linux-kernel - Re: [PATCH] openvswitch: Fix L4 checksum handling when dealing with IP fragments

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Message-ID: <20150803165339.GA11291@google.com>
Date:	Mon, 3 Aug 2015 09:53:39 -0700
From:	Glenn Griffin <ggriffin.kernel@...il.com>
To:	Pravin Shelar <pshelar@...ira.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	"dev@...nvswitch.org" <dev@...nvswitch.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] openvswitch: Fix L4 checksum handling when dealing with
 IP fragments

On Mon, Aug 03, 2015 at 09:25:53AM -0700, Pravin Shelar wrote:
> On Sat, Aug 1, 2015 at 6:31 PM, Glenn Griffin <ggriffin.kernel@...il.com> wrote:
> > openvswitch modifies the L4 checksum of a packet when modifying
> > the ip address. When an IP packet is fragmented only the first
> > fragment contains an L4 header and checksum. Prior to this change
> > openvswitch would modify all fragments, modifying application data
> > in non-first fragments, causing checksum failures in the
> > reassembled packet.
> >
> > Signed-off-by: Glenn Griffin <ggriffin.kernel@...il.com>
> 
> Patch looks good. I have one following comment.
> > ---
> >  net/openvswitch/actions.c | 16 ++++++++++++----
> >  1 file changed, 12 insertions(+), 4 deletions(-)
> >
> > diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> > index 8a8c0b8..bfffb1a 100644
> > --- a/net/openvswitch/actions.c
> > +++ b/net/openvswitch/actions.c
> > @@ -273,28 +273,36 @@ static int set_eth_addr(struct sk_buff *skb, struct sw_flow_key *flow_key,
> >         return 0;
> >  }
> >
> > -static void set_ip_addr(struct sk_buff *skb, struct iphdr *nh,
> > -                       __be32 *addr, __be32 new_addr)
> > +static void update_ip_l4_checksum(struct sk_buff *skb, struct iphdr *nh,
> > +                                 __be32 addr, __be32 new_addr)
> >  {
> >         int transport_len = skb->len - skb_transport_offset(skb);
> >
> > +       if (ntohs(nh->frag_off) & IP_OFFSET)
> > +               return;
> 
> It is efficient to check frag-offset in network byte order.

I'll send a revised patch.
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