hsr: Synchronize sequence number updates.

hsr_register_frame_out() compares new sequence_nr vs the old one
recorded in hsr_node::seq_out and if the new sequence_nr is higher then
it will be written to hsr_node::seq_out as the new value.

This operation isn't locked so it is possible that two frames with the
same sequence number arrive (via the two slave devices) and are fed to
hsr_register_frame_out() at the same time. Both will pass the check and
update the sequence counter later to the same value. As a result the
content of the same packet is fed into the stack twice.

This was noticed by running ping and observing DUP being reported from
time to time.

Instead of using the hsr_priv::seqnr_lock for the whole receive path (as
it is for sending in the master node) add an additional lock that is only
used for sequence number checks and updates.

Add a per-node lock that is used during sequence number reads and
updates.

Fixes: f421436a591d3 ("net/hsr: Add support for the High-availability Seamless Redundancy protocol (HSRv0)")
Signed-off-by: Sebastian Andrzej Siewior <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

net/hsr/hsr_framereg.c

···
 		return NULL;
 
 	ether_addr_copy(new_node->macaddress_A, addr);
+	spin_lock_init(&new_node->seq_out_lock);
 
 	/* We are only interested in time diffs here, so use current jiffies
 	 * as initialization. (0 could trigger an spurious ring error warning).
···
 	}
 
 	ether_addr_copy(node_real->macaddress_B, ethhdr->h_source);
+	spin_lock_bh(&node_real->seq_out_lock);
 	for (i = 0; i < HSR_PT_PORTS; i++) {
 		if (!node_curr->time_in_stale[i] &&
 		    time_after(node_curr->time_in[i], node_real->time_in[i])) {
···
 		if (seq_nr_after(node_curr->seq_out[i], node_real->seq_out[i]))
 			node_real->seq_out[i] = node_curr->seq_out[i];
 	}
+	spin_unlock_bh(&node_real->seq_out_lock);
 	node_real->addr_B_port = port_rcv->type;
 
 	spin_lock_bh(&hsr->list_lock);
···
 int hsr_register_frame_out(struct hsr_port *port, struct hsr_node *node,
 			   u16 sequence_nr)
 {
+	spin_lock_bh(&node->seq_out_lock);
 	if (seq_nr_before_or_eq(sequence_nr, node->seq_out[port->type]) &&
 	    time_is_after_jiffies(node->time_out[port->type] +
-	    msecs_to_jiffies(HSR_ENTRY_FORGET_TIME)))
+	    msecs_to_jiffies(HSR_ENTRY_FORGET_TIME))) {
+		spin_unlock_bh(&node->seq_out_lock);
 		return 1;
+	}
 
 	node->time_out[port->type] = jiffies;
 	node->seq_out[port->type] = sequence_nr;
+	spin_unlock_bh(&node->seq_out_lock);
 	return 0;
 }
 

net/hsr/hsr_framereg.h

···
 
 struct hsr_node {
 	struct list_head	mac_list;
+	/* Protect R/W access to seq_out */
+	spinlock_t		seq_out_lock;
 	unsigned char		macaddress_A[ETH_ALEN];
 	unsigned char		macaddress_B[ETH_ALEN];
 	/* Local slave through which AddrB frames are received from this node */