Re: [dpdk-dev] [PATCH v2 1/2] power: fix power management env detection

[Bruce Richardson <bruce.richardson@intel.com>]

On Mon, Jul 13, 2020 at 03:54:27PM +0100, Anatoly Burakov wrote:
> Anything coming from sysfs has a newline at the end. Cut it off before
> comparing the strings.
> 
> Fixes: 20ab67608a39 ("power: add environment capability probing")
> 
> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> Acked-by: David Hunt <david.hunt@intel.com>
> ---
>  lib/librte_power/power_common.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/lib/librte_power/power_common.c b/lib/librte_power/power_common.c
> index 59023d986b..22b016ca9d 100644
> --- a/lib/librte_power/power_common.c
> +++ b/lib/librte_power/power_common.c
> @@ -15,6 +15,7 @@ int
>  cpufreq_check_scaling_driver(const char *driver_name)
>  {
>  	unsigned int lcore_id = 0; /* always check core 0 */
> +	size_t end_idx;
>  	char fullpath[PATH_MAX];
>  	char readbuf[PATH_MAX];
>  	char *s;
> @@ -39,6 +40,13 @@ cpufreq_check_scaling_driver(const char *driver_name)
>  	if (s == NULL)
>  		return 0;
>  
> +	/* when read from sysfs, driver name has an extra newline at the end */
> +	end_idx = strnlen(readbuf, sizeof(readbuf));
> +	/* prevent underflow if len is zero */
> +	if (end_idx > 0)
> +		end_idx--;
> +	readbuf[end_idx] = '\0';
> +
Would it not be safer to add " && readbuf[end_idx - 1] == '\n'" to the
condition, to check that it's terminated as expected? Theoretically if we
had a long string returned which was truncated, or only just fit, there
would not be a '\n' at the end.

/Bruce