netdev - Re: [PATCH net] net/sched: taprio: always validate TCA_TAPRIO_ATTR

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Message-ID: <87plswv2d5.fsf@intel.com>
Date: Tue, 04 Jun 2024 14:12:38 -0700
From: Vinicius Costa Gomes <vinicius.gomes@...el.com>
To: Eric Dumazet <edumazet@...gle.com>, "David S . Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
 <pabeni@...hat.com>
Cc: Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang
 <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
 netdev@...r.kernel.org, eric.dumazet@...il.com, Eric Dumazet
 <edumazet@...gle.com>, Noam Rathaus <noamr@...-disclosure.com>, Vladimir
 Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net] net/sched: taprio: always validate
 TCA_TAPRIO_ATTR_PRIOMAP

Eric Dumazet <edumazet@...gle.com> writes:

> If one TCA_TAPRIO_ATTR_PRIOMAP attribute has been provided,
> taprio_parse_mqprio_opt() must validate it, or userspace
> can inject arbitrary data to the kernel, the second time
> taprio_change() is called.
>
> First call (with valid attributes) sets dev->num_tc
> to a non zero value.
>
> Second call (with arbitrary mqprio attributes)
> returns early from taprio_parse_mqprio_opt()
> and bad things can happen.
>
> Fixes: a3d43c0d56f1 ("taprio: Add support adding an admin schedule")
> Reported-by: Noam Rathaus <noamr@...-disclosure.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Vinicius Costa Gomes <vinicius.gomes@...el.com>
> Cc: Vladimir Oltean <vladimir.oltean@....com>
> ---
>  net/sched/sch_taprio.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
>
> diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
> index 937a0c513c17..b284a06b5a75 100644
> --- a/net/sched/sch_taprio.c
> +++ b/net/sched/sch_taprio.c
> @@ -1176,16 +1176,13 @@ static int taprio_parse_mqprio_opt(struct net_device *dev,
>  {
>  	bool allow_overlapping_txqs = TXTIME_ASSIST_IS_ENABLED(taprio_flags);
>  
> -	if (!qopt && !dev->num_tc) {
> -		NL_SET_ERR_MSG(extack, "'mqprio' configuration is necessary");
> -		return -EINVAL;
> -	}
> -
> -	/* If num_tc is already set, it means that the user already
> -	 * configured the mqprio part
> -	 */
> -	if (dev->num_tc)
> +	if (!qopt) {
> +		if (!dev->num_tc) {
> +			NL_SET_ERR_MSG(extack, "'mqprio' configuration is necessary");
> +			return -EINVAL;
> +		}
>  		return 0;
> +	}

Nice one. I think I have an idea of what's going on here.

Validating the priomap even if we are not going to install it is good:

Acked-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>

Cheers,
-- 
Vinicius