Re: [RFC PATCH] mm/slab: Add size validation in kmalloc_array_* functions

[viswanath]

On Mon, 22 Sept 2025 at 23:30, Harry Yoo <harry.yoo@xxxxxxxxxx> wrote:

> When bytes > KKMALLOC_MAX_SIZE (8K on my system), kmalloc redirects allocation
> to the buddy allocator, which can allocate up to (PAGE_SIZE << MAX_PAGE_ORDER)
> bytes (4M on my system).

In include/linux/slab.h,
KMALLOC_MAX_SIZE is ultimately defined as PAGE_SIZE << MAX_PAGE_ORDER and
KMALLOC_MAX_CACHE_SIZE as PAGE_SIZE << 1

I was using those definitions

> Because allocating a page with order > MAX_PAGE_ORDER page is never
> supposed to succeed, the caller of kmalloc should be fixed rather than
> kmalloc itself.

So, Is it almost never a good idea to add new validation in the allocator code?

> I think the right fix should be to return -EINVAL in max_vclocks_store()
> if max * sizeof(int) exceeds PAGE_SIZE << MAX_PAGE_ORDER?

Thanks, I will go ahead with this approach

Thanks,
Viswanath