[PATCH v4 0/2] f2fs: Add sanity checks before unlinking and loading inodes

[PATCH v4 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

  Changes from v3:
  - Replace F2FS_I_SB(inode) with already obtained f2fs_sb_info pointer.
  https://lore.kernel.org/linux-f2fs-devel/4de88613-54a2-4ef3-9b56-7963cd3e42e6@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 | 29 ++++++++++++++++++-----------
 2 files changed, 24 insertions(+), 11 deletions(-)

-- 
2.51.0

[PATCH v4 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

Re: [PATCH v4 1/2] f2fs: Rename f2fs_unlink exit label

[Chao Yu]

On 11/5/25 19:09, Nikola Z. Ivanov wrote:
> 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>

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,

[PATCH v4 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 | 17 ++++++++++++-----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 8c4eafe9ffac..e2405b79b3cc 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(sbi, "%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..849cfdc57b30 100644
--- a/fs/f2fs/namei.c
+++ b/fs/f2fs/namei.c
@@ -570,12 +570,13 @@ 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",
+		f2fs_warn(sbi, "%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(sbi, "%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(sbi, SBI_NEED_FSCK);
+	f2fs_folio_put(folio, false);
 out:
 	trace_f2fs_unlink_exit(inode, err);
 	return err;
-- 
2.51.0

Re: [PATCH v4 2/2] f2fs: Add sanity checks before unlinking and loading inodes

[Chao Yu]

On 11/5/25 19:09, 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.
> 
> 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>

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,

Re: [f2fs-dev] [PATCH v4 0/2] f2fs: Add sanity checks before unlinking and loading inodes

[patchwork-bot+f2fs]

Hello:

This series was applied to jaegeuk/f2fs.git (dev)
by Jaegeuk Kim <jaegeuk@kernel.org>:

On Wed,  5 Nov 2025 13:09:41 +0200 you wrote:
> 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
> 
> [...]

Here is the summary with links:
  - [f2fs-dev,v4,1/2] f2fs: Rename f2fs_unlink exit label
    https://git.kernel.org/jaegeuk/f2fs/c/7b4827ce2d2a
  - [f2fs-dev,v4,2/2] f2fs: Add sanity checks before unlinking and loading inodes
    https://git.kernel.org/jaegeuk/f2fs/c/d43f8de77d6c

You are awesome, thank you!
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