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

- From: Haimin Zhang \<hidden\>
- Date: 2021-08-11 08:37:10 
- List: netdev
- Page: https://ratatoskr.run/netdev/2021/08/11209125
- Thread: https://ratatoskr.run/netdev/2021/08/11209119/t.md

```text


在 2021/8/11 15:44, Eric Dumazet 写道:
>
>
> On 8/11/21 7:10 AM, tcs.kernel@gmail.com wrote:
>> From: Haimin Zhang <redacted>
>>
>> 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: <redacted>
>> Signed-off-by: Haimin Zhang <redacted>
>> ---
>>   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.
```