netfilter: bridge: Don't sabotage nf_hook calls from an l3mdev

BugLink: https://bugs.launchpad.net/bugs/1836654
[ Upstream commit a173f066c7cfc031acb8f541708041e009fc9812 ]

For starters, the bridge netfilter code registers operations that
are invoked any time nh_hook is called. Specifically, ip_sabotage_in
watches for nested calls for NF_INET_PRE_ROUTING when a bridge is in
the stack.

Packet wise, the bridge netfilter hook runs first. br_nf_pre_routing
allocates nf_bridge, sets in_prerouting to 1 and calls NF_HOOK for
NF_INET_PRE_ROUTING. It's finish function, br_nf_pre_routing_finish,
then resets in_prerouting flag to 0 and the packet continues up the
stack. The packet eventually makes it to the VRF driver and it invokes
nf_hook for NF_INET_PRE_ROUTING in case any rules have been added against
the vrf device.

Because of the registered operations the call to nf_hook causes
ip_sabotage_in to be invoked. That function sees the nf_bridge on the
skb and that in_prerouting is not set. Thinking it is an invalid nested
call it steals (drops) the packet.

Update ip_sabotage_in to recognize that the bridge or one of its upper
devices (e.g., vlan) can be enslaved to a VRF (L3 master device) and
allow the packet to go through the nf_hook a second time.

Fixes: 73e20b761acf ("net: vrf: Add support for PREROUTING rules on vrf device")
Reported-by: D'Souza, Nelson <ndsouza@ciena.com>
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_hooks.c
index c2eea1b8737a154f561eba1c46999f351c28b112..7582f28ab3060f609c15339fccd3d5e4fe69e35e 100644 (file)
--- a/net/bridge/br_netfilter_hooks.c
+++ b/net/bridge/br_netfilter_hooks.c
@@ -832,7 +832,8 @@ static unsigned int ip_sabotage_in(void *priv,
                                   struct sk_buff *skb,
                                   const struct nf_hook_state *state)
 {
-       if (skb->nf_bridge && !skb->nf_bridge->in_prerouting) {
+       if (skb->nf_bridge && !skb->nf_bridge->in_prerouting &&
+           !netif_is_l3_master(skb->dev)) {
                state->okfn(state->net, state->sk, skb);
                return NF_STOLEN;
        }