userswap: add user mode check for swap-out VA

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I6CAIM

--------------------------------

Add user mode check for swap-out VA to make sure that swap-out VA is
user mode address.
Signed-off-by: NZhangPeng <zhangpeng362@huawei.com>

mm/userswap.c

@@ -367,7 +367,8 @@ unsigned long uswap_mremap(unsigned long old_addr, unsigned long old_len,
 	    offset_in_page(new_addr) || (len % PAGE_SIZE))
 		return ret;
 
-	if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
+	if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len ||
+	    old_addr > TASK_SIZE - old_len)
 		return ret;
 
 	/* Ensure the old/new locations do not overlap */