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

[Eric Dumazet <eric.dumazet@gmail.com>]

On 8/11/21 7:10 AM, tcs.kernel@gmail.com wrote:
> From: Haimin Zhang <tcs_kernel@tencent.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@syzkaller.appspotmail.com
> Signed-off-by: Haimin Zhang <tcs_kernel@tencent.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 ?