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

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Date: Wed, 7 Jun 2023 09:38:44 +0800
From: shaozhengchao <shaozhengchao@...wei.com>
To: <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>, Pedro Tammela <pctammela@...atatu.com>
Subject: Re: [PATCH net] net/sched: taprio: fix slab-out-of-bounds Read in
 taprio_dequeue_from_txq


Hi vinicius,jamal:
	Based on this question, I'm also thinking about whether it's
appropriate to set the tc parameter for dev in taprio_change. The
taprio_change maybe will fail and .graft() will not be invoked to make
qdisc take effect. However, the tc parameter of dev has been modified,
which seems to be incorrect when dequeuing packets. I think the tc
parameter of dev should be configured in .graft() so that the new qdisc
and tc parameters of dev can take effect together. Thank you.
	
Zhengchao Shao

On 2023/6/7 9:15, shaozhengchao wrote:
> 
> On 2023/6/6 23:10, Pedro Tammela wrote:
>> On 06/06/2023 09:10, Zhengchao Shao wrote:
>>> As shown in [1], when qdisc of the taprio type is set, 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. 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>
>>> ---
>>>   net/sched/sch_taprio.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
>>> index 3c4c2c334878..dccb64425852 100644
>>> --- a/net/sched/sch_taprio.c
>>> +++ b/net/sched/sch_taprio.c
>>> @@ -801,7 +801,7 @@ static struct sk_buff 
>>> *taprio_dequeue_tc_priority(struct Qdisc *sch,
>>>               if (skb)
>>>                   return skb;
>>> -        } while (q->cur_txq[tc] != first_txq);
>>> +        } while (q->cur_txq[tc] != first_txq && q->cur_txq[tc] < 
>>> dev->num_tx_queues);
>>
> Hi Pedro:
>      Thank you for youe reply.
>> I'm not sure this is the correct fix.
>> If q->cur_txg[tc] == dev->num_tx_queues the next call to 
>> taprio_dequeue_tc_priority() for the same tc index will have
>> first_txq set to dev->num_tx_queues (no wrap around to first_txq 
>> happens).
> yes, maybe the same problem will occur at the next dequeue skb. It can
> be changed to the following:
>              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);
> However, I prefer to limit the value of count in taprio_change(), so 
> that I don't add extra judgment to the data path.
> 
> Hi Vinicius,
>      Do you have any better suggestions?
>> If count and offset are 0 it will increment q->cur_txg[tc] and then 
>> bail on the while condition but still growing unbounded (just slower 
>> than before).
>>
>>>       }
>>>   taprio_dequeue_tc_priority
>>>       return NULL;
>>
>>