netfilter: nfnetlink_queue: resolve clash for unconfirmed conntracks

In nfqueue, two consecutive skbuffs may race to create the conntrack
entry. Hence, the one that loses the race gets dropped due to clash in
the insertion into the hashes from the nf_conntrack_confirm() path.

This patch adds a new nf_conntrack_update() function which searches for
possible clashes and resolve them. NAT mangling for the packet losing
race is corrected by using the conntrack information that won race.

In order to avoid direct module dependencies with conntrack and NAT, the
nf_ct_hook and nf_nat_hook structures are used for this purpose.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 24 insertions, 4 deletions

diff --git a/net/netfilter/nfnetlink_queue.c b/net/netfilter/nfnetlink_queue.c
index 74a04638ef03..2c173042ac0e 100644
--- a/net/netfilter/nfnetlink_queue.c
+++ b/net/netfilter/nfnetlink_queue.c
@@ -227,6 +227,25 @@ find_dequeue_entry(struct nfqnl_instance *queue, unsigned int id)
 	return entry;
 }
 
+static void nfqnl_reinject(struct nf_queue_entry *entry, unsigned int verdict)
+{
+	struct nf_ct_hook *ct_hook;
+	int err;
+
+	if (verdict == NF_ACCEPT ||
+	    verdict == NF_STOP) {
+		rcu_read_lock();
+		ct_hook = rcu_dereference(nf_ct_hook);
+		if (ct_hook) {
+			err = ct_hook->update(entry->state.net, entry->skb);
+			if (err < 0)
+				verdict = NF_DROP;
+		}
+		rcu_read_unlock();
+	}
+	nf_reinject(entry, verdict);
+}
+
 static void
 nfqnl_flush(struct nfqnl_instance *queue, nfqnl_cmpfn cmpfn, unsigned long data)
 {
@@ -237,7 +256,7 @@ nfqnl_flush(struct nfqnl_instance *queue, nfqnl_cmpfn cmpfn, unsigned long data)
 		if (!cmpfn || cmpfn(entry, data)) {
 			list_del(&entry->list);
 			queue->queue_total--;
-			nf_reinject(entry, NF_DROP);
+			nfqnl_reinject(entry, NF_DROP);
 		}
 	}
 	spin_unlock_bh(&queue->lock);
@@ -686,7 +705,7 @@ err_out_free_nskb:
 err_out_unlock:
 	spin_unlock_bh(&queue->lock);
 	if (failopen)
-		nf_reinject(entry, NF_ACCEPT);
+		nfqnl_reinject(entry, NF_ACCEPT);
 err_out:
 	return err;
 }
@@ -1085,7 +1104,8 @@ static int nfqnl_recv_verdict_batch(struct net *net, struct sock *ctnl,
 	list_for_each_entry_safe(entry, tmp, &batch_list, list) {
 		if (nfqa[NFQA_MARK])
 			entry->skb->mark = ntohl(nla_get_be32(nfqa[NFQA_MARK]));
-		nf_reinject(entry, verdict);
+
+		nfqnl_reinject(entry, verdict);
 	}
 	return 0;
 }
@@ -1208,7 +1228,7 @@ static int nfqnl_recv_verdict(struct net *net, struct sock *ctnl,
 	if (nfqa[NFQA_MARK])
 		entry->skb->mark = ntohl(nla_get_be32(nfqa[NFQA_MARK]));
 
-	nf_reinject(entry, verdict);
+	nfqnl_reinject(entry, verdict);
 	return 0;
 }