Subject: [PATCH 07/48] net: sched: fix use-after-free in tcf_action_destroy and tcf_del_walker

From: Jiri Pirko <[email-masked]>
Date: Wed, 13 Sep 2017 17:32:37 +0200

[ Upstream commit 255cd50f207ae8ec7b22663246c833407744e634 ]

Recent commit d7fb60b9cafb ("net_sched: get rid of tcfa_rcu") removed
freeing in call_rcu, which changed already existing hard-to-hit
race condition into 100% hit:

[  598.599825] BUG: unable to handle kernel NULL pointer dereference at 0000000000000030
[  598.607782] IP: tcf_action_destroy+0xc0/0x140

Or:

[   40.858924] BUG: unable to handle kernel NULL pointer dereference at 0000000000000030
[   40.862840] IP: tcf_generic_walker+0x534/0x820

Fix this by storing the ops and use them directly for module_put call.

Fixes: a85a970af265 ("net_sched: move tc_action into tcf_common")
Signed-off-by: Jiri Pirko <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/sched/act_api.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index f2e9ed34a963..0c5dbb172437 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -174,7 +174,7 @@ static int tcf_del_walker(struct tcf_hashinfo *hinfo, struct sk_buff *skb,
 		hlist_for_each_entry_safe(p, n, head, tcfa_head) {
 			ret = __tcf_hash_release(p, false, true);
 			if (ret == ACT_P_DELETED) {
-				module_put(p->ops->owner);
+				module_put(ops->owner);
 				n_i++;
 			} else if (ret < 0)
 				goto nla_put_failure;
@@ -506,13 +506,15 @@ EXPORT_SYMBOL(tcf_action_exec);
 
 int tcf_action_destroy(struct list_head *actions, int bind)
 {
+	const struct tc_action_ops *ops;
 	struct tc_action *a, *tmp;
 	int ret = 0;
 
 	list_for_each_entry_safe(a, tmp, actions, list) {
+		ops = a->ops;
 		ret = __tcf_hash_release(a, bind, true);
 		if (ret == ACT_P_DELETED)
-			module_put(a->ops->owner);
+			module_put(ops->owner);
 		else if (ret < 0)
 			return ret;
 	}
-- 
2.13.6