[PATCH 5.0 001/139] ipv6: fix src addr routing with the exception table

Greg Kroah-Hartman
2019-05-23T19:19:47Z

From: Wei Wang <weiwan@google.com>

[ Upstream commit 510e2ceda031eed97a7a0f9aad65d271a58b460d ]

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.kernel@lists.m7n.se>
Bisected-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Wei Wang <weiwan@google.com>
Cc: Martin Lau <kafai@fb.com>
Cc: Eric Dumazet <edumazet@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv6/route.c | 51 +++++++++++++++++++++++++++------------------------
1 file changed, 27 insertions(+), 24 deletions(-)

--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -110,8 +110,8 @@ static int rt6_fill_node(struct net *net
int iif, int type, u32 portid, u32 seq,
unsigned int flags);
static struct rt6_info *rt6_find_cached_rt(struct fib6_info *rt,
- struct in6_addr *daddr,
- struct in6_addr *saddr);
+ const struct in6_addr *daddr,
+ const struct in6_addr *saddr);

#ifdef CONFIG_IPV6_ROUTE_INFO
static struct fib6_info *rt6_add_route_info(struct net *net,
@@ -1529,31 +1529,44 @@ out:
* Caller has to hold rcu_read_lock()
*/
static struct rt6_info *rt6_find_cached_rt(struct fib6_info *rt,
- struct in6_addr *daddr,
- struct in6_addr *saddr)
+ const struct in6_addr *daddr,
+ const struct in6_addr *saddr)
{
+ const struct in6_addr *src_key = NULL;
struct rt6_exception_bucket *bucket;
- struct in6_addr *src_key = NULL;
struct rt6_exception *rt6_ex;
struct rt6_info *res = NULL;

- bucket = rcu_dereference(rt->rt6i_exception_bucket);
-
#ifdef CONFIG_IPV6_SUBTREES
/* rt6i_src.plen != 0 indicates rt is in subtree
* and exception table is indexed by a hash of
* both rt6i_dst and rt6i_src.
- * Otherwise, the exception table is indexed by
- * a hash of only rt6i_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 (rt->fib6_src.plen)
src_key = saddr;
+find_ex:
#endif
+ bucket = rcu_dereference(rt->rt6i_exception_bucket);
rt6_ex = __rt6_find_exception_rcu(&bucket, daddr, src_key);

if (rt6_ex && !rt6_check_expired(rt6_ex->rt6i))
res = rt6_ex->rt6i;

+#ifdef CONFIG_IPV6_SUBTREES
+ /* Use fib6_src as src_key and redo lookup */
+ if (!res && src_key && src_key != &rt->fib6_src.addr) {
+ src_key = &rt->fib6_src.addr;
+ goto find_ex;
+ }
+#endif
+
return res;
}

@@ -2614,10 +2627,8 @@ out:
u32 ip6_mtu_from_fib6(struct fib6_info *f6i, struct in6_addr *daddr,
struct in6_addr *saddr)
{
- struct rt6_exception_bucket *bucket;
- struct rt6_exception *rt6_ex;
- struct in6_addr *src_key;
struct inet6_dev *idev;
+ struct rt6_info *rt;
u32 mtu = 0;

if (unlikely(fib6_metric_locked(f6i, RTAX_MTU))) {
@@ -2626,18 +2637,10 @@ u32 ip6_mtu_from_fib6(struct fib6_info *
goto out;
}

- src_key = NULL;
-#ifdef CONFIG_IPV6_SUBTREES
- if (f6i->fib6_src.plen)
- src_key = saddr;
-#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);
-
- if (likely(!mtu)) {
+ rt = rt6_find_cached_rt(f6i, daddr, saddr);
+ if (unlikely(rt)) {
+ mtu = dst_metric_raw(&rt->dst, RTAX_MTU);
+ } else {
struct net_device *dev = fib6_info_nh_dev(f6i);

mtu = IPV6_MIN_MTU;