[PATCH bpf-next 6/6] selftests/bpf: Add ksock test for async callback guard

[Mahe Tardy <mahe.tardy@gmail.com>]

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>
---
 .../selftests/bpf/prog_tests/ksock_wq.c       | 34 ++++++++++
 tools/testing/selftests/bpf/progs/ksock_wq.c  | 62 +++++++++++++++++++
 2 files changed, 96 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/ksock_wq.c
 create mode 100644 tools/testing/selftests/bpf/progs/ksock_wq.c

diff --git a/tools/testing/selftests/bpf/prog_tests/ksock_wq.c b/tools/testing/selftests/bpf/prog_tests/ksock_wq.c
new file mode 100644
index 000000000000..184b134f3823
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/ksock_wq.c
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Isovalent */
+
+#include <unistd.h>
+
+#include "test_progs.h"
+#include "ksock_wq.skel.h"
+
+void test_ksock_wq(void)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, opts);
+	struct ksock_wq *skel;
+	int err;
+
+	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;
+
+	while (!__atomic_load_n(&skel->bss->callback_done, __ATOMIC_ACQUIRE))
+		usleep(1000);
+
+	ASSERT_EQ(skel->bss->create_err, -EOPNOTSUPP,
+		  "workqueue create rejected");
+
+out:
+	ksock_wq__destroy(skel);
+}
diff --git a/tools/testing/selftests/bpf/progs/ksock_wq.c b/tools/testing/selftests/bpf/progs/ksock_wq.c
new file mode 100644
index 000000000000..16a1873d132e
--- /dev/null
+++ b/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";
--
2.34.1