netdev - Re: mac80211 truesize bugs

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Message-ID: <20080501110253.GC7490@gondor.apana.org.au>
Date:	Thu, 1 May 2008 19:02:53 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Miller <davem@...emloft.net>
Cc:	johannes@...solutions.net, mb@...sch.de, netdev@...r.kernel.org,
	linux-wireless@...r.kernel.org
Subject: Re: mac80211 truesize bugs

On Thu, May 01, 2008 at 03:49:50AM -0700, David Miller wrote:
>
> Once that is cured, I think we can detect this better, by adding a
> carefully constructed assertion to pskb_expand_head().  Basically, the
> idea is, if "nhead" or "ntail" are non-zero, and there is a socket
> still attached to the SKB, print a warning message.
> 
> Something like:
> 
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 4fe605f..9bfca08 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -699,6 +699,12 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
>  	if (skb_shared(skb))
>  		BUG();
>  
> +	if (unlikely((nhead || ntail) && skb->sk)) {
> +		printk(KERN_ERR "SKB BUG: Illegal pskb expand (%d:%d) "
> +		       "with socket attached\n",
> +		       nhead, ntail);
> +	}

This could actually work :) I was worried about tunnelling doing
a genuine expansion on such a packet but it turns that it does a
skb_clone first.  So perhaps we should just require that if a
packet is to be expanded while attached to a socket then it must
be cloned first.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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