netdev - Re: [PATCH net,v2] net/sched: taprio: fix slab-out-of-bounds Read in taprio_dequeue_from

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Date: Thu, 8 Jun 2023 11:37:22 -0300
From: Pedro Tammela <pctammela@...atatu.com>
To: Zhengchao Shao <shaozhengchao@...wei.com>, netdev@...r.kernel.org,
 vinicius.gomes@...el.com, jhs@...atatu.com, xiyou.wangcong@...il.com,
 jiri@...nulli.us, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com
Cc: vladimir.oltean@....com, weiyongjun1@...wei.com, yuehaibing@...wei.com
Subject: Re: [PATCH net,v2] net/sched: taprio: fix slab-out-of-bounds Read in
 taprio_dequeue_from_txq

On 08/06/2023 03:27, Zhengchao Shao wrote:
> As shown in [1], out-of-bounds access occurs in two cases:
> 1)when the qdisc of the taprio type is used to replace the previously
> configured taprio, count and offset in tc_to_txq can be set to 0. In this
> case, the value of *txq in taprio_next_tc_txq() will increases
> continuously. When the number of accessed queues exceeds the number of
> queues on the device, out-of-bounds access occurs.
> 2)When packets are dequeued, taprio can be deleted. In this case, the tc
> rule of dev is cleared. The count and offset values are also set to 0. In
> this case, out-of-bounds access is also caused.
> 
> Now the restriction on the queue number is added.
> 
> [1] https://groups.google.com/g/syzkaller-bugs/c/_lYOKgkBVMg
> Fixes: 2f530df76c8c ("net/sched: taprio: give higher priority to higher TCs in software dequeue mode")
> Reported-by: syzbot+04afcb3d2c840447559a@...kaller.appspotmail.com
> Signed-off-by: Zhengchao Shao <shaozhengchao@...wei.com>

Tested-by: Pedro Tammela <pctammela@...atatu.com>

> ---
> v2: set q->cur_txq[tc] to prevent out-of-bounds access during next dequeue
> ---
>   net/sched/sch_taprio.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
> index 3c4c2c334878..82983a6eb8f8 100644
> --- a/net/sched/sch_taprio.c
> +++ b/net/sched/sch_taprio.c
> @@ -799,6 +799,9 @@ static struct sk_buff *taprio_dequeue_tc_priority(struct Qdisc *sch,
>   
>   			taprio_next_tc_txq(dev, tc, &q->cur_txq[tc]);
>   
> +			if (q->cur_txq[tc] >= dev->num_tx_queues)
> +				q->cur_txq[tc] = first_txq;
> +
>   			if (skb)
>   				return skb;
>   		} while (q->cur_txq[tc] != first_txq);