linux-kernel - [PATCH] iio: sx9324: replace deprecated strncpy

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Message-ID: <20230921-strncpy-drivers-iio-proximity-sx9324-c-v1-1-4e8d28fd1e7c@google.com>
Date:   Thu, 21 Sep 2023 07:01:01 +0000
From:   Justin Stitt <justinstitt@...gle.com>
To:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org,
        Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] iio: sx9324: replace deprecated strncpy

`strncpy` is deprecated for use on NUL-terminated destination strings [1].

We should prefer more robust and less ambiguous string interfaces.

`prop` is defined as this string literal with size 30 (including null):
|       #define SX9324_PROXRAW_DEF "semtech,ph01-proxraw-strength"
|      	char prop[] = SX9324_PROXRAW_DEF;

Each of the strncpy->strscpy replacements involve string literals with a
size less than 30 which means there are no current problems with how
strncpy is used. However, let's move away from using strncpy entirely.

A suitable replacement is `strscpy` [2] due to the fact that it
guarantees NUL-termination on the destination buffer without
unnecessarily NUL-padding.

Moreover, let's opt for the more conventional `sizeof()` as opposed to
`ARRAY_SIZE` for these simple strings.

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>
---
FWIW: It seems fragile to base future `prop` stores on the
size of it's default string.

Note: build-tested
---
 drivers/iio/proximity/sx9324.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/proximity/sx9324.c b/drivers/iio/proximity/sx9324.c
index 438f9c9aba6e..25ac2733bcef 100644
--- a/drivers/iio/proximity/sx9324.c
+++ b/drivers/iio/proximity/sx9324.c
@@ -937,11 +937,9 @@ sx9324_get_default_reg(struct device *dev, int idx,
 	case SX9324_REG_AFE_CTRL4:
 	case SX9324_REG_AFE_CTRL7:
 		if (reg_def->reg == SX9324_REG_AFE_CTRL4)
-			strncpy(prop, "semtech,ph01-resolution",
-				ARRAY_SIZE(prop));
+			strscpy(prop, "semtech,ph01-resolution", sizeof(prop));
 		else
-			strncpy(prop, "semtech,ph23-resolution",
-				ARRAY_SIZE(prop));
+			strscpy(prop, "semtech,ph23-resolution", sizeof(prop));
 
 		ret = device_property_read_u32(dev, prop, &raw);
 		if (ret)
@@ -1012,11 +1010,9 @@ sx9324_get_default_reg(struct device *dev, int idx,
 	case SX9324_REG_PROX_CTRL0:
 	case SX9324_REG_PROX_CTRL1:
 		if (reg_def->reg == SX9324_REG_PROX_CTRL0)
-			strncpy(prop, "semtech,ph01-proxraw-strength",
-				ARRAY_SIZE(prop));
+			strscpy(prop, "semtech,ph01-proxraw-strength", sizeof(prop));
 		else
-			strncpy(prop, "semtech,ph23-proxraw-strength",
-				ARRAY_SIZE(prop));
+			strscpy(prop, "semtech,ph23-proxraw-strength", sizeof(prop));
 		ret = device_property_read_u32(dev, prop, &raw);
 		if (ret)
 			break;

---
base-commit: 2cf0f715623872823a72e451243bbf555d10d032
change-id: 20230921-strncpy-drivers-iio-proximity-sx9324-c-8c3437676039

Best regards,
--
Justin Stitt <justinstitt@...gle.com>