Re: FAILED: patch "[PATCH] can: m_can: m_can_tx_handler(): fix use after free of skb" failed to apply to 4.9-stable tree

[Sudip Mukherjee <sudipm.mukherjee@gmail.com>]

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Hi Greg,

On Fri, Apr 01, 2022 at 02:02:19PM +0200, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 4.9-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.

Here is the backport.

--
Regards
Sudip

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From bb339cb5aa90e31d6ceb65ac5d9937944d9666d7 Mon Sep 17 00:00:00 2001
From: Marc Kleine-Budde <mkl@pengutronix.de>
Date: Thu, 17 Mar 2022 08:57:35 +0100
Subject: [PATCH] can: m_can: m_can_tx_handler(): fix use after free of skb

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@pengutronix.de
Cc: stable@vger.kernel.org
Reported-by: Hangyu Hua <hbh25y@gmail.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
[sudip: adjust context]
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
---
 drivers/net/can/m_can/m_can.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
index 197c27d8f584b..85380b63533fd 100644
--- 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(struct sk_buff *skb,
 		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(struct sk_buff *skb,
 
 	/* 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;
-- 
2.30.2