[cogl] matrix-stack: getting parent ptr before freeing

[Robert Bragg <rbragg src gnome org>]

commit e5d836b84acb35a009854a0cc0892320023789d1
Author: Robert Bragg <robert linux intel com>
Date:   Tue Nov 27 22:02:56 2012 +0000

    matrix-stack: getting parent ptr before freeing
    
    When unrefing a CoglMatrixEntry we walk up the ancestry unrefing and
    freeing entries until we find an entry that doesn't need to be freed.
    The problem fixed by this patch was that we didn't dereference the
    parent member of each entry until after the entry was freed and so there
    was the potential for reading a junk parent pointer back.

 cogl/cogl-matrix-stack.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/cogl/cogl-matrix-stack.c b/cogl/cogl-matrix-stack.c
index e5ad10d..4d5b9eb 100644
--- a/cogl/cogl-matrix-stack.c
+++ b/cogl/cogl-matrix-stack.c
@@ -328,8 +328,12 @@ _cogl_matrix_entry_ref (CoglMatrixEntry *entry)
 void
 _cogl_matrix_entry_unref (CoglMatrixEntry *entry)
 {
-  for (; entry && --entry->ref_count <= 0; entry = entry->parent)
+  CoglMatrixEntry *parent;
+
+  for (; entry && --entry->ref_count <= 0; entry = parent)
     {
+      parent = entry->parent;
+
       switch (entry->op)
         {
         case COGL_MATRIX_OP_LOAD_IDENTITY: