[RFC PATCH v2 2/2] mm/mremap: Expose abnormal new_pte during move_ptes

[Pu Lehui <pulehui@huaweicloud.com>]

From: Pu Lehui <pulehui@huawei.com>

When executing move_ptes, the new_pte must be NULL, otherwise it will be
overwritten by the old_pte, and cause the abnormal new_pte to be leaked.
In order to make this problem to be more explicit, let's add
WARN_ON_ONCE when new_pte is not NULL.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Pu Lehui <pulehui@huawei.com>
---
 mm/mremap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/mremap.c b/mm/mremap.c
index 83e359754961..adb3a111b5c1 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -237,6 +237,8 @@ static int move_ptes(struct pagetable_move_control *pmc,
 
 	for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
 				   new_pte++, new_addr += PAGE_SIZE) {
+		WARN_ON_ONCE(!pte_none(*new_pte))
+
 		if (pte_none(ptep_get(old_pte)))
 			continue;
 
-- 
2.34.1