ACPICA: Replace strncpy() with strscpy_pad() in acpi_ut_safe_strncpy()

Replace the deprecated[1] strncpy() with strscpy_pad() in
acpi_ut_safe_strncpy().

The function is a "safe strncpy" wrapper that does
strncpy(dest, source, dest_size) followed by manual NUL-termination
at dest[dest_size - 1]. strscpy_pad() is a direct replacement: it
NUL-terminates, zero-pads the remainder, and the manual termination
is no longer needed.

All callers pass NUL-terminated source strings (C string literals,
__FILE__ via ACPI_MODULE_NAME, or user-provided filenames that have
already been validated). The destinations are fixed-size char arrays
in ACPICA internal structures (allocation->module, aml_op_name,
acpi_gbl_db_debug_filename), all consumed as C strings.

No behavioral change: strscpy_pad() produces identical output to
strncpy() + manual NUL-termination for NUL-terminated sources that
are shorter than dest_size. For sources longer than dest_size,
strncpy() wrote dest_size non-NUL bytes then the manual termination
overwrote the last byte with NUL; strscpy_pad() writes dest_size-1
bytes plus NUL: same result.

Link: https://github.com/KSPP/linux/issues/90 [1]
Signed-off-by: Kees Cook <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Rafael J. Wysocki <[email protected]>

drivers/acpi/acpica/utnonansi.c

@@ -168,8 +168,7 @@ void acpi_ut_safe_strncpy(char *dest, char *source, acpi_size dest_size)
 {
 	/* Always terminate destination string */
 
-	strncpy(dest, source, dest_size);
-	dest[dest_size - 1] = 0;
+	strscpy_pad(dest, source, dest_size);
 }
 
 #endif