can: m_can: m_can_tx_handler(): fix use after free of skb

can_put_echo_skb() will clone skb then free the skb. Move the
can_put_echo_skb() for the m_can version 3.0.x directly before the
start of the xmit in hardware, similar to the 3.1.x branch.

Fixes: 80646733 ("can: m_can: update to support CAN FD features")
Link: https://lore.kernel.org/all/20220317081305.739554-1-mkl@pengutronix.de
Cc: stable@vger.kernel.org
Reported-by: Hangyu Hua <hbh25y@gmail.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/m_can/m_can.c

@@ -1637,8 +1637,6 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
 		if (err)
 			goto out_fail;
 
-		can_put_echo_skb(skb, dev, 0, 0);
-
 		if (cdev->can.ctrlmode & CAN_CTRLMODE_FD) {
 			cccr = m_can_read(cdev, M_CAN_CCCR);
 			cccr &= ~CCCR_CMR_MASK;
@@ -1655,6 +1653,9 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
 			m_can_write(cdev, M_CAN_CCCR, cccr);
 		}
 		m_can_write(cdev, M_CAN_TXBTIE, 0x1);
+
+		can_put_echo_skb(skb, dev, 0, 0);
+
 		m_can_write(cdev, M_CAN_TXBAR, 0x1);
 		/* End of xmit function for version 3.0.x */
 	} else {