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

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

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@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=c07d47c7bc68f47b9083
> Tested-by: syzbot+c07d47c7bc68f47b9083@syzkaller.appspotmail.com
> Signed-off-by: Nikola Z. Ivanov <zlatistiv@gmail.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,

> +		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;



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