net: hsr: Fix PRP duplicate detection

Add PRP specific function for handling duplicate
packets. This is needed because of potential
L2 802.1p prioritization done by network switches.

The L2 prioritization can re-order the PRP packets
from a node causing the existing implementation to
discard the frame(s) that have been received 'late'
because the sequence number is before the previous
received packet. This can happen if the node is
sending multiple frames back-to-back with different
priority.

Signed-off-by: Jaakko Karrenpalo <jkarrenpalo@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250307161700.1045-1-jkarrenpalo@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 92 insertions, 3 deletions

diff --git a/net/hsr/hsr_framereg.c b/net/hsr/hsr_framereg.c
index 73bc6f659812..85991fab7db5 100644
--- a/net/hsr/hsr_framereg.c
+++ b/net/hsr/hsr_framereg.c
@@ -35,6 +35,7 @@ static bool seq_nr_after(u16 a, u16 b)
 
 #define seq_nr_before(a, b)		seq_nr_after((b), (a))
 #define seq_nr_before_or_eq(a, b)	(!seq_nr_after((a), (b)))
+#define PRP_DROP_WINDOW_LEN 32768
 
 bool hsr_addr_is_redbox(struct hsr_priv *hsr, unsigned char *addr)
 {
@@ -176,8 +177,11 @@ static struct hsr_node *hsr_add_node(struct hsr_priv *hsr,
 		new_node->time_in[i] = now;
 		new_node->time_out[i] = now;
 	}
-	for (i = 0; i < HSR_PT_PORTS; i++)
+	for (i = 0; i < HSR_PT_PORTS; i++) {
 		new_node->seq_out[i] = seq_out;
+		new_node->seq_expected[i] = seq_out + 1;
+		new_node->seq_start[i] = seq_out + 1;
+	}
 
 	if (san && hsr->proto_ops->handle_san_frame)
 		hsr->proto_ops->handle_san_frame(san, rx_port, new_node);
@@ -482,9 +486,11 @@ void hsr_register_frame_in(struct hsr_node *node, struct hsr_port *port,
  *	 0 otherwise, or
  *	 negative error code on error
  */
-int hsr_register_frame_out(struct hsr_port *port, struct hsr_node *node,
-			   u16 sequence_nr)
+int hsr_register_frame_out(struct hsr_port *port, struct hsr_frame_info *frame)
 {
+	struct hsr_node *node = frame->node_src;
+	u16 sequence_nr = frame->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] +
@@ -499,6 +505,89 @@ int hsr_register_frame_out(struct hsr_port *port, struct hsr_node *node,
 	return 0;
 }
 
+/* Adaptation of the PRP duplicate discard algorithm described in wireshark
+ * wiki (https://wiki.wireshark.org/PRP)
+ *
+ * A drop window is maintained for both LANs with start sequence set to the
+ * first sequence accepted on the LAN that has not been seen on the other LAN,
+ * and expected sequence set to the latest received sequence number plus one.
+ *
+ * When a frame is received on either LAN it is compared against the received
+ * frames on the other LAN. If it is outside the drop window of the other LAN
+ * the frame is accepted and the drop window is updated.
+ * The drop window for the other LAN is reset.
+ *
+ * 'port' is the outgoing interface
+ * 'frame' is the frame to be sent
+ *
+ * Return:
+ *	 1 if frame can be shown to have been sent recently on this interface,
+ *	 0 otherwise
+ */
+int prp_register_frame_out(struct hsr_port *port, struct hsr_frame_info *frame)
+{
+	enum hsr_port_type other_port;
+	enum hsr_port_type rcv_port;
+	struct hsr_node *node;
+	u16 sequence_diff;
+	u16 sequence_exp;
+	u16 sequence_nr;
+
+	/* out-going frames are always in order
+	 * and can be checked the same way as for HSR
+	 */
+	if (frame->port_rcv->type == HSR_PT_MASTER)
+		return hsr_register_frame_out(port, frame);
+
+	/* for PRP we should only forward frames from the slave ports
+	 * to the master port
+	 */
+	if (port->type != HSR_PT_MASTER)
+		return 1;
+
+	node = frame->node_src;
+	sequence_nr = frame->sequence_nr;
+	sequence_exp = sequence_nr + 1;
+	rcv_port = frame->port_rcv->type;
+	other_port = rcv_port == HSR_PT_SLAVE_A ? HSR_PT_SLAVE_B :
+				 HSR_PT_SLAVE_A;
+
+	spin_lock_bh(&node->seq_out_lock);
+	if (time_is_before_jiffies(node->time_out[port->type] +
+	    msecs_to_jiffies(HSR_ENTRY_FORGET_TIME)) ||
+	    (node->seq_start[rcv_port] == node->seq_expected[rcv_port] &&
+	     node->seq_start[other_port] == node->seq_expected[other_port])) {
+		/* the node hasn't been sending for a while
+		 * or both drop windows are empty, forward the frame
+		 */
+		node->seq_start[rcv_port] = sequence_nr;
+	} else if (seq_nr_before(sequence_nr, node->seq_expected[other_port]) &&
+		   seq_nr_before_or_eq(node->seq_start[other_port], sequence_nr)) {
+		/* drop the frame, update the drop window for the other port
+		 * and reset our drop window
+		 */
+		node->seq_start[other_port] = sequence_exp;
+		node->seq_expected[rcv_port] = sequence_exp;
+		node->seq_start[rcv_port] = node->seq_expected[rcv_port];
+		spin_unlock_bh(&node->seq_out_lock);
+		return 1;
+	}
+
+	/* update the drop window for the port where this frame was received
+	 * and clear the drop window for the other port
+	 */
+	node->seq_start[other_port] = node->seq_expected[other_port];
+	node->seq_expected[rcv_port] = sequence_exp;
+	sequence_diff = sequence_exp - node->seq_start[rcv_port];
+	if (sequence_diff > PRP_DROP_WINDOW_LEN)
+		node->seq_start[rcv_port] = sequence_exp - PRP_DROP_WINDOW_LEN;
+
+	node->time_out[port->type] = jiffies;
+	node->seq_out[port->type] = sequence_nr;
+	spin_unlock_bh(&node->seq_out_lock);
+	return 0;
+}
+
 static struct hsr_port *get_late_port(struct hsr_priv *hsr,
 				      struct hsr_node *node)
 {