netdev - Re: [PATCH] netem: fix possible skb leak

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Message-ID: <20120430092509.54b89ae6@nehalam.linuxnetplumber.net>
Date:	Mon, 30 Apr 2012 09:25:09 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Stephen Hemminger <shemminger@...l.org>
Subject: Re: [PATCH] netem: fix possible skb leak

On Sun, 29 Apr 2012 21:08:22 +0200
Eric Dumazet <eric.dumazet@...il.com> wrote:

> From: Eric Dumazet <edumazet@...gle.com>
> 
> skb_checksum_help(skb) can return an error, we must free skb in this
> case. qdisc_drop(skb, sch) can also be feeded with a NULL skb (if
> skb_unshare() failed), so lets use this generic helper.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Stephen Hemminger <shemminger@...l.org>
> ---
>  net/sched/sch_netem.c |    6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
> index 5da548f..ebd2296 100644
> --- a/net/sched/sch_netem.c
> +++ b/net/sched/sch_netem.c
> @@ -408,10 +408,8 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch)
>  	if (q->corrupt && q->corrupt >= get_crandom(&q->corrupt_cor)) {
>  		if (!(skb = skb_unshare(skb, GFP_ATOMIC)) ||
>  		    (skb->ip_summed == CHECKSUM_PARTIAL &&
> -		     skb_checksum_help(skb))) {
> -			sch->qstats.drops++;
> -			return NET_XMIT_DROP;
> -		}
> +		     skb_checksum_help(skb)))
> +			return qdisc_drop(skb, sch);
>  
>  		skb->data[net_random() % skb_headlen(skb)] ^= 1<<(net_random() % 8);
>  	}
> 
> 

This would crater if skb_unshare() returned NULL. I think the conditional
needs to be split into two paths.
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