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Date: Tue, 4 Aug 2026 12:21:03 +0200
From: Florian Westphal <fw@strlen.de>
To: David Lee <david.lee@trailofbits.com>
Cc: pablo@netfilter.org, davem@davemloft.net, edumazet@google.com,
	kuba@kernel.org, pabeni@redhat.com, Kyle Zeng <kylebot@openai.com>,
	Dominik 'Disconnect3d' Czarnota <dominik.czarnota@trailofbits.com>,
	phil@nwl.cc, horms@kernel.org, netfilter-devel@vger.kernel.org,
	coreteam@netfilter.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH nf] netfilter: nf_reject_ipv4: initialize IPCB at inet
 ingress
Message-ID: <anG9D4P33SG9uubK@strlen.de>
References: <20260804095105.715387-1-david.lee@trailofbits.com>
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In-Reply-To: <20260804095105.715387-1-david.lee@trailofbits.com>

David Lee <david.lee@trailofbits.com> wrote:
> From: Kyle Zeng <kylebot@openai.com>
> 
> The inet ingress hook runs before ip_rcv_core(), so IPCB has not been
> initialized when nft_reject_inet passes an IPv4 packet to
> nf_send_unreach(). skb->cb can therefore retain data from an earlier
> protocol layer.
> 
> icmp_send() treats IPCB(skb)->opt as parsed IPv4 options. Stale option
> offsets can make __ip_options_echo() copy an attacker-controlled length
> into its 40-byte reply option buffer and overflow the stack.
> 
> Clear IPCB for NF_INET_INGRESS and restore its input interface, matching
> the initialization normally performed by ip_rcv_core().

Will you also send a patch for net/ipv6/netfilter/nf_reject_ipv6.c ?

Or: send a v2 that also fixes this up,
Or: send a v2 that mentions why net/ipv6/netfilter/nf_reject_ipv6.c is
fine (I doubt it).