can: isotp: add SF_BROADCAST support for functional addressing

When CAN_ISOTP_SF_BROADCAST is set in the CAN_ISOTP_OPTS flags the CAN_ISOTP
socket is switched into functional addressing mode, where only single frame
(SF) protocol data units can be send on the specified CAN interface and the
given tp.tx_id after bind().

In opposite to normal and extended addressing this socket does not register a
CAN-ID for reception which would be needed for a 1-to-1 ISOTP connection with a
segmented bi-directional data transfer.

Sending SFs on this socket is therefore a TX-only 'broadcast' operation.

Signed-off-by: Oliver Hartkopp <[e-mail]>
Signed-off-by: Thomas Wagner <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Marc Kleine-Budde <[e-mail]>

include/uapi/linux/can/isotp.h

···
 #define CAN_ISOTP_FORCE_RXSTMIN	0x100	/* ignore CFs depending on rx stmin */
 #define CAN_ISOTP_RX_EXT_ADDR	0x200	/* different rx extended addressing */
 #define CAN_ISOTP_WAIT_TX_DONE	0x400	/* wait for tx completion */
-
+#define CAN_ISOTP_SF_BROADCAST	0x800	/* 1-to-N functional addressing */
 
 /* default values */
 

net/can/isotp.c

···
 	if (!size || size > MAX_MSG_LENGTH)
 		return -EINVAL;
 
+	/* take care of a potential SF_DL ESC offset for TX_DL > 8 */
+	off = (so->tx.ll_dl > CAN_MAX_DLEN) ? 1 : 0;
+
+	/* does the given data fit into a single frame for SF_BROADCAST? */
+	if ((so->opt.flags & CAN_ISOTP_SF_BROADCAST) &&
+	    (size > so->tx.ll_dl - SF_PCI_SZ4 - ae - off))
+		return -EINVAL;
+
 	err = memcpy_from_msg(so->tx.buf, msg, size);
 	if (err < 0)
 		return err;
···
 
 	cf = (struct canfd_frame *)skb->data;
 	skb_put(skb, so->ll.mtu);
-
-	/* take care of a potential SF_DL ESC offset for TX_DL > 8 */
-	off = (so->tx.ll_dl > CAN_MAX_DLEN) ? 1 : 0;
 
 	/* check for single frame transmission depending on TX_DL */
 	if (size <= so->tx.ll_dl - SF_PCI_SZ4 - ae - off) {
···
 	hrtimer_cancel(&so->rxtimer);
 
 	/* remove current filters & unregister */
-	if (so->bound) {
+	if (so->bound && (!(so->opt.flags & CAN_ISOTP_SF_BROADCAST))) {
 		if (so->ifindex) {
 			struct net_device *dev;
 
···
 	struct net_device *dev;
 	int err = 0;
 	int notify_enetdown = 0;
+	int do_rx_reg = 1;
 
 	if (len < CAN_REQUIRED_SIZE(struct sockaddr_can, can_addr.tp))
 		return -EINVAL;
 
-	if (addr->can_addr.tp.rx_id == addr->can_addr.tp.tx_id)
-		return -EADDRNOTAVAIL;
+	/* do not register frame reception for functional addressing */
+	if (so->opt.flags & CAN_ISOTP_SF_BROADCAST)
+		do_rx_reg = 0;
 
-	if ((addr->can_addr.tp.rx_id | addr->can_addr.tp.tx_id) &
-	    (CAN_ERR_FLAG | CAN_RTR_FLAG))
+	/* do not validate rx address for functional addressing */
+	if (do_rx_reg) {
+		if (addr->can_addr.tp.rx_id == addr->can_addr.tp.tx_id)
+			return -EADDRNOTAVAIL;
+
+		if (addr->can_addr.tp.rx_id & (CAN_ERR_FLAG | CAN_RTR_FLAG))
+			return -EADDRNOTAVAIL;
+	}
+
+	if (addr->can_addr.tp.tx_id & (CAN_ERR_FLAG | CAN_RTR_FLAG))
 		return -EADDRNOTAVAIL;
 
 	if (!addr->can_ifindex)
···
 
 	ifindex = dev->ifindex;
 
-	can_rx_register(net, dev, addr->can_addr.tp.rx_id,
-			SINGLE_MASK(addr->can_addr.tp.rx_id), isotp_rcv, sk,
-			"isotp", sk);
+	if (do_rx_reg)
+		can_rx_register(net, dev, addr->can_addr.tp.rx_id,
+				SINGLE_MASK(addr->can_addr.tp.rx_id),
+				isotp_rcv, sk, "isotp", sk);
 
 	dev_put(dev);
 
-	if (so->bound) {
+	if (so->bound && do_rx_reg) {
 		/* unregister old filter */
 		if (so->ifindex) {
 			dev = dev_get_by_index(net, so->ifindex);
···
 	case NETDEV_UNREGISTER:
 		lock_sock(sk);
 		/* remove current filters & unregister */
-		if (so->bound)
+		if (so->bound && (!(so->opt.flags & CAN_ISOTP_SF_BROADCAST)))
 			can_rx_unregister(dev_net(dev), dev, so->rxid,
 					  SINGLE_MASK(so->rxid),
 					  isotp_rcv, sk);