On 5/14/19 6:46 PM, Wei Wang wrote:
> From: Wei Wang <wei...@google.com>
>
> When inserting route cache into the exception table, the key is
> generated with both src_addr and dest_addr with src addr routing.
> However, current logic always assumes the src_addr used to generate the
> key is a /128 host address. This is not true in the following scenarios:
> 1. When the route is a gateway route or does not have next hop.
> (rt6_is_gw_or_nonexthop() == false)
> 2. When calling ip6_rt_cache_alloc(), saddr is passed in as NULL.
> This means, when looking for a route cache in the exception table, we
> have to do the lookup twice: first time with the passed in /128 host
> address, second time with the src_addr stored in fib6_info.
>
> This solves the pmtu discovery issue reported by Mikael Magnusson where
> a route cache with a lower mtu info is created for a gateway route with
> src addr. However, the lookup code is not able to find this route cache.
>
> Fixes: 2b760fcf5cfb ("ipv6: hook up exception table to store dst cache")
> Reported-by: Mikael Magnusson <mikael.ker...@lists.m7n.se>
> Bisected-by: David Ahern <dsah...@gmail.com>
> Signed-off-by: Wei Wang <wei...@google.com>
> Acked-by: Eric Dumazet <eduma...@google.com>
> ---
> net/ipv6/route.c | 33 ++++++++++++++++++++++++++++-----
> 1 file changed, 28 insertions(+), 5 deletions(-)
>
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 23a20d62daac..c36900a07a78 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -1574,23 +1574,36 @@ static struct rt6_info *rt6_find_cached_rt(const
> struct fib6_result *res,
> struct rt6_exception *rt6_ex;
> struct rt6_info *ret = NULL;
>
> - bucket = rcu_dereference(res->f6i->rt6i_exception_bucket);
> -
> #ifdef CONFIG_IPV6_SUBTREES
> /* fib6i_src.plen != 0 indicates f6i is in subtree
> * and exception table is indexed by a hash of
> * both fib6_dst and fib6_src.
> - * Otherwise, the exception table is indexed by
> - * a hash of only fib6_dst.
> + * However, the src addr used to create the hash
> + * might not be exactly the passed in saddr which
> + * is a /128 addr from the flow.
> + * So we need to use f6i->fib6_src to redo lookup
> + * if the passed in saddr does not find anything.
> + * (See the logic in ip6_rt_cache_alloc() on how
> + * rt->rt6i_src is updated.)
> */
> if (res->f6i->fib6_src.plen)
> src_key = saddr;
> +find_ex:
> #endif
> + bucket = rcu_dereference(res->f6i->rt6i_exception_bucket);
> rt6_ex = __rt6_find_exception_rcu(&bucket, daddr, src_key);
>
> if (rt6_ex && !rt6_check_expired(rt6_ex->rt6i))
> ret = rt6_ex->rt6i;
>
> +#ifdef CONFIG_IPV6_SUBTREES
> + /* Use fib6_src as src_key and redo lookup */
> + if (!ret && src_key == saddr) {
> + src_key = &res->f6i->fib6_src.addr;
> + goto find_ex;
> + }
> +#endif
> +
> return ret;
> }
>
> @@ -2683,12 +2696,22 @@ u32 ip6_mtu_from_fib6(const struct fib6_result *res,
> #ifdef CONFIG_IPV6_SUBTREES
> if (f6i->fib6_src.plen)
> src_key = saddr;
> +find_ex:
> #endif
> -
> bucket = rcu_dereference(f6i->rt6i_exception_bucket);
> rt6_ex = __rt6_find_exception_rcu(&bucket, daddr, src_key);
> if (rt6_ex && !rt6_check_expired(rt6_ex->rt6i))
> mtu = dst_metric_raw(&rt6_ex->rt6i->dst, RTAX_MTU);
> +#ifdef CONFIG_IPV6_SUBTREES
> + /* Similar logic as in rt6_find_cached_rt().
> + * We need to use f6i->fib6_src to redo lookup in exception
> + * table if saddr did not yield any result.
> + */
> + else if (src_key == saddr) {
> + src_key = &f6i->fib6_src.addr;
> + goto find_ex;
> + }
> +#endif
>
> if (likely(!mtu)) {
> struct net_device *dev = nh->fib_nh_dev;
>
What about rt6_remove_exception_rt?
You can add a 'cache' hook to ip/iproute.c to delete the cached routes
and verify that it works. I seem to have misplaced my patch to do it.
