linux-kernel - Re: [PATCH bpf-next v5 1/2] bpf: support BPF_PROG

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Date:   Fri, 5 Nov 2021 12:51:55 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Di Zhu <zhudi2@...wei.com>
Cc:     davem@...emloft.net, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, jakub@...udflare.com,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 1/2] bpf: support BPF_PROG_QUERY for progs
 attached to sockmap

On Thu, Nov 04, 2021 at 09:07:44AM +0800, Di Zhu wrote:
> +int sock_map_bpf_prog_query(const union bpf_attr *attr,
> +			    union bpf_attr __user *uattr)
> +{
> +	__u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);
> +	u32 prog_cnt = 0, flags = 0, ufd = attr->target_fd;
> +	struct bpf_prog **pprog;
> +	struct bpf_prog *prog;
> +	struct bpf_map *map;
> +	struct fd f;
> +	u32 id = 0;
> +	int ret;
> +
> +	if (attr->query.query_flags)
> +		return -EINVAL;
> +
> +	f = fdget(ufd);
> +	map = __bpf_map_get(f);
> +	if (IS_ERR(map))
> +		return PTR_ERR(map);
> +
> +	rcu_read_lock();
> +
> +	ret = sock_map_prog_lookup(map, &pprog, attr->query.attach_type);
> +	if (ret)
> +		goto end;
> +
> +	prog = *pprog;
> +	prog_cnt = (!prog) ? 0 : 1;
> +
> +	if (!attr->query.prog_cnt || !prog_ids || !prog_cnt)
> +		goto end;

This sanity check (except prog_cnt) can be moved before RCU read lock?

> +
> +	id = prog->aux->id;
> +	if (id == 0)
> +		prog_cnt = 0;

The id seems generic, so why not handle it in bpf_prog_query() for all progs?

> +
> +end:
> +	rcu_read_unlock();
> +
> +	if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)) ||

'flags' is always 0 here, right? So this is not needed as uattr has been already
cleared in __sys_bpf().


Thanks.