netdev - Re: [bpf-next PATCH v2 3/4] bpf: sockmap, BPF_F_INGRESS flag for BPF_SK_SKB_STREAM

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Date:   Wed, 28 Mar 2018 16:21:33 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     John Fastabend <john.fastabend@...il.com>, ast@...nel.org
Cc:     netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [bpf-next PATCH v2 3/4] bpf: sockmap, BPF_F_INGRESS flag for
 BPF_SK_SKB_STREAM_VERDICT:

On 03/27/2018 07:23 PM, John Fastabend wrote:
> Add support for the BPF_F_INGRESS flag in skb redirect helper. To
> do this convert skb into a scatterlist and push into ingress queue.
> This is the same logic that is used in the sk_msg redirect helper
> so it should feel familiar.
> 
> Signed-off-by: John Fastabend <john.fastabend@...il.com>
> ---
>  include/linux/filter.h |    1 +
>  kernel/bpf/sockmap.c   |   94 +++++++++++++++++++++++++++++++++++++++---------
>  net/core/filter.c      |    2 +
>  3 files changed, 78 insertions(+), 19 deletions(-)
[...]
>  		if (!sg->length && md->sg_start == md->sg_end) {
>  			list_del(&md->list);
> +			if (md->skb)
> +				consume_skb(md->skb);
>  			kfree(md);
>  		}
>  	}
> @@ -1045,27 +1048,72 @@ static int smap_verdict_func(struct smap_psock *psock, struct sk_buff *skb)
>  		__SK_DROP;
>  }
>  
> +static int smap_do_ingress(struct smap_psock *psock, struct sk_buff *skb)
> +{
> +	struct sock *sk = psock->sock;
> +	int copied = 0, num_sg;
> +	struct sk_msg_buff *r;
> +
> +	r = kzalloc(sizeof(struct sk_msg_buff), __GFP_NOWARN | GFP_ATOMIC);
> +	if (unlikely(!r))
> +		return -EAGAIN;
> +
> +	if (!sk_rmem_schedule(sk, skb, skb->len)) {
> +		kfree(r);
> +		return -EAGAIN;
> +	}
> +	sk_mem_charge(sk, skb->len);

Usually mem accounting is based on truesize. This is not done here since
you need the exact length of the skb for the sg list later on, right?

> +	sg_init_table(r->sg_data, MAX_SKB_FRAGS);
> +	num_sg = skb_to_sgvec(skb, r->sg_data, 0, skb->len);
> +	if (unlikely(num_sg < 0)) {
> +		kfree(r);

Don't we need to undo the mem charge here in case of error?

> +		return num_sg;
> +	}
> +	copied = skb->len;
> +	r->sg_start = 0;
> +	r->sg_end = num_sg == MAX_SKB_FRAGS ? 0 : num_sg;
> +	r->skb = skb;
> +	list_add_tail(&r->list, &psock->ingress);
> +	sk->sk_data_ready(sk);
> +	return copied;
> +}