From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from Chamillionaire.breakpoint.cc (Chamillionaire.breakpoint.cc [91.216.245.30]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E956047CA87 for ; Thu, 27 Aug 2026 17:44:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.216.245.30 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787852661; cv=none; b=isyVDVMWnkirJKfmeqyOsXVEC6nnzIB7jiHzPelMR05OPrPn6p1Zyv96+rnDMKstsnpIrkDUHCOOiN7ytC64vZt4eae+DO+CmseADnvz+ky9Qgot1O4mB+bPJAMwVb/15zIrRFh0H7xg6n9tUmuuxM8tvOhtJk3fKIKqGehyaXg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787852661; c=relaxed/simple; bh=4QTyasIJPc5xQgemtKv3Y8i446gOKFj9+foRq5BZeDg=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=RGKgAZezxiUW/zGBvjmFUtO1qezBBwOENguiijzhatO29TFtU0KWGxGGVO3lZy5stncSh6I+XwwEnhRODSij5HTl9UmpiwLK6BReEL2XX316l+2rys7GAiSswgTSetOdUk5p4V0gFx3z7y3BkWaIG3z68LCqsXJnRExPCd2Vb0I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=strlen.de; spf=pass smtp.mailfrom=Chamillionaire.breakpoint.cc; arc=none smtp.client-ip=91.216.245.30 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=strlen.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=Chamillionaire.breakpoint.cc Received: by Chamillionaire.breakpoint.cc (Postfix, from userid 1003) id 191F7602F5; Thu, 27 Aug 2026 19:44:10 +0200 (CEST) From: Florian Westphal To: Cc: Florian Westphal , Nikolay Aleksandrov Subject: [PATCH nf] netfilter: disable br_netfilter in user namespaces Date: Thu, 27 Aug 2026 19:41:10 +0200 Message-ID: <20260827174110.11894-1-fw@strlen.de> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: netfilter-devel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit br_netfilter has way too many bugs, schedule for removal and disable the feature in user namespaces. In particular, we get more and more gadgets to have bridge ports escape rcu_read_lock() protection, then underlying device gets reconfigured (macvlan or something else), then reinject into network stack causes crash because net_device is assumed to still have bridge rx data associated with it. br_netfilter is an ancient kludge that emulates ip stack from within the bridge and then calls into ipv4/ipv6 netfilter hooks to have bridged frames processed via iptables/ip6tables by setting the 'call-iptables' sysctls to 1. It is NOT related to ebtables or nftables 'bridge' family at all. Note that in addition to call-iptables, sysctls, the bridge itself exposes call-iptables per port via netlink and sysfs ('BROPT_NF_CALL_IPTABLES') toggles. Those are still available, the brnet structure is scoped to br_netfilter; exposing it bridge-wide is a big no-no. This relies on brnf_device_event() no longer registering the base br_netfilter hooks, so while BROPT_NF_CALL_IPTABLES can be set, it has no effect because the hooks that evaluate this feature bit are never registered. brnf_init_net can no longer depend on CONFIG_SYSCTL, else such builds never disable support in user namespaces. Cc: Nikolay Aleksandrov Signed-off-by: Florian Westphal --- net/bridge/br_netfilter_hooks.c | 33 ++++++++++++++++++++++----------- 1 file changed, 22 insertions(+), 11 deletions(-) diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_hooks.c index 0a394e5f4391..b09b9236e617 100644 --- a/net/bridge/br_netfilter_hooks.c +++ b/net/bridge/br_netfilter_hooks.c @@ -54,6 +54,7 @@ static unsigned int brnf_net_id __read_mostly; struct brnf_net { bool enabled; + bool in_userns; #ifdef CONFIG_SYSCTL struct ctl_table_header *ctl_hdr; @@ -1100,7 +1101,7 @@ static int brnf_device_event(struct notifier_block *unused, unsigned long event, net = dev_net(dev); brnet = net_generic(net, brnf_net_id); - if (brnet->enabled) + if (brnet->enabled || brnet->in_userns) return NOTIFY_OK; ret = nf_register_net_hooks(net, br_nf_ops, ARRAY_SIZE(br_nf_ops)); @@ -1229,9 +1230,11 @@ static inline void br_netfilter_sysctl_default(struct brnf_net *brnf) brnf->filter_pppoe_tagged = 0; brnf->pass_vlan_indev = 0; } +#endif static int br_netfilter_sysctl_init_net(struct net *net) { +#ifdef CONFIG_SYSCTL struct ctl_table *table = brnf_table; struct brnf_net *brnet; @@ -1259,25 +1262,37 @@ static int br_netfilter_sysctl_init_net(struct net *net) return -ENOMEM; } - +#endif return 0; } static void br_netfilter_sysctl_exit_net(struct net *net, struct brnf_net *brnet) { - const struct ctl_table *table = brnet->ctl_hdr->ctl_table_arg; +#ifdef CONFIG_SYSCTL + struct ctl_table_header *header = brnet->ctl_hdr; - unregister_net_sysctl_table(brnet->ctl_hdr); + if (!header) + return; + + unregister_net_sysctl_table(header); if (!net_eq(net, &init_net)) - kfree(table); + kfree(header->ctl_table_arg); +#endif } static int __net_init brnf_init_net(struct net *net) { + if (net->user_ns != &init_user_ns) { + struct brnf_net *brnet = net_generic(net, brnf_net_id); + + brnet->in_userns = true; + pr_warn_once("br_netfilter no longer supported in user namespaces\n"); + return 0; + } + return br_netfilter_sysctl_init_net(net); } -#endif static void __net_exit brnf_exit_net(struct net *net) { @@ -1289,15 +1304,11 @@ static void __net_exit brnf_exit_net(struct net *net) brnet->enabled = false; } -#ifdef CONFIG_SYSCTL br_netfilter_sysctl_exit_net(net, brnet); -#endif } static struct pernet_operations brnf_net_ops __read_mostly = { -#ifdef CONFIG_SYSCTL .init = brnf_init_net, -#endif .exit = brnf_exit_net, .id = &brnf_net_id, .size = sizeof(struct brnf_net), @@ -1318,7 +1329,7 @@ static int __init br_netfilter_init(void) } RCU_INIT_POINTER(nf_br_ops, &br_ops); - printk(KERN_NOTICE "Bridge firewalling registered\n"); + pr_warn("br_netfilter is slated for removal in 2027.\n"); return 0; } -- 2.54.0