > +		return false;
> > +	} else if (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);
> > +		return false;
> > +	}
> > +
> >  	if (f2fs_has_extra_attr(inode)) {
> >  		if (!f2fs_sb_has_extra_attr(sbi)) {
> >  			f2fs_warn(sbi, "%s: inode (ino=%lx) is with extra_attr, but extra_attr feature is off",
> > diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
> > index 40cf80fd9d9a..d13077bad482 100644
> > --- a/fs/f2fs/namei.c
> > +++ b/fs/f2fs/namei.c
> > @@ -572,10 +572,11 @@ 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 out;
> > +		goto corrupted;
> > +	} else if (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 +602,12 @@ static int f2fs_unlink(struct inode *dir, struct dentry *dentry)
> >  
> >  	if (IS_DIRSYNC(dir))
> >  		f2fs_sync_fs(sbi->sb, 1);
> > +
> > +	goto out;
> > +corrupted:
> > +	err = -EFSCORRUPTED;
> > +	set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
> > +	f2fs_folio_put(folio, false);
> >  out:
> >  	trace_f2fs_unlink_exit(inode, err);
> >  	return err;
>