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

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Message-ID: <d82e5a5f-1bbc-455e-b6a7-c636b23591f7@linaro.org>
Date:   Mon, 20 Nov 2023 11:45:05 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Nguyen Dinh Phi <phind.uet@...il.com>, 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 20/11/2023 11:39, Nguyen Dinh Phi wrote:
>>>>           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

...and I see there two errors.

I don't know, maybe I miss something obvious (our brains like to do it
sometimes), but please explain me how this could fix anything?

Best regards,
Krzysztof