[Bridge] [RFC PATCH net-next 1/5] skbuff: bridge: Add layer 2 miss indication

[Ido Schimmel <idosch@nvidia.com>]

Allow the bridge driver to mark packets that did not match a layer 2
entry during forwarding by adding a 'l2_miss' bit to the skb.

Clear the bit whenever a packet enters the bridge (received from a
bridge port or transmitted via the bridge) and set it if the packet did
not match an FDB/MDB entry.

Subsequent patches will allow the flower classifier to match on this
bit. The motivating use case in non-DF (Designated Forwarder) filtering
where we would like to prevent decapsulated packets from being flooded
to a multi-homed host.

Do not allocate the bit if the kernel was not compiled with bridge
support and place it after the two bit fields in accordance with commit
4c60d04c2888 ("net: skbuff: push nf_trace down the bitfield"). The bit
does not increase the size of the structure as it is placed at an
existing hole. Layout with allmodconfig:

struct sk_buff {
[...]
			__u8       csum_not_inet:1;      /*   132: 3  1 */
			__u8       l2_miss:1;            /*   132: 4  1 */

			/* XXX 3 bits hole, try to pack */
			/* XXX 1 byte hole, try to pack */

			__u16      tc_index;             /*   134     2 */
			u16        alloc_cpu;            /*   136     2 */
[...]
} __attribute__((__aligned__(8)));

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
---
 include/linux/skbuff.h  | 4 ++++
 net/bridge/br_device.c  | 1 +
 net/bridge/br_forward.c | 3 +++
 net/bridge/br_input.c   | 1 +
 4 files changed, 9 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 738776ab8838..c7a84767ed48 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -801,6 +801,7 @@ typedef unsigned char *sk_buff_data_t;
  *	@encap_hdr_csum: software checksum is needed
  *	@csum_valid: checksum is already valid
  *	@csum_not_inet: use CRC32c to resolve CHECKSUM_PARTIAL
+ *	@l2_miss: Packet did not match an L2 entry during forwarding
  *	@csum_complete_sw: checksum was completed by software
  *	@csum_level: indicates the number of consecutive checksums found in
  *		the packet minus one that have been verified as
@@ -991,6 +992,9 @@ struct sk_buff {
 #if IS_ENABLED(CONFIG_IP_SCTP)
 	__u8			csum_not_inet:1;
 #endif
+#if IS_ENABLED(CONFIG_BRIDGE)
+	__u8			l2_miss:1;
+#endif
 
 #ifdef CONFIG_NET_SCHED
 	__u16			tc_index;	/* traffic control index */
diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index 8eca8a5c80c6..91dbdae4afd4 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c
@@ -39,6 +39,7 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
 	u16 vid = 0;
 
 	memset(skb->cb, 0, sizeof(struct br_input_skb_cb));
+	skb->l2_miss = 0;
 
 	rcu_read_lock();
 	nf_ops = rcu_dereference(nf_br_ops);
diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
index 57744704ff69..5893648c4da2 100644
--- a/net/bridge/br_forward.c
+++ b/net/bridge/br_forward.c
@@ -203,6 +203,8 @@ void br_flood(struct net_bridge *br, struct sk_buff *skb,
 	struct net_bridge_port *prev = NULL;
 	struct net_bridge_port *p;
 
+	skb->l2_miss = 1;
+
 	list_for_each_entry_rcu(p, &br->port_list, list) {
 		/* Do not flood unicast traffic to ports that turn it off, nor
 		 * other traffic if flood off, except for traffic we originate
@@ -295,6 +297,7 @@ void br_multicast_flood(struct net_bridge_mdb_entry *mdst,
 			allow_mode_include = false;
 	} else {
 		p = NULL;
+		skb->l2_miss = 1;
 	}
 
 	while (p || rp) {
diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
index fc17b9fd93e6..d8ab5890cbe6 100644
--- a/net/bridge/br_input.c
+++ b/net/bridge/br_input.c
@@ -334,6 +334,7 @@ static rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
 		return RX_HANDLER_CONSUMED;
 
 	memset(skb->cb, 0, sizeof(struct br_input_skb_cb));
+	skb->l2_miss = 0;
 
 	p = br_port_get_rcu(skb->dev);
 	if (p->flags & BR_VLAN_TUNNEL)
-- 
2.40.1