netdev - Re: [PATCH] net:sched fix array-index-out-of-bounds in taprio

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Date:   Wed, 11 Aug 2021 16:36:57 +0800
From:   Haimin Zhang <tcs.kernel@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>, vinicius.gomes@...el.com,
        jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org
Cc:     Haimin Zhang <tcs_kernel@...cent.com>
Subject: Re: [PATCH] net:sched fix array-index-out-of-bounds in taprio_change



在 2021/8/11 15:44, Eric Dumazet 写道:
> 
> 
> On 8/11/21 7:10 AM, tcs.kernel@...il.com wrote:
>> From: Haimin Zhang <tcs_kernel@...cent.com>
>>
>> syzbot report an array-index-out-of-bounds in taprio_change
>> index 16 is out of range for type '__u16 [16]'
>> that's because mqprio->num_tc is lager than TC_MAX_QUEUE,so we check
>> the return value of netdev_set_num_tc.
>>
>> Reported-by: syzbot+2b3e5fb6c7ef285a94f6@...kaller.appspotmail.com
>> Signed-off-by: Haimin Zhang <tcs_kernel@...cent.com>
>> ---
>>   net/sched/sch_taprio.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
>> index 9c79374..1ab2fc9 100644
>> --- a/net/sched/sch_taprio.c
>> +++ b/net/sched/sch_taprio.c
>> @@ -1513,7 +1513,9 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt,
>>   	taprio_set_picos_per_byte(dev, q);
>>   
>>   	if (mqprio) {
>> -		netdev_set_num_tc(dev, mqprio->num_tc);
>> +		err = netdev_set_num_tc(dev, mqprio->num_tc);
>> +		if (err)
>> +			goto free_sched;
>>   		for (i = 0; i < mqprio->num_tc; i++)
>>   			netdev_set_tc_queue(dev, i,
>>   					    mqprio->count[i],
>>
> 
> When was the bug added ?
> 
> Hint: Please provide a Fixes: tag
> 
> taprio_parse_mqprio_opt() already checks :
> 
> /* Verify num_tc is not out of max range */
> if (qopt->num_tc > TC_MAX_QUEUE) {
>      NL_SET_ERR_MSG(extack, "Number of traffic classes is outside valid range");
>      return -EINVAL;
> }
> 
> So what is happening exactly ?
> 
> 
> 
> 
syzkaller reported this problem,the log shows mqprio->count[16] is accessed.
here is the log
https://syzkaller.appspot.com/bug?id=3a3677d4e7539ec5e671a81e32882ad40b5f7b64

the added check logic is hurtlessness,and netdev_set_num_tc does have a 
return value.