selftests/bpf: Add ksock test for async callback guard

Because the kfuncs are going through LSM hooks, allowing their use via
workqueue callbacks would expose the wrong credentials. This test
ensures the kfunc are preventing any use from these contexts.

Signed-off-by: Mahe Tardy <mahe.tardy@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Acked-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/bpf/20260813110540.103550-6-mahe.tardy@gmail.com

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

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Isovalent */
+
+#include <unistd.h>
+
+#include "test_progs.h"
+#include "ksock_wq.skel.h"
+
+#define CALLBACK_WAIT_RETRIES 1000
+#define CALLBACK_WAIT_US 1000
+
+void test_ksock_wq(void)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, opts);
+	struct ksock_wq *skel;
+	u32 callback_done;
+	int err, i;
+
+	skel = ksock_wq__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "ksock_wq open and load"))
+		return;
+
+	err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.ksock_wq_start),
+				     &opts);
+	if (!ASSERT_OK(err, "run ksock_wq_start"))
+		goto out;
+	if (!ASSERT_OK(opts.retval, "ksock_wq_start retval"))
+		goto out;
+
+	for (i = 0; i < CALLBACK_WAIT_RETRIES; i++) {
+		if (__atomic_load_n(&skel->bss->callback_done, __ATOMIC_ACQUIRE))
+			break;
+		usleep(CALLBACK_WAIT_US);
+	}
+	callback_done = __atomic_load_n(&skel->bss->callback_done,
+					__ATOMIC_ACQUIRE);
+	if (!ASSERT_EQ(callback_done, 1, "workqueue callback completed"))
+		goto out;
+
+	ASSERT_EQ(skel->bss->create_err, -EOPNOTSUPP,
+		  "workqueue create rejected");
+
+out:
+	ksock_wq__destroy(skel);
+}

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

@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Isovalent */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include "bpf_experimental.h"
+#include "bpf_tracing_net.h"
+#include "errno.h"
+#include "ksock_common.h"
+
+struct ksock_wq_value {
+	struct bpf_wq work;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, u32);
+	__type(value, struct ksock_wq_value);
+} work_map SEC(".maps");
+
+int create_err;
+u32 callback_done;
+
+static int ksock_wq_callback(void *map, int *key, void *value)
+{
+	struct bpf_ksock_create_opts opts = {
+		.family = AF_INET,
+		.type = SOCK_DGRAM,
+		.protocol = IPPROTO_UDP,
+	};
+	struct bpf_ksock *ks;
+	int err = 0;
+
+	ks = bpf_ksock_create(&opts, sizeof(opts), &err);
+	if (ks)
+		bpf_ksock_release(ks);
+	create_err = err;
+	__sync_fetch_and_add(&callback_done, 1);
+	return 0;
+}
+
+SEC("syscall")
+int ksock_wq_start(void *ctx)
+{
+	struct ksock_wq_value *value;
+	u32 key = 0;
+	int err;
+
+	value = bpf_map_lookup_elem(&work_map, &key);
+	if (!value)
+		return -ENOENT;
+	err = bpf_wq_init(&value->work, &work_map, 0);
+	if (err)
+		return err;
+	err = bpf_wq_set_callback(&value->work, ksock_wq_callback, 0);
+	if (err)
+		return err;
+	return bpf_wq_start(&value->work, 0);
+}
+
+char __license[] SEC("license") = "GPL";