linux-kernel - Re: [PATCH net] net: phy: mscc: Fix memory leak when using one step timestamping

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Message-ID: <vmtli7u7fnsj56xhih7eqtzt6w3v4yp7dviyssqyyybvsioznj@lzwdr5dpo5wg>
Date: Wed, 21 May 2025 17:34:39 +0200
From: Antoine Tenart <atenart@...nel.org>
To: Horatiu Vultur <horatiu.vultur@...rochip.com>
Cc: andrew@...n.ch, hkallweit1@...il.com, linux@...linux.org.uk, 
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, 
	richardcochran@...il.com, kory.maincent@...tlin.com, shannon.nelson@....com, 
	viro@...iv.linux.org.uk, atenart@...nel.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: phy: mscc: Fix memory leak when using one step
 timestamping

On Wed, May 21, 2025 at 03:11:14PM +0200, Horatiu Vultur wrote:
> Fix memory leak when running one-step timestamping. When running
> one-step sync timestamping, the HW is configured to insert the TX time
> into the frame, so there is no reason to keep the skb anymore. As in
> this case the HW will never generate an interrupt to say that the frame
> was timestamped, then the frame will never released.
> Fix this by freeing the frame in case of one-step timestamping.
> 
> Fixes: 7d272e63e0979d ("net: phy: mscc: timestamping and PHC support")
> Signed-off-by: Horatiu Vultur <horatiu.vultur@...rochip.com>
> ---
>  drivers/net/phy/mscc/mscc_ptp.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/net/phy/mscc/mscc_ptp.c b/drivers/net/phy/mscc/mscc_ptp.c
> index ed8fb14a7f215..db8ca1dfd5322 100644
> --- a/drivers/net/phy/mscc/mscc_ptp.c
> +++ b/drivers/net/phy/mscc/mscc_ptp.c
> @@ -1173,6 +1173,13 @@ static void vsc85xx_txtstamp(struct mii_timestamper *mii_ts,
>  		return;
>  	}
>  
> +	if (vsc8531->ptp->tx_type == HWTSTAMP_TX_ONESTEP_SYNC) {
> +		if (ptp_msg_is_sync(skb, type)) {
> +			kfree_skb(skb);
> +			return;
> +		}
> +	}

I don't remember everything about TS but I think the above is fine. Also
while looking at this I saw this function is doing the following too:

  if (!vsc8531->ptp->configured)
	return;

I guess we should free the skb for all paths not putting it in the tx
queue. As there would be 3 paths freeing the skb + returning, you might
as well use a label for easier maintenance.

Thanks,
Antoine