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Mon, 20 Nov 2023 10:32:10 -0800 (PST) Received: from [192.168.1.20] ([178.197.222.11]) by smtp.gmail.com with ESMTPSA id kq14-20020a170906abce00b009fcb10eecb2sm1999386ejb.84.2023.11.20.10.32.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Nov 2023 10:32:09 -0800 (PST) Message-ID: <0954d66f-a685-4aaa-90a4-3d3492c79cd4@linaro.org> Date: Mon, 20 Nov 2023 19:32:06 +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 From: Krzysztof Kozlowski 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> <9db5e25f-9fe1-45d9-9a3b-91c45c6cdddf@linaro.org> Autocrypt: addr=krzysztof.kozlowski@linaro.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 20/11/2023 19:29, Krzysztof Kozlowski wrote: > 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. Uh, now I see, I missed that's the if here is for send_buff != NULL, so quite different case than virtual_nci_close(). Best regards, Krzysztof