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[219.203.27.33]) by smtp.gmail.com with ESMTPSA id d65-v6sm2503234pfj.20.2018.07.03.05.07.19 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 03 Jul 2018 05:07:20 -0700 (PDT) Subject: Re: media: dvb-usb-v2/gl861: ensure USB message buffers DMA'able To: Colin Ian King , Mauro Carvalho Chehab , linux-media@vger.kernel.org, Antti Palosaari Cc: "linux-kernel@vger.kernel.org" References: <8308d9f0-2257-101c-69e3-8fe165de9348@canonical.com> From: Akihiro TSUKADA Message-ID: Date: Tue, 3 Jul 2018 21:07:07 +0900 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <8308d9f0-2257-101c-69e3-8fe165de9348@canonical.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, thanks for the report. > 47 buf = NULL; > > Condition rlen > 0, taking false branch. > > 48 if (rlen > 0) { > 49 buf = kmalloc(rlen, GFP_KERNEL); > 50 if (!buf) > 51 return -ENOMEM; > 52 } > > 53 usleep_range(1000, 2000); /* avoid I2C errors */ > 54 > CID 1470241 (#1 of 1): Explicit null dereferenced (FORWARD_NULL). > var_deref_model: Passing null pointer buf to usb_control_msg, which > dereferences it. > > 55 ret = usb_control_msg(d->udev, usb_rcvctrlpipe(d->udev, 0), > req, type, > 56 value, index, buf, rlen, 2000); > > > The assignment of buf = NULL means a null buffer is passed down the usb > control message stack until it eventually gets dereferenced. This only > occurs when rlen <= 0. I was unsure how to fix this for the case when > rlen <= 0, so I am flagging this up as an issue that needs fixing. > Since rlen is an u16, null pointer is passed only when rlen == 0, so I think it is not a problem, but I am OK to add a guard in order to make scan result clean. regards, Akihiro