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 <prankgup@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20210817224221.3257826-3-prankgup@fb.com

1 files changed, 39 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/sockopt_qos_to_cc.c b/tools/testing/selftests/bpf/progs/sockopt_qos_to_cc.c
new file mode 100644
index 000000000000..1bce83b6e3a7
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/sockopt_qos_to_cc.c
@@ -0,0 +1,39 @@
+// 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;
+}