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References: <20240318-strncpy-drivers-thermal-intel-int340x_thermal-acpi_thermal_rel-c-v1-1-08839fbf737a@google.com>
In-Reply-To: <20240318-strncpy-drivers-thermal-intel-int340x_thermal-acpi_thermal_rel-c-v1-1-08839fbf737a@google.com>
From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Tue, 19 Mar 2024 12:39:20 +0100
Message-ID: <CAJZ5v0j=cYbqyfi6y45hnu+Y_tvMGYb9p6d=kpsOA0AsxBoy3g@mail.gmail.com>
Subject: Re: [PATCH] thermal: intel: int340x_thermal: replace deprecated
 strncpy with strscpy
To: Justin Stitt <justinstitt@google.com>, 
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>, Daniel Lezcano <daniel.lezcano@linaro.org>, 
	Zhang Rui <rui.zhang@intel.com>, Lukasz Luba <lukasz.luba@arm.com>, linux-pm@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
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On Mon, Mar 18, 2024 at 11:36=E2=80=AFPM Justin Stitt <justinstitt@google.c=
om> 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 =3D 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#strn=
cpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.h=
tml [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.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/d=
rivers/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 *p=
svt_count, struct psvt **ps
>
>                 if (knob->type =3D=3D ACPI_TYPE_STRING) {
>                         memset(&psvt->limit, 0, sizeof(u64));
> -                       strncpy(psvt->limit.string, psvt_ptr->limit.str_p=
tr, knob->string.length);
> +                       strscpy(psvt->limit.string, psvt_ptr->limit.str_p=
tr, ACPI_LIMIT_STR_MAX_LEN);
>                 } else {
>                         psvt->limit.integer =3D psvt_ptr->limit.integer;
>                 }
> @@ -468,7 +468,7 @@ static int fill_psvt(char __user *ubuf)
>                 psvt_user[i].unlimit_coeff =3D psvts[i].unlimit_coeff;
>                 psvt_user[i].control_knob_type =3D psvts[i].control_knob_=
type;
>                 if (psvt_user[i].control_knob_type =3D=3D ACPI_TYPE_STRIN=
G)
> -                       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 =3D psvts[i].limit.int=
eger;
>
> ---
> base-commit: bf3a69c6861ff4dc7892d895c87074af7bc1c400
> change-id: 20240318-strncpy-drivers-thermal-intel-int340x_thermal-acpi_th=
ermal_rel-c-17070c1e42f3
>
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
>