linux-kernel - [PATCH] f2fs: Perform sanity check before unlinking directory inode

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Message-ID: <20251003134731.470392-1-zlatistiv@gmail.com>
Date: Fri,  3 Oct 2025 16:47:31 +0300
From: "Nikola Z. Ivanov" <zlatistiv@...il.com>
To: jaegeuk@...nel.org,
	chao@...nel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Cc: linux-kernel@...r.kernel.org,
	skhan@...uxfoundation.org,
	david.hunter.linux@...il.com,
	linux-kernel-mentees@...ts.linuxfoundation.org,
	khalid@...nel.org,
	"Nikola Z. Ivanov" <zlatistiv@...il.com>,
	syzbot+c07d47c7bc68f47b9083@...kaller.appspotmail.com
Subject: [PATCH] f2fs: Perform sanity check before unlinking directory inode

Current i_nlink corruption check does not take into account
directory inodes which have one additional i_nlink for their "." entry.

Add additional check and a common corruption path.

Reported-by: syzbot+c07d47c7bc68f47b9083@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c07d47c7bc68f47b9083
Fixes: 81edb983b3f5 ("f2fs: add check for deleted inode")
Signed-off-by: Nikola Z. Ivanov <zlatistiv@...il.com>
---
 fs/f2fs/namei.c | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
index b882771e4699..68b33e8089b0 100644
--- a/fs/f2fs/namei.c
+++ b/fs/f2fs/namei.c
@@ -502,12 +502,14 @@ static struct dentry *f2fs_lookup(struct inode *dir, struct dentry *dentry,
 		goto out;
 	}
 
-	if (inode->i_nlink == 0) {
+	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);
-		goto out_iput;
+		goto corrupted;
+	} else if (unlikely(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;
 	}
 
 	if (IS_ENCRYPTED(dir) &&
@@ -533,6 +535,9 @@ static struct dentry *f2fs_lookup(struct inode *dir, struct dentry *dentry,
 	trace_f2fs_lookup_end(dir, !IS_ERR_OR_NULL(new) ? new : dentry,
 				ino, IS_ERR(new) ? PTR_ERR(new) : err);
 	return new;
+corrupted:
+	err = -EFSCORRUPTED;
+	set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
 out_iput:
 	iput(inode);
 out:
@@ -572,10 +577,11 @@ 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 fail;
+		goto corrupted;
+	} else if (unlikely(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 +607,12 @@ static int f2fs_unlink(struct inode *dir, struct dentry *dentry)
 
 	if (IS_DIRSYNC(dir))
 		f2fs_sync_fs(sbi->sb, 1);
+
+	goto fail;
+corrupted:
+	err = -EFSCORRUPTED;
+	set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
+	f2fs_folio_put(folio, false);
 fail:
 	trace_f2fs_unlink_exit(inode, err);
 	return err;
-- 
2.51.0