On Wed, 2012-08-29 at 01:43 -0700, Eric Dumazet wrote:
> On Wed, 2012-08-29 at 09:02 +0200, Jesper Dangaard Brouer wrote:
> > On Tue, 2012-08-28 at 07:49 -0700, Eric Dumazet wrote:
> > > On Tue, 2012-08-28 at 16:23 +0200, Jesper Dangaard Brouer wrote:
> > > > This patch is necessary, to make IPVS work, after Patrick McHardys
> > > > IPv6 NAT defragmentation changes.
> > > >
> > > > Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
> > > > ---
> > > > In V2: the tunnel mode is no longer a special case.
> > > >
> > > > net/netfilter/ipvs/ip_vs_xmit.c | 9 ++++++++-
> > > > 1 files changed, 8 insertions(+), 1 deletions(-)
> > > >
> > > > diff --git a/net/netfilter/ipvs/ip_vs_xmit.c b/net/netfilter/ipvs/ip_vs_xmit.c
> > > > index 67a3978..56f6d5d 100644
> > > > --- a/net/netfilter/ipvs/ip_vs_xmit.c
> > > > +++ b/net/netfilter/ipvs/ip_vs_xmit.c
> > > > @@ -88,7 +88,14 @@ __ip_vs_dst_check(struct ip_vs_dest *dest, u32 rtos)
> > > > static inline bool
> > > > __mtu_check_toobig_v6(const struct sk_buff *skb, u32 mtu)
> > > > {
> > > > - if (skb->len > mtu && !skb_is_gso(skb)) {
> > > > + if (IP6CB(skb)->frag_max_size) {
> > > > + /* frag_max_size tell us that, this packet have been
> > > > + * defragmented by netfilter IPv6 conntrack module.
> > > > + */
> > > > + if (IP6CB(skb)->frag_max_size > mtu)
> > > > + return true; /* largest fragment violate MTU */
> > Implicit: else
> > return false
> >
> > (if it makes it more clear, not sure)
> > > > + }
> > > > + else if (skb->len > mtu && !skb_is_gso(skb)) {
> > > > return true; /* Packet size violate MTU size */
> > > > }
> > >
> > > Couldnt you use a single test ?
> > >
> > > if (IP6CB(skb)->frag_max_size > mtu)
> > > return true;
> > >
> > > if (skb->len > mtu && !skb_is_gso(skb))
> > > return true;
> > >
> >
> > Nope, this will not work.
> >
> > If (IP6CB(skb)->frag_max_size > 0) then we have a defragmented packet,
> > this means that skb->len cannot be used for MTU checking, because
> > skb->len is now the total length of all the fragments (which your
> > solution will fall-through to)
> >
>
> If the packet was not fragmented, its was a single frame.
>
> But if this frame length is above mtu, packet is not too big ?
Nope... not if its a defragmented/reassembled packet.
> Sorry if its a stupid question.
These changes have to be seen together with Patrick's patch:
"netfilter: nf_conntrack_ipv6: improve fragmentation handling"
http://thread.gmane.org/gmane.linux.network/241517/focus=241518
The IPv6 packet arriving have been defragmented/reassembled by the
nf_conntrack_ipv6 module. Thus, they look like a normal, but big,
packet to us. We let it through, because it will be re-fragmented
again later, but first we need to check if the largest fragment would
violate the MTU.
Hope it makes it more clear.
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