On Thu, 2018-11-01 at 14:47 -0700, Andrew Morton wrote:
> 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;
A bit tidier still might be
if (count > PAGE_SIZE)
count = PAGE_SIZE;
as that would not always cause a write back to count.
