Re: [PATCH v4] mm/page_owner: clamp read count to PAGE_SIZE

[Andrew Morton]

On Fri, 2 Nov 2018 01:00:07 +0800 <miles.c...@mediatek.com> wrote:

> From: Miles Chen <miles.c...@mediatek.com>
> 
> The page owner read might allocate a large size of memory with
> a large read count. Allocation fails can easily occur when doing
> high order allocations.
> 
> Clamp buffer size to PAGE_SIZE to avoid arbitrary size allocation
> and avoid allocation fails due to high order allocation.
> 
> ...
>
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -351,6 +351,7 @@ print_page_owner(char __user *buf, size_t count, unsigned 
> long pfn,
>               .skip = 0
>       };
>  
> +     count = count > PAGE_SIZE ? PAGE_SIZE : count;
>       kbuf = kmalloc(count, GFP_KERNEL);
>       if (!kbuf)
>               return -ENOMEM;

A bit tidier:

--- a/mm/page_owner.c~mm-page_owner-clamp-read-count-to-page_size-fix
+++ a/mm/page_owner.c
@@ -351,7 +351,7 @@ print_page_owner(char __user *buf, size_
                .skip = 0
        };
 
-       count = count > PAGE_SIZE ? PAGE_SIZE : count;
+       count = min_t(size_t, count, PAGE_SIZE);
        kbuf = kmalloc(count, GFP_KERNEL);
        if (!kbuf)
                return -ENOMEM;