[PATCH] platform/x86: dell-wmi-sysman: use strnlen in strlcpy_attr

[Thorsten Blum <thorsten.blum@linux.dev>]

Use strnlen() to limit source string scanning to MAX_BUFF bytes. Return
early on error and make the "empty string means not applicable" case
explicit.

Use 'const char *' for the read-only source string while at it.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
 .../dell/dell-wmi-sysman/dell-wmi-sysman.h    |  2 +-
 .../x86/dell/dell-wmi-sysman/sysman.c         | 20 ++++++++++---------
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/drivers/platform/x86/dell/dell-wmi-sysman/dell-wmi-sysman.h b/drivers/platform/x86/dell/dell-wmi-sysman/dell-wmi-sysman.h
index 5278a93fdaf7..f6943301b857 100644
--- a/drivers/platform/x86/dell/dell-wmi-sysman/dell-wmi-sysman.h
+++ b/drivers/platform/x86/dell/dell-wmi-sysman/dell-wmi-sysman.h
@@ -162,7 +162,7 @@ static ssize_t curr_val##_store(struct kobject *kobj,				\
 
 union acpi_object *get_wmiobj_pointer(int instance_id, const char *guid_string);
 int get_instance_count(const char *guid_string);
-void strlcpy_attr(char *dest, char *src);
+void strlcpy_attr(char *dest, const char *src);
 
 int populate_enum_data(union acpi_object *enumeration_obj, int instance_id,
 			struct kobject *attr_name_kobj, u32 enum_property_count);
diff --git a/drivers/platform/x86/dell/dell-wmi-sysman/sysman.c b/drivers/platform/x86/dell/dell-wmi-sysman/sysman.c
index 51d25fdc1389..6c9911accefc 100644
--- a/drivers/platform/x86/dell/dell-wmi-sysman/sysman.c
+++ b/drivers/platform/x86/dell/dell-wmi-sysman/sysman.c
@@ -234,18 +234,20 @@ static const struct kobj_type attr_name_ktype = {
  * @dest: Where to copy the string to
  * @src: Where to copy the string from
  */
-void strlcpy_attr(char *dest, char *src)
+void strlcpy_attr(char *dest, const char *src)
 {
-	size_t len = strlen(src) + 1;
+	size_t len = strnlen(src, MAX_BUFF);
 
-	if (len > 1 && len <= MAX_BUFF)
-		strscpy(dest, src, len);
-
-	/*len can be zero because any property not-applicable to attribute can
-	 * be empty so check only for too long buffers and log error
-	 */
-	if (len > MAX_BUFF)
+	if (len == MAX_BUFF) {
 		pr_err("Source string returned from BIOS is out of bound!\n");
+		return;
+	}
+
+	/* Empty string means "not applicable" and is skipped intentionally. */
+	if (len == 0)
+		return;
+
+	strscpy(dest, src, len + 1);
 }
 
 /**