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Date:   Fri, 3 Nov 2023 11:25:46 +0100
From:   Florian Westphal <fw@strlen.de>
To:     Pablo Neira Ayuso <pablo@netfilter.org>
Cc:     Florian Westphal <fw@strlen.de>,
        Dan Carpenter <dan.carpenter@linaro.org>,
        Jozsef Kadlecsik <kadlec@netfilter.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-janitors@vger.kernel.org
Subject: Re: [PATCH net] netfilter: nf_tables: fix pointer math issue in
 nft_byteorder_eval()
Message-ID: <20231103102546.GB8035@breakpoint.cc>
References: <15fdceb5-2de5-4453-98b3-cfa9d486e8da@moroto.mountain>
 <20231103091801.GA8035@breakpoint.cc>
 <ZUTBNcA7ApLu5DMA@calendula>
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Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> On Fri, Nov 03, 2023 at 10:18:01AM +0100, Florian Westphal wrote:
> > Dan Carpenter <dan.carpenter@linaro.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').