netdev - Re: bridge: Fix IGMP3 report parsing

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Message-Id: <20100407.205248.113724360.davem@davemloft.net>
Date:	Wed, 07 Apr 2010 20:52:48 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	netdev@...r.kernel.org, banyeer@...oo.com
Subject: Re: bridge: Fix IGMP3 report parsing

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Thu, 8 Apr 2010 09:26:34 +0800

> Hi:
> 
> bridge: Fix IGMP3 report parsing
> 
> The IGMP3 report parsing is looking at the wrong address for
> group records.  This patch fixes it.
> 
> Reported-by: Banyeer <banyeer@...oo.com>
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

I think you're adding as many bugs as you are fixing here :-)

> @@ -719,11 +719,11 @@ static int br_multicast_igmp3_report(struct net_bridge *br,
>  	len = sizeof(*ih);
>  
>  	for (i = 0; i < num; i++) {
> +		grec = (void *)(skb->data + len);
>  		len += sizeof(*grec);
>  		if (!pskb_may_pull(skb, len))
>  			return -EINVAL;
>  
> -		grec = (void *)(skb->data + len);
>  		group = grec->grec_mca;
>  		type = grec->grec_type;
>  

If pskb_may_pull() actually does anything non-trivial,
skb->data will change and you'll be referring to freed
up memory.

That's probably why you had the grec assignment where
you originally had it in the first place :-)
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