flow_dissector: Add control/reporting of fragmentation

Add an input flag to flow dissector on rather dissection should be
attempted on a first fragment. Also add key_control flags to indicate
that a packet is a fragment or first fragment.

Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/flow_dissector.h

@@ -12,6 +12,8 @@
 struct flow_dissector_key_control {
 	u16	thoff;
 	u16	addr_type;
+	u32	is_fragment:1;
+	u32	first_frag:1;
 };
 
 /**
@@ -122,6 +124,8 @@ enum flow_dissector_key_id {
 	FLOW_DISSECTOR_KEY_MAX,
 };
 
+#define FLOW_DISSECTOR_F_PARSE_1ST_FRAG		BIT(0)
+
 struct flow_dissector_key {
 	enum flow_dissector_key_id key_id;
 	size_t offset; /* offset of struct flow_dissector_key_*

net/core/flow_dissector.c

@@ -177,8 +177,6 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 		nhoff += iph->ihl * 4;
 
 		ip_proto = iph->protocol;
-		if (ip_is_fragment(iph))
-			ip_proto = 0;
 
 		if (!skb_flow_dissector_uses_key(flow_dissector,
 						 FLOW_DISSECTOR_KEY_IPV4_ADDRS))
@@ -189,6 +187,19 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 		memcpy(&key_addrs->v4addrs, &iph->saddr,
 		       sizeof(key_addrs->v4addrs));
 		key_control->addr_type = FLOW_DISSECTOR_KEY_IPV4_ADDRS;
+
+		if (ip_is_fragment(iph)) {
+			key_control->is_fragment = 1;
+
+			if (iph->frag_off & htons(IP_OFFSET)) {
+				goto out_good;
+			} else {
+				key_control->first_frag = 1;
+				if (!(flags & FLOW_DISSECTOR_F_PARSE_1ST_FRAG))
+					goto out_good;
+			}
+		}
+
 		break;
 	}
 	case htons(ETH_P_IPV6): {