SELinux: skip file_name_trans_write() when policy downgraded.

When policy version is less than POLICYDB_VERSION_FILENAME_TRANS,
skip file_name_trans_write().
Signed-off-by: Roy.Li <rongqing.li@windriver.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

security/selinux/ss/policydb.c

@@ -3222,6 +3222,9 @@ static int filename_trans_write(struct policydb *p, void *fp)
 	__le32 buf[1];
 	int rc;
 
+	if (p->policyvers < POLICYDB_VERSION_FILENAME_TRANS)
+		return 0;
+
 	nel = 0;
 	rc = hashtab_map(p->filename_trans, hashtab_cnt, &nel);
 	if (rc)