Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:5 as permitted sender) client-ip=2620:137:e000::3:5;
Message-ID: <9db5e25f-9fe1-45d9-9a3b-91c45c6cdddf@linaro.org>
Date:   Mon, 20 Nov 2023 19:29:47 +0100
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH] nfc: virtual_ncidev: Add variable to check if ndev is
 running
Content-Language: en-US
To:     Phi Nguyen <phind.uet@gmail.com>, bongsu.jeon@samsung.com
Cc:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "syzbot+6eb09d75211863f15e3e@syzkaller.appspotmail.com" 
        <syzbot+6eb09d75211863f15e3e@syzkaller.appspotmail.com>
References: <20231119164705.1991375-1-phind.uet@gmail.com>
 <CGME20231119164714epcas2p2c0480d014abc4f0f780c714a445881ca@epcms2p4>
 <20231120044706epcms2p48c4579db14cc4f3274031036caac4718@epcms2p4>
 <bafc3707-8eae-4d63-bc64-8d415d32c4b9@linaro.org>
 <20d93e83-66c0-28d9-4426-a0d4c098f303@gmail.com>
 <d82e5a5f-1bbc-455e-b6a7-c636b23591f7@linaro.org>
 <8bce1251-7a6b-4b4c-b700-9d97c664689f@gmail.com>
From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Autocrypt: addr=krzysztof.kozlowski@linaro.org; keydata=
 xsFNBFVDQq4BEAC6KeLOfFsAvFMBsrCrJ2bCalhPv5+KQF2PS2+iwZI8BpRZoV+Bd5kWvN79
 cFgcqTTuNHjAvxtUG8pQgGTHAObYs6xeYJtjUH0ZX6ndJ33FJYf5V3yXqqjcZ30FgHzJCFUu
 JMp7PSyMPzpUXfU12yfcRYVEMQrmplNZssmYhiTeVicuOOypWugZKVLGNm0IweVCaZ/DJDIH
 gNbpvVwjcKYrx85m9cBVEBUGaQP6AT7qlVCkrf50v8bofSIyVa2xmubbAwwFA1oxoOusjPIE
 J3iadrwpFvsZjF5uHAKS+7wHLoW9hVzOnLbX6ajk5Hf8Pb1m+VH/E8bPBNNYKkfTtypTDUCj
 NYcd27tjnXfG+SDs/EXNUAIRefCyvaRG7oRYF3Ec+2RgQDRnmmjCjoQNbFrJvJkFHlPeHaeS
 BosGY+XWKydnmsfY7SSnjAzLUGAFhLd/XDVpb1Een2XucPpKvt9ORF+48gy12FA5GduRLhQU
 vK4tU7ojoem/G23PcowM1CwPurC8sAVsQb9KmwTGh7rVz3ks3w/zfGBy3+WmLg++C2Wct6nM
 Pd8/6CBVjEWqD06/RjI2AnjIq5fSEH/BIfXXfC68nMp9BZoy3So4ZsbOlBmtAPvMYX6U8VwD
 TNeBxJu5Ex0Izf1NV9CzC3nNaFUYOY8KfN01X5SExAoVTr09ewARAQABzTRLcnp5c3p0b2Yg
 S296bG93c2tpIDxrcnp5c3p0b2Yua296bG93c2tpQGxpbmFyby5vcmc+wsGUBBMBCgA+FiEE
 m9B+DgxR+NWWd7dUG5NDfTtBYpsFAmI+BxMCGwMFCRRfreEFCwkIBwIGFQoJCAsCBBYCAwEC
 HgECF4AACgkQG5NDfTtBYptgbhAAjAGunRoOTduBeC7V6GGOQMYIT5n3OuDSzG1oZyM4kyvO
 XeodvvYv49/ng473E8ZFhXfrre+c1olbr1A8pnz9vKVQs9JGVa6wwr/6ddH7/yvcaCQnHRPK
 mnXyP2BViBlyDWQ71UC3N12YCoHE2cVmfrn4JeyK/gHCvcW3hUW4i5rMd5M5WZAeiJj3rvYh
 v8WMKDJOtZFXxwaYGbvFJNDdvdTHc2x2fGaWwmXMJn2xs1ZyFAeHQvrp49mS6PBQZzcx0XL5
 cU9ZjhzOZDn6Apv45/C/lUJvPc3lo/pr5cmlOvPq1AsP6/xRXsEFX/SdvdxJ8w9KtGaxdJuf
 rpzLQ8Ht+H0lY2On1duYhmro8WglOypHy+TusYrDEry2qDNlc/bApQKtd9uqyDZ+rx8bGxyY
 qBP6bvsQx5YACI4p8R0J43tSqWwJTP/R5oPRQW2O1Ye1DEcdeyzZfifrQz58aoZrVQq+innR
 aDwu8qDB5UgmMQ7cjDSeAQABdghq7pqrA4P8lkA7qTG+aw8Z21OoAyZdUNm8NWJoQy8m4nUP
 gmeeQPRc0vjp5JkYPgTqwf08cluqO6vQuYL2YmwVBIbO7cE7LNGkPDA3RYMu+zPY9UUi/ln5
 dcKuEStFZ5eqVyqVoZ9eu3RTCGIXAHe1NcfcMT9HT0DPp3+ieTxFx6RjY3kYTGLOwU0EVUNc
 NAEQAM2StBhJERQvgPcbCzjokShn0cRA4q2SvCOvOXD+0KapXMRFE+/PZeDyfv4dEKuCqeh0
 hihSHlaxTzg3TcqUu54w2xYskG8Fq5tg3gm4kh1Gvh1LijIXX99ABA8eHxOGmLPRIBkXHqJY
 oHtCvPc6sYKNM9xbp6I4yF56xVLmHGJ61KaWKf5KKWYgA9kfHufbja7qR0c6H79LIsiYqf92
 H1HNq1WlQpu/fh4/XAAaV1axHFt/dY/2kU05tLMj8GjeQDz1fHas7augL4argt4e+jum3Nwt
 yupodQBxncKAUbzwKcDrPqUFmfRbJ7ARw8491xQHZDsP82JRj4cOJX32sBg8nO2N5OsFJOcd
 5IE9v6qfllkZDAh1Rb1h6DFYq9dcdPAHl4zOj9EHq99/CpyccOh7SrtWDNFFknCmLpowhct9
 5ZnlavBrDbOV0W47gO33WkXMFI4il4y1+Bv89979rVYn8aBohEgET41SpyQz7fMkcaZU+ok/
 +HYjC/qfDxT7tjKXqBQEscVODaFicsUkjheOD4BfWEcVUqa+XdUEciwG/SgNyxBZepj41oVq
 FPSVE+Ni2tNrW/e16b8mgXNngHSnbsr6pAIXZH3qFW+4TKPMGZ2rZ6zITrMip+12jgw4mGjy
 5y06JZvA02rZT2k9aa7i9dUUFggaanI09jNGbRA/ABEBAAHCwXwEGAEKACYCGwwWIQSb0H4O
 DFH41ZZ3t1Qbk0N9O0FimwUCYDzvagUJFF+UtgAKCRAbk0N9O0Fim9JzD/0auoGtUu4mgnna
 oEEpQEOjgT7l9TVuO3Qa/SeH+E0m55y5Fjpp6ZToc481za3xAcxK/BtIX5Wn1mQ6+szfrJQ6
 59y2io437BeuWIRjQniSxHz1kgtFECiV30yHRgOoQlzUea7FgsnuWdstgfWi6LxstswEzxLZ
 Sj1EqpXYZE4uLjh6dW292sO+j4LEqPYr53hyV4I2LPmptPE9Rb9yCTAbSUlzgjiyyjuXhcwM
 qf3lzsm02y7Ooq+ERVKiJzlvLd9tSe4jRx6Z6LMXhB21fa5DGs/tHAcUF35hSJrvMJzPT/+u
 /oVmYDFZkbLlqs2XpWaVCo2jv8+iHxZZ9FL7F6AHFzqEFdqGnJQqmEApiRqH6b4jRBOgJ+cY
 qc+rJggwMQcJL9F+oDm3wX47nr6jIsEB5ZftdybIzpMZ5V9v45lUwmdnMrSzZVgC4jRGXzsU
 EViBQt2CopXtHtYfPAO5nAkIvKSNp3jmGxZw4aTc5xoAZBLo0OV+Ezo71pg3AYvq0a3/oGRG
 KQ06ztUMRrj8eVtpImjsWCd0bDWRaaR4vqhCHvAG9iWXZu4qh3ipie2Y0oSJygcZT7H3UZxq
 fyYKiqEmRuqsvv6dcbblD8ZLkz1EVZL6djImH5zc5x8qpVxlA0A0i23v5QvN00m6G9NFF0Le
 D2GYIS41Kv4Isx2dEFh+/Q==
In-Reply-To: <8bce1251-7a6b-4b4c-b700-9d97c664689f@gmail.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 20/11/2023 19:23, Phi Nguyen wrote:
> On 11/20/2023 6:45 PM, Krzysztof Kozlowski wrote:
>> 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.
>>
> These are because I sent email wrongly and syzbot truncates the patch 
> and can not compile
> 
>> 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
>>
> 
> The issue arises when an skb is added to the send_buff after invoking 
> ndev->ops->close() but before unregistering the device. In such cases, 
> the virtual device will generate a copy of skb, but with no consumer 
> thereafter. Consequently, this object persists indefinitely.
> 
> This problem seems to stem from the existence of time gaps between 
> ops->close() and the destruction of the workqueue. During this interval, 
> incoming requests continue to trigger the send function.

I asked how this could fix anything. Can you respond to my original comment?

Look:

>>>> This code looks not effective. At this point vdev->send_buff is always
>>>> false, so the additional check would not bring any value.

Best regards,
Krzysztof