From: Florian Westphal <fw@strlen•de>
To: Antoine Tenart <atenart@kernel•org>
Cc: kuba@kernel•org, pablo@netfilter•org, kadlec@netfilter•org,
fw@strlen•de, roopa@nvidia•com, nikolay@nvidia•com,
netdev@vger•kernel.org, netfilter-devel@vger•kernel.org,
coreteam@netfilter•org, sbrivio@redhat•com
Subject: Re: [PATCH net-next] netfilter: bridge: reset skb->pkt_type after NF_INET_POST_ROUTING traversal
Date: Mon, 23 Nov 2020 19:32:53 +0100 [thread overview]
Message-ID: <20201123183253.GA2730@breakpoint.cc> (raw)
In-Reply-To: <20201123174902.622102-1-atenart@kernel.org>
Antoine Tenart <atenart@kernel•org> wrote:
> Netfilter changes PACKET_OTHERHOST to PACKET_HOST before invoking the
> hooks as, while it's an expected value for a bridge, routing expects
> PACKET_HOST. The change is undone later on after hook traversal. This
> can be seen with pairs of functions updating skb>pkt_type and then
> reverting it to its original value:
>
> For hook NF_INET_PRE_ROUTING:
> setup_pre_routing / br_nf_pre_routing_finish
>
> For hook NF_INET_FORWARD:
> br_nf_forward_ip / br_nf_forward_finish
>
> But the third case where netfilter does this, for hook
> NF_INET_POST_ROUTING, the packet type is changed in br_nf_post_routing
> but never reverted. A comment says:
>
> /* We assume any code from br_dev_queue_push_xmit onwards doesn't care
> * about the value of skb->pkt_type. */
[..]
> But when having a tunnel (say vxlan) attached to a bridge we have the
> following call trace:
> In this specific case, this creates issues such as when an ICMPv6 PTB
> should be sent back. When CONFIG_BRIDGE_NETFILTER is enabled, the PTB
> isn't sent (as skb_tunnel_check_pmtu checks if pkt_type is PACKET_HOST
> and returns early).
>
> If the comment is right and no one cares about the value of
> skb->pkt_type after br_dev_queue_push_xmit (which isn't true), resetting
> it to its original value should be safe.
That comment is 18 years old, safe bet noone thought of
ipv6-in-tunnel-interface-added-as-bridge-port back then.
Reviewed-by: Florian Westphal <fw@strlen•de>
next prev parent reply other threads:[~2020-11-23 18:33 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-23 17:49 [PATCH net-next] netfilter: bridge: reset skb->pkt_type after NF_INET_POST_ROUTING traversal Antoine Tenart
2020-11-23 18:32 ` Florian Westphal [this message]
2020-11-28 0:06 ` Jakub Kicinski
2020-11-28 9:59 ` Florian Westphal
2020-11-28 19:49 ` Jakub Kicinski
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