bpf: Add sock_ops R/W access to tclass

Adds direct write access to sk_txhash and access to tclass for ipv6
flows through getsockopt and setsockopt. Sample usage for tclass:

  bpf_getsockopt(skops, SOL_IPV6, IPV6_TCLASS, &v, sizeof(v))

where skops is a pointer to the ctx (struct bpf_sock_ops).
Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

net/core/filter.c

@@ -3232,6 +3232,29 @@ BPF_CALL_5(bpf_setsockopt, struct bpf_sock_ops_kern *, bpf_sock,
 			ret = -EINVAL;
 		}
 #ifdef CONFIG_INET
+#if IS_ENABLED(CONFIG_IPV6)
+	} else if (level == SOL_IPV6) {
+		if (optlen != sizeof(int) || sk->sk_family != AF_INET6)
+			return -EINVAL;
+
+		val = *((int *)optval);
+		/* Only some options are supported */
+		switch (optname) {
+		case IPV6_TCLASS:
+			if (val < -1 || val > 0xff) {
+				ret = -EINVAL;
+			} else {
+				struct ipv6_pinfo *np = inet6_sk(sk);
+
+				if (val == -1)
+					val = 0;
+				np->tclass = val;
+			}
+			break;
+		default:
+			ret = -EINVAL;
+		}
+#endif
 	} else if (level == SOL_TCP &&
 		   sk->sk_prot->setsockopt == tcp_setsockopt) {
 		if (optname == TCP_CONGESTION) {
@@ -3241,7 +3264,8 @@ BPF_CALL_5(bpf_setsockopt, struct bpf_sock_ops_kern *, bpf_sock,
 			strncpy(name, optval, min_t(long, optlen,
 						    TCP_CA_NAME_MAX-1));
 			name[TCP_CA_NAME_MAX-1] = 0;
-			ret = tcp_set_congestion_control(sk, name, false, reinit);
+			ret = tcp_set_congestion_control(sk, name, false,
+							 reinit);
 		} else {
 			struct tcp_sock *tp = tcp_sk(sk);
 
@@ -3307,6 +3331,22 @@ BPF_CALL_5(bpf_getsockopt, struct bpf_sock_ops_kern *, bpf_sock,
 		} else {
 			goto err_clear;
 		}
+#if IS_ENABLED(CONFIG_IPV6)
+	} else if (level == SOL_IPV6) {
+		struct ipv6_pinfo *np = inet6_sk(sk);
+
+		if (optlen != sizeof(int) || sk->sk_family != AF_INET6)
+			goto err_clear;
+
+		/* Only some options are supported */
+		switch (optname) {
+		case IPV6_TCLASS:
+			*((int *)optval) = (int)np->tclass;
+			break;
+		default:
+			goto err_clear;
+		}
+#endif
 	} else {
 		goto err_clear;
 	}
@@ -3871,6 +3911,7 @@ static bool sock_ops_is_valid_access(int off, int size,
 	if (type == BPF_WRITE) {
 		switch (off) {
 		case offsetof(struct bpf_sock_ops, reply):
+		case offsetof(struct bpf_sock_ops, sk_txhash):
 			if (size != size_default)
 				return false;
 			break;
@@ -4690,7 +4731,8 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
 		break;
 
 	case offsetof(struct bpf_sock_ops, sk_txhash):
-		SOCK_OPS_GET_FIELD(sk_txhash, sk_txhash, struct sock);
+		SOCK_OPS_GET_OR_SET_FIELD(sk_txhash, sk_txhash,
+					  struct sock, type);
 		break;
 
 	case offsetof(struct bpf_sock_ops, bytes_received):
@@ -4701,6 +4743,7 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
 	case offsetof(struct bpf_sock_ops, bytes_acked):
 		SOCK_OPS_GET_FIELD(bytes_acked, bytes_acked, struct tcp_sock);
 		break;
+
 	}
 	return insn - insn_buf;
 }