[PATCH net-next] net: sched: fix unprotected access to rcu cookie pointer

[Vlad Buslov]

Fix action attribute size calculation function to take rcu read lock and
access act_cookie pointer with rcu dereference.

Fixes: eec94fdb0480 ("net: sched: use rcu for action cookie update")
Reported-by: Marcelo Ricardo Leitner <marcelo.leit...@gmail.com>
Signed-off-by: Vlad Buslov <vla...@mellanox.com>
---
 net/sched/act_api.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index 66dc19746c63..148a89ab789b 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -149,10 +149,15 @@ EXPORT_SYMBOL(__tcf_idr_release);
 
 static size_t tcf_action_shared_attrs_size(const struct tc_action *act)
 {
+       struct tc_cookie *act_cookie;
        u32 cookie_len = 0;
 
-       if (act->act_cookie)
-               cookie_len = nla_total_size(act->act_cookie->len);
+       rcu_read_lock();
+       act_cookie = rcu_dereference(act->act_cookie);
+
+       if (act_cookie)
+               cookie_len = nla_total_size(act_cookie->len);
+       rcu_read_unlock();
 
        return  nla_total_size(0) /* action number nested */
                + nla_total_size(IFNAMSIZ) /* TCA_ACT_KIND */
-- 
2.7.5