[glib: 1/2] gscanner: Avoid undefined behaviour copying between union members

[Emmanuele Bassi <ebassi src gnome org>]

commit add3be20869b5aa5b633333c062d9f82f625bfd2
Author: Philip Withnall <pwithnall endlessos org>
Date:   Tue Nov 3 16:59:36 2020 +0000

    gscanner: Avoid undefined behaviour copying between union members
    
    It’s technically undefined behaviour in C to copy between two
    potentially-overlapping regions of memory (just like it is when calling
    `memcpy()`). This can easily happen with union members; and the ones in
    `GScanner` in particular.
    
    Fix that by copying through an intermediate variable.
    
    Coverity CID: #1427317, 1427340
    
    Signed-off-by: Philip Withnall <pwithnall endlessos org>

 glib/gscanner.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)
---
diff --git a/glib/gscanner.c b/glib/gscanner.c
index b77514afe..c858abf9e 100644
--- a/glib/gscanner.c
+++ b/glib/gscanner.c
@@ -1696,12 +1696,19 @@ g_scanner_get_token_i (GScanner *scanner,
       scanner->config->int_2_float)
     {
       *token_p = G_TOKEN_FLOAT;
+
+      /* Have to assign through a temporary variable to avoid undefined behaviour
+       * by copying between potentially-overlapping union members. */
       if (scanner->config->store_int64)
         {
-          value_p->v_float = value_p->v_int64;
+          gint64 temp = value_p->v_int64;
+          value_p->v_float = temp;
         }
       else
-       value_p->v_float = value_p->v_int;
+        {
+          gint temp = value_p->v_int;
+          value_p->v_float = temp;
+        }
     }
   
   errno = 0;