netfilter: kill the fake untracked conntrack objects

resurrect an old patch from Pablo Neira to remove the untracked objects.

Currently, there are four possible states of an skb wrt. conntrack.

1. No conntrack attached, ct is NULL.
2. Normal (kmem cache allocated) ct attached.
3. a template (kmalloc'd), not in any hash tables at any point in time
4. the 'untracked' conntrack, a percpu nf_conn object, tagged via
   IPS_UNTRACKED_BIT in ct->status.

Untracked is supposed to be identical to case 1.  It exists only
so users can check

-m conntrack --ctstate UNTRACKED vs.
-m conntrack --ctstate INVALID

e.g. attempts to set connmark on INVALID or UNTRACKED conntracks is
supposed to be a no-op.

Thus currently we need to check
 ct == NULL || nf_ct_is_untracked(ct)

in a lot of places in order to avoid altering untracked objects.

The other consequence of the percpu untracked object is that all
-j NOTRACK (and, later, kfree_skb of such skbs) result in an atomic op
(inc/dec the untracked conntracks refcount).

This adds a new kernel-private ctinfo state, IP_CT_UNTRACKED, to
make the distinction instead.

The (few) places that care about packet invalid (ct is NULL) vs.
packet untracked now need to test ct == NULL vs. ctinfo == IP_CT_UNTRACKED,
but all other places can omit the nf_ct_is_untracked() check.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 6 insertions, 8 deletions

diff --git a/net/netfilter/nft_ct.c b/net/netfilter/nft_ct.c
index 6e23dbbedd7f4e..6c6fd48b024c2d 100644
--- a/net/netfilter/nft_ct.c
+++ b/net/netfilter/nft_ct.c
@@ -72,12 +72,12 @@ static void nft_ct_get_eval(const struct nft_expr *expr,
 
 	switch (priv->key) {
 	case NFT_CT_STATE:
-		if (ct == NULL)
-			state = NF_CT_STATE_INVALID_BIT;
-		else if (nf_ct_is_untracked(ct))
+		if (ct)
+			state = NF_CT_STATE_BIT(ctinfo);
+		else if (ctinfo == IP_CT_UNTRACKED)
 			state = NF_CT_STATE_UNTRACKED_BIT;
 		else
-			state = NF_CT_STATE_BIT(ctinfo);
+			state = NF_CT_STATE_INVALID_BIT;
 		*dest = state;
 		return;
 	default:
@@ -718,12 +718,10 @@ static void nft_notrack_eval(const struct nft_expr *expr,
 
 	ct = nf_ct_get(pkt->skb, &ctinfo);
 	/* Previously seen (loopback or untracked)?  Ignore. */
-	if (ct)
+	if (ct || ctinfo == IP_CT_UNTRACKED)
 		return;
 
-	ct = nf_ct_untracked_get();
-	atomic_inc(&ct->ct_general.use);
-	nf_ct_set(skb, ct, IP_CT_NEW);
+	nf_ct_set(skb, ct, IP_CT_UNTRACKED);
 }
 
 static struct nft_expr_type nft_notrack_type;