netdev - Re: [PATCH RFC xfrm-next v3 4/8] xfrm: add TX datapath support for IPsec full offload mode

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Date:   Tue, 27 Sep 2022 07:04:35 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Leon Romanovsky <leon@...nel.org>
CC:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "Jakub Kicinski" <kuba@...nel.org>, <netdev@...r.kernel.org>,
        Paolo Abeni <pabeni@...hat.com>, Raed Salem <raeds@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Bharat Bhushan <bbhushan2@...vell.com>
Subject: Re: [PATCH RFC xfrm-next v3 4/8] xfrm: add TX datapath support for
 IPsec full offload mode

On Mon, Sep 26, 2022 at 09:06:48AM +0300, Leon Romanovsky wrote:
> On Sun, Sep 25, 2022 at 11:16:03AM +0200, Steffen Klassert wrote:
> > On Sun, Sep 04, 2022 at 04:15:38PM +0300, Leon Romanovsky wrote:
> > > From: Leon Romanovsky <leonro@...dia.com>
> > > diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
> > > index 9a5e79a38c67..dde009be8463 100644
> > > --- a/net/xfrm/xfrm_output.c
> > > +++ b/net/xfrm/xfrm_output.c
> > > @@ -494,7 +494,7 @@ static int xfrm_output_one(struct sk_buff *skb, int err)
> > >  	struct xfrm_state *x = dst->xfrm;
> > >  	struct net *net = xs_net(x);
> > >  
> > > -	if (err <= 0)
> > > +	if (err <= 0 || x->xso.type == XFRM_DEV_OFFLOAD_FULL)
> > >  		goto resume;
> > 
> > You check here that the state is marked as 'full offload' before
> > you skip the SW xfrm handling, but I don't see where you check
> > that the policy that led to this state is offloaded too. Also,
> > we have to make sure that both, policy and state is offloaded to
> > the same device. Looks like this part is missing.
> 
> In SW flow, users are not required to configure policy. If they don't
> have policy, the packet will be encrypted and sent anyway.

No, it is not! You can't lookup a TX SA without a policy. The lookup
happens in two stages. The packet header is matched against the TS of
the policy. Then the template found at the policy is used to lookup
the SA.

> The full offload follows same semantic. The missing offloaded policy is
> equal to no policy at all.

No policy at all means that the packets are sent out unencrypted in
plaintext, and this is certainly not what you want.

> I don't think that extra checks are needed.

We need this checks. This is one of the reasons why I want to separate
the SW and HW databases.