selftests/bpf: Verify socket storage in cgroup/sock_{create, release}

Augment udp_limit test to set and verify socket storage value.
That should be enough to exercise the changes from the previous
patch.
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20200729003104.1280813-2-sdf@google.com

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

@@ -6,14 +6,28 @@
 
 int invocations = 0, in_use = 0;
 
+struct {
+	__uint(type, BPF_MAP_TYPE_SK_STORAGE);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__type(key, int);
+	__type(value, int);
+} sk_map SEC(".maps");
+
 SEC("cgroup/sock_create")
 int sock(struct bpf_sock *ctx)
 {
+	int *sk_storage;
 	__u32 key;
 
 	if (ctx->type != SOCK_DGRAM)
 		return 1;
 
+	sk_storage = bpf_sk_storage_get(&sk_map, ctx, 0,
+					BPF_SK_STORAGE_GET_F_CREATE);
+	if (!sk_storage)
+		return 0;
+	*sk_storage = 0xdeadbeef;
+
 	__sync_fetch_and_add(&invocations, 1);
 
 	if (in_use > 0) {
@@ -31,11 +45,16 @@ int sock(struct bpf_sock *ctx)
 SEC("cgroup/sock_release")
 int sock_release(struct bpf_sock *ctx)
 {
+	int *sk_storage;
 	__u32 key;
 
 	if (ctx->type != SOCK_DGRAM)
 		return 1;
 
+	sk_storage = bpf_sk_storage_get(&sk_map, ctx, 0, 0);
+	if (!sk_storage || *sk_storage != 0xdeadbeef)
+		return 0;
+
 	__sync_fetch_and_add(&invocations, 1);
 	__sync_fetch_and_add(&in_use, -1);
 	return 1;