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From: Florian Westphal <fw@strlen.de>
To: Florian Westphal <fw@strlen.de>
Cc: netfilter-devel@vger.kernel.org, eric@garver.life, phil@nwl.cc,
	kadlec@netfilter.org
Subject: Re: [PATCH RFC 2/2] netfilter: nf_nat: don't allow source ports that shadow local port
Date: Fri, 1 Oct 2021 15:21:28 +0200	[thread overview]
Message-ID: <20211001132128.GG2935@breakpoint.cc> (raw)
In-Reply-To: <20210923131243.24071-3-fw@strlen.de>

Florian Westphal <fw@strlen.de> wrote:
> PoC, incomplete -- ipv4 udp only.
> 
> Ipv6 support needs help from ipv6 indirection infra.
> 
> Also lacks direction support: the check should only be done
> for nf_conn objects created by externally generated packets.
 
Alternate fix idea:

1. store skb->skb_iif in nf_conn.

This means locally vs. remote-generated nf_conn can be identified
via ct->skb_iff != 0.

2. For "remote" case, force following behaviour:
   check that sport > dport and sport > 1024.

OTOH, this isn't transparent to users and might cause issues
with very very old "credential passing" applications that insist
on using privileged port range (< 1024) :-/

  reply	other threads:[~2021-10-01 13:21 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-23 13:12 [PATCH nf 0/1.5 RFC] netfilter: nat: source port shadowing Florian Westphal
2021-09-23 13:12 ` [PATCH nf 1/2] selftests: nft_nat: add udp hole punch test case Florian Westphal
2021-10-11 23:42   ` Pablo Neira Ayuso
2021-09-23 13:12 ` [PATCH RFC 2/2] netfilter: nf_nat: don't allow source ports that shadow local port Florian Westphal
2021-10-01 13:21   ` Florian Westphal [this message]
2021-10-04 10:16     ` Pablo Neira Ayuso
2021-10-04 10:41       ` Florian Westphal

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