selftests/bpf: Add tests for {set|get} socket option from setsockopt BPF

Adding selftests for the newly added functionality to call bpf_setsockopt()
and bpf_getsockopt() from setsockopt BPF programs.

Test Details:

1. BPF Program

Checks for changes in IPV6_TCLASS(SOL_IPV6) via setsockopt
If the cca for the socket is not cubic do nothing
If the newly set value for IPV6_TCLASS is 45 (0x2d) (as per our use-case)
then change the cc from cubic to reno

2. User Space Program

Creates an AF_INET6 socket and set the cca for that to be "cubic"
Attach the program and set the IPV6_TCLASS to 0x2d using setsockopt
Verify the cca for the socket changed to reno

Signed-off-by: Prankur Gupta <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Acked-by: Song Liu <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/bpf_tcp_helpers.h

···
 SEC("struct_ops/"#name) \
 BPF_PROG(name, args)
 
+#ifndef SOL_TCP
+#define SOL_TCP 6
+#endif
+
 #define tcp_jiffies32 ((__u32)bpf_jiffies64())
 
 struct sock_common {
···
 		return tp->snd_cwnd < 2 * tp->max_packets_out;
 
 	return !!BPF_CORE_READ_BITFIELD(tp, is_cwnd_limited);
+}
+
+static __always_inline bool tcp_cc_eq(const char *a, const char *b)
+{
+	int i;
+
+	for (i = 0; i < TCP_CA_NAME_MAX; i++) {
+		if (a[i] != b[i])
+			return false;
+		if (!a[i])
+			break;
+	}
+
+	return true;
 }
 
 extern __u32 tcp_slow_start(struct tcp_sock *tp, __u32 acked) __ksym;

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

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include <test_progs.h>
+#include <netinet/tcp.h>
+#include "sockopt_qos_to_cc.skel.h"
+
+static void run_setsockopt_test(int cg_fd, int sock_fd)
+{
+	socklen_t optlen;
+	char cc[16]; /* TCP_CA_NAME_MAX */
+	int buf;
+	int err = -1;
+
+	buf = 0x2D;
+	err = setsockopt(sock_fd, SOL_IPV6, IPV6_TCLASS, &buf, sizeof(buf));
+	if (!ASSERT_OK(err, "setsockopt(sock_fd, IPV6_TCLASS)"))
+		return;
+
+	/* Verify the setsockopt cc change */
+	optlen = sizeof(cc);
+	err = getsockopt(sock_fd, SOL_TCP, TCP_CONGESTION, cc, &optlen);
+	if (!ASSERT_OK(err, "getsockopt(sock_fd, TCP_CONGESTION)"))
+		return;
+
+	if (!ASSERT_STREQ(cc, "reno", "getsockopt(sock_fd, TCP_CONGESTION)"))
+		return;
+}
+
+void test_sockopt_qos_to_cc(void)
+{
+	struct sockopt_qos_to_cc *skel;
+	char cc_cubic[16] = "cubic"; /* TCP_CA_NAME_MAX */
+	int cg_fd = -1;
+	int sock_fd = -1;
+	int err;
+
+	cg_fd = test__join_cgroup("/sockopt_qos_to_cc");
+	if (!ASSERT_GE(cg_fd, 0, "cg-join(sockopt_qos_to_cc)"))
+		return;
+
+	skel = sockopt_qos_to_cc__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel"))
+		goto done;
+
+	sock_fd = socket(AF_INET6, SOCK_STREAM, 0);
+	if (!ASSERT_GE(sock_fd, 0, "v6 socket open"))
+		goto done;
+
+	err = setsockopt(sock_fd, SOL_TCP, TCP_CONGESTION, &cc_cubic,
+			 sizeof(cc_cubic));
+	if (!ASSERT_OK(err, "setsockopt(sock_fd, TCP_CONGESTION)"))
+		goto done;
+
+	skel->links.sockopt_qos_to_cc =
+		bpf_program__attach_cgroup(skel->progs.sockopt_qos_to_cc,
+					   cg_fd);
+	if (!ASSERT_OK_PTR(skel->links.sockopt_qos_to_cc,
+			   "prog_attach(sockopt_qos_to_cc)"))
+		goto done;
+
+	run_setsockopt_test(cg_fd, sock_fd);
+
+done:
+	if (sock_fd != -1)
+		close(sock_fd);
+	if (cg_fd != -1)
+		close(cg_fd);
+	/* destroy can take null and error pointer */
+	sockopt_qos_to_cc__destroy(skel);
+}

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

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include <string.h>
+#include <linux/tcp.h>
+#include <netinet/in.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_tcp_helpers.h"
+
+char _license[] SEC("license") = "GPL";
+
+SEC("cgroup/setsockopt")
+int sockopt_qos_to_cc(struct bpf_sockopt *ctx)
+{
+	void *optval_end = ctx->optval_end;
+	int *optval = ctx->optval;
+	char buf[TCP_CA_NAME_MAX];
+	char cc_reno[TCP_CA_NAME_MAX] = "reno";
+	char cc_cubic[TCP_CA_NAME_MAX] = "cubic";
+
+	if (ctx->level != SOL_IPV6 || ctx->optname != IPV6_TCLASS)
+		return 1;
+
+	if (optval + 1 > optval_end)
+		return 0; /* EPERM, bounds check */
+
+	if (bpf_getsockopt(ctx->sk, SOL_TCP, TCP_CONGESTION, &buf, sizeof(buf)))
+		return 0;
+
+	if (!tcp_cc_eq(buf, cc_cubic))
+		return 0;
+
+	if (*optval == 0x2d) {
+		if (bpf_setsockopt(ctx->sk, SOL_TCP, TCP_CONGESTION, &cc_reno,
+				sizeof(cc_reno)))
+			return 0;
+	}
+	return 1;
+}