netdev - Re: [Patch net-next] net_sched: properly check for empty skb array on error path

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Message-ID: <4caae5f5-63e2-65c8-522e-0dfe736a7738@gmail.com>
Date:   Mon, 18 Dec 2017 19:58:44 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [Patch net-next] net_sched: properly check for empty skb array on
 error path

On 12/18/2017 06:20 PM, Cong Wang wrote:
> On Mon, Dec 18, 2017 at 5:25 PM, John Fastabend
> <john.fastabend@...il.com> wrote:
>> On 12/18/2017 02:34 PM, Cong Wang wrote:
>>> First, the check of &q->ring.queue against NULL is wrong, it
>>> is always false. We should check the value rather than the address.
>>>
>>
>> Thanks.
>>
>>> Secondly, we need the same check in pfifo_fast_reset() too,
>>> as both ->reset() and ->destroy() are called in qdisc_destroy().
>>>
>>
>> not that it hurts to have the check here, but if init fails
>> in qdisc_create it seems only ->destroy() is called without
>> a ->reset().
>>
>> Is there another path for init() to fail that I'm missing.
> 
> Pretty sure ->reset() is called in qdisc_destroy() and also before
> ->destroy():
> 

Except, the failed init path does not call qdisc_destroy.

static struct Qdisc *qdisc_create(struct net_device *dev,
[...]

        if (ops->init) {
                err = ops->init(sch, tca[TCA_OPTIONS]);
                if (err != 0)
                        goto err_out5;
        }
[...]

err_out5:
        /* ops->init() failed, we call ->destroy() like qdisc_create_dflt() */
        if (ops->destroy)
                ops->destroy(sch);
err_out3:
        dev_put(dev);
        kfree((char *) sch - sch->padded);
err_out2:
        module_put(ops->owner);
err_out:
        *errp = err;
        return NULL;
[...]



> 
> void qdisc_destroy(struct Qdisc *qdisc)
> {
>         const struct Qdisc_ops  *ops = qdisc->ops;
>         struct sk_buff *skb, *tmp;
> 
>         if (qdisc->flags & TCQ_F_BUILTIN ||
>             !refcount_dec_and_test(&qdisc->refcnt))
>                 return;
> 
> #ifdef CONFIG_NET_SCHED
>         qdisc_hash_del(qdisc);
> 
>         qdisc_put_stab(rtnl_dereference(qdisc->stab));
> #endif
>         gen_kill_estimator(&qdisc->rate_est);
>         if (ops->reset)
>                 ops->reset(qdisc);
>         if (ops->destroy)
>                 ops->destroy(qdisc);
>