linux-kernel - Re: [PATCH nf-next] netfilter: nf_ct

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Date:	Tue, 14 Jul 2015 18:42:25 +0200
From:	Michal Kubecek <mkubecek@...e.cz>
To:	Florian Westphal <fw@...len.de>
Cc:	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	linux-api@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Patrick McHardy <kaber@...sh.net>,
	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH nf-next] netfilter: nf_ct_sctp: minimal multihoming
 support

On Tue, Jul 14, 2015 at 03:42:03PM +0200, Florian Westphal wrote:
> Michal Kubecek <mkubecek@...e.cz> wrote:
> > +	case SCTP_CID_HEARTBEAT:
> > +		pr_debug("SCTP_CID_HEARTBEAT");
> > +		i = 9;
> > +		break;
> > +	case SCTP_CID_HEARTBEAT_ACK:
> > +		pr_debug("SCTP_CID_HEARTBEAT_ACK");
> > +		i = 10;
> > +		break;
> >  	default:
> >  		/* Other chunks like DATA, SACK, HEARTBEAT and
> >  		its ACK do not cause a change in state */
> > @@ -329,6 +351,8 @@ static int sctp_packet(struct nf_conn *ct,
> >  	    !test_bit(SCTP_CID_COOKIE_ECHO, map) &&
> >  	    !test_bit(SCTP_CID_ABORT, map) &&
> >  	    !test_bit(SCTP_CID_SHUTDOWN_ACK, map) &&
> > +	    !test_bit(SCTP_CID_HEARTBEAT, map) &&
> > +	    !test_bit(SCTP_CID_HEARTBEAT_ACK, map) &&
> >  	    sh->vtag != ct->proto.sctp.vtag[dir]) {
> >  		pr_debug("Verification tag check failed\n");
> >  		goto out;
> > @@ -357,6 +381,16 @@ static int sctp_packet(struct nf_conn *ct,
> >  			/* Sec 8.5.1 (D) */
> >  			if (sh->vtag != ct->proto.sctp.vtag[dir])
> >  				goto out_unlock;
> > +		} else if (sch->type == SCTP_CID_HEARTBEAT ||
> > +			   sch->type == SCTP_CID_HEARTBEAT_ACK) {
> > +			if (ct->proto.sctp.vtag[dir] == 0) {
> > +				pr_debug("Setting vtag %x for dir %d\n",
> > +					 sh->vtag, dir);
> > +				ct->proto.sctp.vtag[dir] = sh->vtag;
> 
> Could you please elaborate on the [dir] == 0 test?
> 
> I see this might happen for SCTP_CID_HEARTBEAT_ACK, but why is this
> needed for SCTP_CID_HEARTBEAT ?
> 
> We found a conntrack entry so shouldn't the vtag[dir] already be > 0?

Yes, you are right. This was originally intended to handle the case when
a HEARTBEAT in the reply direction is seen before the HEARTBEAT-ACK but
such HEARTBEAT would be dropped anyway in current version.

On the other hand, an alternative would be

		} else if (sch->type == SCTP_CID_HEARTBEAT_ACK &&
			   ct->proto.sctp.vtag[dir] == 0) {
			pr_debug("Setting vtag %x for dir %d\n",
				 sh->vtag, dir);
			ct->proto.sctp.vtag[dir] = sh->vtag;
		} else if ((sch->type == SCTP_CID_HEARTBEAT ||
			    sch->type == SCTP_CID_HEARTBEAT_ACK) &&
			   sh->vtag != ct->proto.sctp.vtag[dir]) {
			pr_debug("Verification tag check failed\n");
			goto out_unlock;
		}

I'm not sure it looks better.

Michal Kubecek
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