leds: core: Bail out when composed name can't fit the buffer

GCC compiler complains about snprintf() calls that may potentially cut
the output:

 drivers/leds/led-core.c:551:78: error: ‘snprintf’ output may be truncated before the last format character [-Werror=format-truncation=]
 drivers/leds/led-core.c:554:78: error: ‘snprintf’ output may be truncated before the last format character [-Werror=format-truncation=]
 ...

Fix these by checking for the potential overflow. This requires
to align all the branches to use the same callee, i.e. snprintf(),
otherwise the code will be blown up and return different error codes
for the different branches.

Signed-off-by: Andy Shevchenko <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Lee Jones <[email protected]>

Author: andy-shev

drivers/leds/led-core.c

@@ -529,6 +529,7 @@ int led_compose_name(struct device *dev, struct led_init_data *init_data,
 	struct led_properties props = {};
 	struct fwnode_handle *fwnode = init_data->fwnode;
 	const char *devicename = init_data->devicename;
+	int n;
 
 	if (!led_classdev_name)
 		return -EINVAL;
@@ -542,45 +543,49 @@ int led_compose_name(struct device *dev, struct led_init_data *init_data,
 		 * Otherwise the label is prepended with devicename to compose
 		 * the final LED class device name.
 		 */
-		if (!devicename) {
-			strscpy(led_classdev_name, props.label,
-				LED_MAX_NAME_SIZE);
+		if (devicename) {
+			n = snprintf(led_classdev_name, LED_MAX_NAME_SIZE, "%s:%s",
+				     devicename, props.label);
 		} else {
-			snprintf(led_classdev_name, LED_MAX_NAME_SIZE, "%s:%s",
-				 devicename, props.label);
+			n = snprintf(led_classdev_name, LED_MAX_NAME_SIZE, "%s", props.label);
 		}
 	} else if (props.function || props.color_present) {
 		char tmp_buf[LED_MAX_NAME_SIZE];
 
 		if (props.func_enum_present) {
-			snprintf(tmp_buf, LED_MAX_NAME_SIZE, "%s:%s-%d",
-				 props.color_present ? led_colors[props.color] : "",
-				 props.function ?: "", props.func_enum);
+			n = snprintf(tmp_buf, LED_MAX_NAME_SIZE, "%s:%s-%d",
+				     props.color_present ? led_colors[props.color] : "",
+				     props.function ?: "", props.func_enum);
 		} else {
-			snprintf(tmp_buf, LED_MAX_NAME_SIZE, "%s:%s",
-				 props.color_present ? led_colors[props.color] : "",
-				 props.function ?: "");
+			n = snprintf(tmp_buf, LED_MAX_NAME_SIZE, "%s:%s",
+				     props.color_present ? led_colors[props.color] : "",
+				     props.function ?: "");
 		}
+		if (n >= LED_MAX_NAME_SIZE)
+			return -E2BIG;
+
 		if (init_data->devname_mandatory) {
-			snprintf(led_classdev_name, LED_MAX_NAME_SIZE, "%s:%s",
-				 devicename, tmp_buf);
+			n = snprintf(led_classdev_name, LED_MAX_NAME_SIZE, "%s:%s",
+				     devicename, tmp_buf);
 		} else {
-			strscpy(led_classdev_name, tmp_buf, LED_MAX_NAME_SIZE);
-
+			n = snprintf(led_classdev_name, LED_MAX_NAME_SIZE, "%s", tmp_buf);
 		}
 	} else if (init_data->default_label) {
 		if (!devicename) {
 			dev_err(dev, "Legacy LED naming requires devicename segment");
 			return -EINVAL;
 		}
-		snprintf(led_classdev_name, LED_MAX_NAME_SIZE, "%s:%s",
-			 devicename, init_data->default_label);
+		n = snprintf(led_classdev_name, LED_MAX_NAME_SIZE, "%s:%s",
+			     devicename, init_data->default_label);
 	} else if (is_of_node(fwnode)) {
-		strscpy(led_classdev_name, to_of_node(fwnode)->name,
-			LED_MAX_NAME_SIZE);
+		n = snprintf(led_classdev_name, LED_MAX_NAME_SIZE, "%s",
+			     to_of_node(fwnode)->name);
 	} else
 		return -EINVAL;
 
+	if (n >= LED_MAX_NAME_SIZE)
+		return -E2BIG;
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(led_compose_name);