From: Zi Yan <ziy@nvidia.com>

When dealing with hugetlb pages, manipulating struct page pointers
directly can get to wrong struct page, since struct page is not guaranteed
to be contiguous on SPARSEMEM without VMEMMAP. Use nth_page() to handle
it properly.

Fixes: 57a196a58421 ("hugetlb: simplify hugetlb handling in follow_page_mask")
Cc: <stable@vger.kernel.org>
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/hugetlb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index af74e83d92aa..8e68e6c53e66 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6469,7 +6469,7 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
 			}
 		}
 
-		page += ((address & ~huge_page_mask(h)) >> PAGE_SHIFT);
+		page = nth_page(page, ((address & ~huge_page_mask(h)) >> PAGE_SHIFT));
 
 		/*
 		 * Note that page may be a sub-page, and with vmemmap
-- 
2.40.1

On 13 Sep 2023, at 16:12, Zi Yan wrote:

> From: Zi Yan <ziy@nvidia.com>
>
> When dealing with hugetlb pages, manipulating struct page pointers
> directly can get to wrong struct page, since struct page is not guaranteed
> to be contiguous on SPARSEMEM without VMEMMAP. Use nth_page() to handle
> it properly.
>
> Fixes: 57a196a58421 ("hugetlb: simplify hugetlb handling in follow_page_mask")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> Reviewed-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  mm/hugetlb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index af74e83d92aa..8e68e6c53e66 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6469,7 +6469,7 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
>  			}
>  		}
>
> -		page += ((address & ~huge_page_mask(h)) >> PAGE_SHIFT);
> +		page = nth_page(page, ((address & ~huge_page_mask(h)) >> PAGE_SHIFT));
>
>  		/*
>  		 * Note that page may be a sub-page, and with vmemmap
> -- 
> 2.40.1

A wrong or non-existing page might be tried to be grabbed, either leading to
a non freeable page or kernel memory access errors. No bug is reported.
It comes from code inspection.


--
Best Regards,
Yan, Zi