bpf/flow_dissector: support ipv6 flow_label and BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL

Add support for exporting ipv6 flow label via bpf_flow_keys.
Export flow label from bpf_flow.c and also return early when
BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL is passed.

Acked-by: Petar Penkov <ppenkov@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Acked-by: Song Liu <songliubraving@fb.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Petar Penkov <ppenkov@google.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/uapi/linux/bpf.h

@@ -3533,6 +3533,7 @@ struct bpf_flow_keys {
 		};
 	};
 	__u32	flags;
+	__be32	flow_label;
 };
 
 struct bpf_func_info {

net/core/flow_dissector.c

@@ -737,6 +737,7 @@ static void __skb_flow_bpf_to_target(const struct bpf_flow_keys *flow_keys,
 	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_tags *key_tags;
 
 	key_control = skb_flow_dissector_target(flow_dissector,
 						FLOW_DISSECTOR_KEY_CONTROL,
@@ -781,6 +782,14 @@ static void __skb_flow_bpf_to_target(const struct bpf_flow_keys *flow_keys,
 		key_ports->src = flow_keys->sport;
 		key_ports->dst = flow_keys->dport;
 	}
+
+	if (dissector_uses_key(flow_dissector,
+			       FLOW_DISSECTOR_KEY_FLOW_LABEL)) {
+		key_tags = skb_flow_dissector_target(flow_dissector,
+						     FLOW_DISSECTOR_KEY_FLOW_LABEL,
+						     target_container);
+		key_tags->flow_label = ntohl(flow_keys->flow_label);
+	}
 }
 
 bool bpf_flow_dissect(struct bpf_prog *prog, struct bpf_flow_dissector *ctx,

tools/include/uapi/linux/bpf.h

@@ -3530,6 +3530,7 @@ struct bpf_flow_keys {
 		};
 	};
 	__u32	flags;
+	__be32	flow_label;
 };
 
 struct bpf_func_info {

tools/testing/selftests/bpf/prog_tests/flow_dissector.c

@@ -20,6 +20,7 @@
 	      "is_encap=%u/%u "						\
 	      "ip_proto=0x%x/0x%x "					\
 	      "n_proto=0x%x/0x%x "					\
+	      "flow_label=0x%x/0x%x "					\
 	      "sport=%u/%u "						\
 	      "dport=%u/%u\n",						\
 	      got.nhoff, expected.nhoff,				\
@@ -30,6 +31,7 @@
 	      got.is_encap, expected.is_encap,				\
 	      got.ip_proto, expected.ip_proto,				\
 	      got.n_proto, expected.n_proto,				\
+	      got.flow_label, expected.flow_label,			\
 	      got.sport, expected.sport,				\
 	      got.dport, expected.dport)
 
@@ -257,6 +259,50 @@ struct test tests[] = {
 			.is_first_frag = true,
 		},
 	},
+	{
+		.name = "ipv6-flow-label",
+		.pkt.ipv6 = {
+			.eth.h_proto = __bpf_constant_htons(ETH_P_IPV6),
+			.iph.nexthdr = IPPROTO_TCP,
+			.iph.payload_len = __bpf_constant_htons(MAGIC_BYTES),
+			.iph.flow_lbl = { 0xb, 0xee, 0xef },
+			.tcp.doff = 5,
+			.tcp.source = 80,
+			.tcp.dest = 8080,
+		},
+		.keys = {
+			.nhoff = ETH_HLEN,
+			.thoff = ETH_HLEN + sizeof(struct ipv6hdr),
+			.addr_proto = ETH_P_IPV6,
+			.ip_proto = IPPROTO_TCP,
+			.n_proto = __bpf_constant_htons(ETH_P_IPV6),
+			.sport = 80,
+			.dport = 8080,
+			.flow_label = __bpf_constant_htonl(0xbeeef),
+		},
+	},
+	{
+		.name = "ipv6-no-flow-label",
+		.pkt.ipv6 = {
+			.eth.h_proto = __bpf_constant_htons(ETH_P_IPV6),
+			.iph.nexthdr = IPPROTO_TCP,
+			.iph.payload_len = __bpf_constant_htons(MAGIC_BYTES),
+			.iph.flow_lbl = { 0xb, 0xee, 0xef },
+			.tcp.doff = 5,
+			.tcp.source = 80,
+			.tcp.dest = 8080,
+		},
+		.keys = {
+			.flags = BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL,
+			.nhoff = ETH_HLEN,
+			.thoff = ETH_HLEN + sizeof(struct ipv6hdr),
+			.addr_proto = ETH_P_IPV6,
+			.ip_proto = IPPROTO_TCP,
+			.n_proto = __bpf_constant_htons(ETH_P_IPV6),
+			.flow_label = __bpf_constant_htonl(0xbeeef),
+		},
+		.flags = BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL,
+	},
 };
 
 static int create_tap(const char *ifname)

tools/testing/selftests/bpf/progs/bpf_flow.c

@@ -83,6 +83,12 @@ static __always_inline int export_flow_keys(struct bpf_flow_keys *keys,
 	return ret;
 }
 
+#define IPV6_FLOWLABEL_MASK		__bpf_constant_htonl(0x000FFFFF)
+static inline __be32 ip6_flowlabel(const struct ipv6hdr *hdr)
+{
+	return *(__be32 *)hdr & IPV6_FLOWLABEL_MASK;
+}
+
 static __always_inline void *bpf_flow_dissect_get_header(struct __sk_buff *skb,
 							 __u16 hdr_size,
 							 void *buffer)
@@ -308,6 +314,10 @@ PROG(IPV6)(struct __sk_buff *skb)
 
 	keys->thoff += sizeof(struct ipv6hdr);
 	keys->ip_proto = ip6h->nexthdr;
+	keys->flow_label = ip6_flowlabel(ip6h);
+
+	if (keys->flags & BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL)
+		return export_flow_keys(keys, BPF_OK);
 
 	return parse_ipv6_proto(skb, ip6h->nexthdr);
 }