[PATCH bpf] bpf: fix memory leak in lpm_trie map_free callback function

[Yonghong Song]

There is a memory leak happening in lpm_trie map_free callback
function trie_free. The trie structure itself does not get freed.

Also, trie_free function did not do synchronize_rcu before freeing
various data structures. This is incorrect as some rcu_read_lock
region(s) for lookup, update, delete or get_next_key may not complete yet.
The fix is to add synchronize_rcu in the beginning of trie_free.
The useless spin_lock is removed from this function as well.

Fixes: b95a5c4db09b ("bpf: add a longest prefix match trie map implementation")
Reported-by: Mathieu Malaterre <ma...@debian.org>
Reported-by: Alexei Starovoitov <a...@kernel.org>
Tested-by: Mathieu Malaterre <ma...@debian.org>
Signed-off-by: Yonghong Song <y...@fb.com>
---
 kernel/bpf/lpm_trie.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index 7b469d1..9b41ea4 100644
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -555,7 +555,12 @@ static void trie_free(struct bpf_map *map)
        struct lpm_trie_node __rcu **slot;
        struct lpm_trie_node *node;
 
-       raw_spin_lock(&trie->lock);
+       /* at this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
+        * so the programs (can be more than one that used this map) were
+        * disconnected from events. Wait for outstanding programs to complete
+        * update/lookup/delete/get_next_key and free the trie.
+        */
+       synchronize_rcu();
 
        /* Always start at the root and walk down to a node that has no
         * children. Then free that node, nullify its reference in the parent
@@ -588,7 +593,7 @@ static void trie_free(struct bpf_map *map)
        }
 
 unlock:
-       raw_spin_unlock(&trie->lock);
+       kfree(trie);
 }
 
 static int trie_get_next_key(struct bpf_map *map, void *_key, void *_next_key)
-- 
2.9.5