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

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Message-Id: <1531157207-10850-1-git-send-email-vladbu@mellanox.com>
Date:   Mon,  9 Jul 2018 20:26:47 +0300
From:   Vlad Buslov <vladbu@...lanox.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, jhs@...atatu.com, xiyou.wangcong@...il.com,
        jiri@...nulli.us, marcelo.leitner@...il.com,
        Vlad Buslov <vladbu@...lanox.com>
Subject: [PATCH net-next] net: sched: fix unprotected access to rcu cookie pointer

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.leitner@...il.com>
Signed-off-by: Vlad Buslov <vladbu@...lanox.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