[PATCH v3 bpf-next 4/4] selftests/bpf: Test bpf_{get,set}_retval behavior with cgroup/sockopt

[YiFei Zhu <zhuyifei@google.com>]

The tests checks how different ways of interacting with the helpers
(getting retval, setting EUNATCH, EISCONN, and legacy reject
returning 0 without setting retval), produce different results in
both the setsockopt syscall and the retval returned by the helper.
A few more tests verify the interaction between the retval of the
helper and the retval in getsockopt context.

Signed-off-by: YiFei Zhu <zhuyifei@google.com>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
---
 .../bpf/prog_tests/cgroup_getset_retval.c     | 481 ++++++++++++++++++
 .../progs/cgroup_getset_retval_getsockopt.c   |  45 ++
 .../progs/cgroup_getset_retval_setsockopt.c   |  52 ++
 3 files changed, 578 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_getset_retval.c
 create mode 100644 tools/testing/selftests/bpf/progs/cgroup_getset_retval_getsockopt.c
 create mode 100644 tools/testing/selftests/bpf/progs/cgroup_getset_retval_setsockopt.c

diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_getset_retval.c b/tools/testing/selftests/bpf/prog_tests/cgroup_getset_retval.c
new file mode 100644
index 000000000000..0b47c3c000c7
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/cgroup_getset_retval.c
@@ -0,0 +1,481 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * Copyright 2021 Google LLC.
+ */
+
+#include <test_progs.h>
+#include <cgroup_helpers.h>
+#include <network_helpers.h>
+
+#include "cgroup_getset_retval_setsockopt.skel.h"
+#include "cgroup_getset_retval_getsockopt.skel.h"
+
+#define SOL_CUSTOM	0xdeadbeef
+
+static int zero;
+
+static void test_setsockopt_set(int cgroup_fd, int sock_fd)
+{
+	struct cgroup_getset_retval_setsockopt *obj;
+	struct bpf_link *link_set_eunatch = NULL;
+
+	obj = cgroup_getset_retval_setsockopt__open_and_load();
+	if (!ASSERT_OK_PTR(obj, "skel-load"))
+		return;
+
+	/* Attach setsockopt that sets EUNATCH, assert that
+	 * we actually get that error when we run setsockopt()
+	 */
+	link_set_eunatch = bpf_program__attach_cgroup(obj->progs.set_eunatch,
+						      cgroup_fd);
+	if (!ASSERT_OK_PTR(link_set_eunatch, "cg-attach-set_eunatch"))
+		goto close_bpf_object;
+
+	if (!ASSERT_ERR(setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR,
+				   &zero, sizeof(int)), "setsockopt"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(errno, EUNATCH, "setsockopt-errno"))
+		goto close_bpf_object;
+
+	if (!ASSERT_EQ(obj->bss->invocations, 1, "invocations"))
+		goto close_bpf_object;
+	if (!ASSERT_FALSE(obj->bss->assertion_error, "assertion_error"))
+		goto close_bpf_object;
+
+close_bpf_object:
+	bpf_link__destroy(link_set_eunatch);
+
+	cgroup_getset_retval_setsockopt__destroy(obj);
+}
+
+static void test_setsockopt_set_and_get(int cgroup_fd, int sock_fd)
+{
+	struct cgroup_getset_retval_setsockopt *obj;
+	struct bpf_link *link_set_eunatch = NULL, *link_get_retval = NULL;
+
+	obj = cgroup_getset_retval_setsockopt__open_and_load();
+	if (!ASSERT_OK_PTR(obj, "skel-load"))
+		return;
+
+	/* Attach setsockopt that sets EUNATCH, and one that gets the
+	 * previously set errno. Assert that we get the same errno back.
+	 */
+	link_set_eunatch = bpf_program__attach_cgroup(obj->progs.set_eunatch,
+						      cgroup_fd);
+	if (!ASSERT_OK_PTR(link_set_eunatch, "cg-attach-set_eunatch"))
+		goto close_bpf_object;
+	link_get_retval = bpf_program__attach_cgroup(obj->progs.get_retval,
+						     cgroup_fd);
+	if (!ASSERT_OK_PTR(link_get_retval, "cg-attach-get_retval"))
+		goto close_bpf_object;
+
+	if (!ASSERT_ERR(setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR,
+				   &zero, sizeof(int)), "setsockopt"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(errno, EUNATCH, "setsockopt-errno"))
+		goto close_bpf_object;
+
+	if (!ASSERT_EQ(obj->bss->invocations, 2, "invocations"))
+		goto close_bpf_object;
+	if (!ASSERT_FALSE(obj->bss->assertion_error, "assertion_error"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(obj->bss->retval_value, -EUNATCH, "retval_value"))
+		goto close_bpf_object;
+
+close_bpf_object:
+	bpf_link__destroy(link_set_eunatch);
+	bpf_link__destroy(link_get_retval);
+
+	cgroup_getset_retval_setsockopt__destroy(obj);
+}
+
+static void test_setsockopt_default_zero(int cgroup_fd, int sock_fd)
+{
+	struct cgroup_getset_retval_setsockopt *obj;
+	struct bpf_link *link_get_retval = NULL;
+
+	obj = cgroup_getset_retval_setsockopt__open_and_load();
+	if (!ASSERT_OK_PTR(obj, "skel-load"))
+		return;
+
+	/* Attach setsockopt that gets the previously set errno.
+	 * Assert that, without anything setting one, we get 0.
+	 */
+	link_get_retval = bpf_program__attach_cgroup(obj->progs.get_retval,
+						     cgroup_fd);
+	if (!ASSERT_OK_PTR(link_get_retval, "cg-attach-get_retval"))
+		goto close_bpf_object;
+
+	if (!ASSERT_OK(setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR,
+				  &zero, sizeof(int)), "setsockopt"))
+		goto close_bpf_object;
+
+	if (!ASSERT_EQ(obj->bss->invocations, 1, "invocations"))
+		goto close_bpf_object;
+	if (!ASSERT_FALSE(obj->bss->assertion_error, "assertion_error"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(obj->bss->retval_value, 0, "retval_value"))
+		goto close_bpf_object;
+
+close_bpf_object:
+	bpf_link__destroy(link_get_retval);
+
+	cgroup_getset_retval_setsockopt__destroy(obj);
+}
+
+static void test_setsockopt_default_zero_and_set(int cgroup_fd, int sock_fd)
+{
+	struct cgroup_getset_retval_setsockopt *obj;
+	struct bpf_link *link_get_retval = NULL, *link_set_eunatch = NULL;
+
+	obj = cgroup_getset_retval_setsockopt__open_and_load();
+	if (!ASSERT_OK_PTR(obj, "skel-load"))
+		return;
+
+	/* Attach setsockopt that gets the previously set errno, and then
+	 * one that sets the errno to EUNATCH. Assert that the get does not
+	 * see EUNATCH set later, and does not prevent EUNATCH from being set.
+	 */
+	link_get_retval = bpf_program__attach_cgroup(obj->progs.get_retval,
+						     cgroup_fd);
+	if (!ASSERT_OK_PTR(link_get_retval, "cg-attach-get_retval"))
+		goto close_bpf_object;
+	link_set_eunatch = bpf_program__attach_cgroup(obj->progs.set_eunatch,
+						      cgroup_fd);
+	if (!ASSERT_OK_PTR(link_set_eunatch, "cg-attach-set_eunatch"))
+		goto close_bpf_object;
+
+	if (!ASSERT_ERR(setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR,
+				   &zero, sizeof(int)), "setsockopt"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(errno, EUNATCH, "setsockopt-errno"))
+		goto close_bpf_object;
+
+	if (!ASSERT_EQ(obj->bss->invocations, 2, "invocations"))
+		goto close_bpf_object;
+	if (!ASSERT_FALSE(obj->bss->assertion_error, "assertion_error"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(obj->bss->retval_value, 0, "retval_value"))
+		goto close_bpf_object;
+
+close_bpf_object:
+	bpf_link__destroy(link_get_retval);
+	bpf_link__destroy(link_set_eunatch);
+
+	cgroup_getset_retval_setsockopt__destroy(obj);
+}
+
+static void test_setsockopt_override(int cgroup_fd, int sock_fd)
+{
+	struct cgroup_getset_retval_setsockopt *obj;
+	struct bpf_link *link_set_eunatch = NULL, *link_set_eisconn = NULL;
+	struct bpf_link *link_get_retval = NULL;
+
+	obj = cgroup_getset_retval_setsockopt__open_and_load();
+	if (!ASSERT_OK_PTR(obj, "skel-load"))
+		return;
+
+	/* Attach setsockopt that sets EUNATCH, then one that sets EISCONN,
+	 * and then one that gets the exported errno. Assert both the syscall
+	 * and the helper sees the last set errno.
+	 */
+	link_set_eunatch = bpf_program__attach_cgroup(obj->progs.set_eunatch,
+						      cgroup_fd);
+	if (!ASSERT_OK_PTR(link_set_eunatch, "cg-attach-set_eunatch"))
+		goto close_bpf_object;
+	link_set_eisconn = bpf_program__attach_cgroup(obj->progs.set_eisconn,
+						      cgroup_fd);
+	if (!ASSERT_OK_PTR(link_set_eisconn, "cg-attach-set_eisconn"))
+		goto close_bpf_object;
+	link_get_retval = bpf_program__attach_cgroup(obj->progs.get_retval,
+						     cgroup_fd);
+	if (!ASSERT_OK_PTR(link_get_retval, "cg-attach-get_retval"))
+		goto close_bpf_object;
+
+	if (!ASSERT_ERR(setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR,
+				   &zero, sizeof(int)), "setsockopt"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(errno, EISCONN, "setsockopt-errno"))
+		goto close_bpf_object;
+
+	if (!ASSERT_EQ(obj->bss->invocations, 3, "invocations"))
+		goto close_bpf_object;
+	if (!ASSERT_FALSE(obj->bss->assertion_error, "assertion_error"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(obj->bss->retval_value, -EISCONN, "retval_value"))
+		goto close_bpf_object;
+
+close_bpf_object:
+	bpf_link__destroy(link_set_eunatch);
+	bpf_link__destroy(link_set_eisconn);
+	bpf_link__destroy(link_get_retval);
+
+	cgroup_getset_retval_setsockopt__destroy(obj);
+}
+
+static void test_setsockopt_legacy_eperm(int cgroup_fd, int sock_fd)
+{
+	struct cgroup_getset_retval_setsockopt *obj;
+	struct bpf_link *link_legacy_eperm = NULL, *link_get_retval = NULL;
+
+	obj = cgroup_getset_retval_setsockopt__open_and_load();
+	if (!ASSERT_OK_PTR(obj, "skel-load"))
+		return;
+
+	/* Attach setsockopt that return a reject without setting errno
+	 * (legacy reject), and one that gets the errno. Assert that for
+	 * backward compatibility the syscall result in EPERM, and this
+	 * is also visible to the helper.
+	 */
+	link_legacy_eperm = bpf_program__attach_cgroup(obj->progs.legacy_eperm,
+						       cgroup_fd);
+	if (!ASSERT_OK_PTR(link_legacy_eperm, "cg-attach-legacy_eperm"))
+		goto close_bpf_object;
+	link_get_retval = bpf_program__attach_cgroup(obj->progs.get_retval,
+						     cgroup_fd);
+	if (!ASSERT_OK_PTR(link_get_retval, "cg-attach-get_retval"))
+		goto close_bpf_object;
+
+	if (!ASSERT_ERR(setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR,
+				   &zero, sizeof(int)), "setsockopt"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(errno, EPERM, "setsockopt-errno"))
+		goto close_bpf_object;
+
+	if (!ASSERT_EQ(obj->bss->invocations, 2, "invocations"))
+		goto close_bpf_object;
+	if (!ASSERT_FALSE(obj->bss->assertion_error, "assertion_error"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(obj->bss->retval_value, -EPERM, "retval_value"))
+		goto close_bpf_object;
+
+close_bpf_object:
+	bpf_link__destroy(link_legacy_eperm);
+	bpf_link__destroy(link_get_retval);
+
+	cgroup_getset_retval_setsockopt__destroy(obj);
+}
+
+static void test_setsockopt_legacy_no_override(int cgroup_fd, int sock_fd)
+{
+	struct cgroup_getset_retval_setsockopt *obj;
+	struct bpf_link *link_set_eunatch = NULL, *link_legacy_eperm = NULL;
+	struct bpf_link *link_get_retval = NULL;
+
+	obj = cgroup_getset_retval_setsockopt__open_and_load();
+	if (!ASSERT_OK_PTR(obj, "skel-load"))
+		return;
+
+	/* Attach setsockopt that sets EUNATCH, then one that return a reject
+	 * without setting errno, and then one that gets the exported errno.
+	 * Assert both the syscall and the helper's errno are unaffected by
+	 * the second prog (i.e. legacy rejects does not override the errno
+	 * to EPERM).
+	 */
+	link_set_eunatch = bpf_program__attach_cgroup(obj->progs.set_eunatch,
+						      cgroup_fd);
+	if (!ASSERT_OK_PTR(link_set_eunatch, "cg-attach-set_eunatch"))
+		goto close_bpf_object;
+	link_legacy_eperm = bpf_program__attach_cgroup(obj->progs.legacy_eperm,
+						       cgroup_fd);
+	if (!ASSERT_OK_PTR(link_legacy_eperm, "cg-attach-legacy_eperm"))
+		goto close_bpf_object;
+	link_get_retval = bpf_program__attach_cgroup(obj->progs.get_retval,
+						     cgroup_fd);
+	if (!ASSERT_OK_PTR(link_get_retval, "cg-attach-get_retval"))
+		goto close_bpf_object;
+
+	if (!ASSERT_ERR(setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR,
+				   &zero, sizeof(int)), "setsockopt"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(errno, EUNATCH, "setsockopt-errno"))
+		goto close_bpf_object;
+
+	if (!ASSERT_EQ(obj->bss->invocations, 3, "invocations"))
+		goto close_bpf_object;
+	if (!ASSERT_FALSE(obj->bss->assertion_error, "assertion_error"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(obj->bss->retval_value, -EUNATCH, "retval_value"))
+		goto close_bpf_object;
+
+close_bpf_object:
+	bpf_link__destroy(link_set_eunatch);
+	bpf_link__destroy(link_legacy_eperm);
+	bpf_link__destroy(link_get_retval);
+
+	cgroup_getset_retval_setsockopt__destroy(obj);
+}
+
+static void test_getsockopt_get(int cgroup_fd, int sock_fd)
+{
+	struct cgroup_getset_retval_getsockopt *obj;
+	struct bpf_link *link_get_retval = NULL;
+	int buf;
+	socklen_t optlen = sizeof(buf);
+
+	obj = cgroup_getset_retval_getsockopt__open_and_load();
+	if (!ASSERT_OK_PTR(obj, "skel-load"))
+		return;
+
+	/* Attach getsockopt that gets previously set errno. Assert that the
+	 * error from kernel is in both ctx_retval_value and retval_value.
+	 */
+	link_get_retval = bpf_program__attach_cgroup(obj->progs.get_retval,
+						     cgroup_fd);
+	if (!ASSERT_OK_PTR(link_get_retval, "cg-attach-get_retval"))
+		goto close_bpf_object;
+
+	if (!ASSERT_ERR(getsockopt(sock_fd, SOL_CUSTOM, 0,
+				   &buf, &optlen), "getsockopt"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(errno, EOPNOTSUPP, "getsockopt-errno"))
+		goto close_bpf_object;
+
+	if (!ASSERT_EQ(obj->bss->invocations, 1, "invocations"))
+		goto close_bpf_object;
+	if (!ASSERT_FALSE(obj->bss->assertion_error, "assertion_error"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(obj->bss->retval_value, -EOPNOTSUPP, "retval_value"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(obj->bss->ctx_retval_value, -EOPNOTSUPP, "ctx_retval_value"))
+		goto close_bpf_object;
+
+close_bpf_object:
+	bpf_link__destroy(link_get_retval);
+
+	cgroup_getset_retval_getsockopt__destroy(obj);
+}
+
+static void test_getsockopt_override(int cgroup_fd, int sock_fd)
+{
+	struct cgroup_getset_retval_getsockopt *obj;
+	struct bpf_link *link_set_eisconn = NULL;
+	int buf;
+	socklen_t optlen = sizeof(buf);
+
+	obj = cgroup_getset_retval_getsockopt__open_and_load();
+	if (!ASSERT_OK_PTR(obj, "skel-load"))
+		return;
+
+	/* Attach getsockopt that sets retval to -EISCONN. Assert that this
+	 * overrides the value from kernel.
+	 */
+	link_set_eisconn = bpf_program__attach_cgroup(obj->progs.set_eisconn,
+						      cgroup_fd);
+	if (!ASSERT_OK_PTR(link_set_eisconn, "cg-attach-set_eisconn"))
+		goto close_bpf_object;
+
+	if (!ASSERT_ERR(getsockopt(sock_fd, SOL_CUSTOM, 0,
+				   &buf, &optlen), "getsockopt"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(errno, EISCONN, "getsockopt-errno"))
+		goto close_bpf_object;
+
+	if (!ASSERT_EQ(obj->bss->invocations, 1, "invocations"))
+		goto close_bpf_object;
+	if (!ASSERT_FALSE(obj->bss->assertion_error, "assertion_error"))
+		goto close_bpf_object;
+
+close_bpf_object:
+	bpf_link__destroy(link_set_eisconn);
+
+	cgroup_getset_retval_getsockopt__destroy(obj);
+}
+
+static void test_getsockopt_retval_sync(int cgroup_fd, int sock_fd)
+{
+	struct cgroup_getset_retval_getsockopt *obj;
+	struct bpf_link *link_set_eisconn = NULL, *link_clear_retval = NULL;
+	struct bpf_link *link_get_retval = NULL;
+	int buf;
+	socklen_t optlen = sizeof(buf);
+
+	obj = cgroup_getset_retval_getsockopt__open_and_load();
+	if (!ASSERT_OK_PTR(obj, "skel-load"))
+		return;
+
+	/* Attach getsockopt that sets retval to -EISCONN, and one that clears
+	 * ctx retval. Assert that the clearing ctx retval is synced to helper
+	 * and clears any errors both from kernel and BPF..
+	 */
+	link_set_eisconn = bpf_program__attach_cgroup(obj->progs.set_eisconn,
+						      cgroup_fd);
+	if (!ASSERT_OK_PTR(link_set_eisconn, "cg-attach-set_eisconn"))
+		goto close_bpf_object;
+	link_clear_retval = bpf_program__attach_cgroup(obj->progs.clear_retval,
+						       cgroup_fd);
+	if (!ASSERT_OK_PTR(link_clear_retval, "cg-attach-clear_retval"))
+		goto close_bpf_object;
+	link_get_retval = bpf_program__attach_cgroup(obj->progs.get_retval,
+						     cgroup_fd);
+	if (!ASSERT_OK_PTR(link_get_retval, "cg-attach-get_retval"))
+		goto close_bpf_object;
+
+	if (!ASSERT_OK(getsockopt(sock_fd, SOL_CUSTOM, 0,
+				  &buf, &optlen), "getsockopt"))
+		goto close_bpf_object;
+
+	if (!ASSERT_EQ(obj->bss->invocations, 3, "invocations"))
+		goto close_bpf_object;
+	if (!ASSERT_FALSE(obj->bss->assertion_error, "assertion_error"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(obj->bss->retval_value, 0, "retval_value"))
+		goto close_bpf_object;
+	if (!ASSERT_EQ(obj->bss->ctx_retval_value, 0, "ctx_retval_value"))
+		goto close_bpf_object;
+
+close_bpf_object:
+	bpf_link__destroy(link_set_eisconn);
+	bpf_link__destroy(link_clear_retval);
+	bpf_link__destroy(link_get_retval);
+
+	cgroup_getset_retval_getsockopt__destroy(obj);
+}
+
+void test_cgroup_getset_retval(void)
+{
+	int cgroup_fd = -1;
+	int sock_fd = -1;
+
+	cgroup_fd = test__join_cgroup("/cgroup_getset_retval");
+	if (!ASSERT_GE(cgroup_fd, 0, "cg-create"))
+		goto close_fd;
+
+	sock_fd = start_server(AF_INET, SOCK_DGRAM, NULL, 0, 0);
+	if (!ASSERT_GE(sock_fd, 0, "start-server"))
+		goto close_fd;
+
+	if (test__start_subtest("setsockopt-set"))
+		test_setsockopt_set(cgroup_fd, sock_fd);
+
+	if (test__start_subtest("setsockopt-set_and_get"))
+		test_setsockopt_set_and_get(cgroup_fd, sock_fd);
+
+	if (test__start_subtest("setsockopt-default_zero"))
+		test_setsockopt_default_zero(cgroup_fd, sock_fd);
+
+	if (test__start_subtest("setsockopt-default_zero_and_set"))
+		test_setsockopt_default_zero_and_set(cgroup_fd, sock_fd);
+
+	if (test__start_subtest("setsockopt-override"))
+		test_setsockopt_override(cgroup_fd, sock_fd);
+
+	if (test__start_subtest("setsockopt-legacy_eperm"))
+		test_setsockopt_legacy_eperm(cgroup_fd, sock_fd);
+
+	if (test__start_subtest("setsockopt-legacy_no_override"))
+		test_setsockopt_legacy_no_override(cgroup_fd, sock_fd);
+
+	if (test__start_subtest("getsockopt-get"))
+		test_getsockopt_get(cgroup_fd, sock_fd);
+
+	if (test__start_subtest("getsockopt-override"))
+		test_getsockopt_override(cgroup_fd, sock_fd);
+
+	if (test__start_subtest("getsockopt-retval_sync"))
+		test_getsockopt_retval_sync(cgroup_fd, sock_fd);
+
+close_fd:
+	close(cgroup_fd);
+}
diff --git a/tools/testing/selftests/bpf/progs/cgroup_getset_retval_getsockopt.c b/tools/testing/selftests/bpf/progs/cgroup_getset_retval_getsockopt.c
new file mode 100644
index 000000000000..b2a409e6382a
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/cgroup_getset_retval_getsockopt.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * Copyright 2021 Google LLC.
+ */
+
+#include <errno.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+__u32 invocations = 0;
+__u32 assertion_error = 0;
+__u32 retval_value = 0;
+__u32 ctx_retval_value = 0;
+
+SEC("cgroup/getsockopt")
+int get_retval(struct bpf_sockopt *ctx)
+{
+	retval_value = bpf_get_retval();
+	ctx_retval_value = ctx->retval;
+	__sync_fetch_and_add(&invocations, 1);
+
+	return 1;
+}
+
+SEC("cgroup/getsockopt")
+int set_eisconn(struct bpf_sockopt *ctx)
+{
+	__sync_fetch_and_add(&invocations, 1);
+
+	if (bpf_set_retval(-EISCONN))
+		assertion_error = 1;
+
+	return 1;
+}
+
+SEC("cgroup/getsockopt")
+int clear_retval(struct bpf_sockopt *ctx)
+{
+	__sync_fetch_and_add(&invocations, 1);
+
+	ctx->retval = 0;
+
+	return 1;
+}
diff --git a/tools/testing/selftests/bpf/progs/cgroup_getset_retval_setsockopt.c b/tools/testing/selftests/bpf/progs/cgroup_getset_retval_setsockopt.c
new file mode 100644
index 000000000000..d6e5903e06ba
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/cgroup_getset_retval_setsockopt.c
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * Copyright 2021 Google LLC.
+ */
+
+#include <errno.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+__u32 invocations = 0;
+__u32 assertion_error = 0;
+__u32 retval_value = 0;
+
+SEC("cgroup/setsockopt")
+int get_retval(struct bpf_sockopt *ctx)
+{
+	retval_value = bpf_get_retval();
+	__sync_fetch_and_add(&invocations, 1);
+
+	return 1;
+}
+
+SEC("cgroup/setsockopt")
+int set_eunatch(struct bpf_sockopt *ctx)
+{
+	__sync_fetch_and_add(&invocations, 1);
+
+	if (bpf_set_retval(-EUNATCH))
+		assertion_error = 1;
+
+	return 0;
+}
+
+SEC("cgroup/setsockopt")
+int set_eisconn(struct bpf_sockopt *ctx)
+{
+	__sync_fetch_and_add(&invocations, 1);
+
+	if (bpf_set_retval(-EISCONN))
+		assertion_error = 1;
+
+	return 0;
+}
+
+SEC("cgroup/setsockopt")
+int legacy_eperm(struct bpf_sockopt *ctx)
+{
+	__sync_fetch_and_add(&invocations, 1);
+
+	return 0;
+}
-- 
2.34.1.448.ga2b2bfdf31-goog