[PATCH bpf 3/3] selftests/bpf: Add test to verify no memleak when updating hash maps

[Leon Hwang <leon.hwang@linux.dev>]

Add two tests to verify that updating hash maps does not leak memory
when BPF_KPTR_REF objects are involved.

The test performs the following steps:

1. Call update_elem() to insert an initial value.
2. Use bpf_refcount_acquire() to increment the refcount.
3. Store the node pointer in the map value.
4. Add the node to a linked list.
5. Probe-read the refcount and verify it is *2*.
6. Call update_elem() again to trigger refcount decrement.
7. Verify that the field has been reset.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 .../bpf/prog_tests/refcounted_kptr.c          |  93 ++++++++++++++++
 .../selftests/bpf/progs/refcounted_kptr.c     | 101 ++++++++++++++++++
 2 files changed, 194 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/refcounted_kptr.c b/tools/testing/selftests/bpf/prog_tests/refcounted_kptr.c
index d6bd5e16e6372..9dc9a425cc65d 100644
--- a/tools/testing/selftests/bpf/prog_tests/refcounted_kptr.c
+++ b/tools/testing/selftests/bpf/prog_tests/refcounted_kptr.c
@@ -44,3 +44,96 @@ void test_refcounted_kptr_wrong_owner(void)
 	ASSERT_OK(opts.retval, "rbtree_wrong_owner_remove_fail_a2 retval");
 	refcounted_kptr__destroy(skel);
 }
+
+static void test_refcnt_leak(void *values, size_t values_sz, u64 flags, bool lock_hash)
+{
+	struct refcounted_kptr *skel;
+	int ret, fd, key = 0;
+	struct bpf_map *map;
+	LIBBPF_OPTS(bpf_test_run_opts, opts,
+		    .data_in = &pkt_v4,
+		    .data_size_in = sizeof(pkt_v4),
+		    .repeat = 1,
+	);
+
+	skel = refcounted_kptr__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "refcounted_kptr__open_and_load"))
+		return;
+
+	map = skel->maps.pcpu_hash;
+	if (lock_hash)
+		map = skel->maps.lock_hash;
+
+	ret = bpf_map__update_elem(map, &key, sizeof(key), values, values_sz, flags);
+	if (!ASSERT_OK(ret, "bpf_map__update_elem first"))
+		goto out;
+
+	fd = bpf_program__fd(skel->progs.pcpu_hash_refcount_leak);
+	if (lock_hash)
+		fd = bpf_program__fd(skel->progs.hash_lock_refcount_leak);
+
+	ret = bpf_prog_test_run_opts(fd, &opts);
+	if (!ASSERT_OK(ret, "test_run_opts"))
+		goto out;
+	if (!ASSERT_EQ(opts.retval, 2, "retval refcount"))
+		goto out;
+
+	ret = bpf_map__update_elem(map, &key, sizeof(key), values, values_sz, flags);
+	if (!ASSERT_OK(ret, "bpf_map__update_elem second"))
+		goto out;
+
+	fd = bpf_program__fd(skel->progs.check_pcpu_hash_refcount);
+	if (lock_hash)
+		fd = bpf_program__fd(skel->progs.check_hash_lock_refcount);
+
+	ret = bpf_prog_test_run_opts(fd, &opts);
+	if (!ASSERT_OK(ret, "test_run_opts"))
+		goto out;
+	if (!ASSERT_EQ(opts.retval, 1, "retval"))
+		goto out;
+
+out:
+	refcounted_kptr__destroy(skel);
+}
+
+static void test_percpu_hash_refcount_leak(void)
+{
+	size_t values_sz;
+	u64 *values;
+	int cpu_nr;
+
+	cpu_nr = libbpf_num_possible_cpus();
+	if (!ASSERT_GT(cpu_nr, 0, "libbpf_num_possible_cpus"))
+		return;
+
+	values = calloc(cpu_nr, sizeof(u64));
+	if (!ASSERT_OK_PTR(values, "calloc values"))
+		return;
+
+	values_sz = cpu_nr * sizeof(u64);
+	memset(values, 0, values_sz);
+
+	test_refcnt_leak(values, values_sz, 0, false);
+
+	free(values);
+}
+
+struct hash_lock_value {
+	struct bpf_spin_lock lock;
+	u64 node;
+};
+
+static void test_hash_lock_refcount_leak(void)
+{
+	struct hash_lock_value value = {};
+
+	test_refcnt_leak(&value, sizeof(value), BPF_F_LOCK, true);
+}
+
+void test_refcount_leak(void)
+{
+	if (test__start_subtest("percpu_hash_refcount_leak"))
+		test_percpu_hash_refcount_leak();
+	if (test__start_subtest("hash_lock_refcount_leak"))
+		test_hash_lock_refcount_leak();
+}
diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr.c b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
index 893a4fdb4b6e9..8c41fe53da9e3 100644
--- a/tools/testing/selftests/bpf/progs/refcounted_kptr.c
+++ b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
@@ -568,4 +568,105 @@ int BPF_PROG(rbtree_sleepable_rcu_no_explicit_rcu_lock,
 	return 0;
 }
 
+static int __insert_in_list(struct bpf_list_head *head, struct bpf_spin_lock *lock,
+			    struct node_data __kptr **node)
+{
+	struct node_data *n, *m;
+	u32 refcnt;
+	void *ref;
+
+	n = bpf_obj_new(typeof(*n));
+	if (!n)
+		return -1;
+
+	m = bpf_refcount_acquire(n);
+	n = bpf_kptr_xchg(node, n);
+	if (n) {
+		bpf_obj_drop(n);
+		bpf_obj_drop(m);
+		return -2;
+	}
+
+	bpf_spin_lock(lock);
+	bpf_list_push_front(head, &m->l);
+	ref = (void *) &m->ref;
+	bpf_spin_unlock(lock);
+
+	bpf_probe_read_kernel(&refcnt, sizeof(refcnt), ref);
+	return refcnt;
+}
+
+static void *__lookup_map(void *map)
+{
+	int key = 0;
+
+	return bpf_map_lookup_elem(map, &key);
+}
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERCPU_HASH);
+	__type(key, int);
+	__type(value, struct map_value);
+	__uint(max_entries, 1);
+} pcpu_hash SEC(".maps");
+
+SEC("tc")
+int pcpu_hash_refcount_leak(void *ctx)
+{
+	struct map_value *v;
+
+	v = __lookup_map(&pcpu_hash);
+	if (!v)
+		return 0;
+
+	return __insert_in_list(&head, &lock, &v->node);
+}
+
+SEC("tc")
+int check_pcpu_hash_refcount(void *ctx)
+{
+	struct map_value *v;
+
+	v = __lookup_map(&pcpu_hash);
+	return v && v->node == NULL;
+}
+
+struct hash_lock_map_value {
+	struct node_data __kptr *node;
+	struct bpf_spin_lock lock;
+	int value;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__type(key, int);
+	__type(value, struct hash_lock_map_value);
+	__uint(max_entries, 1);
+} lock_hash SEC(".maps");
+
+SEC("tc")
+int hash_lock_refcount_leak(void *ctx)
+{
+	struct hash_lock_map_value *v;
+
+	v = __lookup_map(&lock_hash);
+	if (!v)
+		return 0;
+
+	bpf_spin_lock(&v->lock);
+	v->value = 42;
+	bpf_spin_unlock(&v->lock);
+
+	return __insert_in_list(&head, &lock, &v->node);
+}
+
+SEC("tc")
+int check_hash_lock_refcount(void *ctx)
+{
+	struct hash_lock_map_value *v;
+
+	v = __lookup_map(&lock_hash);
+	return v && v->node == NULL;
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.51.0