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

Lee Jones
2023-12-13T11:49:14Z

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@linaro.org>
> ---
> drivers/usb/fotg210/fotg210-hcd.c | 3 ---
> 1 file changed, 3 deletions(-)

Super additional clean-up, thanks.

Reviewed-by: Lee Jones <lee@kernel.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]