Subject: Re: [BUG] net_cls: Panic occured when net_cls subsystem use

From: Jarek Poplawski <[email-masked]>
Date: Fri, 29 May 2009 07:48:12 +0000

On 29-05-2009 07:18, Minoru Usui wrote:
> Hi, 
> 
> On Thu, 21 May 2009 09:22:56 +0900
> Minoru Usui <[email-masked]> wrote:
> 
>> Hi

Hi,
>>
>> Unfortunately this is only panic report.
>>
>> I used cgroup net_cls subsystem, then kernel panic occured.
>> I attach panic message and kernel config in this mail's last paragraph.
>> If my operation is wrong, could you tell me how to use net_cls and
>> where the documentation is. 
>>
>> # But I think panic is very bad even if my operation is wrong.
> 
> I investigated this problem, and I found a bug in tc_ctl_tfilter() in net/sched/cls_api.c.
> 
> When 'tc filter add' command is executed and proto-tcf does not exist, 
> tcf_ctl_tfilter() allocates, initializes and chanins proto-tcf(tp) to
> cops->tcf_chain()'s chain before calling tp->ops->change().
> 
> If tp->ops->change() returns an error, tcf_ctl_tfilter() returns an error
> too, but proto-tcf(tp) is not unchained yet. 
> 
> I think tcf_ctl_tfilter() shouldn't chain proto-tcf to the chain before it returns
> an error.

I didn't verify this too much, so I might be wrong, but it looks like
cls_cgroup_classify() does things a bit different than others (doesn't
check the 'head' etc. for NULL), so maybe you should consider fixing
it instead? (Btw., the tc classifier maintainer added to Cc).

Cheers, 
Jarek P.

> 
> Signed-off-by: Minoru Usui <[email-masked]>
> 
> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
> index 0759f32..756148b 100644
> --- a/net/sched/cls_api.c
> +++ b/net/sched/cls_api.c
> @@ -266,11 +266,6 @@ replay:
>  			goto errout;
>  		}
>  
> -		spin_lock_bh(root_lock);
> -		tp->next = *back;
> -		*back = tp;
> -		spin_unlock_bh(root_lock);
> -
>  	} else if (tca[TCA_KIND] && nla_strcmp(tca[TCA_KIND], tp->ops->kind))
>  		goto errout;
>  
> @@ -314,8 +309,17 @@ replay:
>  	}
>  
>  	err = tp->ops->change(tp, cl, t->tcm_handle, tca, &fh);
> -	if (err == 0)
> -		tfilter_notify(skb, n, tp, fh, RTM_NEWTFILTER);
> +	if (err) {
> +		tcf_destroy(tp);
> +		goto errout;
> +	}
> +
> +	spin_lock_bh(root_lock);
> +	tp->next = *back;
> +	*back = tp;
> +	spin_unlock_bh(root_lock);
> +
> +	tfilter_notify(skb, n, tp, fh, RTM_NEWTFILTER);
>  
>  errout:
>  	if (cl)
>