All of lore.kernel.org
 help / color / mirror / Atom feed
From: Lorenz Bauer <lmb@cloudflare.com>
To: bpf <bpf@vger.kernel.org>
Cc: kernel-team <kernel-team@cloudflare.com>
Subject: Checksum behaviour of bpf_redirected packets
Date: Mon, 4 May 2020 17:11:41 +0100	[thread overview]
Message-ID: <CACAyw9-uU_52esMd1JjuA80fRPHJv5vsSg8GnfW3t_qDU4aVKQ@mail.gmail.com> (raw)

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?

1: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/testing/selftests/bpf/progs/test_cls_redirect.c#n370
-- 
Lorenz Bauer  |  Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK

www.cloudflare.com

             reply	other threads:[~2020-05-04 16:11 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-04 16:11 Lorenz Bauer [this message]
2020-05-06  1:28 ` Checksum behaviour of bpf_redirected packets Alexei Starovoitov
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CACAyw9-uU_52esMd1JjuA80fRPHJv5vsSg8GnfW3t_qDU4aVKQ@mail.gmail.com \
    --to=lmb@cloudflare.com \
    --cc=bpf@vger.kernel.org \
    --cc=kernel-team@cloudflare.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.