netdev - Re: [PATCH ipsec] xfrm: Provide private skb extensions for segmented and hw offloaded ESP packets

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Date:   Tue, 23 Mar 2021 13:02:35 +0100
From:   Florian Westphal <fw@...len.de>
To:     Steffen Klassert <steffen.klassert@...unet.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH ipsec] xfrm: Provide private skb extensions for segmented
 and hw offloaded ESP packets

Steffen Klassert <steffen.klassert@...unet.com> wrote:
> Commit 94579ac3f6d0 ("xfrm: Fix double ESP trailer insertion in IPsec
> crypto offload.") added a XFRM_XMIT flag to avoid duplicate ESP trailer
> insertion on HW offload. This flag is set on the secpath that is shared
> amongst segments. This lead to a situation where some segments are
> not transformed correctly when segmentation happens at layer 3.
> 
> Fix this by using private skb extensions for segmented and hw offloaded
> ESP packets.
> 
> Fixes: 94579ac3f6d0 ("xfrm: Fix double ESP trailer insertion in IPsec crypto offload.")
> Signed-off-by: Steffen Klassert <steffen.klassert@...unet.com>
> ---
>  include/linux/skbuff.h  |  1 +
>  net/core/skbuff.c       | 23 ++++++++++++++++++-----
>  net/ipv4/esp4_offload.c | 16 +++++++++++++++-
>  net/ipv6/esp6_offload.c | 16 +++++++++++++++-
>  net/xfrm/xfrm_device.c  |  2 --
>  5 files changed, 49 insertions(+), 9 deletions(-)
> 
> -	if (hw_offload)
> +	if (hw_offload) {
> +		ext = skb_ext_cow(skb->extensions, skb->active_extensions);

It should be possible to do

	if (hw_offload) {
		if (!skb_ext_add(skb, SKB_EXT_SECPATH);
			return -ENOMEM;

		xo = xfrm_offload(skb);
		....

without need for a new 'cow' function.
skb_ext_add() will auto-COW if the extension area has a refcount > 1.