ipv4: Fix fib_trie rebalancing, part 3

Alas current delaying of freeing old tnodes by RCU in trie_rebalance
is still not enough because we can free a top tnode before updating a
t->trie pointer.

Reported-by: Pawel Staszewski <pstaszewski@itcare.pl>
Tested-by: Pawel Staszewski <pstaszewski@itcare.pl>
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 012cf5a68581..00a54b246dfe 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -1021,6 +1021,9 @@ static void trie_rebalance(struct trie *t, struct tnode *tn)
                                       (struct node *)tn, wasfull);
 
                 tp = node_parent((struct node *) tn);
+                if (!tp)
+                        rcu_assign_pointer(t->trie, (struct node *)tn);
+
                 tnode_free_flush();
                 if (!tp)
                         break;