Re: [Xen-devel] [PATCH net v2] xen-netback: fix fragment detection in checksum setup

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: annie li [mailto:annie.li@xxxxxxxxxx]
> Sent: 29 November 2013 05:36
> To: Paul Durrant
> Cc: xen-devel@xxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; Wei Liu; Ian Campbell;
> David Vrabel
> Subject: Re: [PATCH net v2] xen-netback: fix fragment detection in checksum
> setup
> 
> 
> On 2013/11/28 21:23, Paul Durrant wrote:
> > The code to detect fragments in checksum_setup() was missing for IPv4
> and
> > too eager for IPv6. (It transpires that Windows seems to send IPv6 packets
> > with a fragment header even if they are not a fragment - i.e. offset is 
> > zero,
> > and M bit is not set).
> >
> > Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> > Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> > Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
> > ---
> > v2
> >
> > - Added comments noting what fragment/offset masks mean
> >
> >   drivers/net/xen-netback/netback.c |   33
> ++++++++++++++++++++++++++++++---
> >   1 file changed, 30 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-
> netback/netback.c
> > index 919b650..c7464d8 100644
> > --- a/drivers/net/xen-netback/netback.c
> > +++ b/drivers/net/xen-netback/netback.c
> > @@ -1165,15 +1165,28 @@ static int checksum_setup_ip(struct xenvif *vif,
> struct sk_buff *skb,
> >     struct iphdr *iph = (void *)skb->data;
> >     unsigned int header_size;
> >     unsigned int off;
> > +   bool fragment;
> >     int err = -EPROTO;
> >
> > +   fragment = false;
> 
> Is it better to initialize fragment directly as following?
> bool fragment = false;
> 

I think that's a matter of personal taste. I tend to favour this style.

  Paul

> > +
> >     off = sizeof(struct iphdr);
> >
> >     header_size = skb->network_header + off + MAX_IPOPTLEN;
> >     maybe_pull_tail(skb, header_size);
> >
> > +   /* 3fff -> fragment offset != 0 OR more fragments */
> > +   if (ntohs(iph->frag_off) & 0x3fff)
> > +           fragment = true;
> > +
> >     off = iph->ihl * 4;
> >
> > +   if (fragment) {
> > +           if (net_ratelimit())
> > +                   netdev_err(vif->dev, "Packet is a fragment!\n");
> > +           goto out;
> > +   }
> > +
> >     switch (iph->protocol) {
> >     case IPPROTO_TCP:
> >             if (!skb_partial_csum_set(skb, off,
> > @@ -1237,6 +1250,7 @@ static int checksum_setup_ipv6(struct xenvif *vif,
> struct sk_buff *skb,
> >     bool fragment;
> >     bool done;
> >
> > +   fragment = false;
> >     done = false;
> 
> Same as above for "done" and "fragment"...
> 
> Thanks
> Annie
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