linux-kernel - Re: [PATCH net] net: nixge: fix potential memory leak in nixge_start

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Date:   Wed, 16 Nov 2022 14:36:19 -0800
From:   Saeed Mahameed <saeed@...nel.org>
To:     Zhang Changzhong <zhangchangzhong@...wei.com>
Cc:     Francois Romieu <romieu@...zoreil.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Moritz Fischer <mdf@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: nixge: fix potential memory leak in
 nixge_start_xmit()

On 15 Nov 21:20, Zhang Changzhong wrote:
>On 2022/11/14 18:40, Francois Romieu wrote:
>> Zhang Changzhong <zhangchangzhong@...wei.com> :
>>> The nixge_start_xmit() returns NETDEV_TX_OK but does not free skb on two
>>> error handling cases, which can lead to memory leak.
>>>
>>> To fix this, return NETDEV_TX_BUSY in case of nixge_check_tx_bd_space()
>>> fails and add dev_kfree_skb_any() in case of dma_map_single() fails.
>>
>> This patch merge two unrelated changes. Please split.
>>
>>> Fixes: 492caffa8a1a ("net: ethernet: nixge: Add support for National Instruments XGE netdev")
>>> Signed-off-by: Zhang Changzhong <zhangchangzhong@...wei.com>
>>> ---
>>>  drivers/net/ethernet/ni/nixge.c | 6 ++++--
>>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/net/ethernet/ni/nixge.c b/drivers/net/ethernet/ni/nixge.c
>>> index 19d043b593cc..b9091f9bbc77 100644
>>> --- a/drivers/net/ethernet/ni/nixge.c
>>> +++ b/drivers/net/ethernet/ni/nixge.c
>>> @@ -521,13 +521,15 @@ static netdev_tx_t nixge_start_xmit(struct sk_buff *skb,
>>>  	if (nixge_check_tx_bd_space(priv, num_frag)) {
>>>  		if (!netif_queue_stopped(ndev))
>>>  			netif_stop_queue(ndev);
>>> -		return NETDEV_TX_OK;
>>> +		return NETDEV_TX_BUSY;
>>>  	}
>>
>> The driver should probably check the available room before returning
>> from hard_start_xmit and turn the check above unlikely().
>>
>> Btw there is no lock and the Tx completion is irq driven: the driver
>> is racy. :o(
>>
>
>Hi Francois,
>
>Thanks for you review. I'll make v2 according to your suggestion.
>

you will probably need to check out: Transmit path guidelines:
https://www.kernel.org/doc/Documentation/networking/driver.rst