Subject: Re: [RFC ipsec-next v2 6/8] iptfs: xfrm: Add mode_cbs module functionality

From: Sabrina Dubroca <[email-masked]>
Date: Thu, 30 Nov 2023 16:35:13 +0100

2023-11-12, 22:52:17 -0500, Christian Hopps wrote:
> From: Christian Hopps <[email-masked]>
> 
> Add a set of callbacks xfrm_mode_cbs to xfrm_state. These callbacks
> enable the addition of new xfrm modes, such as IP-TFS to be defined
> in modules.

Not a big fan of bringing back modes in modules :(
Florian's work made the code a lot more readable.

> diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
> index 662c83beb345..4390c111410d 100644
> --- a/net/xfrm/xfrm_output.c
> +++ b/net/xfrm/xfrm_output.c
> @@ -280,7 +280,9 @@ static int xfrm4_tunnel_encap_add(struct xfrm_state *x, struct sk_buff *skb)
>  	skb_set_inner_network_header(skb, skb_network_offset(skb));
>  	skb_set_inner_transport_header(skb, skb_transport_offset(skb));
>  
> -	skb_set_network_header(skb, -x->props.header_len);
> +	/* backup to add space for the outer encap */
> +	skb_set_network_header(skb,
> +			       -x->props.header_len + x->props.enc_hdr_len);

Since this only gets called for XFRM_MODE_TUNNEL, and only iptfs sets
enc_hdr_len, do we need this change? (and same for xfrm6_tunnel_encap_add)

>  	skb->mac_header = skb->network_header +
>  			  offsetof(struct iphdr, protocol);
>  	skb->transport_header = skb->network_header + sizeof(*top_iph);
> @@ -325,7 +327,8 @@ static int xfrm6_tunnel_encap_add(struct xfrm_state *x, struct sk_buff *skb)
>  	skb_set_inner_network_header(skb, skb_network_offset(skb));
>  	skb_set_inner_transport_header(skb, skb_transport_offset(skb));
>  
> -	skb_set_network_header(skb, -x->props.header_len);
> +	skb_set_network_header(skb,
> +			       -x->props.header_len + x->props.enc_hdr_len);
>  	skb->mac_header = skb->network_header +
>  			  offsetof(struct ipv6hdr, nexthdr);
>  	skb->transport_header = skb->network_header + sizeof(*top_iph);
> @@ -472,6 +475,8 @@ static int xfrm_outer_mode_output(struct xfrm_state *x, struct sk_buff *skb)
>  		WARN_ON_ONCE(1);
>  		break;
>  	default:
> +		if (x->mode_cbs->prepare_output)

Can x->mode_cbs be NULL here? Every other use of mode_cbs does
    if (x->mode_cbs && x->mode_cbs->FOO)

(I think not at the moment since only IPTFS (and IN_TRIGGER) can reach
this, but this inconsistency with the rest of the series struck me)

-- 
Sabrina