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

[annie li <annie.li@xxxxxxxxxx>]

On 2013/11/29 17:10, Paul Durrant wrote:
> > -----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.
That is OK, I point this out because it is inconsistent with other 
variable initialization in netback.c.
Thanks
Annie
> > > +
> > >         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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