Re: [PATCH net-next] net: Fix vti use case with oif in dst lookups for IPv6

[David Ahern]

On 10/20/15 6:31 AM, Hajime Tazaki wrote:
yes, this sendmsg uses non-zero flowi6_oif.

the conditions are

- sendmsg () with INET6/RAW socket (with IPPROTO_MH)
- ip6_pktinfo.ipi6_addr (fl6.saddr) and ipi6_oif
   (fl6.flowi6_oif) are non-NULL.
=> ipi6_addr (fl6.saddr) is not the IP address of oif, but
     another interfaces (home address of mip6)

interesting. so forcing a send out of interface X but using the source 
address of interface Y.

Does the attached patch work for you?
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index d0619632723a..2701cb3d88e9 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1171,6 +1171,7 @@ struct dst_entry *ip6_route_output(struct net *net, const 
struct sock *sk,
 {
        struct dst_entry *dst;
        int flags = 0;
+       bool any_src;
 
        dst = l3mdev_rt6_dst_by_oif(net, fl6);
        if (dst)
@@ -1178,11 +1179,12 @@ struct dst_entry *ip6_route_output(struct net *net, 
const struct sock *sk,
 
        fl6->flowi6_iif = LOOPBACK_IFINDEX;
 
+       any_src = ipv6_addr_any(&fl6->saddr);
        if ((sk && sk->sk_bound_dev_if) || rt6_need_strict(&fl6->daddr) ||
-           fl6->flowi6_oif)
+           (fl6->flowi6_oif && any_src))
                flags |= RT6_LOOKUP_F_IFACE;
 
-       if (!ipv6_addr_any(&fl6->saddr))
+       if (!any_src)
                flags |= RT6_LOOKUP_F_HAS_SADDR;
        else if (sk)
                flags |= rt6_srcprefs2flags(inet6_sk(sk)->srcprefs);