netdev - Re: [PATCH net] netfilter: nf_tables: fix pointer math issue in nft_byteorder

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Date: Fri, 3 Nov 2023 11:25:46 +0100
From: Florian Westphal <fw@...len.de>
To: Pablo Neira Ayuso <pablo@...filter.org>
Cc: Florian Westphal <fw@...len.de>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Jozsef Kadlecsik <kadlec@...filter.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net] netfilter: nf_tables: fix pointer math issue in
 nft_byteorder_eval()

Pablo Neira Ayuso <pablo@...filter.org> wrote:
> On Fri, Nov 03, 2023 at 10:18:01AM +0100, Florian Westphal wrote:
> > Dan Carpenter <dan.carpenter@...aro.org> wrote:
> > > The problem is in nft_byteorder_eval() where we are iterating through a
> > > loop and writing to dst[0], dst[1], dst[2] and so on...  On each
> > > iteration we are writing 8 bytes.  But dst[] is an array of u32 so each
> > > element only has space for 4 bytes.  That means that every iteration
> > > overwrites part of the previous element.
> > > 
> > > I spotted this bug while reviewing commit caf3ef7468f7 ("netfilter:
> > > nf_tables: prevent OOB access in nft_byteorder_eval") which is a related
> > > issue.  I think that the reason we have not detected this bug in testing
> > > is that most of time we only write one element.
> > 
> > LGTM, thanks Dan.  We will route this via nf.git.
> 
> Thanks for your patch.
> 
> One question, is this update really required?

I think so, yes.  Part of this bug here is that this helper-niceness
masks whats really happening in the caller (advancing in strides of
'u32', rather than 'u64').