netdev - Re: [PATCH 0/3] Check gso_size of packets when forwarding

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Message-ID: <CAOrHB_AAMzYCLsFe6+3ODSqYUe79vYtP5jSxK=GDj5rKeQXyDA@mail.gmail.com>
Date:   Thu, 18 Jan 2018 00:28:01 -0800
From:   Pravin Shelar <pshelar@....org>
To:     Daniel Axtens <dja@...ens.net>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Manish.Chopra@...ium.com, ovs dev <dev@...nvswitch.org>
Subject: Re: [PATCH 0/3] Check gso_size of packets when forwarding

On Mon, Jan 15, 2018 at 6:09 PM, Daniel Axtens <dja@...ens.net> wrote:
> When regular packets are forwarded, we validate their size against the
> MTU of the destination device. However, when GSO packets are
> forwarded, we do not validate their size against the MTU. We
> implicitly assume that when they are segmented, the resultant packets
> will be correctly sized.
>
> This is not always the case.
>
> We observed a case where a packet received on an ibmveth device had a
> GSO size of around 10kB. This was forwarded by Open vSwitch to a bnx2x
> device, where it caused a firmware assert. This is described in detail
> at [0] and was the genesis of this series. Rather than fixing it in
> the driver, this series fixes the forwarding path.
>
Are there any other possible forwarding path in networking stack? TC
is one subsystem that could forward such a packet to the bnx2x device,
how is that handled ?

> To fix this:
>
>  - Move a helper in patch 1.
>
>  - Validate GSO segment lengths in is_skb_forwardable() in the GSO
>    case, rather than assuming all will be well. This fixes bridges.
>    This is patch 2.
>
>  - Open vSwitch uses its own slightly specialised algorithm for
>    checking lengths. Wire up checking for that in patch 3.
>
> [0]: https://patchwork.ozlabs.org/patch/859410/
>
> Cc: Manish.Chopra@...ium.com
> Cc: dev@...nvswitch.org
>
> Daniel Axtens (3):
>   net: move skb_gso_mac_seglen to skbuff.h
>   net: is_skb_forwardable: validate length of GSO packet segments
>   openvswitch: drop GSO packets that are too large
>
>  include/linux/skbuff.h  | 16 ++++++++++++++++
>  net/core/dev.c          |  7 ++++---
>  net/core/skbuff.c       | 34 ++++++++++++++++++++++++++++++++++
>  net/openvswitch/vport.c | 37 ++++++++++++++++++++++++++++++-------
>  net/sched/sch_tbf.c     | 10 ----------
>  5 files changed, 84 insertions(+), 20 deletions(-)
>
> --
> 2.14.1
>