From: Florian Westphal <fw@strlen.de>
To: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: netfilter-devel@vger.kernel.org
Subject: Re: [PATCH nf] netfilter: nft_payload: restrict checksum offsets to known values
Date: Wed, 21 Oct 2026 11:03:41 +0200 [thread overview]
Message-ID: <ath_7a3pT6AOj0_l@strlen.de> (raw)
In-Reply-To: <ath6GRzpTiUBUS1B@chamomile>
Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> On Fri, Sep 04, 2026 at 11:57:23AM +0200, Florian Westphal wrote:
> > We need to prevent userspace from corrupting e.g. tcp->doff, because
> > many locations in conntrack and conntrack helpers rely on
> > nf_conntrack_in() having validated the packet headers.
> > nft_payload allows to alter headers later which invalidates this
> > assumption.
> >
> > The 'Fixes' commit restricts writes to safe fields, but there is
> > another side channel: the checksum location.
> >
> > Restrict this too. Reported via sashiko/gemini.
> >
> > v2: add missing IPPROTO_ICMP handling, else 'icmp code set 42' won't
> > update icmp checksum.
>
> This patch is now upstream.
>
> Would it be possible to fully/partially revert this patch?
>
> commit 968cc2c96390f06e56ed6a43f935bfebdefed28f
> Author: Florian Westphal <fw@strlen.de>
> Date: Sat May 16 23:23:21 2026 +0800
>
> netfilter: disable payload mangling in userns
I hope so, I will follow up on this.
next prev parent reply other threads:[~2026-10-21 9:03 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-04 9:57 [PATCH nf] netfilter: nft_payload: restrict checksum offsets to known values Florian Westphal
2026-10-21 8:38 ` Pablo Neira Ayuso
2026-10-21 9:03 ` Florian Westphal [this message]
-- strict thread matches above, loose matches on Subject: below --
2026-08-24 19:28 Florian Westphal
2026-08-24 19:56 ` Florian Westphal
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