On Sat, 28 May 2022 23:39:33 +0800 Chen Lin <chen45464546@xxxxxxx> wrote:
> netdev_alloc_frag->page_frag_alloc may cause memory corruption in
> the following process:
>
> 1. A netdev_alloc_frag function call need alloc 200 Bytes to build a skb.
>
> 2. Insufficient memory to alloc PAGE_FRAG_CACHE_MAX_ORDER(32K) in
> __page_frag_cache_refill to fill frag cache, then one page(eg:4K)
> is allocated, now current frag cache is 4K, alloc is success,
> nc->pagecnt_bias--.
>
> 3. Then this 200 bytes skb in step 1 is freed, page->_refcount--.
>
> 4. Another netdev_alloc_frag function call need alloc 5k, page->_refcount
> is equal to nc->pagecnt_bias, reset page count bias and offset to
> start of new frag. page_frag_alloc will return the 4K memory for a
> 5K memory request.
>
> 5. The caller write on the extra 1k memory which is not actual allocated
> will cause memory corruption.
>
> page_frag_alloc is for fragmented allocation. We should warn the caller
> to avoid memory corruption.
>
Let's cc Alexander and the networking developers.
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5574,6 +5574,11 @@ void *page_frag_alloc_align(struct page_frag_cache *nc,
> struct page *page;
> int offset;
>
> + /* frag_alloc is not suitable for memory alloc which fragsz
> + * is bigger than PAGE_SIZE, use kmalloc or alloc_pages instead.
> + */
> + WARN_ON(fragsz > PAGE_SIZE);
> +
> if (unlikely(!nc->va)) {
> refill:
> page = __page_frag_cache_refill(nc, gfp_mask);
Odd. All this does is generate a warning. If the kernel is corrupting
memory, that's a bug which needs fixing?
