[ovs-dev] [PATCH net-next v2] net: openvswitch: Be liberal in tcp conntrack.

[nusiddiq at redhat.com]

From: Numan Siddique <nusiddiq at redhat.com>

There is no easy way to distinguish if a conntracked tcp packet is
marked invalid because of tcp_in_window() check error or because
it doesn't belong to an existing connection. With this patch,
openvswitch sets liberal tcp flag for the established sessions so
that out of window packets are not marked invalid.

A helper function - nf_ct_set_tcp_be_liberal(nf_conn) is added which
sets this flag for both the directions of the nf_conn.

Suggested-by: Florian Westphal <fw at strlen.de>
Signed-off-by: Numan Siddique <nusiddiq at redhat.com>
---
 include/net/netfilter/nf_conntrack_l4proto.h | 14 ++++++++++++++
 net/netfilter/nf_conntrack_proto_tcp.c       |  6 ------
 net/openvswitch/conntrack.c                  |  8 ++++++++
 3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/include/net/netfilter/nf_conntrack_l4proto.h b/include/net/netfilter/nf_conntrack_l4proto.h
index 88186b95b3c2..9be7320b994f 100644
--- a/include/net/netfilter/nf_conntrack_l4proto.h
+++ b/include/net/netfilter/nf_conntrack_l4proto.h
@@ -203,6 +203,20 @@ static inline struct nf_icmp_net *nf_icmpv6_pernet(struct net *net)
 {
 	return &net->ct.nf_ct_proto.icmpv6;
 }
+
+/* Caller must check nf_ct_protonum(ct) is IPPROTO_TCP before calling. */
+static inline void nf_ct_set_tcp_be_liberal(struct nf_conn *ct)
+{
+	ct->proto.tcp.seen[0].flags |= IP_CT_TCP_FLAG_BE_LIBERAL;
+	ct->proto.tcp.seen[1].flags |= IP_CT_TCP_FLAG_BE_LIBERAL;
+}
+
+/* Caller must check nf_ct_protonum(ct) is IPPROTO_TCP before calling. */
+static inline bool nf_conntrack_tcp_established(const struct nf_conn *ct)
+{
+	return ct->proto.tcp.state == TCP_CONNTRACK_ESTABLISHED &&
+	       test_bit(IPS_ASSURED_BIT, &ct->status);
+}
 #endif
 
 #ifdef CONFIG_NF_CT_PROTO_DCCP
diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index c8fb2187ad4b..811c6c9b59e1 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -834,12 +834,6 @@ static noinline bool tcp_new(struct nf_conn *ct, const struct sk_buff *skb,
 	return true;
 }
 
-static bool nf_conntrack_tcp_established(const struct nf_conn *ct)
-{
-	return ct->proto.tcp.state == TCP_CONNTRACK_ESTABLISHED &&
-	       test_bit(IPS_ASSURED_BIT, &ct->status);
-}
-
 /* Returns verdict for packet, or -1 for invalid. */
 int nf_conntrack_tcp_packet(struct nf_conn *ct,
 			    struct sk_buff *skb,
diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
index 4beb96139d77..6a88daab0190 100644
--- a/net/openvswitch/conntrack.c
+++ b/net/openvswitch/conntrack.c
@@ -1037,6 +1037,14 @@ static int __ovs_ct_lookup(struct net *net, struct sw_flow_key *key,
 		    ovs_ct_helper(skb, info->family) != NF_ACCEPT) {
 			return -EINVAL;
 		}
+
+		if (nf_ct_protonum(ct) == IPPROTO_TCP &&
+		    nf_ct_is_confirmed(ct) && nf_conntrack_tcp_established(ct)) {
+			/* Be liberal for tcp packets so that out-of-window
+			 * packets are not marked invalid.
+			 */
+			nf_ct_set_tcp_be_liberal(ct);
+		}
 	}
 
 	return 0;
-- 
2.28.0