From: Pablo Neira Ayuso <pablo@netfilter.org>
To: Fernando Fernandez Mancera <fmancera@suse.de>
Cc: netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
phil@nwl.cc, fw@strlen.de
Subject: Re: [PATCH 3/3 nf v5] netfilter: xtables: fix L4 header parsing for non-first fragments
Date: Thu, 30 Apr 2026 08:08:31 +0200 [thread overview]
Message-ID: <afLx347nrAJLqsyf@chamomile> (raw)
In-Reply-To: <20260428102548.6750-3-fmancera@suse.de>
Hi Fernando,
On Tue, Apr 28, 2026 at 12:25:48PM +0200, Fernando Fernandez Mancera wrote:
> Multiple targets and matches relies on L4 header to operate. For
> fragmented packets, every fragment carries the transport protocol
> identifier, but only the first fragment contains the L4 header.
>
> As the 'raw' table can be configured to run at priority -450 (before
> defragmentation at -400), the target/match can be reached before
> reassembly. In this case, non-first fragments have their payload
> incorrectly parsed as a TCP/UDP header. This would be of course a
> misconfiguration scenario. In most of the cases this just lead to a
> unreliable behavior for fragmented traffic.
>
> Add a fragment check to ensure target/match only evaluates unfragmented
> packets or the first fragment in the stream.
One more little issue here: There seems to be an issue in
xt_hashlimit, hashlimit_init_dst() drops packets via hotdrop if it
returns -1.
next prev parent reply other threads:[~2026-04-30 6:08 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-28 10:25 [PATCH 1/3 nf v5] netfilter: nf_socket: skip socket lookup for non-first fragments Fernando Fernandez Mancera
2026-04-28 10:25 ` [PATCH 2/3 nf v5] netfilter: nf_tables: skip L4 header parsing " Fernando Fernandez Mancera
2026-04-28 10:25 ` [PATCH 3/3 nf v5] netfilter: xtables: fix " Fernando Fernandez Mancera
2026-04-30 6:08 ` Pablo Neira Ayuso [this message]
2026-04-30 14:53 ` Fernando Fernandez Mancera
2026-04-30 15:06 ` Pablo Neira Ayuso
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