netdev - Re: [Bug 9189] New: Oops in kernel 2.6.21-rc4 through 2.6.23, page allocation failure

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Date:	Sun, 21 Oct 2007 16:28:13 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	jheffner@....edu, shemminger@...ux-foundation.org,
	netdev@...r.kernel.org, bugme-daemon@...zilla.kernel.org
Subject: Re: [Bug 9189] New: Oops in kernel 2.6.21-rc4 through 2.6.23, page
 allocation failure

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Sun, 21 Oct 2007 12:56:01 +0800

> [NET]: Fix SKB_WITH_OVERHEAD calculation
> 
> The calculation in SKB_WITH_OVERHEAD is incorrect in that it can cause
> an overflow across a page boundary which is what it's meant to prevent.
> In particular, the header length (X) should not be lumped together with
> skb_shared_info.  The latter needs to be aligned properly while the header
> has no choice but to sit in front of wherever the payload is.
> 
> Therefore the correct calculation is to take away the aligned size of
> skb_shared_info, and then subtract the header length.  The resulting
> quantity L satisfies the following inequality:
> 
> 	SKB_DATA_ALIGN(L + X) + sizeof(struct skb_shared_info) <= PAGE_SIZE
> 
> This is the quantity used by alloc_skb to do the actual allocation.
> 
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

Applied, I'll push this to -stable too, thanks!
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