linux-kernel - [PATCH net-next v2 2/4] flow_dissector: skip the ICMP dissector for non ICMP packets

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Message-Id: <20191029135053.10055-3-mcroce@redhat.com>
Date:   Tue, 29 Oct 2019 14:50:51 +0100
From:   Matteo Croce <mcroce@...hat.com>
To:     netdev@...r.kernel.org
Cc:     Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David S . Miller " <davem@...emloft.net>,
        Stanislav Fomichev <sdf@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Song Liu <songliubraving@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Paul Blakey <paulb@...lanox.com>, linux-kernel@...r.kernel.org
Subject: [PATCH net-next v2 2/4] flow_dissector: skip the ICMP dissector for non ICMP packets

FLOW_DISSECTOR_KEY_ICMP is checked for every packet, not only ICMP ones.
Even if the test overhead is probably negligible, move the
ICMP dissector code under the big 'switch(ip_proto)' so it gets called
only for ICMP packets.

Signed-off-by: Matteo Croce <mcroce@...hat.com>
---
 net/core/flow_dissector.c | 34 +++++++++++++++++++++++++---------
 1 file changed, 25 insertions(+), 9 deletions(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index affde70dad47..6443fac65ce8 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -203,6 +203,25 @@ __be32 __skb_flow_get_ports(const struct sk_buff *skb, int thoff, u8 ip_proto,
 }
 EXPORT_SYMBOL(__skb_flow_get_ports);
 
+/* If FLOW_DISSECTOR_KEY_ICMP is set, get the Type and Code from an ICMP packet
+ * using skb_flow_get_be16().
+ */
+static void __skb_flow_dissect_icmp(const struct sk_buff *skb,
+				    struct flow_dissector *flow_dissector,
+				    void *target_container,
+				    void *data, int thoff, int hlen)
+{
+	struct flow_dissector_key_icmp *key_icmp;
+
+	if (!dissector_uses_key(flow_dissector, FLOW_DISSECTOR_KEY_ICMP))
+		return;
+
+	key_icmp = skb_flow_dissector_target(flow_dissector,
+					     FLOW_DISSECTOR_KEY_ICMP,
+					     target_container);
+	key_icmp->icmp = skb_flow_get_be16(skb, thoff, data, hlen);
+}
+
 void skb_flow_dissect_meta(const struct sk_buff *skb,
 			   struct flow_dissector *flow_dissector,
 			   void *target_container)
@@ -853,7 +872,6 @@ bool __skb_flow_dissect(const struct net *net,
 	struct flow_dissector_key_basic *key_basic;
 	struct flow_dissector_key_addrs *key_addrs;
 	struct flow_dissector_key_ports *key_ports;
-	struct flow_dissector_key_icmp *key_icmp;
 	struct flow_dissector_key_tags *key_tags;
 	struct flow_dissector_key_vlan *key_vlan;
 	struct bpf_prog *attached = NULL;
@@ -1295,6 +1313,12 @@ bool __skb_flow_dissect(const struct net *net,
 				       data, nhoff, hlen);
 		break;
 
+	case IPPROTO_ICMP:
+	case IPPROTO_ICMPV6:
+		__skb_flow_dissect_icmp(skb, flow_dissector, target_container,
+					data, nhoff, hlen);
+		break;
+
 	default:
 		break;
 	}
@@ -1308,14 +1332,6 @@ bool __skb_flow_dissect(const struct net *net,
 							data, hlen);
 	}
 
-	if (dissector_uses_key(flow_dissector,
-			       FLOW_DISSECTOR_KEY_ICMP)) {
-		key_icmp = skb_flow_dissector_target(flow_dissector,
-						     FLOW_DISSECTOR_KEY_ICMP,
-						     target_container);
-		key_icmp->icmp = skb_flow_get_be16(skb, nhoff, data, hlen);
-	}
-
 	/* Process result of IP proto processing */
 	switch (fdret) {
 	case FLOW_DISSECT_RET_PROTO_AGAIN:
-- 
2.21.0