netdev - Re: [PATCH bpf-next 06/11] bpf: add bpf_skb_cgroup

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Date:   Tue, 29 May 2018 13:15:02 +0100
From:   Quentin Monnet <quentin.monnet@...ronome.com>
To:     Daniel Borkmann <daniel@...earbox.net>, ast@...nel.org
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next 06/11] bpf: add bpf_skb_cgroup_id helper

Hi Daniel,

2018-05-28 02:43 UTC+0200 ~ Daniel Borkmann <daniel@...earbox.net>
> Add a new bpf_skb_cgroup_id() helper that allows to retrieve the
> cgroup id from the skb's socket. This is useful in particular to
> enable bpf_get_cgroup_classid()-like behavior for cgroup v1 in
> cgroup v2 by allowing ID based matching on egress. This can in
> particular be used in combination with applying policy e.g. from
> map lookups, and also complements the older bpf_skb_under_cgroup()
> interface. In user space the cgroup id for a given path can be
> retrieved through the f_handle as demonstrated in [0] recently.
> 
>   [0] https://lkml.org/lkml/2018/5/22/1190
> 
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> Acked-by: Alexei Starovoitov <ast@...nel.org>
> ---
>  include/uapi/linux/bpf.h | 17 ++++++++++++++++-
>  net/core/filter.c        | 29 +++++++++++++++++++++++++++--
>  2 files changed, 43 insertions(+), 3 deletions(-)
> 
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 9b8c6e3..e2853aa 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2004,6 +2004,20 @@ union bpf_attr {
>   * 		direct packet access.
>   *	Return
>   * 		0 on success, or a negative error in case of failure.
> + *
> + * uint64_t bpf_skb_cgroup_id(struct sk_buff *skb)
> + * 	Description
> + * 		Return the cgroup v2 id of the socket associated with the *skb*.
> + * 		This is roughly similar to the **bpf_get_cgroup_classid**\ ()
> + * 		helper for cgroup v1 by providing a tag resp. identifier that
> + * 		can be matched on or used for map lookups e.g. to implement
> + * 		policy. The cgroup v2 id of a given path in the hierarchy is
> + * 		exposed in user space through the f_handle API in order to get
> + * 		to the same 64-bit id.
> + *
> + * 		This helper can be used on TC egress path, but not on ingress.

Nitpick: Maybe mention that the kernel must be built with
CONFIG_SOCK_CGROUP_DATA option for the helper to be available?

Best,
Quentin


> + * 	Return
> + * 		The id is returned or 0 in case the id could not be retrieved.
>   */
>  #define __BPF_FUNC_MAPPER(FN)		\
>  	FN(unspec),			\
> @@ -2082,7 +2096,8 @@ union bpf_attr {
>  	FN(lwt_push_encap),		\
>  	FN(lwt_seg6_store_bytes),	\
>  	FN(lwt_seg6_adjust_srh),	\
> -	FN(lwt_seg6_action),
> +	FN(lwt_seg6_action),		\
> +	FN(skb_cgroup_id),
>  
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>   * function eBPF program intends to call
> diff --git a/net/core/filter.c b/net/core/filter.c
> index acf1f4f..717c740 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -3661,6 +3661,27 @@ static const struct bpf_func_proto bpf_skb_under_cgroup_proto = {
>  	.arg3_type	= ARG_ANYTHING,
>  };
>  
> +#ifdef CONFIG_SOCK_CGROUP_DATA
> +BPF_CALL_1(bpf_skb_cgroup_id, const struct sk_buff *, skb)
> +{
> +	struct sock *sk = skb_to_full_sk(skb);
> +	struct cgroup *cgrp;
> +
> +	if (!sk || !sk_fullsock(sk))
> +		return 0;
> +
> +	cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data);
> +	return cgrp->kn->id.id;
> +}
> +
> +static const struct bpf_func_proto bpf_skb_cgroup_id_proto = {
> +	.func           = bpf_skb_cgroup_id,
> +	.gpl_only       = false,
> +	.ret_type       = RET_INTEGER,
> +	.arg1_type      = ARG_PTR_TO_CTX,
> +};
> +#endif
> +
>  static unsigned long bpf_xdp_copy(void *dst_buff, const void *src_buff,
>  				  unsigned long off, unsigned long len)
>  {
> @@ -4741,12 +4762,16 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  		return &bpf_get_socket_cookie_proto;
>  	case BPF_FUNC_get_socket_uid:
>  		return &bpf_get_socket_uid_proto;
> +	case BPF_FUNC_fib_lookup:
> +		return &bpf_skb_fib_lookup_proto;
>  #ifdef CONFIG_XFRM
>  	case BPF_FUNC_skb_get_xfrm_state:
>  		return &bpf_skb_get_xfrm_state_proto;
>  #endif
> -	case BPF_FUNC_fib_lookup:
> -		return &bpf_skb_fib_lookup_proto;
> +#ifdef CONFIG_SOCK_CGROUP_DATA
> +	case BPF_FUNC_skb_cgroup_id:
> +		return &bpf_skb_cgroup_id_proto;
> +#endif
>  	default:
>  		return bpf_base_func_proto(func_id);
>  	}
>