netdev - Re: [RFC v2 PATCH 2/4] ebpf: Add sg_filter

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Date:   Fri, 29 Jun 2018 10:32:21 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Tushar Dave <tushar.n.dave@...cle.com>, ast@...nel.org,
        davem@...emloft.net, jakub.kicinski@...ronome.com,
        quentin.monnet@...ronome.com, jiong.wang@...ronome.com,
        guro@...com, sandipan@...ux.vnet.ibm.com, john.fastabend@...il.com,
        kafai@...com, rdna@...com, brakmo@...com, netdev@...r.kernel.org,
        acme@...hat.com, sowmini.varadhan@...cle.com
Subject: Re: [RFC v2 PATCH 2/4] ebpf: Add sg_filter_run and sg helper

On 06/19/2018 08:00 PM, Tushar Dave wrote:
[...]
> +int sg_filter_run(struct sock *sk, struct scatterlist *sg)
> +{
> +	struct sk_filter *filter;
> +	int err;
> +
> +	rcu_read_lock();
> +	filter = rcu_dereference(sk->sk_filter);
> +	if (filter) {
> +		struct bpf_scatterlist bpfsg;
> +		int num_sg;
> +
> +		if (!sg) {
> +			err = -EINVAL;
> +			goto out;
> +		}
> +
> +		num_sg = sg_nents(sg);
> +		if (num_sg <= 0) {
> +			err = -EINVAL;
> +			goto out;
> +		}
> +
> +		/* We store a reference  to the sg list so it can later used by
> +		 * eBPF helpers to retrieve the next sg element.
> +		 */
> +		bpfsg.num_sg = num_sg;
> +		bpfsg.cur_sg = 0;
> +		bpfsg.sg = sg;
> +
> +		/* For the first sg element, we store the pkt access pointers
> +		 * into start and end so eBPF program can have pkt access using
> +		 * data and data_end. The pkt access for subsequent element of
> +		 * sg list is possible when eBPF program invokes bpf_sg_next
> +		 * which takes care of setting start and end to the correct sg
> +		 * element.
> +		 */
> +		bpfsg.start = sg_virt(sg);
> +		bpfsg.end = bpfsg.start + sg->length;
> +		BPF_PROG_RUN(filter->prog, &bpfsg);

Return code here from BPF prog is ignored entirely, I thought you wanted to
use it also for dropping packets? If UAPI would get frozen like this then it's
baked in stone.

> +	}
> +out:
> +	rcu_read_unlock();
> +
> +	return err;
> +}
> +EXPORT_SYMBOL(sg_filter_run);