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Hello,
On Wed, 3 Apr 2019, Simon Horman wrote:
> On Sun, Mar 31, 2019 at 01:26:21PM +0300, Julian Anastasov wrote:
> > Recognize UDP tunnels in received ICMP errors and
> > properly strip the tunnel headers. GUE is what we
> > have for now.
> >
> > Signed-off-by: Julian Anastasov <ja@xxxxxx>
> > ---
> > net/netfilter/ipvs/ip_vs_core.c | 58 +++++++++++++++++++++++++++++++++
> > 1 file changed, 58 insertions(+)
> >
> > diff --git a/net/netfilter/ipvs/ip_vs_core.c
> > b/net/netfilter/ipvs/ip_vs_core.c
> > index 4447ee512b88..0b624e8e7982 100644
> > --- a/net/netfilter/ipvs/ip_vs_core.c
> > +++ b/net/netfilter/ipvs/ip_vs_core.c
> > @@ -39,6 +39,7 @@
> > #include <net/tcp.h>
> > #include <net/udp.h>
> > #include <net/icmp.h> /* for icmp_send */
> > +#include <net/gue.h>
> > #include <net/route.h>
> > #include <net/ip6_checksum.h>
> > #include <net/netns/generic.h> /* net_generic() */
> > @@ -1579,6 +1580,34 @@ ip_vs_try_to_schedule(struct netns_ipvs *ipvs, int
> > af, struct sk_buff *skb,
> > return 1;
> > }
> >
> > +/* Check the UDP tunnel and return its header length */
> > +static int ipvs_udp_decap(struct netns_ipvs *ipvs, struct sk_buff *skb,
> > + unsigned int offset, __u16 af, __be16 dport,
> > + const union nf_inet_addr *daddr, __u8 *proto)
> > +{
> > + struct ip_vs_dest *dest = ip_vs_find_tunnel(ipvs, af, daddr, dport);
> > +
> > + if (!dest)
> > + goto unk;
> > + if (dest->tun_type == IP_VS_CONN_F_TUNNEL_TYPE_GUE) {
> > + struct guehdr _gueh, *gueh;
> > +
> > + gueh = skb_header_pointer(skb, offset, sizeof(_gueh), &_gueh);
> > + if (!gueh)
> > + goto unk;
> > + if (gueh->control != 0 || gueh->version != 0)
> > + goto unk;
> > + /* Later we can support also IPPROTO_IPV6 */
> > + if (gueh->proto_ctype != IPPROTO_IPIP)
> > + goto unk;
> > + *proto = gueh->proto_ctype;
> > + return sizeof(struct guehdr) + (gueh->hlen << 2);
>
> I think that the gue-specific portions of the above, which is most of
> ipvs_udp_decap() should be a separate helper which is part of net/gue.h or
> net/ipv4/fou.c - this seems to be a subset of the logic in gue_udp_recv().
Yes but fou.c strips the headers in all cases while
in IPVS we should do it only when connection is found because
we do not want to mess with non-IPVS traffic.
>
> > + }
> > +
> > +unk:
> > + return -1;
> > +}
> > +
> > /*
> > * Handle ICMP messages in the outside-to-inside direction (incoming).
> > * Find any that might be relevant, check against existing connections,
> > @@ -1658,8 +1687,37 @@ ip_vs_in_icmp(struct netns_ipvs *ipvs, struct
> > sk_buff *skb, int *related,
> > if (cih == NULL)
> > return NF_ACCEPT; /* The packet looks wrong, ignore */
> > ipip = true;
> > + } else if (cih->protocol == IPPROTO_UDP) { /* Can be UDP encap */
>
> Can we consider factoring out the logic in this else-if clause
> out into a function to avoid the use of goto?
We can even safely return NF_ACCEPT instead of the goto
>
> > + struct udphdr _udph, *udph;
> > + __u8 iproto;
> > + int ulen;
> > +
> > + if (unlikely(cih->frag_off & htons(IP_OFFSET)))
> > + return NF_ACCEPT;
>
> I think a comment is warranted regarding the behaviour implemented
> for fragments.
I'll add in v2.
>
> > + /* Error for our tunnel must arrive at LOCAL_IN */
> > + if (!(skb_rtable(skb)->rt_flags & RTCF_LOCAL))
> > + return NF_ACCEPT;
> > + offset2 = offset + cih->ihl * 4;
> > + udph = skb_header_pointer(skb, offset2, sizeof(_udph), &_udph);
> > + if (!udph)
> > + goto check;
>
> > + offset2 += sizeof(struct udphdr);
> > + ulen = ipvs_udp_decap(ipvs, skb, offset2, AF_INET, udph->dest,
> > + raddr, &iproto);
> > + if (ulen < 0)
> > + goto check;
> > + /* Skip IP + UDP + ulen */
> > + offset = offset2 + ulen;
> > + /* Now we should be at the original IP header */
> > + cih = skb_header_pointer(skb, offset, sizeof(_ciph), &_ciph);
> > + if (cih && cih->version == 4 && cih->ihl >= 5 &&
> > + iproto == IPPROTO_IPIP)
> > + ipip = true;
> > + else
> > + return NF_ACCEPT;
>
> Skipping over tunnel headers and determining the inner IP protocol really
> feels like something that should be handled code common to other UDP
> encapsulation implementations.
We can easily add simple FOU in ipvs_udp_decap() by
returning 0 and correct *proto. Or you prefer to use common
code from other files to parse the headers? Currently, there
is no any GUE func that can be used for this.
Regards
--
Julian Anastasov <ja@xxxxxx>
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