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

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Message-ID: <YL59jlLrQrZvoMa0@krava>
Date:   Mon, 7 Jun 2021 22:11:58 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Yonghong Song <yhs@...com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>, Daniel Xu <dxu@...uu.xyz>,
        Viktor Malik <vmalik@...hat.com>
Subject: 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