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Date:	Thu, 01 May 2008 13:38:33 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	David Miller <davem@...emloft.net>
Cc:	herbert@...dor.apana.org.au, mb@...sch.de, netdev@...r.kernel.org,
	linux-wireless@...r.kernel.org
Subject: Re: mac80211 truesize bugs


> That makes more sense, good catch Herbert.
> 
> I guess it's the pskb_expand_head() calls done by net/mac80211/tx.c
> I suspect we'll need to orphan early in order to accomodate these
> adjustments, otherwise socket memory buffer allocations will
> be corrupted.
> 
> 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);
> +	}
> +
>  	size = SKB_DATA_ALIGN(size);

Ok I think I'm starting to understand this a little better. However,
shouldn't this function update skb->truesize so if the skb is later
attached to a different socket again it has the right size?

johannes

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