From: Pablo Neira Ayuso <pablo@netfilter.org>
To: Florian Westphal <fw@strlen.de>
Cc: Ren Wei <n05ec@lzu.edu.cn>,
netfilter-devel@vger.kernel.org, phil@nwl.cc,
yuantan098@gmail.com, yifanwucs@gmail.com,
tomapufckgml@gmail.com, zcliangcn@gmail.com, bird@lzu.edu.cn,
bronzed_45_vested@icloud.com
Subject: Re: [PATCH nf 1/1] netfilter: xt_nat: reject unsupported target families
Date: Sun, 14 Jun 2026 00:15:14 +0200 [thread overview]
Message-ID: <ai3WcsS00Rbjy61u@chamomile> (raw)
In-Reply-To: <ai3TGFyMlkS1m8O3@strlen.de>
On Sun, Jun 14, 2026 at 12:00:56AM +0200, Florian Westphal wrote:
> Florian Westphal <fw@strlen.de> wrote:
> > Ren Wei <n05ec@lzu.edu.cn> wrote:
> > > xt_nat SNAT and DNAT target handlers assume IP-family conntrack state
> > > is present and can dereference a NULL pointer when instantiated from an
> > > unsupported family through nft_compat. A bridge-family compat rule can
> > > therefore trigger a NULL-dereference in nf_nat_setup_info().
> >
> > Are you sure this is related to nft_compat? What prevents attaching
> > -j D|SNAT to classic ebtables?
> >
> > > Reject non-IP families in xt_nat_checkentry() so unsupported targets
> > > cannot be installed. Keep NFPROTO_INET allowed for valid inet NAT
> > > compat users and leave the runtime fast path unchanged.
> >
> > Not so sure, I don't think there is harm in allowing NFPROTO_INET but
> > such users should not exist.
> >
> > Patch is fine. There are already many different targets here,
> > I don't think we should do a NFPROTO_IPV4 / IPV6 split in this case.
>
> I take that back. This problem goes beyond xt_nat.c; see
> 11ff7288beb2 ("netfilter: ebtables: reject non-bridge targets")
>
> Can you make a patch like this one for nft_compat?
> We can only use NFPROTO_BRIDGE targets, never UNSPEC, for NF_BRIDGE
> caller.
Maybe it is simply this patch:
commit b6fe26f86a1649f84e057f3f15605b08eda15497
Author: Pablo Neira Ayuso <pablo@netfilter.org>
Date: Wed Apr 15 12:21:00 2026 +0200
netfilter: xtables: restrict several matches to inet family
which was missing xt_nat.c?
next prev parent reply other threads:[~2026-06-13 22:15 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-13 10:27 [PATCH nf 0/1] netfilter: xt_nat: bridge nft_compat rule can trigger NULL-deref Ren Wei
2026-06-13 10:27 ` [PATCH nf 1/1] netfilter: xt_nat: reject unsupported target families Ren Wei
2026-06-13 21:31 ` Florian Westphal
2026-06-13 22:00 ` Florian Westphal
2026-06-13 22:15 ` Pablo Neira Ayuso [this message]
2026-06-13 22:25 ` Florian Westphal
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