linux-kernel - Re: [PATCH 2/2] test_firmware: silence underflow warning in test_dev_config_update

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Date:   Thu, 21 Feb 2019 10:54:58 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 2/2] test_firmware: silence underflow warning in
 test_dev_config_update_u8()

On Thu, 21 Feb 2019 21:38:26 +0300 Dan Carpenter <dan.carpenter@...cle.com> wrote:

> We put an upper bound on "new" but we don't check for negatives.

U8_MAX has unsigned type, so `if (new > U8_MAX)' does check for negative.

> In
> this case the underflow doesn't matter very much, but we may as well
> make the static checker happy.
> 
> ...
>
> --- a/lib/test_firmware.c
> +++ b/lib/test_firmware.c
> @@ -326,15 +326,12 @@ static ssize_t test_dev_config_show_int(char *buf, int cfg)
>  static int test_dev_config_update_u8(const char *buf, size_t size, u8 *cfg)
>  {
>  	int ret;
> -	long new;
> +	u8 new;
>  
> -	ret = kstrtol(buf, 10, &new);
> +	ret = kstrtou8(buf, 10, &new);
>  	if (ret)
>  		return ret;
>  
> -	if (new > U8_MAX)
> -		return -EINVAL;
> -
>  	mutex_lock(&test_fw_mutex);
>  	*(u8 *)cfg = new;
>  	mutex_unlock(&test_fw_mutex);

if *buf=="257",

previous behavior: -EINVAL
new behavior: *cfg = 1

yes?

The old behavior seems better.