Subject: Re: [PATCH net/jkirsher] bpf, xdp, i40e: fix i40e_build_skb skb reserve and truesize

From: Keith Busch <[email-masked]>
Date: Wed, 13 Jun 2018 07:30:55 -0600

On Wed, Jun 13, 2018 at 11:04:36AM +0200, Daniel Borkmann wrote:
> Using skb_reserve(skb, I40E_SKB_PAD + (xdp->data - xdp->data_hard_start))
> is clearly wrong since I40E_SKB_PAD already points to the offset where
> the original xdp->data was sitting since xdp->data_hard_start is defined
> as xdp->data - i40e_rx_offset(rx_ring) where latter offsets to I40E_SKB_PAD
> when build skb is used.
> 
> However, also before cc5b114dcf98 ("bpf, i40e: add meta data support")
> this seems broken since bpf_xdp_adjust_head() helper could have been used
> to alter headroom and enlarge / shrink the frame and with that the assumption
> that the xdp->data remains unchanged does not hold and would push a bogus
> packet to upper stack.
> 
> ixgbe got this right in 924708081629 ("ixgbe: add XDP support for pass and
> drop actions"). In any case, fix it by removing the I40E_SKB_PAD from both
> skb_reserve() and truesize calculation.
> 
> Fixes: cc5b114dcf98 ("bpf, i40e: add meta data support")
> Fixes: 0c8493d90b6b ("i40e: add XDP support for pass and drop actions")
> Reported-by: Keith Busch <[email-masked]>
> Reported-by: Toshiaki Makita <[email-masked]>
> Signed-off-by: Daniel Borkmann <[email-masked]>
> Cc: Björn Töpel <[email-masked]>
> Cc: John Fastabend <[email-masked]>

Thanks for the quick fix! This works for me.

Tested-by: Keith Busch <[email-masked]>