linux-kernel - Re: [PATCH] nfc: virtual_ncidev: Add variable to check if ndev is running

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Date:   Mon, 20 Nov 2023 18:39:46 +0800
From:   Nguyen Dinh Phi <phind.uet@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        bongsu.jeon@...sung.com
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "syzbot+6eb09d75211863f15e3e@...kaller.appspotmail.com" 
        <syzbot+6eb09d75211863f15e3e@...kaller.appspotmail.com>
Subject: Re: [PATCH] nfc: virtual_ncidev: Add variable to check if ndev is
 running



On 20/11/23 5:06 pm, Krzysztof Kozlowski wrote:
> On 20/11/2023 05:47, Bongsu Jeon wrote:
>>
>> On 20/11/2023 01:47, Nguyen Dinh Phi wrote:
>>
>>> syzbot reported an memory leak that happens when an skb is add to
>>> send_buff after virtual nci closed.
>>> This patch adds a variable to track if the ndev is running before
>>> handling new skb in send function.
>>>
>>> Reported-by: syzbot+6eb09d75211863f15e3e@...kaller.appspotmail.com
>>> Closes: https://lore.kernel.org/lkml/00000000000075472b06007df4fb@google.com
>>> Signed-off-by: Nguyen Dinh Phi <phind.uet@...il.com>
>>> ---
>>>   drivers/nfc/virtual_ncidev.c | 9 +++++++--
>>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/nfc/virtual_ncidev.c b/drivers/nfc/virtual_ncidev.c
>>> index b027be0b0b6f..ac8226db54e2 100644
>>> --- a/drivers/nfc/virtual_ncidev.c
>>> +++ b/drivers/nfc/virtual_ncidev.c
>>> @@ -20,26 +20,31 @@
>>>                                    NFC_PROTO_ISO14443_MASK | \
>>>                                    NFC_PROTO_ISO14443_B_MASK | \
>>>                                    NFC_PROTO_ISO15693_MASK)
>>> +#define NCIDEV_RUNNING 0
>> This define isn't used.
>>
>>>   
>>>   struct virtual_nci_dev {
>>>           struct nci_dev *ndev;
>>>           struct mutex mtx;
>>>           struct sk_buff *send_buff;
>>>           struct wait_queue_head wq;
>>> +        bool running;
>>>   };
>>>   
>>>   static int virtual_nci_open(struct nci_dev *ndev)
>>>   {
>>> +        struct virtual_nci_dev *vdev = nci_get_drvdata(ndev);
>>> +
>>> +        vdev->running = true;
>>>           return 0;
>>>   }
>>>   
>>>   static int virtual_nci_close(struct nci_dev *ndev)
>>>   {
>>>           struct virtual_nci_dev *vdev = nci_get_drvdata(ndev);
>>> -
>>>           mutex_lock(&vdev->mtx);
>>>           kfree_skb(vdev->send_buff);
>>>           vdev->send_buff = NULL;
>>> +        vdev->running = false;
>>>           mutex_unlock(&vdev->mtx);
>>>   
>>>           return 0;
>>> @@ -50,7 +55,7 @@ static int virtual_nci_send(struct nci_dev *ndev, struct sk_buff *skb)
>>>           struct virtual_nci_dev *vdev = nci_get_drvdata(ndev);
>>>   
>>>           mutex_lock(&vdev->mtx);
>>> -        if (vdev->send_buff) {
>>> +        if (vdev->send_buff || !vdev->running) {
>>
>> Dear Krzysztof,
>>
>> I agree this defensive code.
>> But i think NFC submodule has to avoid this situation.(calling send function of closed nci_dev)
>> Could you check this?
> 
> This code looks not effective. At this point vdev->send_buff is always
> false, so the additional check would not bring any value.
> 
> I don't see this fixing anything. Syzbot also does not seem to agree.
> 
> Nguyen, please test your patches against syzbot *before* sending them.
> If you claim this fixes the report, please provide me the link to syzbot
> test results confirming it is fixed.
> 
> I looked at syzbot dashboard and do not see this issue fixed with this
> patch.
> 
> Best regards,
> Krzysztof
> 

Hi Krzysztof,

I've submitted it to syzbot, it is the test request that created at 
[2023/11/20 09:39] in dashboard link 
https://syzkaller.appspot.com/bug?extid=6eb09d75211863f15e3e

Best regards,
Phi