[PATCH] net: lpc_eth: Fix a possible memory leak in lpc_mii_probe()

[Vladimir Zapolskiy]

Hello Ma Ke.

On 4/1/26 16:18, Ma Ke wrote:
> On 3/30/26 13:04, Vladimir Zapolskiy wrote:
>> On 3/30/26 11:16, Ma Ke wrote:
>>> lpc_mii_probe() calls of_phy_find_device() to obtain a phy_device
>>> pointer. of_phy_find_device() increments the refcount of the device.
>>> The current implementation does not decrement the refcount after using
>>> the pointer, which leads to a memory leak.
>>
>> this is correct, there is an actual detected bug.
>>
>>>
>>> Add phy_device_free() to balance the refcount.
>>
>> But this does not sound right, you shoud use of_node_put(pldat->phy_node).
>>
>>>
>>> Found by code review.
>>>
>>> Signed-off-by: Ma Ke <make24 at iscas.ac.cn>
>>> Cc: stable at vger.kernel.org
>>> Fixes: 3503bf024b3e ("net: lpc_eth: parse phy nodes from device tree")
>>> ---
>>>    drivers/net/ethernet/nxp/lpc_eth.c | 11 ++++++-----
>>>    1 file changed, 6 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/net/ethernet/nxp/lpc_eth.c b/drivers/net/ethernet/nxp/lpc_eth.c
>>> index 8b9a3e3bba30..8ce7c9bb6dd6 100644
>>> --- a/drivers/net/ethernet/nxp/lpc_eth.c
>>> +++ b/drivers/net/ethernet/nxp/lpc_eth.c
>>> @@ -751,7 +751,7 @@ static void lpc_handle_link_change(struct net_device *ndev)
>>>    static int lpc_mii_probe(struct net_device *ndev)
>>>    {
>>>    	struct netdata_local *pldat = netdev_priv(ndev);
>>> -	struct phy_device *phydev;
>>> +	struct phy_device *phydev, *phydev_tmp;
>>>    
>>>    	/* Attach to the PHY */
>>>    	if (lpc_phy_interface_mode(&pldat->pdev->dev) == PHY_INTERFACE_MODE_MII)
>>> @@ -760,17 +760,18 @@ static int lpc_mii_probe(struct net_device *ndev)
>>>    		netdev_info(ndev, "using RMII interface\n");
>>>    
>>>    	if (pldat->phy_node)
>>> -		phydev =  of_phy_find_device(pldat->phy_node);
>>> +		phydev_tmp =  of_phy_find_device(pldat->phy_node);
>>>    	else
>>> -		phydev = phy_find_first(pldat->mii_bus);
>>> -	if (!phydev) {
>>> +		phydev_tmp = phy_find_first(pldat->mii_bus);
>>> +	if (!phydev_tmp) {
>>
>> I didn't get it, why the new phydev_tmp is needed above, please
>> restore the original code above.
>>
>>>    		netdev_err(ndev, "no PHY found\n");
>>>    		return -ENODEV;
>>>    	}
>>>    
>>> -	phydev = phy_connect(ndev, phydev_name(phydev),
>>> +	phydev = phy_connect(ndev, phydev_name(phydev_tmp),
>>>    			     &lpc_handle_link_change,
>>>    			     lpc_phy_interface_mode(&pldat->pdev->dev));
>>> +	phy_device_free(phydev_tmp);
>>
>> This is plainly wrong and has to be dropped or changed to
>>
>> 	if (pldat->phy_node)
>> 		of_node_put(pldat->phy_node);
>>
>>>    	if (IS_ERR(phydev)) {
>>>    		netdev_err(ndev, "Could not attach to PHY\n");
>>>    		return PTR_ERR(phydev);
>>
>> Is it AI generated fix or what?.. The change looks bad, it introduces
>> more severe issues than it fixes.
>>
>> If you think you cannot create a proper change, let me know.
>>
> Thank you very much for your detailed review and guidance.
> 
> Now I think your point probably is: you are saying that the real leak
> is not from of_phy_find_device(), but from the device node

I was pretty indelicate in my comment, let's split the change into parts.

1) I still do not understand, why phydev_tmp is introduced, please explain
or remove this part of the change;

2) phydev = of_phy_find_device() requires phy_device_free(phydev), but
I do not see why phy_find_first() requires it, while it was added in your
change.

Let's start from resolving these two points.

> pldat->phy_node which was obtained earlier (probably by
> of_parse_phandle()) and never freed by of_node_put(). And you suggest
> to add of_node_put(pldat->phy_node) instead of my wrong
> phy_device_free().
> 
> However, I am still a little confused. In lpc_mii_probe(),
> of_phy_find_device() is called. From my understanding, this function
> increases the reference count of the device. To balance it, I thought
> phy_device_free() (which calls put_device()) should be used.
> 
> Could you please kindly advise the correct patch? I will follow your
> guidance and submit a proper fix.
> 
> I apologize again for my previous wrong patch. Thank you very much for
> your help.

-- 
Best wishes,
Vladimir