netdev - Re: [PATCH v4 2/6] cgroup: add support for eBPF programs

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Date:   Tue, 06 Sep 2016 19:18:00 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Daniel Mack <daniel@...que.org>, htejun@...com, ast@...com
CC:     davem@...emloft.net, kafai@...com, fw@...len.de,
        pablo@...filter.org, harald@...hat.com, netdev@...r.kernel.org,
        sargun@...gun.me, cgroups@...r.kernel.org
Subject: Re: [PATCH v4 2/6] cgroup: add support for eBPF programs

On 09/06/2016 03:46 PM, Daniel Mack wrote:
> This patch adds two sets of eBPF program pointers to struct cgroup.
> One for such that are directly pinned to a cgroup, and one for such
> that are effective for it.
>
> To illustrate the logic behind that, assume the following example
> cgroup hierarchy.
>
>    A - B - C
>          \ D - E
>
> If only B has a program attached, it will be effective for B, C, D
> and E. If D then attaches a program itself, that will be effective for
> both D and E, and the program in B will only affect B and C. Only one
> program of a given type is effective for a cgroup.
>
> Attaching and detaching programs will be done through the bpf(2)
> syscall. For now, ingress and egress inet socket filtering are the
> only supported use-cases.
>
> Signed-off-by: Daniel Mack <daniel@...que.org>
[...]
> +/**
> + * __cgroup_bpf_run_filter() - Run a program for packet filtering
> + * @sk: The socken sending or receiving traffic
> + * @skb: The skb that is being sent or received
> + * @type: The type of program to be exectuted
> + *
> + * If no socket is passed, or the socket is not of type INET or INET6,
> + * this function does nothing and returns 0.
> + *
> + * The program type passed in via @type must be suitable for network
> + * filtering. No further check is performed to assert that.
> + *
> + * This function will return %-EPERM if any if an attached program was found
> + * and if it returned != 1 during execution. In all other cases, 0 is returned.
> + */
> +int __cgroup_bpf_run_filter(struct sock *sk,
> +			    struct sk_buff *skb,
> +			    enum bpf_attach_type type)
> +{
> +	struct bpf_prog *prog;
> +	struct cgroup *cgrp;
> +	int ret = 0;
> +
> +	if (!sk)
> +		return 0;

Doesn't this also need to check || !sk_fullsock(sk)?

> +
> +	if (sk->sk_family != AF_INET &&
> +	    sk->sk_family != AF_INET6)
> +		return 0;
> +
> +	cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data);
> +
> +	rcu_read_lock();
> +
> +	prog = rcu_dereference(cgrp->bpf.effective[type]);
> +	if (prog) {
> +		unsigned int offset = skb->data - skb_mac_header(skb);
> +
> +		__skb_push(skb, offset);
> +		ret = bpf_prog_run_clear_cb(prog, skb) == 1 ? 0 : -EPERM;
> +		__skb_pull(skb, offset);
> +	}
> +
> +	rcu_read_unlock();
> +
> +	return ret;
> +}