bcachefs: Guard against unknown k.k->type in __bkey_invalid()

For forwards compatibility we have to allow unknown key types, and only
run the checks that make sense against them.

Fix a missing guard on k.k->type being known.

Reported-by: syzbot+ae4dc916da3ce51f284f@syzkaller.appspotmail.com
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bkey_methods.c

@@ -171,8 +171,8 @@ int __bch2_bkey_invalid(struct bch_fs *c, struct bkey_s_c k,
 	if (type >= BKEY_TYPE_NR)
 		return 0;
 
-	bkey_fsck_err_on((type == BKEY_TYPE_btree ||
-			  (flags & BKEY_INVALID_COMMIT)) &&
+	bkey_fsck_err_on(k.k->type < KEY_TYPE_MAX &&
+			 (type == BKEY_TYPE_btree || (flags & BKEY_INVALID_COMMIT)) &&
 			 !(bch2_key_types_allowed[type] & BIT_ULL(k.k->type)), c, err,
 			 bkey_invalid_type_for_btree,
 			 "invalid key type for btree %s (%s)",