Re: [PATCH 15/19] libbpf: Add support to link multi func tracing program

On Mon, Jun 07, 2021 at 12:42:51PM -0700, Yonghong Song wrote:

SNIP

+static int bpf_tracing_multi_attach(struct bpf_prog *prog,
+				    const union bpf_attr *attr)
+{
+	void __user *ubtf_ids = u64_to_user_ptr(attr->link_create.multi_btf_ids);
+	u32 size, i, cnt = attr->link_create.multi_btf_ids_cnt;
+	struct bpf_tracing_multi_link *link = NULL;
+	struct bpf_link_primer link_primer;
+	struct bpf_trampoline *tr = NULL;
+	int err = -EINVAL;
+	u8 nr_args = 0;
+	u32 *btf_ids;
+
+	if (check_multi_prog_type(prog))
+		return -EINVAL;
+
+	size = cnt * sizeof(*btf_ids);
+	btf_ids = kmalloc(size, GFP_USER | __GFP_NOWARN);
+	if (!btf_ids)
+		return -ENOMEM;
+
+	err = -EFAULT;
+	if (ubtf_ids && copy_from_user(btf_ids, ubtf_ids, size))
+		goto out_free;
+
+	link = kzalloc(sizeof(*link), GFP_USER);
+	if (!link)
+		goto out_free;
+
+	for (i = 0; i < cnt; i++) {
+		struct bpf_attach_target_info tgt_info = {};
+
+		err = bpf_check_attach_target(NULL, prog, NULL, btf_ids[i],
+					      &tgt_info);
+		if (err)
+			goto out_free;
+
+		if (ftrace_set_filter_ip(&link->ops, tgt_info.tgt_addr, 0, 0))
+			goto out_free;
+
+		if (nr_args < tgt_info.fmodel.nr_args)
+			nr_args = tgt_info.fmodel.nr_args;
+	}
+
+	tr = bpf_trampoline_multi_alloc();
+	if (!tr)
+		goto out_free;
+
+	bpf_func_model_nargs(&tr->func.model, nr_args);
+
+	err = bpf_trampoline_link_prog(prog, tr);
+	if (err)
+		goto out_free;
+
+	err = register_ftrace_direct_multi(&link->ops, (unsigned long)
tr->cur_image->image);
+	if (err)
+		goto out_free;
+
+	bpf_link_init(&link->link, BPF_LINK_TYPE_TRACING_MULTI,
+		      &bpf_tracing_multi_link_lops, prog);
+	link->attach_type = prog->expected_attach_type;
+
+	err = bpf_link_prime(&link->link, &link_primer);
+	if (err)
+		goto out_unlink;
+
+	link->tr = tr;
+	/* Take extra ref so we are even with progs added by link_update. */
+	bpf_prog_inc(prog);
+	return bpf_link_settle(&link_primer);
+
+out_unlink:
+	unregister_ftrace_direct_multi(&link->ops);
+out_free:
+	kfree(tr);
+	kfree(btf_ids);
+	kfree(link);
+	return err;
+}
+

Looks like cnt = 0 is okay in bpf_tracing_multi_attach().

right, we should fail for that with EINVAL, also the
maximum with prog->aux->attach_btf->nr_types at least

thanks,
jirka