Re: [net 0/3] seg6: fix skb checksum for SRH encapsulation/insertion

sdf
2022-07-12T22:14:59Z

On 07/12, Andrea Mayer wrote:
> The Linux kernel supports Segment Routing Header (SRH)
> encapsulation/insertion operations by providing the capability to: i)
> encapsulate a packet in an outer IPv6 header with a specified SRH; ii)
> insert a specified SRH directly after the IPv6 header of the packet.
> Note that the insertion operation is also referred to as 'injection'.

> The two operations are respectively supported by seg6_do_srh_encap() and
> seg6_do_srh_inline(), which operate on the skb associated to the packet as
> needed (e.g. adding the necessary headers and initializing them, while
> taking care to recalculate the skb checksum).

> seg6_do_srh_encap() and seg6_do_srh_inline() do not initialize the payload
> length of the IPv6 header, which is carried out by the caller functions.
> However, this approach causes the corruption of the skb checksum which
> needs to be updated only after initialization of headers is completed
> (thanks to Paolo Abeni for detecting this issue).

> The patchset fixes the skb checksum corruption by moving the IPv6 header
> payload length initialization from the callers of seg6_do_srh_encap() and
> seg6_do_srh_inline() directly into these functions.

> This patchset is organized as follows:
> - patch 1/3, seg6: fix skb checksum evaluation in SRH
> encapsulation/insertion;
> (* SRH encapsulation/insertion available since v4.10)

> - patch 2/3, seg6: fix skb checksum in SRv6 End.B6 and End.B6.Encaps
> behaviors;
> (* SRv6 End.B6 and End.B6.Encaps behaviors available since v4.14)

> - patch 3/3, seg6: bpf: fix skb checksum in bpf_push_seg6_encap();
> (* bpf IPv6 Segment Routing helpers available since v4.18)

BPF changes make sense. I've tested them by applying the whole series and
running test_lwt_seg6local.sh.

Reviewed-by: Stanislav Fomichev <sdf@google.com>
Tested-by: Stanislav Fomichev <sdf@google.com>

> Thank you all,
> Andrea

> Andrea Mayer (3):
> seg6: fix skb checksum evaluation in SRH encapsulation/insertion
> seg6: fix skb checksum in SRv6 End.B6 and End.B6.Encaps behaviors
> seg6: bpf: fix skb checksum in bpf_push_seg6_encap()

> net/core/filter.c | 1 -
> net/ipv6/seg6_iptunnel.c | 5 ++++-
> net/ipv6/seg6_local.c | 2 --
> 3 files changed, 4 insertions(+), 4 deletions(-)

> --
> 2.20.1