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Date: Mon, 18 Mar 2024 22:36:10 +0000
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Message-ID: <20240318-strncpy-drivers-thermal-intel-int340x_thermal-acpi_thermal_rel-c-v1-1-08839fbf737a@google.com>
Subject: [PATCH] thermal: intel: int340x_thermal: replace deprecated strncpy
 with strscpy
From: Justin Stitt <justinstitt@google.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>, Daniel Lezcano <daniel.lezcano@linaro.org>, 
	Zhang Rui <rui.zhang@intel.com>, Lukasz Luba <lukasz.luba@arm.com>
Cc: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-hardening@vger.kernel.org, Justin Stitt <justinstitt@google.com>
Content-Type: text/plain; charset="utf-8"

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@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
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@google.com>