linux-hardening - Re: [PATCH] thermal: intel: int340x_thermal: replace deprecated strncpy with strscpy

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Date: Tue, 19 Mar 2024 12:39:20 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Justin Stitt <justinstitt@...gle.com>, 
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Daniel Lezcano <daniel.lezcano@...aro.org>, 
	Zhang Rui <rui.zhang@...el.com>, Lukasz Luba <lukasz.luba@....com>, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] thermal: intel: int340x_thermal: replace deprecated
 strncpy with strscpy

On Mon, Mar 18, 2024 at 11:36 PM Justin Stitt <justinstitt@...gle.com> wrote:
>
> strncpy() is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
>
> psvt->limit.string can only be 8 bytes so let's use the appropriate size
> macro ACPI_LIMIT_STR_MAX_LEN.
>
> Neither psvt->limit.string or psvt_user[i].limit.string requires the
> NUL-padding behavior that strncpy() provides as they have both been
> filled with NUL-bytes prior to the string operation.
> |       memset(&psvt->limit, 0, sizeof(u64));
> and
> |       psvt_user = kzalloc(psvt_len, GFP_KERNEL);
>
> Let's use `strscpy` [2] due to the fact that it guarantees
> NUL-termination on the destination buffer without unnecessarily
> NUL-padding.
>
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Srinivas, any objections?

> ---
> Note: build-tested only.
>
> Found with: $ rg "strncpy\("
> ---
>  drivers/thermal/intel/int340x_thermal/acpi_thermal_rel.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/thermal/intel/int340x_thermal/acpi_thermal_rel.c b/drivers/thermal/intel/int340x_thermal/acpi_thermal_rel.c
> index dc519a665c18..4b4a4d63e61f 100644
> --- a/drivers/thermal/intel/int340x_thermal/acpi_thermal_rel.c
> +++ b/drivers/thermal/intel/int340x_thermal/acpi_thermal_rel.c
> @@ -309,7 +309,7 @@ static int acpi_parse_psvt(acpi_handle handle, int *psvt_count, struct psvt **ps
>
>                 if (knob->type == ACPI_TYPE_STRING) {
>                         memset(&psvt->limit, 0, sizeof(u64));
> -                       strncpy(psvt->limit.string, psvt_ptr->limit.str_ptr, knob->string.length);
> +                       strscpy(psvt->limit.string, psvt_ptr->limit.str_ptr, ACPI_LIMIT_STR_MAX_LEN);
>                 } else {
>                         psvt->limit.integer = psvt_ptr->limit.integer;
>                 }
> @@ -468,7 +468,7 @@ static int fill_psvt(char __user *ubuf)
>                 psvt_user[i].unlimit_coeff = psvts[i].unlimit_coeff;
>                 psvt_user[i].control_knob_type = psvts[i].control_knob_type;
>                 if (psvt_user[i].control_knob_type == ACPI_TYPE_STRING)
> -                       strncpy(psvt_user[i].limit.string, psvts[i].limit.string,
> +                       strscpy(psvt_user[i].limit.string, psvts[i].limit.string,
>                                 ACPI_LIMIT_STR_MAX_LEN);
>                 else
>                         psvt_user[i].limit.integer = psvts[i].limit.integer;
>
> ---
> base-commit: bf3a69c6861ff4dc7892d895c87074af7bc1c400
> change-id: 20240318-strncpy-drivers-thermal-intel-int340x_thermal-acpi_thermal_rel-c-17070c1e42f3
>
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
>