netdev - Re: [PATCH net] sch_netem: fix skb leak in netem

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Date:   Mon, 5 Mar 2018 18:11:42 -0500
From:   Neil Horman <nhorman@...driver.com>
To:     Alexey Kodanev <alexey.kodanev@...cle.com>
Cc:     netdev@...r.kernel.org, David Miller <davem@...emloft.net>
Subject: Re: [PATCH net] sch_netem: fix skb leak in netem_enqueue()

On Mon, Mar 05, 2018 at 03:57:52PM +0300, Alexey Kodanev wrote:
> On 03/03/2018 03:20 PM, Neil Horman wrote:
> > On Fri, Mar 02, 2018 at 09:16:48PM +0300, Alexey Kodanev wrote:
> >> When we exceed current packets limit and have more than one
> >> segment in the list returned by skb_gso_segment(), netem drops
> >> only the first one, skipping the rest, hence kmemleak reports:
> >>
> ...
> >>
> >> Fix it by adding the rest of the segments, if any, to skb
> >> 'to_free' list in that case.
> >>
> >> Fixes: 6071bd1aa13e ("netem: Segment GSO packets on enqueue")
> >> Signed-off-by: Alexey Kodanev <alexey.kodanev@...cle.com>
> >> ---
> >>  net/sched/sch_netem.c | 8 +++++++-
> >>  1 file changed, 7 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
> >> index 7c179ad..a5023a2 100644
> >> --- a/net/sched/sch_netem.c
> >> +++ b/net/sched/sch_netem.c
> >> @@ -508,8 +508,14 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
> >>  			1<<(prandom_u32() % 8);
> >>  	}
> >>  
> >> -	if (unlikely(sch->q.qlen >= sch->limit))
> >> +	if (unlikely(sch->q.qlen >= sch->limit)) {
> >> +		while (segs) {
> >> +			skb2 = segs->next;
> >> +			__qdisc_drop(segs, to_free);
> >> +			segs = skb2;
> >> +		}
> >>  		return qdisc_drop(skb, sch, to_free);
> >> +	}
> >>  
> > It seems like it might be nice to wrap up this drop loop into a
> > qdisc_drop_all inline function.  Then we can easily drop segments in other
> > locations if we should need to
> 
> 
> Agree, will prepare the patch. I guess we could just add 'segs' to 'to_free'
> list, then add qdisc_drop_all() with stats counter and returning status,
> something like this:
> 
> @@ -824,6 +824,18 @@ static inline void __qdisc_drop(struct sk_buff *skb, struct sk_buff **to_free)
>         *to_free = skb;
>  }
> 
> +static inline void __qdisc_drop_all(struct sk_buff *skb,
> +                                   struct sk_buff **to_free)
> +{
> +       struct sk_buff *first = skb;
> +
> +       while (skb->next)
> +               skb = skb->next;
> +
> +       skb->next = *to_free;
> +       *to_free = first;
> +}
> 
 I agree

Thanks!
Neil

> Thanks,
> Alexey
>