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

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Date:   Thu, 12 Aug 2021 10:53:21 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     tcs.kernel@...il.com, vinicius.gomes@...el.com
Cc:     jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        davem@...emloft.net, netdev@...r.kernel.org,
        Haimin Zhang <tcs_kernel@...cent.com>
Subject: Re: [PATCH] net:sched fix array-index-out-of-bounds in
 taprio_change

On Wed, 11 Aug 2021 13:10:09 +0800 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;

taprio_set_picos_per_byte() already got called and applied some of the
changes. It seems like the early return from taprio_parse_mqprio_opt()
if dev->num_tc is non-zero is incorrect. That function is supposed to
validate that mqprio_opt() is correct AFAIU. That would mean:

Fixes: a3d43c0d56f1 ("taprio: Add support adding an admin schedule")

Vinicius - WDYT?

>  		for (i = 0; i < mqprio->num_tc; i++)
>  			netdev_set_tc_queue(dev, i,
>  					    mqprio->count[i],