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De Francesco" , Phillip Potter Cc: Larry Finger , Greg KH , Michael Straube , "open list:STAGING SUBSYSTEM" , Linux Kernel Mailing List References: <9004eb2972780455db4cba9694244a2c572abba8.1629642658.git.paskripkin@gmail.com> <2424268.2DCLMNk6Lg@localhost.localdomain> From: Pavel Skripkin Message-ID: <2355365e-d75e-8d1b-aad8-6979b70f33ec@gmail.com> Date: Tue, 24 Aug 2021 09:40:18 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <2424268.2DCLMNk6Lg@localhost.localdomain> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/24/21 3:10 AM, Fabio M. De Francesco wrote: > On Tuesday, August 24, 2021 1:33:46 AM CEST Phillip Potter wrote: >> On Sun, 22 Aug 2021 at 15:36, Pavel Skripkin wrote: >> > -static u32 usb_read32(struct intf_hdl *pintfhdl, u32 addr) >> > +static int usb_read32(struct intf_hdl *pintfhdl, u32 addr, u32 *data) >> > { >> > u8 requesttype; >> > u16 wvalue; >> > u16 len; >> > - __le32 data; >> > + int res; >> > + __le32 tmp; >> > + >> > + if (WARN_ON(unlikely(!data))) >> > + return -EINVAL; >> > >> > requesttype = 0x01;/* read_in */ >> > >> > wvalue = (u16)(addr & 0x0000ffff); >> > len = 4; >> > >> > - usbctrl_vendorreq(pintfhdl, wvalue, &data, len, requesttype); >> > + res = usbctrl_vendorreq(pintfhdl, wvalue, &data, len, requesttype); >> > + if (res < 0) { >> > + dev_err(dvobj_to_dev(pintfhdl->pintf_dev), "Failed to read 32 bytes: %d\n", res); >> > + } else { >> > + /* Noone cares about positive return value */ >> > + *data = le32_to_cpu(tmp); >> > + res = 0; >> > + } >> > >> > - return le32_to_cpu(data); >> > + return res; >> > } >> >> Dear Pavel, >> >> OK, found the issue with decoded stack trace after reviewing this >> usb_read32 function. Your line: >> res = usbctrl_vendorreq(pintfhdl, wvalue, &data, len, requesttype); >> >> should read: >> res = usbctrl_vendorreq(pintfhdl, wvalue, &tmp, len, requesttype); > > Dear Philip, > > No, it should read: > > res = usbctrl_vendorreq(pintfhdl, wvalue, data, len, requesttype); > > I suspect that Pavel didn't notice he was reusing a line of the old code > wth no due changes. > >> With this change, the driver runs fine with no crashes/oopses. I will >> explain the issue but you can probably see already, so I hope I'm not >> coming across as patronising, just trying to be helpful :-) >> >> Essentially, you are taking the address of the data function parameter >> on this line with &data, a pointer to u32, which is giving you a >> pointer to a pointer to u32 (u32 **) for this function parameter >> variable. When passed to usbctrl_vendorreq, it is being passed to >> memcpy inside this function as a void *, meaning that memcpy >> subsequently overwrites the value of the memory address inside data to >> point to a different location, which is problem when it is later >> deferenced at: >> *data = le32_to_cpu(tmp); >> causing the OOPS >> >> Also, as written, you can probably see that tmp is uninitialised. This >> looks like a typo, so guessing this wasn't your intention. Anyhow, >> with that small change, usbctrl_vendorreq reads into tmp, which is >> then passed to le32_to_cpu whose return value is stored via the >> deferenced data ptr (which now has its original address within and not >> inadvertently modified). Hope this helps, and I'd be happy to Ack the >> series if you want to resend this patch. Many thanks. > > I think that another typo is having 'tmp', because that variable is unnecessary > and "*data = le32_to_cpu(tmp);" is wrong too. > > Now I also see that also usb_read16() is wrong, while usb_read8() (the one that > I had read yesterday) is the only correct function of the three usb_read*(). > Hi, guys! Sorry for breaking your system, Phillip. This code was part of "last minute" changes and yes, it's broken :) I get what Phillip said, because I _should_ read into tmp variable instead of directly to data, but I don't get Fabio's idea, sorry. Data from chip comes in little-endian, so we _should_ convert it to cpu's endian. Temp variable is needed to make smatch and all other static anylis tools happy about this code. If I am missing something, please, let me know :) v3 is on the way... With regards, Pavel Skripkin