netdev - Re: [PATCH net 1/1] net: sched: fix cleanup NULL pointer exception in act

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Date:   Thu, 21 Mar 2019 11:05:21 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     John Hurley <john.hurley@...ronome.com>
Cc:     Jiri Pirko <jiri@...lanox.com>, David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Vlad Buslov <vladbu@...lanox.com>, oss-drivers@...ronome.com
Subject: Re: [PATCH net 1/1] net: sched: fix cleanup NULL pointer exception in act_mirr

On Wed, Mar 20, 2019 at 11:12 AM John Hurley <john.hurley@...ronome.com> wrote:
>
> A new mirred action is created by the tcf_mirred_init function. This
> contains a list head struct which is inserted into a global list on
> successful creation of a new action. However, after a creation, it is
> still possible to error out if the egress device does not exist. This
> calls the act_mirr cleanup function via __tcf_idr_release and
> __tcf_action_put. This cleanup function tries to delete the list entry
> which is as yet uninitialised, leading to a NULL pointer exception.

Hmm, good catch but can this be just fixed by initializing it before
taking the netdevice refcnt? Like this:

@@ -163,6 +163,9 @@ static int tcf_mirred_init(struct net *net, struct
nlattr *nla,
        m->tcf_action = parm->action;
        m->tcfm_eaction = parm->eaction;

+       if (ret == ACT_P_CREATED)
+               INIT_LIST_HEAD(&m->tcfm_list);
+
        if (parm->ifindex) {
                dev = dev_get_by_index(net, parm->ifindex);
                if (!dev) {

which is also much simpler.

Thanks.