linux-kernel - [PATCH v5] hfs: update sanity check of the root record

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Message-ID: <56dd2ace-7e72-424d-a51a-67c48ae58686@I-love.SAKURA.ne.jp>
Date: Fri, 12 Sep 2025 23:59:27 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Viacheslav Dubeyko <Slava.Dubeyko@....com>,
        Viacheslav Dubeyko <slava@...eyko.com>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Yangtao Li <frank.li@...o.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: [PATCH v5] 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.

Viacheslav Dubeyko considers that the fix should be in hfs_read_inode()
but Viacheslav has no time for proposing the fix [1]. Also, we can't
guarantee that the inode number of the record retrieved as a result of
hfs_cat_find_brec(HFS_ROOT_CNID) is HFS_ROOT_CNID if we validate only in
hfs_read_inode(). Therefore, while what Viacheslav would propose might
partially overwrap with my proposal, let's fix an 1000+ days old bug by
adding a sanity check in hfs_fill_super().

Reported-by: syzbot+97e301b4b82ae803d21b@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=97e301b4b82ae803d21b
Link: https://lkml.kernel.org/r/a3d1464ee40df7f072ea1c19e1ccf533e34554ca.camel@ibm.com [1]
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
---
 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 388a318297ec..ae6dbc4bb813 100644
--- a/fs/hfs/super.c
+++ b/fs/hfs/super.c
@@ -354,7 +354,7 @@ 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)
-- 
2.51.0