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

Nikola Z. Ivanov
2025-11-04T08:46:45Z

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