netdev - Re: [PATCH net] net: sched: fix possible crash in tcf_action

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Date:   Wed, 18 Sep 2019 14:37:21 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        syzbot <syzkaller@...glegroups.com>,
        Vlad Buslov <vladbu@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>
Subject: Re: [PATCH net] net: sched: fix possible crash in tcf_action_destroy()

On Wed, Sep 18, 2019 at 12:57 PM 'Eric Dumazet' via syzkaller
<syzkaller@...glegroups.com> wrote:
>
> If the allocation done in tcf_exts_init() failed,
> we end up with a NULL pointer in exts->actions.
...
> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
> index efd3cfb80a2ad775dc8ab3c4900bd73d52c7aaad..9aef93300f1c11791acbb9262dfe77996872eafe 100644
> --- a/net/sched/cls_api.c
> +++ b/net/sched/cls_api.c
> @@ -3027,8 +3027,10 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb)
>  void tcf_exts_destroy(struct tcf_exts *exts)
>  {
>  #ifdef CONFIG_NET_CLS_ACT
> -       tcf_action_destroy(exts->actions, TCA_ACT_UNBIND);
> -       kfree(exts->actions);
> +       if (exts->actions) {

I think it is _slightly_ better to check exts->nr_actions!=0 here,
as it would help exts->actions!=NULL&& exts->nr_actions==0
cases too.

What do you think?