[PATCH v3 0/2] f2fs: Add sanity checks before unlinking and loading inodes

[PATCH v3 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

  Changes from v2:
  - Remove i_nlink == 0 check from sanity_check_inode.
  - Wrap i_nlink == 1 in unlikely() marco.
  https://lore.kernel.org/linux-f2fs-devel/1f519357-a489-41fe-8159-a8e319aedd17@kernel.org/T/#u

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

 fs/f2fs/inode.c |  6 ++++++
 fs/f2fs/namei.c | 27 +++++++++++++++++----------
 2 files changed, 23 insertions(+), 10 deletions(-)

-- 
2.51.0

[PATCH v3 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 v3 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 check for 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 |  6 ++++++
 fs/f2fs/namei.c | 15 +++++++++++----
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 8c4eafe9ffac..b808e1dc2ae7 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -294,6 +294,12 @@ static bool sanity_check_inode(struct inode *inode, struct folio *node_folio)
 		return false;
 	}
 
+	if (S_ISDIR(inode->i_mode) && unlikely(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..65af1d56a99e 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) && unlikely(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 v3 2/2] f2fs: Add sanity checks before unlinking and loading inodes

[Chao Yu]

On 11/4/25 16:46, 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 check for i_nlink == 1 in
> sanity_check_inode in order to detect on-disk corruption early.
> 

Cc: stable@kernel.org

> 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 |  6 ++++++
>  fs/f2fs/namei.c | 15 +++++++++++----
>  2 files changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> index 8c4eafe9ffac..b808e1dc2ae7 100644
> --- a/fs/f2fs/inode.c
> +++ b/fs/f2fs/inode.c
> @@ -294,6 +294,12 @@ static bool sanity_check_inode(struct inode *inode, struct folio *node_folio)
>  		return false;
>  	}
>  
> +	if (S_ISDIR(inode->i_mode) && unlikely(inode->i_nlink == 1)) {
> +		f2fs_warn(F2FS_I_SB(inode), "%s: directory inode (ino=%lx) has a single i_nlink",

s/F2FS_I_SB(inode)/sbi

> +			  __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..65af1d56a99e 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) && unlikely(inode->i_nlink == 1)) {
> +		f2fs_warn(F2FS_I_SB(inode), "%s: directory inode (ino=%lx) has a single i_nlink",

Ditto,

> +			  __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);

Ditto,

Thanks,

> +	f2fs_folio_put(folio, false);
>  out:
>  	trace_f2fs_unlink_exit(inode, err);
>  	return err;