On Wed, 2013-10-16 at 09:02 +0900, Simon Horman wrote:
> In v3.9 6fd6ce2056de2709 ("ipv6: Do not depend on rt->n in
> ip6_finish_output2()") changed the behaviour of ip6_finish_output2()
> such that it creates and uses a neigh entry if none is found.
> Subsequently the 'n' field was removed from struct rt6_info.
>
> Unfortunately my analysis is that in the case of IPVS direct routing this
> change leads to incorrect behaviour as in this case packets may be output
> to a destination other than where they would be output according to the
> route table. In particular, the destination address may actually be a local
> address and empirically a neighbour lookup seems to result in it becoming
> unreachable.
>
> This patch resolves the problem by providing the destination address
> determined by IPVS to ip6_finish_output2() in the skb callback. Although
> this seems to work I can see several problems with this approach:
>
> * It is rather ugly, stuffing an IPVS exception right in
> the middle of IPv6 code. The overhead could be eliminated for many users
> by using a staic key. But none the less it is not attractive.
>
> * The use of the skb callback is may not be valid
> as it crosses from IPVS to IPv6 code. A possible, though unpleasant,
> alternative is to add a new field to struct sk_buff.
Please no ;)
>
> * This covers all IPv6 packets output by IPVS but actually
> only those output using IPVS Direct-Routing need this. One way to
> resolve this would be to add a more fine-grained ipvs_property to
> struct sk_buff.
>
> Reported-by: Mark Brooks <mark@xxxxxxxxxxxxxxxx>
> Signed-off-by: Simon Horman <horms@xxxxxxxxxxxx>
> ---
> include/net/ip_vs.h | 6 ++++++
> net/ipv6/ip6_output.c | 9 +++++++--
> net/netfilter/ipvs/ip_vs_xmit.c | 2 ++
> 3 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
> index 1c2e1b9..11d90a6 100644
> --- a/include/net/ip_vs.h
> +++ b/include/net/ip_vs.h
> @@ -1649,4 +1649,10 @@ ip_vs_dest_conn_overhead(struct ip_vs_dest *dest)
> atomic_read(&dest->inactconns);
> }
>
> +struct ipvs_skb_cb {
> + struct in6_addr *daddr;
> +};
So we pass a reference.
> +
> +#define IP_VS_SKB_CB(skb) ((struct ipvs_skb_cb *)&(skb)->cb)
> +
> #endif /* _NET_IP_VS_H */
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index a54c45c..a340180 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -52,6 +52,7 @@
> #include <net/addrconf.h>
> #include <net/rawv6.h>
> #include <net/icmp.h>
> +#include <net/ip_vs.h>
> #include <net/xfrm.h>
> #include <net/checksum.h>
> #include <linux/mroute6.h>
> @@ -61,7 +62,7 @@ static int ip6_finish_output2(struct sk_buff *skb)
> struct dst_entry *dst = skb_dst(skb);
> struct net_device *dev = dst->dev;
> struct neighbour *neigh;
> - struct in6_addr *nexthop;
> + struct in6_addr *nexthop, *daddr;
> int ret;
>
> skb->protocol = htons(ETH_P_IPV6);
> @@ -105,7 +106,11 @@ static int ip6_finish_output2(struct sk_buff *skb)
> }
>
> rcu_read_lock_bh();
> - nexthop = rt6_nexthop((struct rt6_info *)dst, &ipv6_hdr(skb)->daddr);
> + if (unlikely(IS_ENABLED(CONFIG_IP_VS) && skb->ipvs_property))
> + daddr = IP_VS_SKB_CB(skb)->daddr;
What guarantee do we have daddr points to valid memory (not already
freed/reused) ?
I guess things like NFQUEUE could happen ?
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