[PATCH 4.9 28/28] can: m_can: m_can_tx_handler(): fix use after free of skb

[Greg Kroah-Hartman]

From: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>

commit 2e8e79c416aae1de224c0f1860f2e3350fa171f8 upstream.

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: 80646733f11c ("can: m_can: update to support CAN FD features")
Link: https://lore.kernel.org/all/20220317081305.739554-1-mkl@xxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Hangyu Hua <hbh25y@xxxxxxxxx>
Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
[sudip: adjust context]
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/can/m_can/m_can.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/net/can/m_can/m_can.c
+++ b/drivers/net/can/m_can/m_can.c
@@ -1068,8 +1068,6 @@ static netdev_tx_t m_can_start_xmit(stru
 		m_can_fifo_write(priv, 0, M_CAN_FIFO_DATA(i / 4),
 				 *(u32 *)(cf->data + i));
 
-	can_put_echo_skb(skb, dev, 0);
-
 	if (priv->can.ctrlmode & CAN_CTRLMODE_FD) {
 		cccr = m_can_read(priv, M_CAN_CCCR);
 		cccr &= ~(CCCR_CMR_MASK << CCCR_CMR_SHIFT);
@@ -1086,6 +1084,9 @@ static netdev_tx_t m_can_start_xmit(stru
 
 	/* enable first TX buffer to start transfer  */
 	m_can_write(priv, M_CAN_TXBTIE, 0x1);
+
+	can_put_echo_skb(skb, dev, 0);
+
 	m_can_write(priv, M_CAN_TXBAR, 0x1);
 
 	return NETDEV_TX_OK;