linux-kernel - Re: [PATCH] USB: realtek_cr: fix return check for dma functions

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Date:   Tue, 11 Aug 2020 10:29:29 -0700
From:   Tom Rix <trix@...hat.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     gregkh@...uxfoundation.org, acozzette@...hmc.edu,
        linux-usb@...r.kernel.org, usb-storage@...ts.one-eyed-alien.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: realtek_cr: fix return check for dma functions


On 8/11/20 9:03 AM, Alan Stern wrote:
> On Tue, Aug 11, 2020 at 08:15:05AM -0700, trix@...hat.com wrote:
>> From: Tom Rix <trix@...hat.com>
>>
>> clang static analysis reports this representative problem
>>
>> realtek_cr.c:639:3: warning: The left expression of the compound
>>   assignment is an uninitialized value. The computed value will
>>   also be garbage
>>     SET_BIT(value, 2);
>>     ^~~~~~~~~~~~~~~~~
>>
>> value is set by a successful call to rts51x_read_mem()
>>
>> 	retval = rts51x_read_mem(us, 0xFE77, &value, 1);
>> 	if (retval < 0)
>> 		return -EIO;
>>
>> A successful call to rts51x_read_mem returns 0, failure can
>> return positive and negative values.  This check is wrong
>> for a number of functions.  Fix the retval check.
>>
>> Fixes: 065e60964e29 ("ums_realtek: do not use stack memory for DMA")
>> Signed-off-by: Tom Rix <trix@...hat.com>
>> ---
>>  drivers/usb/storage/realtek_cr.c | 36 ++++++++++++++++----------------
>>  1 file changed, 18 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/usb/storage/realtek_cr.c b/drivers/usb/storage/realtek_cr.c
>> index 3789698d9d3c..b983753e2368 100644
>> --- a/drivers/usb/storage/realtek_cr.c
>> +++ b/drivers/usb/storage/realtek_cr.c
>> @@ -481,16 +481,16 @@ static int enable_oscillator(struct us_data *us)
>>  	u8 value;
>>  
>>  	retval = rts51x_read_mem(us, 0xFE77, &value, 1);
>> -	if (retval < 0)
>> +	if (retval != STATUS_SUCCESS)
>>  		return -EIO;
> Instead of changing all these call sites, wouldn't it be a lot easier 
> just to change rts51x_read_mem() to make it always return a negative 
> value (such as -EIO) when there's an error?
>
> Alan Stern

I thought about that but there was already existing (retval != STATUS_SUCCESS) checks for these calls.

Tom

>