netdev - Re: [RFC PATCH 4/5] net: filter: run cgroup eBPF programs

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Date:	Wed, 17 Aug 2016 11:23:29 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Daniel Mack <daniel@...que.org>
Cc:	htejun@...com, daniel@...earbox.net, ast@...com,
	davem@...emloft.net, kafai@...com, fw@...len.de,
	pablo@...filter.org, harald@...hat.com, netdev@...r.kernel.org
Subject: Re: [RFC PATCH 4/5] net: filter: run cgroup eBPF programs

On Wed, Aug 17, 2016 at 11:20:29AM -0700, Alexei Starovoitov wrote:
> On Wed, Aug 17, 2016 at 04:00:47PM +0200, Daniel Mack wrote:
> > If CONFIG_CGROUP_BPF is enabled, and the cgroup associated with the
> > receiving socket has an eBPF programs installed, run them from
> > sk_filter_trim_cap().
> > 
> > eBPF programs used in this context are expected to either return 1 to
> > let the packet pass, or != 1 to drop them. The programs have access to
> > the full skb, including the MAC headers.
> > 
> > This patch only implements the call site for ingress packets.
> > 
> > Signed-off-by: Daniel Mack <daniel@...que.org>
> > ---
> >  net/core/filter.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 44 insertions(+)
> > 
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index c5d8332..a1dd94b 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -52,6 +52,44 @@
> >  #include <net/dst.h>
> >  #include <net/sock_reuseport.h>
> >  
> > +#ifdef CONFIG_CGROUP_BPF
> > +static int sk_filter_cgroup_bpf(struct sock *sk, struct sk_buff *skb,
> > +				enum bpf_attach_type type)
> > +{
> > +	struct sock_cgroup_data *skcd = &sk->sk_cgrp_data;
> > +	struct cgroup *cgrp = sock_cgroup_ptr(skcd);
> > +	struct bpf_prog *prog;
> > +	int ret = 0;
> > +
> > +	rcu_read_lock();
> > +
> > +	switch (type) {
> > +	case BPF_ATTACH_TYPE_CGROUP_EGRESS:
> > +		prog = rcu_dereference(cgrp->bpf_egress);
> > +		break;
> > +	case BPF_ATTACH_TYPE_CGROUP_INGRESS:
> > +		prog = rcu_dereference(cgrp->bpf_ingress);
> > +		break;
> > +	default:
> > +		WARN_ON_ONCE(1);
> > +		ret = -EINVAL;
> > +		break;
> > +	}
> > +
> > +	if (prog) {
> 
> I really like how in this version of the patches it became
> a single load+cmp of per-packet cost when this feature is off.
> Please move
> +	struct cgroup *cgrp = sock_cgroup_ptr(skcd);
> into if (prog) {..}
> to make sure it's actually single load.
> The compiler cannot avoid that load when it's placed at the top.

sorry. brain fart. it is two loads. scratch that.

> > +		unsigned int offset = skb->data - skb_mac_header(skb);
> > +
> > +		__skb_push(skb, offset);
> > +		ret = bpf_prog_run_clear_cb(prog, skb) > 0 ? 0 : -EPERM;
> 
> that doesn't match commit log. The above '> 0' makes sense to me though.
> If we want to do it for 1 only we have to define it in uapi/bpf.h
> as action code, so we can extend to 2, 3 in the future if necessary.
> 
> It also have to be bpf_prog_run_save_cb() (as sk_filter_trim_cap() does)
> instead of bpf_prog_run_clear_cb().
> See commit ff936a04e5f2 ("bpf: fix cb access in socket filter programs")
> 
> > +		__skb_pull(skb, offset);
> > +	}
> > +
> > +	rcu_read_unlock();
> > +
> > +	return ret;
> > +}
> > +#endif /* !CONFIG_CGROUP_BPF */
> > +
> >  /**
> >   *	sk_filter_trim_cap - run a packet through a socket filter
> >   *	@sk: sock associated with &sk_buff
> > @@ -78,6 +116,12 @@ int sk_filter_trim_cap(struct sock *sk, struct sk_buff *skb, unsigned int cap)
> >  	if (skb_pfmemalloc(skb) && !sock_flag(sk, SOCK_MEMALLOC))
> >  		return -ENOMEM;
> >  
> > +#ifdef CONFIG_CGROUP_BPF
> > +	err = sk_filter_cgroup_bpf(sk, skb, BPF_ATTACH_TYPE_CGROUP_INGRESS);
> > +	if (err)
> > +		return err;
> > +#endif
> > +
> >  	err = security_sock_rcv_skb(sk, skb);
> >  	if (err)
> >  		return err;
> > -- 
> > 2.5.5
> >