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Mon, 20 Nov 2023 10:29:49 -0800 (PST) Received: from [192.168.1.20] ([178.197.222.11]) by smtp.gmail.com with ESMTPSA id x26-20020a1709065ada00b009fd04a1a1dfsm1880622ejs.40.2023.11.20.10.29.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Nov 2023 10:29:48 -0800 (PST) Message-ID: <9db5e25f-9fe1-45d9-9a3b-91c45c6cdddf@linaro.org> Date: Mon, 20 Nov 2023 19:29:47 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 , bongsu.jeon@samsung.com Cc: "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "syzbot+6eb09d75211863f15e3e@syzkaller.appspotmail.com" References: <20231119164705.1991375-1-phind.uet@gmail.com> <20231120044706epcms2p48c4579db14cc4f3274031036caac4718@epcms2p4> <20d93e83-66c0-28d9-4426-a0d4c098f303@gmail.com> <8bce1251-7a6b-4b4c-b700-9d97c664689f@gmail.com> From: Krzysztof Kozlowski Autocrypt: addr=krzysztof.kozlowski@linaro.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit 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