bridge: Fix incorrect re-injection of LLDP packets

Commit 8626c56c ("bridge: fix potential use-after-free when hook
returns QUEUE or STOLEN verdict") caused LLDP packets arriving through a
bridge port to be re-injected to the Rx path with skb->dev set to the
bridge device, but this breaks the lldpad daemon.

The lldpad daemon opens a packet socket with protocol set to ETH_P_LLDP
for any valid device on the system, which doesn't not include soft
devices such as bridge and VLAN.

Since packet sockets (ptype_base) are processed in the Rx path after the
Rx handler, LLDP packets with skb->dev set to the bridge device never
reach the lldpad daemon.

Fix this by making the bridge's Rx handler re-inject LLDP packets with
RX_HANDLER_PASS, which effectively restores the behaviour prior to the
mentioned commit.

This means netfilter will never receive LLDP packets coming through a
bridge port, as I don't see a way in which we can have okfn() consume
the packet without breaking existing behaviour. I've already carried out
a similar fix for STP packets in commit 56fae404 ("bridge: Fix
incorrect re-injection of STP packets").

Fixes: 8626c56c ("bridge: fix potential use-after-free when hook returns QUEUE or STOLEN verdict")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Cc: Florian Westphal <fw@strlen.de>
Cc: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_input.c

@@ -283,6 +283,14 @@ rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
 		case 0x01:	/* IEEE MAC (Pause) */
 			goto drop;
 
+		case 0x0E:	/* 802.1AB LLDP */
+			fwd_mask |= p->br->group_fwd_mask;
+			if (fwd_mask & (1u << dest[5]))
+				goto forward;
+			*pskb = skb;
+			__br_handle_local_finish(skb);
+			return RX_HANDLER_PASS;
+
 		default:
 			/* Allow selective forwarding for most other protocols */
 			fwd_mask |= p->br->group_fwd_mask;