[gtk] Terminate strncpy() buffers correctly

[Emmanuele Bassi <ebassi src gnome org>]

commit 14c8a603e3b307d2f247764a828d390980854b0d
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Tue Apr 10 14:51:27 2018 +0100

    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.

 modules/printbackends/gtkprintbackendcups.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/modules/printbackends/gtkprintbackendcups.c b/modules/printbackends/gtkprintbackendcups.c
index 09e18b170e..52614069d2 100644
--- a/modules/printbackends/gtkprintbackendcups.c
+++ b/modules/printbackends/gtkprintbackendcups.c
@@ -5590,7 +5590,10 @@ 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;
@@ -5609,7 +5612,8 @@ 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);
            }
        }