Re: [PATCH v2] can: m_can: m_can_tx_handler(): fix use after free of skb

[Hangyu Hua <hbh25y@gmail.com>]

I agree with you.

By the way, i find two similar questions about can_put_echo_skb. I hope 
you can also check them out:
mcba_usb:
https://lore.kernel.org/all/20220311080208.45047-1-hbh25y@gmail.com/
usb_8dev:
https://lore.kernel.org/all/20220311080614.45229-1-hbh25y@gmail.com/

They are the same issue as the following patches:
https://lore.kernel.org/all/20220228083639.38183-1-hbh25y@gmail.com/

Thanks,
Hangyu Hua

On 2022/3/17 16:13, Marc Kleine-Budde wrote:
> 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.
> 
> Reported-by: Hangyu Hua <hbh25y@gmail.com>
> Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
> ---
> 
> Hello,
> 
> picking up Hangyu Hua's work from:
> 
> | https://lore.kernel.org/all/20220317030143.14668-1-hbh25y@gmail.com/
> 
> Instead of using a temporary variable, move the can_put_echo_skb() instead.
> 
> regads,
> Marc
> 
>   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 1a4b56f6fa8c..b3b5bc1c803b 100644
> --- a/drivers/net/can/m_can/m_can.c
> +++ b/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 {