Subject: Re: [PATCH 1/3] ipv6: Select fragment id during UFO/GSO segmentation if not set.

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 27 Jan 2015 10:42:08 +0200

On Tue, Jan 27, 2015 at 02:47:54AM +0000, Ben Hutchings wrote:
> On Mon, 2015-01-26 at 09:37 -0500, Vladislav Yasevich wrote:
> > If the IPv6 fragment id has not been set and we perform
> > fragmentation due to UFO, select a new fragment id.
> > When we store the fragment id into skb_shinfo, set the bit
> > in the skb so we can re-use the selected id.
> > This preserves the behavior of UFO packets generated on the
> > host and solves the issue of id generation for packet sockets
> > and tap/macvtap devices.
> > 
> > This patch moves ipv6_select_ident() back in to the header file.  
> > It also provides the helper function that sets skb_shinfo() frag
> > id and sets the bit.
> > 
> > It also makes sure that we select the fragment id when doing
> > just gso validation, since it's possible for the packet to
> > come from an untrusted source (VM) and be forwarded through
> > a UFO enabled device which will expect the fragment id.
> > 
> > CC: Eric Dumazet <[email-masked]>
> > Signed-off-by: Vladislav Yasevich <[email-masked]>
> > ---
> >  include/linux/skbuff.h |  3 ++-
> >  include/net/ipv6.h     |  2 ++
> >  net/ipv6/ip6_output.c  |  4 ++--
> >  net/ipv6/output_core.c |  9 ++++++++-
> >  net/ipv6/udp_offload.c | 10 +++++++++-
> >  5 files changed, 23 insertions(+), 5 deletions(-)
> > 
> > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> > index 85ab7d7..3ad5203 100644
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -605,7 +605,8 @@ struct sk_buff {
> >  	__u8			ipvs_property:1;
> >  	__u8			inner_protocol_type:1;
> >  	__u8			remcsum_offload:1;
> > -	/* 3 or 5 bit hole */
> > +	__u8			ufo_fragid_set:1;
> [...]
> 
> Doesn't the flag belong in struct skb_shared_info, rather than struct
> sk_buff?  Otherwise this looks fine.
> 
> Ben.

Hmm we seem to be out of tx flags.
Maybe ip6_frag_id == 0 should mean "not set".

> -- 
> Ben Hutchings
> When in doubt, use brute force. - Ken Thompson