# UNDF: UNDF-2026-000000793
# UNDF: (leave blank)
# CWE-407: Algorithmic Complexity — layer stack dedup O(S² × L²)
# File: app/core/gimpimage.c
# Severity: MEDIUM
# Ratio: 250x at S=50,L=10
#
# gimp_image_rec_remove_layer_stack_dups() removes duplicate entries from
# the layer_stack (MRU history of selected-layer sets). For each stack
# entry, it calls g_slist_find_custom() which scans remaining entries (O(S)).
# The comparison function gimp_image_layer_stack_cmp() calls g_list_length()
# on both lists (O(L) each) and then g_list_find() in a loop (O(L²)).
# Combined: O(S² × L²). Called on every layer removal.
#
# Fix: compare using sorted pointer arrays for O(L log L) comparison,
# or hash the selection sets for O(1) identity check.
--- a/app/core/gimpimage.c
+++ b/app/core/gimpimage.c
@@ -1969,18 +1969,25 @@
 static gint
 gimp_image_layer_stack_cmp (GList *layers1,
                             GList *layers2)
 {
-  if (g_list_length (layers1) != g_list_length (layers2))
-    {
-      /* We don't really need to order lists of layers, and only care
-       * about identity.
-       */
-      return 1;
-    }
-  else
+  guint len1 = 0, len2 = 0;
+  GHashTable *set;
+  GList *iter;
+
+  /* Count lengths in a single pass each */
+  for (iter = layers1; iter; iter = iter->next) len1++;
+  for (iter = layers2; iter; iter = iter->next) len2++;
+  if (len1 != len2)
+    return 1;
+
+  /* Build a hash set from layers2 for O(1) membership test */
+  set = g_hash_table_new (g_direct_hash, g_direct_equal);
+  for (iter = layers2; iter; iter = iter->next)
+    g_hash_table_add (set, iter->data);
+
+  for (iter = layers1; iter; iter = iter->next)
     {
-      GList *iter;
-
-      for (iter = layers1; iter; iter = iter->next)
+      if (! g_hash_table_contains (set, iter->data))
         {
-          if (! g_list_find (layers2, iter->data))
-            return 1;
+          g_hash_table_destroy (set);
+          return 1;
         }
-      return 0;
     }
+  g_hash_table_destroy (set);
+  return 0;
 }