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From: Qi Tang <tpluszz77@gmail•com>
To: fw@strlen•de
Cc: jiayuan.chen@linux•dev, pablo@netfilter•org,
	netfilter-devel@vger•kernel.org, davem@davemloft•net,
	kuba@kernel•org, pabeni@redhat•com, edumazet@google•com,
	netdev@vger•kernel.org, dsahern@kernel•org, idosch@nvidia•com,
	horms@kernel•org, lyutoon@gmail•com, stable@vger•kernel.org,
	Qi Tang <tpluszz77@gmail•com>
Subject: Re: [PATCH net] ipv4: validate ip_forward_options() option fields against skb tail
Date: Fri, 29 May 2026 18:43:56 +0800	[thread overview]
Message-ID: <20260529104356.911666-1-tpluszz77@gmail.com> (raw)
In-Reply-To: <ahlfI38aDciPfG2S@strlen.de>

Florian Westphal <fw@strlen•de> wrote:
> I'm not sure netfilter is the only facility that can munge data this
> way nowadays.  The plan is to disable arbitrary network header rewrites:
>
> https://lore.kernel.org/netfilter-devel/20260527121147.22076-1-fw@strlen.de/

Agreed, the source side is the better place for this on mainline.

I went looking for other ways into the window between option compile
(ip_rcv_options() in ip_rcv_finish_core, after PREROUTING) and
ip_forward_options(), and only found nft_payload and nfqueue at the
FORWARD hook. tc/cls-act run before compile (ingress) or after
ip_forward_options (egress), BPF at the netfilter hook can't write the
packet (base helpers only, no bpf_skb_store_bytes), and the LWT_IN BPF
path is blocked by the verifier. So your two-part restriction closes the
only in-tree triggers I could find.

This is just one consumer of the pattern; __ip_options_echo(),
ipmr_cache_report() and the CIPSO/CALIPSO netlbl_skbuff_getattr() path
are the same, posted as a series here:

  https://lore.kernel.org/netdev/20260524041442.2432071-1-tpluszz77@gmail.com/

so if the source-side restriction is the way to go it probably makes
more sense to drop these consumer-side checks than to fix each site.
Your call.

Thanks,
Qi

next prev parent reply	other threads:[~2026-05-29 10:44 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-05-28 11:12 [PATCH net] ipv4: validate ip_forward_options() option fields against skb tail Qi Tang
2026-05-28 13:48 ` Jiayuan Chen
2026-05-28 16:32   ` Qi Tang
2026-05-29  2:55     ` Jiayuan Chen
2026-05-29  9:40       ` Florian Westphal
2026-05-29 10:43         ` Qi Tang [this message]
2026-05-31 12:17           ` Ido Schimmel
2026-06-04  8:46             ` Paolo Abeni

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