linux-kernel - Re: [PATCH v4] f2fs: add check for deleted inode

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Message-ID: <Z76KaW6iAsafDDbB@google.com>
Date: Wed, 26 Feb 2025 03:28:41 +0000
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <chao@...nel.org>
Cc: linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	Leo Stone <leocstone@...il.com>,
	syzbot+b01a36acd7007e273a83@...kaller.appspotmail.com
Subject: Re: [PATCH v4] f2fs: add check for deleted inode

On 02/24, Chao Yu wrote:
> On 2/14/25 09:44, Chao Yu wrote:
> > On 2/14/25 01:38, Jaegeuk Kim wrote:
> >> On 02/13, Chao Yu wrote:
> >>> On 2/13/25 00:47, Jaegeuk Kim wrote:
> >>>> On 02/12, Chao Yu wrote:
> >>>>> From: Leo Stone <leocstone@...il.com>
> >>>>>
> >>>>> The syzbot reproducer mounts a f2fs image, then tries to unlink an
> >>>>> existing file. However, the unlinked file already has a link count of 0
> >>>>> when it is read for the first time in do_read_inode().
> >>>>>
> >>>>> Add a check to sanity_check_inode() for i_nlink == 0.
> >>>>>
> >>>>> [Chao Yu: rebase the code and fix orphan inode recovery issue]
> >>>>> Reported-by: syzbot+b01a36acd7007e273a83@...kaller.appspotmail.com
> >>>>> Closes: https://syzkaller.appspot.com/bug?extid=b01a36acd7007e273a83
> >>>>> Fixes: 39a53e0ce0df ("f2fs: add superblock and major in-memory structure")
> >>>>> Signed-off-by: Leo Stone <leocstone@...il.com>
> >>>>> Signed-off-by: Chao Yu <chao@...nel.org>
> >>>>> ---
> >>>>>  fs/f2fs/checkpoint.c | 4 ++++
> >>>>>  fs/f2fs/f2fs.h       | 1 +
> >>>>>  fs/f2fs/inode.c      | 6 ++++++
> >>>>>  3 files changed, 11 insertions(+)
> >>>>>
> >>>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> >>>>> index bd890738b94d..ada2c548645c 100644
> >>>>> --- a/fs/f2fs/checkpoint.c
> >>>>> +++ b/fs/f2fs/checkpoint.c
> >>>>> @@ -751,6 +751,8 @@ int f2fs_recover_orphan_inodes(struct f2fs_sb_info *sbi)
> >>>>>  	if (is_sbi_flag_set(sbi, SBI_IS_WRITABLE))
> >>>>>  		f2fs_info(sbi, "orphan cleanup on readonly fs");
> >>>>>  
> >>>>> +	set_sbi_flag(sbi, SBI_ORPHAN_RECOVERY);
> >>>>
> >>>> What about using SBI_POR_DOING?
> >>>
> >>> SBI_POR_DOING will cover most flow of f2fs_fill_super(), I think we can add a
> >>> separated flag just covering f2fs_recover_orphan_inodes(), so that we can allow
> >>> iget() of root_inode and all inodes during roll-forward recovery to do sanity
> >>> check nlink w/ zero. What do you think?
> >>
> >> Can we do this sanity check after f2fs_iget in the f2fs_unlink() only?
> > 
> > Sure, we need to cover f2fs_rename() as well, please check this:
> > 
> > https://lore.kernel.org/all/67450f9a.050a0220.21d33d.0003.GAE@google.com
> 
> Hi Jaegeuk,
> 
> I'm testing this, seems there is a problem, once we opened an inode that
> has zeroed nlink, in f2fs_evict_inode(), the inode and all its data will be
> deleted, then leaving its stale dir entry in parent directory.
> 
> What do you think using v4? so that we may has chance to repair it w/ fsck
> rather than just deleting it?

Do you mean v4 as the below change?

> 
> ---
>  fs/f2fs/namei.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
> index a278c7da8177..949621bc0d07 100644
> --- a/fs/f2fs/namei.c
> +++ b/fs/f2fs/namei.c
> @@ -547,6 +547,16 @@ static int f2fs_unlink(struct inode *dir, struct dentry *dentry)
>  		goto fail;
>  	}
> 
> +	if (unlikely(S_ISDIR(inode->i_mode) ?
> +			inode->i_nlink <= 1 : inode->i_nlink == 0)) {
> +		f2fs_err_ratelimited(sbi, "%s: inode (ino=%lx) has inconsistent nlink: %u, isdir: %d",
> +				__func__, inode->i_ino, inode->i_nlink,
> +				S_ISDIR(inode->i_mode));
> +		err = -EFSCORRUPTED;
> +		set_sbi_flag(sbi, SBI_NEED_FSCK);
> +		goto fail;
> +	}
> +
>  	err = f2fs_dquot_initialize(dir);
>  	if (err)
>  		goto fail;
> @@ -968,6 +978,15 @@ static int f2fs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
>  	}
> 
>  	if (new_inode) {
> +		if (unlikely(old_is_dir ?
> +			new_inode->i_nlink <= 1 : new_inode->i_nlink == 0)) {
> +			f2fs_err_ratelimited(sbi, "%s: inode (ino=%lx) has inconsistent nlink: %u, isdir: %d",
> +				__func__, new_inode->i_ino, new_inode->i_nlink,
> +				S_ISDIR(new_inode->i_mode));
> +			err = -EFSCORRUPTED;
> +			set_sbi_flag(sbi, SBI_NEED_FSCK);
> +			goto out_dir;
> +		}
> 
>  		err = -ENOTEMPTY;
>  		if (old_is_dir && !f2fs_empty_dir(new_inode))
> -- 
> 2.48.1.601.g30ceb7b040-goog
> 
> > 
> > Thanks,
> > 
> >>
> >>>
> >>> Thanks,
> >>>
> >>>>
> >>>>> +
> >>>>>  	start_blk = __start_cp_addr(sbi) + 1 + __cp_payload(sbi);
> >>>>>  	orphan_blocks = __start_sum_addr(sbi) - 1 - __cp_payload(sbi);
> >>>>>  
> >>>>> @@ -778,9 +780,11 @@ int f2fs_recover_orphan_inodes(struct f2fs_sb_info *sbi)
> >>>>>  		}
> >>>>>  		f2fs_put_page(page, 1);
> >>>>>  	}
> >>>>> +
> >>>>>  	/* clear Orphan Flag */
> >>>>>  	clear_ckpt_flags(sbi, CP_ORPHAN_PRESENT_FLAG);
> >>>>>  out:
> >>>>> +	clear_sbi_flag(sbi, SBI_ORPHAN_RECOVERY);
> >>>>>  	set_sbi_flag(sbi, SBI_IS_RECOVERED);
> >>>>>  
> >>>>>  	return err;
> >>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >>>>> index 05879c6dc4d6..1c75081c0c14 100644
> >>>>> --- a/fs/f2fs/f2fs.h
> >>>>> +++ b/fs/f2fs/f2fs.h
> >>>>> @@ -1322,6 +1322,7 @@ enum {
> >>>>>  	SBI_IS_CLOSE,				/* specify unmounting */
> >>>>>  	SBI_NEED_FSCK,				/* need fsck.f2fs to fix */
> >>>>>  	SBI_POR_DOING,				/* recovery is doing or not */
> >>>>> +	SBI_ORPHAN_RECOVERY,			/* orphan inodes recovery is doing */
> >>>>>  	SBI_NEED_SB_WRITE,			/* need to recover superblock */
> >>>>>  	SBI_NEED_CP,				/* need to checkpoint */
> >>>>>  	SBI_IS_SHUTDOWN,			/* shutdown by ioctl */
> >>>>> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> >>>>> index d6ad7810df69..02f1b69d03d8 100644
> >>>>> --- a/fs/f2fs/inode.c
> >>>>> +++ b/fs/f2fs/inode.c
> >>>>> @@ -386,6 +386,12 @@ static bool sanity_check_inode(struct inode *inode, struct page *node_page)
> >>>>>  		}
> >>>>>  	}
> >>>>>  
> >>>>> +	if (inode->i_nlink == 0 && !is_sbi_flag_set(sbi, SBI_ORPHAN_RECOVERY)) {
> >>>>> +		f2fs_warn(sbi, "%s: inode (ino=%lx) has a link count of 0",
> >>>>> +			  __func__, inode->i_ino);
> >>>>> +		return false;
> >>>>> +	}
> >>>>> +
> >>>>>  	return true;
> >>>>>  }
> >>>>>  
> >>>>> -- 
> >>>>> 2.48.1.502.g6dc24dfdaf-goog
> >