Revision a82c25c366b0963d33ddf699196e6cf57f6d89b1 authored by Florian Westphal on 08 March 2022, 12:52:11 UTC, committed by Florian Westphal on 08 March 2022, 12:52:11 UTC
This reverts commit 878aed8db324bec64f3c3f956e64d5ae7375a5de.

This change breaks existing setups where conntrack is used with
asymmetric paths.

In these cases, the NAT transformation occurs on the syn-ack instead of
the syn:

1. SYN    x:12345 -> y -> 443 // sent by initiator, receiverd by responder
2. SYNACK y:443 -> x:12345 // First packet seen by conntrack, as sent by responder
3. tuple_force_port_remap() gets called, sees:
  'tcp from 443 to port 12345 NAT' -> pick a new source port, inititor receives
4. SYNACK y:$RANDOM -> x:12345   // connection is never established

While its possible to avoid the breakage with NOTRACK rules, a kernel
update should not break working setups.

An alternative to the revert is to augment conntrack to tag
mid-stream connections plus more code in the nat core to skip NAT
for such connections, however, this leads to more interaction/integration
between conntrack and NAT.

Therefore, revert, users will need to add explicit nat rules to avoid
port shadowing.

Link: https://lore.kernel.org/netfilter-devel/20220302105908.GA5852@breakpoint.cc/#R
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2051413
Signed-off-by: Florian Westphal <fw@strlen.de>
1 parent f8e9bd3
Raw File
xt_mark.c
// SPDX-License-Identifier: GPL-2.0-only
/*
 *	xt_mark - Netfilter module to match NFMARK value
 *
 *	(C) 1999-2001 Marc Boucher <marc@mbsi.ca>
 *	Copyright © CC Computer Consultants GmbH, 2007 - 2008
 *	Jan Engelhardt <jengelh@medozas.de>
 */

#include <linux/module.h>
#include <linux/skbuff.h>

#include <linux/netfilter/xt_mark.h>
#include <linux/netfilter/x_tables.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
MODULE_DESCRIPTION("Xtables: packet mark operations");
MODULE_ALIAS("ipt_mark");
MODULE_ALIAS("ip6t_mark");
MODULE_ALIAS("ipt_MARK");
MODULE_ALIAS("ip6t_MARK");
MODULE_ALIAS("arpt_MARK");

static unsigned int
mark_tg(struct sk_buff *skb, const struct xt_action_param *par)
{
	const struct xt_mark_tginfo2 *info = par->targinfo;

	skb->mark = (skb->mark & ~info->mask) ^ info->mark;
	return XT_CONTINUE;
}

static bool
mark_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
	const struct xt_mark_mtinfo1 *info = par->matchinfo;

	return ((skb->mark & info->mask) == info->mark) ^ info->invert;
}

static struct xt_target mark_tg_reg __read_mostly = {
	.name           = "MARK",
	.revision       = 2,
	.family         = NFPROTO_UNSPEC,
	.target         = mark_tg,
	.targetsize     = sizeof(struct xt_mark_tginfo2),
	.me             = THIS_MODULE,
};

static struct xt_match mark_mt_reg __read_mostly = {
	.name           = "mark",
	.revision       = 1,
	.family         = NFPROTO_UNSPEC,
	.match          = mark_mt,
	.matchsize      = sizeof(struct xt_mark_mtinfo1),
	.me             = THIS_MODULE,
};

static int __init mark_mt_init(void)
{
	int ret;

	ret = xt_register_target(&mark_tg_reg);
	if (ret < 0)
		return ret;
	ret = xt_register_match(&mark_mt_reg);
	if (ret < 0) {
		xt_unregister_target(&mark_tg_reg);
		return ret;
	}
	return 0;
}

static void __exit mark_mt_exit(void)
{
	xt_unregister_match(&mark_mt_reg);
	xt_unregister_target(&mark_tg_reg);
}

module_init(mark_mt_init);
module_exit(mark_mt_exit);
back to top