kernel: backport fix for initializing skb->cb in the bridge code to 5.4

Fixes issues with proxyarp

Signed-off-by: Felix Fietkau <nbd@nbd.name>

1 files changed, 28 insertions, 0 deletions

diff --git a/target/linux/generic/backport-5.4/610-v5.9-net-bridge-clear-bridge-s-private-skb-space-on-xmit.patch b/target/linux/generic/backport-5.4/610-v5.9-net-bridge-clear-bridge-s-private-skb-space-on-xmit.patch
new file mode 100644
index 0000000000..f1862943f8
--- /dev/null
+++ b/target/linux/generic/backport-5.4/610-v5.9-net-bridge-clear-bridge-s-private-skb-space-on-xmit.patch
@@ -0,0 +1,28 @@
+From: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
+Date: Fri, 31 Jul 2020 19:26:16 +0300
+Subject: [PATCH] net: bridge: clear bridge's private skb space on xmit
+
+We need to clear all of the bridge private skb variables as they can be
+stale due to the packet being recirculated through the stack and then
+transmitted through the bridge device. Similar memset is already done on
+bridge's input. We've seen cases where proxyarp_replied was 1 on routed
+multicast packets transmitted through the bridge to ports with neigh
+suppress which were getting dropped. Same thing can in theory happen with
+the port isolation bit as well.
+
+Fixes: 821f1b21cabb ("bridge: add new BR_NEIGH_SUPPRESS port flag to suppress arp and nd flood")
+Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+
+--- a/net/bridge/br_device.c
++++ b/net/bridge/br_device.c
+@@ -36,6 +36,8 @@ netdev_tx_t br_dev_xmit(struct sk_buff *
+ 	struct ethhdr *eth;
+ 	u16 vid = 0;
+ 
++	memset(skb->cb, 0, sizeof(struct br_input_skb_cb));
++
+ 	rcu_read_lock();
+ 	nf_ops = rcu_dereference(nf_br_ops);
+ 	if (nf_ops && nf_ops->br_dev_xmit_hook(skb)) {