netdev - Re: [PATCH net-next v2 1/2] bpf: Allow CGROUP_SKB eBPF program to access sk

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Date:   Tue, 06 Jun 2017 14:04:00 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Chenbo Feng <chenbofeng.kernel@...il.com>, netdev@...r.kernel.org,
        David Miller <davem@...emloft.net>
CC:     Lorenzo Colitti <lorenzo@...gle.com>,
        Chenbo Feng <fengc@...gle.com>, ast@...com
Subject: Re: [PATCH net-next v2 1/2] bpf: Allow CGROUP_SKB eBPF program to
 access sk_buff

On 06/01/2017 03:15 AM, Chenbo Feng wrote:
> From: Chenbo Feng <fengc@...gle.com>
>
> This allows cgroup eBPF program to classify packet based on their
> protocol or other detail information. Currently program need
> CAP_NET_ADMIN privilege to attach a cgroup eBPF program, and A
> process with CAP_NET_ADMIN can already see all packets on the system,
> for example, by creating an iptables rules that causes the packet to
> be passed to userspace via NFLOG.
>
> Signed-off-by: Chenbo Feng <fengc@...gle.com>

Sorry, but I am puzzled what above change log has to do with the
below diff?! Back then we decided not to add BPF_PROG_TYPE_CGROUP_SKB
to may_access_skb(), since one can already use bpf_skb_load_bytes()
helper to access pkt data, which is a much more flexible interface.
Mind to elaborate why you cannot use bpf_skb_load_bytes() instead?

> ---
>   kernel/bpf/verifier.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 339c8a1..94a9bc9 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2419,6 +2419,7 @@ static bool may_access_skb(enum bpf_prog_type type)
>   	case BPF_PROG_TYPE_SOCKET_FILTER:
>   	case BPF_PROG_TYPE_SCHED_CLS:
>   	case BPF_PROG_TYPE_SCHED_ACT:
> +	case BPF_PROG_TYPE_CGROUP_SKB:
>   		return true;
>   	default:
>   		return false;
>