[PATCH v3] iio: sx9324: avoid copying property strings

[Justin Stitt]

We're doing some needless string copies when trying to assign the proper
`prop` string. We can make `prop` a const char* and simply assign to
string literals.

For the case where a format string is used, let's extract the parsing
logic out into sx9324_parse_phase_prop(). We no longer need to create
copies or allocate new memory.

sx9324_parse_phase_prop() will simply return the default def value if it
fails.

This also cleans up some deprecated strncpy() uses [1].

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@xxxxxxxxxxxxxxx
Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
---
Changes in v3:
- extract logic into sx9324_parse_phase_prop() and use string literals
  (thanks Stephen)
- rebase onto mainline bee0e7762ad2c602
- Link to v2: https://lore.kernel.org/r/20231026-strncpy-drivers-iio-proximity-sx9324-c-v2-1-cee6e5db700c@xxxxxxxxxx

Changes in v2:
- make prop a const char* and do simple assignments (thanks Jonathan)
- rebase onto 3a568e3a961ba330
- Link to v1: https://lore.kernel.org/r/20230921-strncpy-drivers-iio-proximity-sx9324-c-v1-1-4e8d28fd1e7c@xxxxxxxxxx
---
---
 drivers/iio/proximity/sx9324.c | 69 ++++++++++++++++++++++++++----------------
 1 file changed, 43 insertions(+), 26 deletions(-)

diff --git a/drivers/iio/proximity/sx9324.c b/drivers/iio/proximity/sx9324.c
index 438f9c9aba6e..e3bc30b57b19 100644
--- a/drivers/iio/proximity/sx9324.c
+++ b/drivers/iio/proximity/sx9324.c
@@ -873,6 +873,32 @@ static int sx9324_init_compensation(struct iio_dev *indio_dev)
 					20000, 2000000);
 }
 
+static u32 sx9324_parse_phase_prop(struct device *dev,
+				   struct sx_common_reg_default *reg_def,
+				   int idx, const char *prop)
+{
+	unsigned int pin_defs[SX9324_NUM_PINS];
+	int count, ret, pin;
+	u8 default_def;
+	u32 raw = 0;
+
+	default_def = sx9324_default_regs[idx].def;
+
+	count = device_property_count_u32(dev, prop);
+	if (count != ARRAY_SIZE(pin_defs))
+		return default_def;
+	ret = device_property_read_u32_array(dev, prop, pin_defs,
+					     ARRAY_SIZE(pin_defs));
+	if (ret)
+		return default_def;
+
+	for (pin = 0; pin < SX9324_NUM_PINS; pin++)
+		raw |= (pin_defs[pin] << (2 * pin)) &
+		       SX9324_REG_AFE_PH0_PIN_MASK(pin);
+
+	return raw;
+}
+
 static const struct sx_common_reg_default *
 sx9324_get_default_reg(struct device *dev, int idx,
 		       struct sx_common_reg_default *reg_def)
@@ -884,35 +910,30 @@ sx9324_get_default_reg(struct device *dev, int idx,
 #define SX9324_PIN_DEF "semtech,ph0-pin"
 #define SX9324_RESOLUTION_DEF "semtech,ph01-resolution"
 #define SX9324_PROXRAW_DEF "semtech,ph01-proxraw-strength"
-	unsigned int pin_defs[SX9324_NUM_PINS];
-	char prop[] = SX9324_PROXRAW_DEF;
+	const char *prop = SX9324_PROXRAW_DEF;
 	u32 start = 0, raw = 0, pos = 0;
-	int ret, count, ph, pin;
 	const char *res;
+	int ret;
 
 	memcpy(reg_def, &sx9324_default_regs[idx], sizeof(*reg_def));
 
 	sx_common_get_raw_register_config(dev, reg_def);
 	switch (reg_def->reg) {
 	case SX9324_REG_AFE_PH0:
+		reg_def->def = sx9324_parse_phase_prop(dev, reg_def, idx,
+						       "semtech,ph0-pin");
+		break;
 	case SX9324_REG_AFE_PH1:
+		reg_def->def = sx9324_parse_phase_prop(dev, reg_def, idx,
+						       "semtech,ph1-pin");
+		break;
 	case SX9324_REG_AFE_PH2:
+		reg_def->def = sx9324_parse_phase_prop(dev, reg_def, idx,
+						       "semtech,ph2-pin");
+		break;
 	case SX9324_REG_AFE_PH3:
-		ph = reg_def->reg - SX9324_REG_AFE_PH0;
-		snprintf(prop, ARRAY_SIZE(prop), "semtech,ph%d-pin", ph);
-
-		count = device_property_count_u32(dev, prop);
-		if (count != ARRAY_SIZE(pin_defs))
-			break;
-		ret = device_property_read_u32_array(dev, prop, pin_defs,
-						     ARRAY_SIZE(pin_defs));
-		if (ret)
-			break;
-
-		for (pin = 0; pin < SX9324_NUM_PINS; pin++)
-			raw |= (pin_defs[pin] << (2 * pin)) &
-			       SX9324_REG_AFE_PH0_PIN_MASK(pin);
-		reg_def->def = raw;
+		reg_def->def = sx9324_parse_phase_prop(dev, reg_def, idx,
+						       "semtech,ph3-pin");
 		break;
 	case SX9324_REG_AFE_CTRL0:
 		ret = device_property_read_string(dev,
@@ -937,11 +958,9 @@ 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));
+			prop = "semtech,ph01-resolution";
 		else
-			strncpy(prop, "semtech,ph23-resolution",
-				ARRAY_SIZE(prop));
+			prop = "semtech,ph23-resolution";
 
 		ret = device_property_read_u32(dev, prop, &raw);
 		if (ret)
@@ -1012,11 +1031,9 @@ 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));
+			prop = "semtech,ph01-proxraw-strength";
 		else
-			strncpy(prop, "semtech,ph23-proxraw-strength",
-				ARRAY_SIZE(prop));
+			prop = "semtech,ph23-proxraw-strength";
 		ret = device_property_read_u32(dev, prop, &raw);
 		if (ret)
 			break;

---
base-commit: bee0e7762ad2c6025b9f5245c040fcc36ef2bde8
change-id: 20230921-strncpy-drivers-iio-proximity-sx9324-c-8c3437676039

Best regards,
--
Justin Stitt <justinstitt@xxxxxxxxxx>