linux-kernel - Re: [PATCH] staging: rtl8723bs: hal: Fix memcpy calls

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Message-ID: <b3a92ac3-b097-3359-8729-ad353fac2a0d@linux.com>
Date:   Mon, 30 Sep 2019 18:40:34 +0300
From:   Denis Efremov <efremov@...ux.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Bastien Nocera <hadess@...ess.net>,
        Larry Finger <Larry.Finger@...inger.net>,
        Jes Sorensen <jes.sorensen@...il.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH] staging: rtl8723bs: hal: Fix memcpy calls

On 9/30/19 4:18 PM, David Laight wrote:
> From: Denis Efremov
>> Sent: 30 September 2019 12:02
>> memcpy() in phy_ConfigBBWithParaFile() and PHY_ConfigRFWithParaFile() is
>> called with "src == NULL && len == 0". This is an undefined behavior.
> 
> I'm pretty certain it is well defined (to do nothing).
> 
>> Moreover this if pre-condition "pBufLen && (*pBufLen == 0) && !pBuf"
>> is constantly false because it is a nested if in the else brach, i.e.,
>> "if (cond) { ... } else { if (cond) {...} }". This patch alters the
>> if condition to check "pBufLen && pBuf" pointers are not NULL.
>>
> ...
>> ---
>> Not tested. I don't have the hardware. The fix is based on my guess.
>>
>>  drivers/staging/rtl8723bs/hal/hal_com_phycfg.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/staging/rtl8723bs/hal/hal_com_phycfg.c b/drivers/staging/rtl8723bs/hal/hal_com_phycfg.c
>> index 6539bee9b5ba..0902dc3c1825 100644
>> --- a/drivers/staging/rtl8723bs/hal/hal_com_phycfg.c
>> +++ b/drivers/staging/rtl8723bs/hal/hal_com_phycfg.c
>> @@ -2320,7 +2320,7 @@ int phy_ConfigBBWithParaFile(
>>  			}
>>  		}
>>  	} else {
>> -		if (pBufLen && (*pBufLen == 0) && !pBuf) {
>> +		if (pBufLen && pBuf) {
>>  			memcpy(pHalData->para_file_buf, pBuf, *pBufLen);
> 
> The existing code is clearly garbage.
> It only ever does memcpy(tgt, NULL, 0).
> 
> Under the assumption that the code has been tested the copy clearly isn't needed at all
> and can be deleted completely!

Initially I also thought that this is just a dead code and it could be simply removed. However, if
we look at it more carefully, this if condition looks like a copy-paste error:

if (pBufLen && (*pBufLen == 0) && !pBuf) {
	// get proper len
	// allocate pBuf
	...
	memcpy(pBuf, pHalData->para_file_buf, rlen);
	...
} else {
	if (pBufLen && (*pBufLen == 0) && !pBuf) { // <== condition in patch
		memcpy(pHalData->para_file_buf, pBuf, *pBufLen);
		rtStatus = _SUCCESS;
	} else
		DBG_871X("%s(): Critical Error !!!\n", __func__);
}

Thus, I think it will be incorrect to delete the second memcpy.

> 
> OTOH if the code hasn't been tested maybe the entire source file should be removed :-)
> 
> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
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