bpf: Add sock_ops R/W access to ipv4 tos

Sample usage for tos ...

  bpf_getsockopt(skops, SOL_IP, IP_TOS, &v, sizeof(v))

... where skops is a pointer to the ctx (struct bpf_sock_ops).
Signed-off-by: Nikita V. Shirokov <tehnerd@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

net/core/filter.c

@@ -3462,6 +3462,27 @@ BPF_CALL_5(bpf_setsockopt, struct bpf_sock_ops_kern *, bpf_sock,
 			ret = -EINVAL;
 		}
 #ifdef CONFIG_INET
+	} else if (level == SOL_IP) {
+		if (optlen != sizeof(int) || sk->sk_family != AF_INET)
+			return -EINVAL;
+
+		val = *((int *)optval);
+		/* Only some options are supported */
+		switch (optname) {
+		case IP_TOS:
+			if (val < -1 || val > 0xff) {
+				ret = -EINVAL;
+			} else {
+				struct inet_sock *inet = inet_sk(sk);
+
+				if (val == -1)
+					val = 0;
+				inet->tos = val;
+			}
+			break;
+		default:
+			ret = -EINVAL;
+		}
 #if IS_ENABLED(CONFIG_IPV6)
 	} else if (level == SOL_IPV6) {
 		if (optlen != sizeof(int) || sk->sk_family != AF_INET6)
@@ -3561,6 +3582,20 @@ BPF_CALL_5(bpf_getsockopt, struct bpf_sock_ops_kern *, bpf_sock,
 		} else {
 			goto err_clear;
 		}
+	} else if (level == SOL_IP) {
+		struct inet_sock *inet = inet_sk(sk);
+
+		if (optlen != sizeof(int) || sk->sk_family != AF_INET)
+			goto err_clear;
+
+		/* Only some options are supported */
+		switch (optname) {
+		case IP_TOS:
+			*((int *)optval) = (int)inet->tos;
+			break;
+		default:
+			goto err_clear;
+		}
 #if IS_ENABLED(CONFIG_IPV6)
 	} else if (level == SOL_IPV6) {
 		struct ipv6_pinfo *np = inet6_sk(sk);