netdev - Re: [PATCH bpf-next v2 3/7] net: sched: add bpf

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Date:   Fri, 4 Jun 2021 20:08:17 -0700
From:   Yonghong Song <yhs@...com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>, <bpf@...r.kernel.org>
CC:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Vlad Buslov <vladbu@...dia.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 3/7] net: sched: add bpf_link API for bpf
 classifier



On 6/3/21 11:31 PM, Kumar Kartikeya Dwivedi wrote:
> This commit introduces a bpf_link based kernel API for creating tc
> filters and using the cls_bpf classifier. Only a subset of what netlink
> API offers is supported, things like TCA_BPF_POLICE, TCA_RATE and
> embedded actions are unsupported.
> 
> The kernel API and the libbpf wrapper added in a subsequent patch are
> more opinionated and mirror the semantics of low level netlink based
> TC-BPF API, i.e. always setting direct action mode, always setting
> protocol to ETH_P_ALL, and only exposing handle and priority as the
> variables the user can control. We add an additional gen_flags parameter
> though to allow for offloading use cases. It would be trivial to extend
> the current API to support specifying other attributes in the future,
> but for now I'm sticking how we want to push usage.
> 
> The semantics around bpf_link support are as follows:
> 
> A user can create a classifier attached to a filter using the bpf_link
> API, after which changing it and deleting it only happens through the
> bpf_link API. It is not possible to bind the bpf_link to existing
> filter, and any such attempt will fail with EEXIST. Hence EEXIST can be
> returned in two cases, when existing bpf_link owned filter exists, or
> existing netlink owned filter exists.
> 
> Removing bpf_link owned filter from netlink returns EPERM, denoting that
> netlink is locked out from filter manipulation when bpf_link is
> involved.
> 
> Whenever a filter is detached due to chain removal, or qdisc tear down,
> or net_device shutdown, the bpf_link becomes automatically detached.
> 
> In this way, the netlink API and bpf_link creation path are exclusive
> and don't stomp over one another. Filters created using bpf_link API
> cannot be replaced by netlink API, and filters created by netlink API are
> never replaced by bpf_link. Netfilter also cannot detach bpf_link filters.
> 
> We serialize all changes dover rtnl_lock as cls_bpf API doesn't support the

dover => over?

> unlocked classifier API.
> 
> Reviewed-by: Toke Høiland-Jørgensen <toke@...hat.com>.
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
> ---
>   include/linux/bpf_types.h |   3 +
>   include/net/pkt_cls.h     |  13 ++
>   include/net/sch_generic.h |   6 +-
>   include/uapi/linux/bpf.h  |  15 +++
>   kernel/bpf/syscall.c      |  10 +-
>   net/sched/cls_api.c       | 139 ++++++++++++++++++++-
>   net/sched/cls_bpf.c       | 250 +++++++++++++++++++++++++++++++++++++-
>   7 files changed, 430 insertions(+), 6 deletions(-)
> 
[...]
>   subsys_initcall(tc_filter_init);
> +
> +#if IS_ENABLED(CONFIG_NET_CLS_BPF)
> +
> +int bpf_tc_link_attach(union bpf_attr *attr, struct bpf_prog *prog)
> +{
> +	struct net *net = current->nsproxy->net_ns;
> +	struct tcf_chain_info chain_info;
> +	u32 chain_index, prio, parent;
> +	struct tcf_block *block;
> +	struct tcf_chain *chain;
> +	struct tcf_proto *tp;
> +	int err, tp_created;
> +	unsigned long cl;
> +	struct Qdisc *q;
> +	__be16 protocol;
> +	void *fh;
> +
> +	/* Caller already checks bpf_capable */
> +	if (!ns_capable(current->nsproxy->net_ns->user_ns, CAP_NET_ADMIN))

net->user_ns?

> +		return -EPERM;
> +
> +	if (attr->link_create.flags ||
> +	    !attr->link_create.target_ifindex ||
> +	    !tc_flags_valid(attr->link_create.tc.gen_flags))
> +		return -EINVAL;
> +
[...]