From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <JBeulich@suse.com>
Subject: Re: [Xen-devel] [PATCH] xen-netfront: pull on receive skb may
 need to happen earlier
Date: Wed, 10 Jul 2013 11:46:57 +0100
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Cc: <davem@davemloft.net>, "Dion Kant" <g.w.kant@hunenet.nl>,
	<xen-devel@lists.xen.org>, <netdev@vger.kernel.org>,
	<stable@vger.kernel.org>
To: "Ian Campbell" <ian.campbell@citrix.com>,
	"Wei Liu" <wei.liu2@citrix.com>
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>>> On 10.07.13 at 12:04, Wei Liu <wei.liu2@citrix.com> wrote:
> Jan, looking at the commit log, the overrun issue in
> xennet_get_responses was not introduced by __pskb_pull_tail. The call to
> xennet_fill_frags has always been in the same place.

I'm convinced it was: Prior to that commit, if the first response slot
contained up to RX_COPY_THRESHOLD bytes, it got entirely
consumed into the linear portion of the SKB, leaving the number of
fragments available for filling at MAX_SKB_FRAGS. Said commit
dropped the early copying, leaving the fragment count at 1
unconditionally, and now accumulates all of the response slots into
fragments, only pulling after all of them got filled in. It neglected to
realize - due to the count now always being 1 at the beginning - that
this can lead to MAX_SKB_FRAGS + 1 frags getting filled, corrupting
memory.

Ian - I have to admit that I'm slightly irritated by you so far not
having participated at all in sorting out the fix for this bug that a
change of yours introduced.

Jan