netdev - Re: [PATCH net v2 1/4] net/sched: sch_qfq: reintroduce lmax bound check for MTU

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Date: Mon, 10 Jul 2023 13:18:49 -0300
From: Pedro Tammela <pctammela@...atatu.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: netdev@...r.kernel.org, jhs@...atatu.com, xiyou.wangcong@...il.com,
 jiri@...nulli.us, davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
 shuah@...nel.org, shaozhengchao@...wei.com, victor@...atatu.com,
 simon.horman@...igine.com, paolo.valente@...more.it
Subject: Re: [PATCH net v2 1/4] net/sched: sch_qfq: reintroduce lmax bound
 check for MTU

On 08/07/2023 05:14, Eric Dumazet wrote:
> On Sat, Jul 8, 2023 at 12:01 AM Pedro Tammela <pctammela@...atatu.com> wrote:
>>
>> 25369891fcef deletes a check for the case where no 'lmax' is
>> specified which 3037933448f6 previously fixed as 'lmax'
>> could be set to the device's MTU without any bound checking
>> for QFQ_LMAX_MIN and QFQ_LMAX_MAX. Therefore, reintroduce the check.
>>
>> Fixes: 25369891fcef ("net/sched: sch_qfq: refactor parsing of netlink parameters")
>> Acked-by: Jamal Hadi Salim <jhs@...atatu.com>
>> Signed-off-by: Pedro Tammela <pctammela@...atatu.com>
>> ---
>>   net/sched/sch_qfq.c | 11 +++++++++--
>>   1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/sched/sch_qfq.c b/net/sched/sch_qfq.c
>> index dfd9a99e6257..63a5b277c117 100644
>> --- a/net/sched/sch_qfq.c
>> +++ b/net/sched/sch_qfq.c
>> @@ -423,10 +423,17 @@ static int qfq_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
>>          else
>>                  weight = 1;
>>
>> -       if (tb[TCA_QFQ_LMAX])
>> +       if (tb[TCA_QFQ_LMAX]) {
>>                  lmax = nla_get_u32(tb[TCA_QFQ_LMAX]);
>> -       else
>> +       } else {
>> +               /* MTU size is user controlled */
>>                  lmax = psched_mtu(qdisc_dev(sch));
>> +               if (lmax < QFQ_MIN_LMAX || lmax > QFQ_MAX_LMAX) {
>> +                       NL_SET_ERR_MSG_MOD(extack,
>> +                                          "MTU size out of bounds for qfq");
>> +                       return -EINVAL;
>> +               }
>> +       }
>>
> 
> Reviewed-by: Eric Dumazet <edumazet@...gle.com>
> 
> Speaking of psched_mtu(), I see that net/sched/sch_pie.c is using it
> without holding RTNL,
> so dev->mtu can be changed underneath. KCSAN could issue a warning.
> 
> Feel free to submit this fix (I am currently traveling)

Sure! Thank you Eric.

> 
> diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
> index e98aac9d5ad5737592ab7cd409c174707cd68681..15960564e0c364ef430f1e3fcdd0e835c2f94a77
> 100644
> --- a/include/net/pkt_sched.h
> +++ b/include/net/pkt_sched.h
> @@ -134,7 +134,7 @@ extern const struct nla_policy rtm_tca_policy[TCA_MAX + 1];
>    */
>   static inline unsigned int psched_mtu(const struct net_device *dev)
>   {
> -       return dev->mtu + dev->hard_header_len;
> +       return READ_ONCE(dev->mtu) + dev->hard_header_len;
>   }
> 
>   static inline struct net *qdisc_net(struct Qdisc *q)