From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Lorenz Bauer <lmb@cloudflare.com>
Cc: bpf <bpf@vger.kernel.org>, kernel-team <kernel-team@cloudflare.com>
Subject: Re: Checksum behaviour of bpf_redirected packets
Date: Tue, 5 May 2020 18:28:40 -0700 [thread overview]
Message-ID: <CAADnVQKZ63d5A+Jv8bbXzo2RKNCXFH78zos0AjpbJ3ii9OHW0g@mail.gmail.com> (raw)
In-Reply-To: <CACAyw9-uU_52esMd1JjuA80fRPHJv5vsSg8GnfW3t_qDU4aVKQ@mail.gmail.com>
On Mon, May 4, 2020 at 9:12 AM Lorenz Bauer <lmb@cloudflare.com> wrote:
>
> In our TC classifier cls_redirect [1], we use the following sequence
> of helper calls to
> decapsulate a GUE (basically IP + UDP + custom header) encapsulated packet:
>
> skb_adjust_room(skb, -encap_len,
> BPF_ADJ_ROOM_MAC, BPF_F_ADJ_ROOM_FIXED_GSO)
> bpf_redirect(skb->ifindex, BPF_F_INGRESS)
>
> It seems like some checksums of the inner headers are not validated in
> this case.
> For example, a TCP SYN packet with invalid TCP checksum is still accepted by the
> network stack and elicits a SYN ACK.
>
> Is this known but undocumented behaviour or a bug? In either case, is
> there a work
> around I'm not aware of?
I thought inner and outer csums are covered by different flags and driver
suppose to set the right one depending on level of in-hw checking it did.
next prev parent reply other threads:[~2020-05-06 1:28 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-04 16:11 Checksum behaviour of bpf_redirected packets Lorenz Bauer
2020-05-06 1:28 ` Alexei Starovoitov [this message]
2020-05-06 16:24 ` Lorenz Bauer
2020-05-06 17:26 ` Jakub Kicinski
2020-05-06 21:55 ` Daniel Borkmann
2020-05-07 15:54 ` Lorenz Bauer
2020-05-07 16:43 ` Daniel Borkmann
2020-05-07 21:25 ` Jakub Kicinski
2020-05-11 9:31 ` Lorenz Bauer
2020-05-11 9:29 ` Lorenz Bauer
2020-05-12 21:25 ` Daniel Borkmann
2020-05-13 14:14 ` Lorenz Bauer
2020-06-01 17:48 ` Alan Maguire
2020-06-01 20:13 ` Daniel Borkmann
2020-06-01 21:25 ` Alan Maguire
2020-06-02 10:13 ` Lorenz Bauer
2020-06-02 15:01 ` Daniel Borkmann
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