Date:   Thu, 29 Aug 2019 14:34:09 +0200
From:   Sabrina Dubroca <sd@...asysnail.net>
To:     Steffen Klassert <steffen.klassert@...unet.com>
Cc:     netdev@...r.kernel.org, Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH ipsec-next 7/7] xfrm: add espintcp (RFC 8229)

2019-08-29, 09:04:31 +0200, Steffen Klassert wrote:
> On Wed, Aug 21, 2019 at 11:46:25PM +0200, Sabrina Dubroca wrote:
> > +static struct sock *esp_find_tcp_sk(struct xfrm_state *x)
> > +{
> > +	struct xfrm_encap_tmpl *encap = x->encap;
> > +	struct esp_tcp_sk *esk;
> > +	__be16 sport, dport;
> > +	struct sock *nsk;
> > +	struct sock *sk;
> > +
> > +	sk = rcu_dereference(x->encap_sk);
> > +	if (sk && sk->sk_state == TCP_ESTABLISHED)
> > +		return sk;
> > +
> > +	spin_lock_bh(&x->lock);
> > +	sport = encap->encap_sport;
> > +	dport = encap->encap_dport;
> > +	nsk = rcu_dereference_protected(x->encap_sk,
> > +					lockdep_is_held(&x->lock));
> > +	if (sk && sk == nsk) {
> > +		esk = kmalloc(sizeof(*esk), GFP_ATOMIC);
> > +		if (!esk) {
> > +			spin_unlock_bh(&x->lock);
> > +			return ERR_PTR(-ENOMEM);
> > +		}
> > +		RCU_INIT_POINTER(x->encap_sk, NULL);
> > +		esk->sk = sk;
> > +		call_rcu(&esk->rcu, esp_free_tcp_sk);
> 
> I don't understand this, can you please explain what you are doing here?

If we get to this block, the current encap_sk is not in ESTABLISHED
state and cannot be used to send data. We want to get rid of it (reset
x->encap_sk) and find a new usable socket. The weird kmalloc dance is
just here so that we can do the sock_put after an RCU grace period,
which I think is needed so that we don't destruct a socket that's
still used by packets in flight.

That's code I copied from Herbert's first submission, I may be missing
some details here.

> > +	}
> > +	spin_unlock_bh(&x->lock);
> > +
> > +	sk = inet_lookup_established(xs_net(x), &tcp_hashinfo, x->id.daddr.a4,
> > +				     dport, x->props.saddr.a4, sport, 0);
> > +	if (!sk)
> > +		return ERR_PTR(-ENOENT);
> > +
> > +	if (!tcp_is_ulp_esp(sk)) {
> > +		sock_put(sk);
> > +		return ERR_PTR(-EINVAL);
> > +	}
> > +
> > +	spin_lock_bh(&x->lock);
> > +	nsk = rcu_dereference_protected(x->encap_sk,
> > +					lockdep_is_held(&x->lock));
> > +	if (encap->encap_sport != sport ||
> > +	    encap->encap_dport != dport) {
> > +		sock_put(sk);
> > +		sk = nsk ?: ERR_PTR(-EREMCHG);
> > +	} else if (sk == nsk) {
> > +		sock_put(sk);
> > +	} else {
> > +		rcu_assign_pointer(x->encap_sk, sk);
> > +	}
> > +	spin_unlock_bh(&x->lock);
> > +
> > +	return sk;
> > +}
> > +
> > +static int esp_output_tcp_finish(struct xfrm_state *x, struct sk_buff *skb)
> > +{
> > +	struct sock *sk;
> > +	int err;
> > +
> > +	rcu_read_lock();
> > +
> > +	sk = esp_find_tcp_sk(x);
> > +	err = PTR_ERR(sk);
> > +	if (IS_ERR(sk))
> 
> Maybe better 'if (err)'?

That will work if I replace PTR_ERR with PTR_ERR_OR_ZERO.

> > +		goto out;
> > +
> > +	bh_lock_sock(sk);
> > +	if (sock_owned_by_user(sk)) {
> > +		err = espintcp_queue_out(sk, skb);
> > +		if (err < 0)
> > +			goto unlock_sock;
> 
> This goto is not needed.

Will fix.

> > +	} else {
> > +		err = espintcp_push_skb(sk, skb);
> > +	}
> > +
> > +unlock_sock:
> > +	bh_unlock_sock(sk);
> > +out:
> > +	rcu_read_unlock();
> > +	return err;
> > +}
> > +
> > +static int esp_output_tcp_encap_cb(struct net *net, struct sock *sk,
> > +				   struct sk_buff *skb)
> > +{
> > +	struct dst_entry *dst = skb_dst(skb);
> > +	struct xfrm_state *x = dst->xfrm;
> > +
> > +	return esp_output_tcp_finish(x, skb);
> > +}
> > +
> > +static int esp_output_tail_tcp(struct xfrm_state *x, struct sk_buff *skb)
> > +{
> > +	int err;
> > +
> > +	local_bh_disable();
> > +	err = xfrm_trans_queue_net(xs_net(x), skb, esp_output_tcp_encap_cb);
> > +	local_bh_enable();
> > +
> > +	/* EINPROGRESS just happens to do the right thing.  It
> > +	 * actually means that the skb has been consumed and
> > +	 * isn't coming back.
> > +	 */
> > +	return err ?: -EINPROGRESS;
> > +}
> > +#endif
> > +
> >  static void esp_output_done(struct crypto_async_request *base, int err)
> >  {
> >  	struct sk_buff *skb = base->data;
> > @@ -147,7 +272,13 @@ static void esp_output_done(struct crypto_async_request *base, int err)
> >  		secpath_reset(skb);
> >  		xfrm_dev_resume(skb);
> >  	} else {
> > -		xfrm_output_resume(skb, err);
> > +#ifdef CONFIG_XFRM_ESPINTCP
> 
> Do we really need all these ifdef? I guess most of them could
> be avoided with some code refactorization.

If we compile espintcp out, esp_output_tail_tcp will be dead code so
it might as well not be compiled in either.

The more trivial operations (like in esp_input_done2) could be
compiled in anyway. That might be considered a bit inconsistent,
because I need to keep the ifdef in esp_init_state (so that we land in
the default case and error out when espintcp is disabled).

Then I can provide variants of some functions (esp_output_tcp_encap,
esp_output_tail_tcp) that always fail for !XFRM_ESPINTCP.

> > +		if (!err &&
> > +		    x->encap && x->encap->encap_type == TCP_ENCAP_ESPINTCP)
> > +			esp_output_tail_tcp(x, skb);
> > +		else
> > +#endif
> > +			xfrm_output_resume(skb, err);
> >  	}
> >  }
> 
> ...
> 
> > @@ -296,7 +460,7 @@ int esp_output_head(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *
> >  	struct sk_buff *trailer;
> >  	int tailen = esp->tailen;
> >  
> > -	/* this is non-NULL only with UDP Encapsulation */
> > +	/* this is non-NULL only with TCP/UDP Encapsulation */
> >  	if (x->encap) {
> >  		int err = esp_output_encap(x, skb, esp);
> >  
> > @@ -491,6 +655,11 @@ int esp_output_tail(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *
> >  	if (sg != dsg)
> >  		esp_ssg_unref(x, tmp);
> >  
> > +#ifdef CONFIG_XFRM_ESPINTCP
> > +	if (!err && x->encap && x->encap->encap_type == TCP_ENCAP_ESPINTCP)
> > +		err = esp_output_tail_tcp(x, skb);
> > +#endif
> > +
> >  error_free:
> >  	kfree(tmp);
> >  error:
> > @@ -617,10 +786,16 @@ int esp_input_done2(struct sk_buff *skb, int err)
> >  
> >  	if (x->encap) {
> >  		struct xfrm_encap_tmpl *encap = x->encap;
> > +		struct tcphdr *th = (void *)(skb_network_header(skb) + ihl);
> 
> This gives a unused variable warning if CONFIG_XFRM_ESPINTCP
> is not set.

Oops, will fix. Or that will take care of itself if I just remove the ifdef below.

> >  		struct udphdr *uh = (void *)(skb_network_header(skb) + ihl);
> >  		__be16 source;
> >  
> >  		switch (x->encap->encap_type) {
> > +#ifdef CONFIG_XFRM_ESPINTCP

(this one)

> > +		case TCP_ENCAP_ESPINTCP:
> > +			source = th->source;
> > +			break;
> > +#endif
> >  		case UDP_ENCAP_ESPINUDP:
> >  		case UDP_ENCAP_ESPINUDP_NON_IKE:
> >  			source = uh->source;
> > @@ -1017,6 +1192,14 @@ static int esp_init_state(struct xfrm_state *x)
> >  		case UDP_ENCAP_ESPINUDP_NON_IKE:
> >  			x->props.header_len += sizeof(struct udphdr) + 2 * sizeof(u32);
> >  			break;
> > +#ifdef CONFIG_XFRM_ESPINTCP
> > +		case TCP_ENCAP_ESPINTCP:
> > +			/* only the length field, TCP encap is done by
> > +			 * the socket
> > +			 */
> > +			x->props.header_len += 2;
> > +			break;
> > +#endif
> >  		}
> >  	}
> >  
> > diff --git a/net/xfrm/Kconfig b/net/xfrm/Kconfig
> > index c967fc3c38c8..ccc012b3ea10 100644
> > --- a/net/xfrm/Kconfig
> > +++ b/net/xfrm/Kconfig
> > @@ -71,6 +71,15 @@ config XFRM_IPCOMP
> >  	select CRYPTO
> >  	select CRYPTO_DEFLATE
> >  
> > +config XFRM_ESPINTCP
> > +	bool "ESP in TCP encapsulation (RFC 8229)"
> > +	depends on XFRM && INET_ESP
> > +	select STREAM_PARSER
> 
> I'm getting these compile errors:
> 
> espintcp.o: In function `espintcp_close':
> /home/klassert/git/linux-stk/net/xfrm/espintcp.c:469: undefined reference to `sk_msg_free'
> net/xfrm/espintcp.o: In function `espintcp_sendmsg':
> /home/klassert/git/linux-stk/net/xfrm/espintcp.c:302: undefined reference to `sk_msg_alloc'
> /home/klassert/git/linux-stk/net/xfrm/espintcp.c:316: undefined reference to `sk_msg_memcopy_from_iter'
> /home/klassert/git/linux-stk/net/xfrm/espintcp.c:341: undefined reference to `sk_msg_free'
> /home/klassert/git/linux-stk/net/xfrm/espintcp.c:321: undefined reference to `sk_msg_memcopy_from_iter'
> /home/klassert/git/linux-stk/Makefile:1067: recipe for target 'vmlinux' failed
> make[1]: *** [vmlinux] Error 1
> 
> I guess you need to select NET_SOCK_MSG.

Right, I'll go fix the Kconfig entry.

> Btw. I've updated the ipsec-next tree, so patch 1 is not needed anymore.

Cool, I'll drop it.

> Everything else looks good!

Thanks for the review.

-- 
Sabrina

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