Terminate strncpy() buffers correctly

When using strncpy() with a buffer we need to account for the
terminating NUL character. GCC 8 started warning when using PPD_MAX_NAME
as the buffer length for strncpy() because the buffer we're copying into
has the same length — which means that the terminating NUL may be
skipped if the source string has a length of PPD_MAX_NAME.

The appropriate way to handle the case where we're copying a source with
a length bigger than of PPD_MAX_NAME is, as reported in the strncpy()
documentation, to copy `PPD_MAX_NAME - 1` bytes, and explicitly NUL
terminate the destination buffer. This has the additional benefit of
avoiding the compiler warning.

1 files changed, 6 insertions, 2 deletions

diff --git a/modules/printbackends/cups/gtkprintbackendcups.c b/modules/printbackends/cups/gtkprintbackendcups.c
index 97c74d6bf4..f12b5eb60d 100644
--- a/modules/printbackends/cups/gtkprintbackendcups.c
+++ b/modules/printbackends/cups/gtkprintbackendcups.c
@@ -5645,7 +5645,10 @@ cups_printer_get_options (GtkPrinter           *printer,
 	  ppd_name = gtk_paper_size_get_ppd_name (paper_size);
 
 	  if (ppd_name)
-	    strncpy (ppd_option->defchoice, ppd_name, PPD_MAX_NAME);
+            {
+              strncpy (ppd_option->defchoice, ppd_name, PPD_MAX_NAME - 1);
+              ppd_option->defchoice[PPD_MAX_NAME - 1] = '\0';
+            }
 	  else
 	    {
 	      gchar *custom_name;
@@ -5664,7 +5667,8 @@ cups_printer_get_options (GtkPrinter           *printer,
 	       * 230.4x142.9"
                */
 	      custom_name = g_strdup_printf (_("Custom %s×%s"), width, height);
-	      strncpy (ppd_option->defchoice, custom_name, PPD_MAX_NAME);
+              strncpy (ppd_option->defchoice, custom_name, PPD_MAX_NAME - 1);
+              ppd_option->defchoice[PPD_MAX_NAME - 1] = '\0';
 	      g_free (custom_name);
 	    }
 	}