linux-kernel - [PATCH v2 2/2] hfs: Update sanity check of the root record

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Message-ID: <20251104014738.131872-4-contact@gvernon.com>
Date: Tue,  4 Nov 2025 01:47:37 +0000
From: George Anthony Vernon <contact@...rnon.com>
To: slava@...eyko.com,
	glaubitz@...sik.fu-berlin.de,
	frank.li@...o.com,
	linux-fsdevel@...r.kernel.org,
	skhan@...uxfoundation.org
Cc: George Anthony Vernon <contact@...rnon.com>,
	linux-kernel@...r.kernel.org,
	linux-kernel-mentees@...ts.linux.dev,
	penguin-kernel@...ove.sakura.ne.jp,
	syzbot+97e301b4b82ae803d21b@...kaller.appspotmail.com,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: [PATCH v2 2/2] hfs: Update sanity check of the root record

syzbot is reporting that BUG() in hfs_write_inode() fires upon unmount
operation when the inode number of the record retrieved as a result of
hfs_cat_find_brec(HFS_ROOT_CNID) is not HFS_ROOT_CNID, for commit
b905bafdea21 ("hfs: Sanity check the root record") checked the record
size and the record type but did not check the inode number.

Reported-by: syzbot+97e301b4b82ae803d21b@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=97e301b4b82ae803d21b
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Signed-off-by: George Anthony Vernon <contact@...rnon.com>
---
 fs/hfs/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/hfs/super.c b/fs/hfs/super.c
index 47f50fa555a4..a7dd20f2d743 100644
--- a/fs/hfs/super.c
+++ b/fs/hfs/super.c
@@ -358,7 +358,7 @@ static int hfs_fill_super(struct super_block *sb, struct fs_context *fc)
 			goto bail_hfs_find;
 		}
 		hfs_bnode_read(fd.bnode, &rec, fd.entryoffset, fd.entrylength);
-		if (rec.type != HFS_CDR_DIR)
+		if (rec.type != HFS_CDR_DIR || rec.dir.DirID != cpu_to_be32(HFS_ROOT_CNID))
 			res = -EIO;
 	}
 	if (res)
-- 
2.50.1