[Linaro-mm-sig] Re: [PATCH 02/12] skbuff: Proactively round up to kmalloc bucket size

On Wed, 21 Sep 2022 20:10:03 -0700 Kees Cook wrote:

diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 974bbbbe7138..4fe4c7544c1d 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -427,14 +427,15 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask, */ size = SKB_DATA_ALIGN(size); size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));

• data = kmalloc_reserve(size, gfp_mask, node, &pfmemalloc);
• if (unlikely(!data))

• goto nodata;
  

• /* kmalloc(size) might give us more room than requested.

• /* kmalloc(size) might give us more room than requested, so

• * allocate the true bucket size up front.
  

  • Put skb_shared_info exactly at the end of allocated zone,
  • to allow max possible filling before reallocation.
  */

• osize = ksize(data);

• osize = kmalloc_size_roundup(size);
• data = kmalloc_reserve(osize, gfp_mask, node, &pfmemalloc);
• if (unlikely(!data))

• goto nodata;
  

  size = SKB_WITH_OVERHEAD(osize); prefetchw(data + size);

I'd rename osize here to alloc_size for consistency but one could argue either way :)

Acked-by: Jakub Kicinski kuba@kernel.org