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@xxxxxxxxxx>
---
net/bridge/br_netfilter_hooks.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
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;
--
2.28.0
