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Date:   Thu, 19 Mar 2020 11:52:48 +0100
From:   Florian Westphal <fw@strlen.de>
To:     Pablo Neira Ayuso <pablo@netfilter.org>
Cc:     Florian Westphal <fw@strlen.de>,
        Martin Zaharinov <micron10@gmail.com>,
        netfilter-devel@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: Bug URGENT Report with new kernel 5.5.10-5.6-rc6
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Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> On Thu, Mar 19, 2020 at 11:34:38AM +0100, Florian Westphal wrote:
> > Martin Zaharinov <micron10@gmail.com> wrote:
> > 
> > [ trimming CC ]
> > 
> > Please revert
> > 
> > commit 28f8bfd1ac948403ebd5c8070ae1e25421560059
> > netfilter: Support iif matches in POSTROUTING
> 
> Please, specify a short description to append to the revert.

TCP makes use of the rb_node in sk_buff for its retransmit queue,
amongst others.  skb->dev aliases to this storage, i.e., passing
skb->dev as the input interface in postrouting may point to another
sk_buff instead.
This will cause crashes and data corruption with nf_queue, as we will
attempt to increment a random pcpu variable when calling dev_hold().

Also, the memory address may also be free'd, which gives UAF splat.