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

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Date:   Tue, 11 Aug 2020 12:03:48 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     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 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