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

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Date:   Tue, 11 Aug 2020 13:53:38 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Tom Rix <trix@...hat.com>
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 Tue, Aug 11, 2020 at 10:29:29AM -0700, Tom Rix wrote:
> 
> 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.

The only values that routine currently returns are 
USB_STOR_TRANSPORT_ERROR, -EIO, and 0.  None of the callers distinguish 
between the first two values, so you can just change the first to the 
second.

Note that STATUS_SUCCESS is simply 0.

Alan Stern