[PATCH] hfs: Sanity check the root record

[Leo Stone]

In the syzbot reproducer, the hfs_cat_rec for the root dir has type
HFS_CDR_FIL after being read with hfs_bnode_read() in hfs_super_fill().
This indicates it should be used as an hfs_cat_file, which is 102 bytes.
Only the first 70 bytes of that struct are initialized, however,
because the entrylength passed into hfs_bnode_read() is still the length of
a directory record. This causes uninitialized values to be used later on,
when the hfs_cat_rec union is treated as the larger hfs_cat_file struct.

Add a check to make sure the retrieved record has the correct type
for the root directory (HFS_CDR_DIR).

Reported-by: syzbot+2db3c7526ba68f4ea776@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=2db3c7526ba68f4ea776
Tested-by: syzbot+2db3c7526ba68f4ea776@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Leo Stone <leocstone@xxxxxxxxx>
---
 fs/hfs/super.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/hfs/super.c b/fs/hfs/super.c
index 3bee9b5dba5e..02d78992eefd 100644
--- a/fs/hfs/super.c
+++ b/fs/hfs/super.c
@@ -354,6 +354,8 @@ 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)
+			res = -EIO;
 	}
 	if (res)
 		goto bail_hfs_find;
-- 
2.43.0