netdev - Re: [PATCH] net-gre-gro: Fix a bug that breaks the forwarding path

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Date:	Mon, 3 Mar 2014 11:30:26 +0200
From:	Or Gerlitz <or.gerlitz@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	Jerry Chu <hkchu@...gle.com>, Eric Dumazet <edumazet@...gle.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Joseph Gasparakis <joseph.gasparakis@...el.com>
Subject: Re: [PATCH] net-gre-gro: Fix a bug that breaks the forwarding path

On Fri, Feb 28, 2014 at 11:56 PM, David Miller <davem@...emloft.net> wrote:
> From: Jerry Chu <hkchu@...gle.com>
> Date: Thu, 27 Feb 2014 15:39:47 -0800
>
>> On Thu, Feb 27, 2014 at 2:25 PM, Or Gerlitz <or.gerlitz@...il.com> wrote:
>>>
>>> On Thu, Feb 27, 2014 at 11:26 PM, H.K. Jerry Chu <hkchu@...gle.com> wrote:
>>> > From: Jerry Chu <hkchu@...gle.com>
>>> >
>>> > I stumbled across a bug that was introduced by my own GRE-GRO
>>> > patch (bf5a755f5e9186406bbf50f4087100af5bd68e40
>>> > net-gre-gro: Add GRE support to the GRO stack) submitted a while
>>> > back that breaks the forwarding path because various GSO related
>>> > fields were not set. This will cause on the egress path either
>>> > the GSO code to fail, or a GRE-TSO capable (NETIF_F_GSO_GRE)
>>> > NICs to choke. The following fix has been tested for both cases.
>>> >
>>> > Signed-off-by: H.K. Jerry Chu <hkchu@...gle.com>
>>> > ---
>>> >  net/core/dev.c           | 2 ++
>>> >  net/ipv4/af_inet.c       | 3 +++
>>> >  net/ipv4/gre_offload.c   | 3 +++
>>> >  net/ipv4/tcp_offload.c   | 2 +-
>>> >  net/ipv6/tcpv6_offload.c | 2 +-
>>> >  5 files changed, 10 insertions(+), 2 deletions(-)
>>> >
>>> > diff --git a/net/core/dev.c b/net/core/dev.c
>>> > index b1b0c8d..75517d8 100644
>>> > --- a/net/core/dev.c
>>> > +++ b/net/core/dev.c
>>> > @@ -4045,6 +4045,8 @@ static void napi_reuse_skb(struct napi_struct *napi, struct sk_buff *skb)
>>> >         skb->vlan_tci = 0;
>>> >         skb->dev = napi->dev;
>>> >         skb->skb_iif = 0;
>>> > +       skb->encapsulation = 0;
>>> > +       skb_shinfo(skb)->gso_type = 0;
>>> >
>>> >         napi->skb = skb;
>>> >  }
>>> > diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
>>> > index ecd2c3f..68229ca 100644
>>> > --- a/net/ipv4/af_inet.c
>>> > +++ b/net/ipv4/af_inet.c
>>> > @@ -1431,6 +1431,9 @@ static int inet_gro_complete(struct sk_buff *skb, int nhoff)
>>> >         int proto = iph->protocol;
>>> >         int err = -ENOSYS;
>>> >
>>> > +       if (skb->encapsulation)
>>> > +               skb_set_inner_network_header(skb, nhoff);
>>> > +
>>>
>>> Note that packets (e.g those who are UDP encapsulated) will pass here
>>> twice, once for the external IP header and once for the internal, so
>>> if the driver marks the encapsulation sign the inner header setting
>>> will happen twice, is that what we want?
>>
>> The inner most hdr will be the last to set. But I don't know
>> all the rules regarding skb->encapsulation. E.g., in this patch
>> napi_reuse_skb() will reset skb->encapsulation. If that's problematic
>> then I could call skb_set_inner_network_header() inside gre_gro_receive()
>> (but that will require checking against "type" in order to compute the right
>> offset).
>
> The topic of the skb->encapsulation semantics has come up several times in the
> past few weeks.
>
> We cannot move forward on any changes in this area until the semantics
> are well defined, and documented.
>
> Can someone work on a patch which documents skb->encapsulation properly,
> and then we can come back to fixing this bug?


Yep, seems we need to be a bit more formal/precise here, we started to discuss
that couple of weeks ago on this thread
http://marc.info/?l=linux-netdev&m=139233048521647&w=2
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