netdev - Re: [PATCH net-next v6 11/11] net: sched: change action API to use array of pointers to actions

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Date:   Wed, 08 Aug 2018 14:41:08 +0300
From:   Vlad Buslov <vladbu@...lanox.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yevgeny Kliteynik <kliteyn@...lanox.com>
Subject: Re: [PATCH net-next v6 11/11] net: sched: change action API to use array of pointers to actions


On Tue 07 Aug 2018 at 23:26, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On Thu, Jul 5, 2018 at 7:24 AM Vlad Buslov <vladbu@...lanox.com> wrote:
>>         attr_size = tcf_action_full_attrs_size(attr_size);
>>
>>         if (event == RTM_GETACTION)
>> -               ret = tcf_get_notify(net, portid, n, &actions, event, extack);
>> +               ret = tcf_get_notify(net, portid, n, actions, event, extack);
>>         else { /* delete */
>> -               ret = tcf_del_notify(net, n, &actions, portid, attr_size, extack);
>> +               ret = tcf_del_notify(net, n, actions, &acts_deleted, portid,
>> +                                    attr_size, extack);
>>                 if (ret)
>>                         goto err;
>>                 return ret;
>>         }
>>  err:
>> -       tcf_action_put_lst(&actions);
>> +       tcf_action_put_many(&actions[acts_deleted]);
>>         return ret;
>
> How does this even work?
>
> You save an index in 'acts_deleted', but you pass &actions[acts_deleted]
> to tcf_action_put_many(), which seems you want to start from
> where it fails, but inside tcf_action_put_many() it starts from 0
> to TCA_ACT_MAX_PRIO, out-of-bound access at least?

Actions array is declared to be TCA_ACT_MAX_PRIO+1 in size, and
initialized to NULL pointers. In loop inside tcf_action_put_many() there
are two checks: One is that index is less than TCA_ACT_MAX_PRIO and
another one that pointer is not NULL. In this case I rely on extra NULL
pointer at the end of actions array to prevent out-of-bound access.