selftests/bpf: Add ksock kfunc test

Add a selftest that exercises the ksock kfuncs end-to-end. One syscall
BPF setup program creates a ksock context and connects the socket.
Another LSM sleepable BPF program looks up the context and send test
data. The userspace harness creates a network namespace and a new socket
on loopback, run the setup syscall prog and send LSM BPF prog then check
that the userspace socket received the data from BPF.

Signed-off-by: Mahe Tardy <mahe.tardy@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://lore.kernel.org/bpf/20260813110540.103550-4-mahe.tardy@gmail.com

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

@@ -0,0 +1,124 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Isovalent */
+
+#include <arpa/inet.h>
+
+#include "test_progs.h"
+#include "network_helpers.h"
+#include "ksock_lsm.skel.h"
+
+#define NS_TEST "ksock_lsm_ns"
+#define RECV_PORT 7777
+#define RECV_TIMEOUT_SEC 5
+
+struct ksock_test_env {
+	struct nstoken *nstoken;
+	int rfd;
+};
+
+static bool ksock_test_env_setup(struct ksock_test_env *env)
+{
+	struct sockaddr_in addr = {
+		.sin_family = AF_INET,
+		.sin_addr.s_addr = htonl(INADDR_LOOPBACK),
+		.sin_port = htons(RECV_PORT),
+	};
+	struct timeval tv = { .tv_sec = RECV_TIMEOUT_SEC };
+	int err;
+
+	memset(env, 0, sizeof(*env));
+	env->rfd = -1;
+
+	if (!ASSERT_OK(make_netns(NS_TEST), "make_netns"))
+		goto fail;
+
+	env->nstoken = open_netns(NS_TEST);
+	if (!ASSERT_OK_PTR(env->nstoken, "open_netns"))
+		goto fail;
+
+	env->rfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+	if (!ASSERT_OK_FD(env->rfd, "receiver socket"))
+		goto fail;
+
+	err = bind(env->rfd, (struct sockaddr *)&addr, sizeof(addr));
+	if (!ASSERT_OK(err, "bind receiver"))
+		goto fail;
+
+	err = setsockopt(env->rfd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
+	if (!ASSERT_OK(err, "set rcvtimeo"))
+		goto fail;
+
+	return true;
+
+fail:
+	return false;
+}
+
+void test_ksock_lsm(void)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, opts);
+	struct ksock_test_env env;
+	struct sockaddr_in trigger_addr = {
+		.sin_family = AF_INET,
+		.sin_addr.s_addr = htonl(INADDR_LOOPBACK),
+	};
+	struct ksock_lsm *skel;
+	char recv_data[sizeof(skel->data->send_data)] = {};
+	ssize_t n;
+	int tfd = -1;
+	int err;
+
+	skel = ksock_lsm__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel open_and_load"))
+		return;
+
+	if (!ksock_test_env_setup(&env))
+		goto fail;
+
+	/* Step 1: Run the setup SYSCALL prog to create the ksock */
+	skel->bss->ipv4_remote = htonl(INADDR_LOOPBACK);
+	skel->bss->remote_port = RECV_PORT;
+	err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.ksock_setup),
+				     &opts);
+	if (!ASSERT_OK(err, "ksock_setup run"))
+		goto fail;
+	if (!ASSERT_OK(opts.retval, "ksock_setup retval"))
+		goto fail;
+
+	/* Step 2: Attach LSM prog and trigger socket_bind from userspace */
+	skel->links.ksock_socket_bind =
+		bpf_program__attach_lsm(skel->progs.ksock_socket_bind);
+	if (!ASSERT_OK_PTR(skel->links.ksock_socket_bind,
+			   "attach socket_bind lsm"))
+		goto fail;
+
+	tfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+	if (!ASSERT_OK_FD(tfd, "trigger socket"))
+		goto fail;
+
+	skel->bss->target_pid = getpid();
+	err = bind(tfd, (struct sockaddr *)&trigger_addr, sizeof(trigger_addr));
+	skel->bss->target_pid = 0;
+	if (!ASSERT_OK(err, "trigger bind"))
+		goto fail;
+
+	/* Step 3: Verify the LSM hook sent the notification */
+	if (!ASSERT_EQ(skel->data->send_ret, sizeof(skel->data->send_data),
+		       "LSM send bytes"))
+		goto fail;
+
+	n = recvfrom(env.rfd, recv_data, sizeof(recv_data), 0, NULL, NULL);
+	if (ASSERT_EQ(n, sizeof(recv_data), "recvfrom len"))
+		ASSERT_MEMEQ(recv_data, skel->data->send_data, sizeof(recv_data),
+			     "payload match");
+
+fail:
+	if (tfd >= 0)
+		close(tfd);
+	if (env.rfd >= 0)
+		close(env.rfd);
+	if (env.nstoken)
+		close_netns(env.nstoken);
+	remove_netns(NS_TEST);
+	ksock_lsm__destroy(skel);
+}

tools/testing/selftests/bpf/progs/ksock_common.h

@@ -0,0 +1,78 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2026 Isovalent */
+
+#ifndef _KSOCK_COMMON_H
+#define _KSOCK_COMMON_H
+
+#include "errno.h"
+
+#define SOCK_DGRAM	2
+#define IPPROTO_UDP	17
+
+struct bpf_ksock *bpf_ksock_create(const struct bpf_ksock_create_opts *opts,
+				   u32 opts__sz, int *err__uninit) __ksym;
+int bpf_ksock_connect(struct bpf_ksock *ks, const union bpf_ksock_addr *addr,
+		      u32 addr__sz) __ksym;
+struct bpf_ksock *bpf_ksock_acquire(struct bpf_ksock *ks) __ksym;
+void bpf_ksock_release(struct bpf_ksock *ks) __ksym;
+int bpf_ksock_send(struct bpf_ksock *ks, const void *data, u32 data__sz) __ksym;
+void bpf_rcu_read_lock(void) __ksym;
+void bpf_rcu_read_unlock(void) __ksym;
+
+struct __ksock_ctx_value {
+	struct bpf_ksock __kptr * ctx;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, int);
+	__type(value, struct __ksock_ctx_value);
+	__uint(max_entries, 1);
+} __ksock_ctx_map SEC(".maps");
+
+static inline struct __ksock_ctx_value *ksock_ctx_value_lookup(void)
+{
+	u32 key = 0;
+
+	return bpf_map_lookup_elem(&__ksock_ctx_map, &key);
+}
+
+static inline struct bpf_ksock *ksock_ctx_get(void)
+{
+	struct __ksock_ctx_value *v;
+	struct bpf_ksock *ks = NULL, *tmp;
+
+	v = ksock_ctx_value_lookup();
+	if (!v)
+		return NULL;
+
+	bpf_rcu_read_lock();
+	tmp = v->ctx;
+	if (tmp)
+		ks = bpf_ksock_acquire(tmp);
+	bpf_rcu_read_unlock();
+
+	return ks;
+}
+
+static inline int ksock_ctx_insert(struct bpf_ksock *ctx)
+{
+	struct __ksock_ctx_value *v;
+	struct bpf_ksock *old;
+
+	v = ksock_ctx_value_lookup();
+	if (!v) {
+		bpf_ksock_release(ctx);
+		return -ENOENT;
+	}
+
+	old = bpf_kptr_xchg(&v->ctx, ctx);
+	if (old) {
+		bpf_ksock_release(old);
+		return -EEXIST;
+	}
+
+	return 0;
+}
+
+#endif /* _KSOCK_COMMON_H */

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

@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Isovalent */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_endian.h>
+#include "bpf_tracing_net.h"
+#include "ksock_common.h"
+
+char send_data[32] = "hello from bpf ksock";
+
+__be32 ipv4_remote;
+__u16 remote_port;
+int target_pid;
+int send_ret = -1;
+
+SEC("syscall")
+int ksock_setup(void *ctx)
+{
+	struct bpf_ksock_create_opts create_opts = {};
+	union bpf_ksock_addr addr = {};
+	struct bpf_ksock *ks;
+	int err = 0;
+
+	create_opts.family = AF_INET;
+	create_opts.type = SOCK_DGRAM;
+	create_opts.protocol = IPPROTO_UDP;
+
+	ks = bpf_ksock_create(&create_opts, sizeof(create_opts), &err);
+	if (!ks)
+		return err;
+
+	addr.sin.sin_family = AF_INET;
+	addr.sin.sin_port = bpf_htons(remote_port);
+	addr.sin.sin_addr.s_addr = ipv4_remote;
+
+	err = bpf_ksock_connect(ks, &addr, sizeof(addr));
+	if (err) {
+		bpf_ksock_release(ks);
+		return err;
+	}
+
+	err = ksock_ctx_insert(ks);
+	if (err && err != -EEXIST)
+		return err;
+	return 0;
+}
+
+SEC("lsm.s/socket_bind")
+int BPF_PROG(ksock_socket_bind, struct socket *sock, struct sockaddr *address,
+	     int addrlen, int ret)
+{
+	struct bpf_ksock *ks;
+	u32 pid = bpf_get_current_pid_tgid() >> 32;
+
+	if (ret || pid != target_pid)
+		return ret;
+
+	ks = ksock_ctx_get();
+	if (!ks) {
+		send_ret = -ENOENT;
+		return ret;
+	}
+
+	send_ret = bpf_ksock_send(ks, send_data, sizeof(send_data));
+	bpf_ksock_release(ks);
+
+	return ret;
+}
+
+char __license[] SEC("license") = "GPL";