[PATCH v2 0/2] f2fs: Add sanity checks before unlinking and loading inodes

[PATCH v2 0/2] f2fs: Add sanity checks before unlinking and loading inodes

[Nikola Z. Ivanov]

This series is provoked by syzbot warnings caused by corrupted directory
inode with i_nlink == 1 that passes the initial sanity check which will
only mark the filesystem as corrupted in case i_nlink == 0.

Tests:
- fio/fsmark parallel create/unlink on VM with f2fs root filesystem.
- syzbot

Changelog:
Changes from v1:
- Rename exit label in f2fs_unlink().
- Add sanity check in sanity_check_inode() and remove it from f2fs_iget().
  as suggested by Chao Yu in order to detect on-disk corruption early.
https://lore.kernel.org/linux-f2fs-devel/d4b7c03c-6554-4407-b823-aecfcdf7dc3f@kernel.org/T/#t

Nikola Z. Ivanov (2):
  f2fs: Rename f2fs_unlink exit label
  f2fs: Add sanity checks before unlinking and loading  inodes

 fs/f2fs/inode.c | 10 ++++++++++
 fs/f2fs/namei.c | 27 +++++++++++++++++----------
 2 files changed, 27 insertions(+), 10 deletions(-)

-- 
2.51.0

[PATCH v2 1/2] f2fs: Rename f2fs_unlink exit label

[Nikola Z. Ivanov]

Rename "fail" label to "out" as it's used as a default
exit path out of f2fs_unlink as well as error path.

Signed-off-by: Nikola Z. Ivanov <zlatistiv@gmail.com>
---
 fs/f2fs/namei.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
index b882771e4699..40cf80fd9d9a 100644
--- a/fs/f2fs/namei.c
+++ b/fs/f2fs/namei.c
@@ -552,21 +552,21 @@ static int f2fs_unlink(struct inode *dir, struct dentry *dentry)
 
 	if (unlikely(f2fs_cp_error(sbi))) {
 		err = -EIO;
-		goto fail;
+		goto out;
 	}
 
 	err = f2fs_dquot_initialize(dir);
 	if (err)
-		goto fail;
+		goto out;
 	err = f2fs_dquot_initialize(inode);
 	if (err)
-		goto fail;
+		goto out;
 
 	de = f2fs_find_entry(dir, &dentry->d_name, &folio);
 	if (!de) {
 		if (IS_ERR(folio))
 			err = PTR_ERR(folio);
-		goto fail;
+		goto out;
 	}
 
 	if (unlikely(inode->i_nlink == 0)) {
@@ -575,7 +575,7 @@ static int f2fs_unlink(struct inode *dir, struct dentry *dentry)
 		err = -EFSCORRUPTED;
 		set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
 		f2fs_folio_put(folio, false);
-		goto fail;
+		goto out;
 	}
 
 	f2fs_balance_fs(sbi, true);
@@ -585,7 +585,7 @@ static int f2fs_unlink(struct inode *dir, struct dentry *dentry)
 	if (err) {
 		f2fs_unlock_op(sbi);
 		f2fs_folio_put(folio, false);
-		goto fail;
+		goto out;
 	}
 	f2fs_delete_entry(de, folio, dir, inode);
 	f2fs_unlock_op(sbi);
@@ -601,7 +601,7 @@ static int f2fs_unlink(struct inode *dir, struct dentry *dentry)
 
 	if (IS_DIRSYNC(dir))
 		f2fs_sync_fs(sbi->sb, 1);
-fail:
+out:
 	trace_f2fs_unlink_exit(inode, err);
 	return err;
 }
-- 
2.51.0

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

[Nikola Z. Ivanov]

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)) {
+		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;
-- 
2.51.0

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

[Chao Yu]

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;

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

[Nikola Z. Ivanov]

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@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,
> 

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;
> 

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

[Chao Yu]

On 11/3/25 15:55, Nikola Z. Ivanov wrote:
> 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@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,
>>
> 
> Hi Chao,
> 
> Do you suggest that it should not be wrapped in unlikely()?

Nikola,

No, I think we should not add this sanity check "inode->i_nlink == 0"
into sanity_check_inode(), as for an orphan inode, its i_nlink is zero.
We expect to get the inode w/o failure in recover_orphan_inode().

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

Looks fine to add unlike for the "dir->i_nlink == 1" case.

Thanks,

> 
> 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;
>>