linux-kernel - Re: [PATCH] usb: fotg210-hcd: delete an incorrect bounds test

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Date:   Wed, 13 Dec 2023 11:49:06 +0000
From:   Lee Jones <lee@...nel.org>
To:     Dan Carpenter <dan.carpenter@...aro.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] usb: fotg210-hcd: delete an incorrect bounds test

On Fri, 08 Dec 2023, Dan Carpenter wrote:

> Here "temp" is the number of characters that we have written and "size"
> is the size of the buffer.  The intent was clearly to say that if we have
> written to the end of the buffer then stop.
> 
> However, for that to work the comparison should have been done on the
> original "size" value instead of the "size -= temp" value.  Not only
> will that not trigger when we want to, but there is a small chance that
> it will trigger incorrectly before we want it to and we break from the
> loop slightly earlier than intended.
> 
> This code was recently changed from using snprintf() to scnprintf().  With
> snprintf() we likely would have continued looping and passed a negative
> size parameter to snprintf().  This would have triggered an annoying
> WARN().  Now that we have converted to scnprintf() "size" will never
> drop below 1 and there is no real need for this test.  We could change
> the condition to "if (temp <= 1) goto done;" but just deleting the test
> is cleanest.
> 
> Fixes: 1dd33a9f1b95 ("usb: fotg210: Collect pieces of dual mode controller")
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> ---
>  drivers/usb/fotg210/fotg210-hcd.c | 3 ---
>  1 file changed, 3 deletions(-)

Super additional clean-up, thanks.

Reviewed-by: Lee Jones <lee@...nel.org>

> diff --git a/drivers/usb/fotg210/fotg210-hcd.c b/drivers/usb/fotg210/fotg210-hcd.c
> index b2f8b53cc8ef..8c5aaf860635 100644
> --- a/drivers/usb/fotg210/fotg210-hcd.c
> +++ b/drivers/usb/fotg210/fotg210-hcd.c
> @@ -426,8 +426,6 @@ static void qh_lines(struct fotg210_hcd *fotg210, struct fotg210_qh *qh,
>  				td->urb);
>  		size -= temp;
>  		next += temp;
> -		if (temp == size)
> -			goto done;
>  	}
>  
>  	temp = scnprintf(next, size, "\n");
> @@ -435,7 +433,6 @@ static void qh_lines(struct fotg210_hcd *fotg210, struct fotg210_qh *qh,
>  	size -= temp;
>  	next += temp;
>  
> -done:
>  	*sizep = size;
>  	*nextp = next;
>  }
> -- 
> 2.42.0
> 

-- 
Lee Jones [李琼斯]