linux-kernel - Re: [PATCH] bridge: don't try to update timers in case of broken MLD queries

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Message-ID: <20130806003227.GH25436@Linus-Debian>
Date:	Tue, 6 Aug 2013 02:32:27 +0200
From:	Linus Lüssing <linus.luessing@....de>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	bridge@...ts.linux-foundation.org,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Cong Wang <amwang@...hat.com>,
	Adam Baker <linux@...er-net.org.uk>,
	Paul Bolle <pebolle@...cali.nl>, linus.luessing@....de
Subject: Re: [PATCH] bridge: don't try to update timers in case of broken MLD
 queries

On Mon, Aug 05, 2013 at 03:42:22PM -0700, Stephen Hemminger wrote:
> On Tue,  6 Aug 2013 00:32:05 +0200
> Linus Lüssing <linus.luessing@....de> wrote:
> 
> > Currently we are reading an uninitialized value for the max_delay
> > variable when snooping an MLD query message of invalid length and would
> > update our timers with that.
> > 
> > Fixing this by simply ignoring such broken MLD queries (just like we do
> > for IGMP already).
> > 
> > This is a regression introduced by:
> > "bridge: disable snooping if there is no querier" (b00589af3b04)
> > 
> > Reported-by: Paul Bolle <pebolle@...cali.nl>
> > Signed-off-by: Linus Lüssing <linus.luessing@....de>
> > ---
> >  net/bridge/br_multicast.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
> > index 61c5e81..08e576a 100644
> > --- a/net/bridge/br_multicast.c
> > +++ b/net/bridge/br_multicast.c
> > @@ -1195,7 +1195,7 @@ static int br_ip6_multicast_query(struct net_bridge *br,
> >  		max_delay = msecs_to_jiffies(ntohs(mld->mld_maxdelay));
> >  		if (max_delay)
> >  			group = &mld->mld_mca;
> > -	} else if (skb->len >= sizeof(*mld2q)) {
> > +	} else {
> >  		if (!pskb_may_pull(skb, sizeof(*mld2q))) {
> >  			err = -EINVAL;
> >  			goto out;
> 
> Why not use else if here, other than that looks great.

Because it isn't really necessary, it is basically included
in the pskb_may_pull() already, just like it is in the according IGMP
code path.

And I thought it'd be nicer to handle it the same way as in the
IGMP code path to avoid diverging too much.

Cheers, Linus
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