Re: [PATCH] netem: fix possible skb leak

[Eric Dumazet <eric.dumazet@gmail.com>]

On Mon, 2012-04-30 at 09:25 -0700, Stephen Hemminger wrote:
> On Sun, 29 Apr 2012 21:08:22 +0200
> Eric Dumazet <eric.dumazet@gmail.com> wrote:
> 
> > From: Eric Dumazet <edumazet@google.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@google.com>
> > Cc: Stephen Hemminger <shemminger@osdl.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.

Maybe you can read the changelog where I explained this was safe ;)