netdev - Re: [PATCH] net: sched: matchall: verify that filter is not NULL in mall

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Date:   Mon, 18 Feb 2019 12:00:40 +0000
From:   Vlad Buslov <vladbu@...lanox.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
CC:     Ido Schimmel <idosch@...sch.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH] net: sched: matchall: verify that filter is not NULL in
 mall_walk()


On Sat 16 Feb 2019 at 00:24, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On Fri, Feb 15, 2019 at 4:11 AM Vlad Buslov <vladbu@...lanox.com> wrote:
>>
>> Check that filter is not NULL before passing it to tcf_walker->fn()
>> callback. This can happen when mall_change() failed to offload filter to
>> hardware.
>>
>> Signed-off-by: Vlad Buslov <vladbu@...lanox.com>
>> ---
>>  net/sched/cls_matchall.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/net/sched/cls_matchall.c b/net/sched/cls_matchall.c
>> index a37137430e61..1f9d481b0fbb 100644
>> --- a/net/sched/cls_matchall.c
>> +++ b/net/sched/cls_matchall.c
>> @@ -247,6 +247,9 @@ static void mall_walk(struct tcf_proto *tp, struct tcf_walker *arg,
>>
>>         if (arg->count < arg->skip)
>>                 goto skip;
>> +
>> +       if (!head)
>> +               return;
>
> So head==NULL still counts one given that you check NULL after
> checking arg->count. Is this expected?

My intention was to fix the problem (arg->fn() call with NULL filter)
without changing any other functionality, and always incrementing
arg->count once seemed to be the intended behavior. However, since
mall_delete() just returns -EOPNOTSUPP, it might be the case that author
of matchall expected to always have single filter configured when cls
API calls mall_walk(). What would you suggest?