| Message ID | 20201123174902.622102-1-atenart@kernel.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [net-next] netfilter: bridge: reset skb->pkt_type after NF_INET_POST_ROUTING traversal | expand |
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>
On Mon, 23 Nov 2020 19:32:53 +0100 Florian Westphal wrote: > 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> Sounds like a fix. Probably hard to pin point which commit to blame, but this should go to net, not net-next, right?
Jakub Kicinski <kuba@kernel.org> wrote: > On Mon, 23 Nov 2020 19:32:53 +0100 Florian Westphal wrote: > > 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> > > Sounds like a fix. Probably hard to pin point which commit to blame, > but this should go to net, not net-next, right? The commit predates git history, so probably a good idea to add Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") ... and apply it to net tree.
On Sat, 28 Nov 2020 10:59:29 +0100 Florian Westphal wrote: > Jakub Kicinski <kuba@kernel.org> wrote: > > On Mon, 23 Nov 2020 19:32:53 +0100 Florian Westphal wrote: > > > 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> > > > > Sounds like a fix. Probably hard to pin point which commit to blame, > > but this should go to net, not net-next, right? > > The commit predates git history, so probably a good idea to add > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > > ... and apply it to net tree. Done, thanks!
diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_hooks.c index 04c3f9a82650..8edfb98ae1d5 100644 --- a/net/bridge/br_netfilter_hooks.c +++ b/net/bridge/br_netfilter_hooks.c @@ -735,6 +735,11 @@ static int br_nf_dev_queue_xmit(struct net *net, struct sock *sk, struct sk_buff mtu_reserved = nf_bridge_mtu_reduction(skb); mtu = skb->dev->mtu; + if (nf_bridge->pkt_otherhost) { + skb->pkt_type = PACKET_OTHERHOST; + nf_bridge->pkt_otherhost = false; + } + if (nf_bridge->frag_max_size && nf_bridge->frag_max_size < mtu) mtu = nf_bridge->frag_max_size; @@ -835,8 +840,6 @@ static unsigned int br_nf_post_routing(void *priv, else return NF_ACCEPT; - /* We assume any code from br_dev_queue_push_xmit onwards doesn't care - * about the value of skb->pkt_type. */ if (skb->pkt_type == PACKET_OTHERHOST) { skb->pkt_type = PACKET_HOST; nf_bridge->pkt_otherhost = true;
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: br_nf_pre_routing br_nf_pre_routing_ipv6 br_nf_pre_routing_finish br_nf_forward_ip br_nf_forward_finish br_nf_post_routing <- pkt_type is updated to PACKET_HOST br_nf_dev_queue_xmit <- but not reverted to its original value vxlan_xmit vxlan_xmit_one skb_tunnel_check_pmtu <- a check on pkt_type is performed 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. Signed-off-by: Antoine Tenart <atenart@kernel.org> --- net/bridge/br_netfilter_hooks.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)