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Subject[PATCH 4.9 047/105] net: sched: fix use-after-free in tcf_action_destroy and tcf_del_walker
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jiri Pirko <jiri@mellanox.com>


[ 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 <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sched/act_api.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -141,7 +141,7 @@ static int tcf_del_walker(struct tcf_has
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;
@@ -450,13 +450,15 @@ 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;
}

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