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Message-ID: <600008e5e2e80_1eeef20852@john-XPS-13-9370.notmuch>
Date: Thu, 14 Jan 2021 01:03:33 -0800
From: John Fastabend <john.fastabend@...il.com>
To: Jesper Dangaard Brouer <brouer@...hat.com>, bpf@...r.kernel.org
Cc: Jesper Dangaard Brouer <brouer@...hat.com>, netdev@...r.kernel.org,
Daniel Borkmann <borkmann@...earbox.net>,
Alexei Starovoitov <alexei.starovoitov@...il.com>,
maze@...gle.com, lmb@...udflare.com, shaun@...era.io,
Lorenzo Bianconi <lorenzo@...nel.org>, marek@...udflare.com,
John Fastabend <john.fastabend@...il.com>,
Jakub Kicinski <kuba@...nel.org>, eyal.birger@...il.com,
colrack@...il.com
Subject: RE: [PATCH bpf-next V11 5/7] bpf: drop MTU check when doing TC-BPF
redirect to ingress
Jesper Dangaard Brouer wrote:
> The use-case for dropping the MTU check when TC-BPF does redirect to
> ingress, is described by Eyal Birger in email[0]. The summary is the
> ability to increase packet size (e.g. with IPv6 headers for NAT64) and
> ingress redirect packet and let normal netstack fragment packet as needed.
>
> [0] https://lore.kernel.org/netdev/CAHsH6Gug-hsLGHQ6N0wtixdOa85LDZ3HNRHVd0opR=19Qo4W4Q@mail.gmail.com/
>
> V9:
> - Make net_device "up" (IFF_UP) check explicit in skb_do_redirect
>
> V4:
> - Keep net_device "up" (IFF_UP) check.
> - Adjustment to handle bpf_redirect_peer() helper
>
> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> ---
> include/linux/netdevice.h | 31 +++++++++++++++++++++++++++++--
> net/core/dev.c | 19 ++-----------------
> net/core/filter.c | 14 +++++++++++---
> 3 files changed, 42 insertions(+), 22 deletions(-)
>
[...]
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 3f2e593244ca..1908800b671c 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2083,13 +2083,21 @@ static const struct bpf_func_proto bpf_csum_level_proto = {
>
> static inline int __bpf_rx_skb(struct net_device *dev, struct sk_buff *skb)
> {
> - return dev_forward_skb(dev, skb);
> + int ret = ____dev_forward_skb(dev, skb, false);
> +
> + if (likely(!ret)) {
> + skb->protocol = eth_type_trans(skb, dev);
> + skb_postpull_rcsum(skb, eth_hdr(skb), ETH_HLEN);
> + ret = netif_rx(skb);
> + }
> +
> + return ret;
How about putting above block into a dev.c routine call it
dev_forward_skb_nomtu(...)
or something like that. Then we keep this code next to its pair
with mtu check, dev_forward_skb().
dev_forward_skb() also uses netif_rx_internal() looks like maybe we should
just do the same here?
Thanks,
John
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