Commit 255cd50f authored Sep 13, 2017 by Jiri Pirko Committed by David S. Miller Sep 13, 2017

net: sched: fix use-after-free in tcf_action_destroy and tcf_del_walker



Recent commit d7fb60b9 ("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: a85a970a ("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>

parent 822f8565

net/sched/act_api.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -180,7 +180,7 @@ static int tcf_del_walker(struct tcf_idrinfo idrinfo, struct sk_buff skb,
		idr_for_each_entry_ext(idr, p, id) {
		ret = __tcf_idr_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;
		@@ -514,13 +514,15 @@ 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_idr_release(a, bind, true);
		if (ret == ACT_P_DELETED)
		module_put(a->ops->owner);
		module_put(ops->owner);
		else if (ret < 0)
		return ret;
		}