[gmime] gmime_multipart_foreach: avoid stack overflow from recursion

[Rico Tzschichholz <ricotz src gnome org>]

commit 6d7c904e52bdfd723db990a326527fd65e45320a
Author: Eric Wong <e 80x24 org>
Date:   Sat Nov 9 07:55:45 2019 -0500

    gmime_multipart_foreach: avoid stack overflow from recursion
    
    We can use a GQueue to emulate the behavior of an stack on the
    heap.  This allows us to parse deeply nested MIME parts since
    RLIMIT_STACK is typically only a few megabytes while typical
    GNU/Linux systems can use all available virtual memory for the
    heap.

 gmime/gmime-multipart.c | 52 ++++++++++++++++++++++++++++++++++---------------
 1 file changed, 36 insertions(+), 16 deletions(-)
---
diff --git a/gmime/gmime-multipart.c b/gmime/gmime-multipart.c
index ade11d5b..f27dbb51 100644
--- a/gmime/gmime-multipart.c
+++ b/gmime/gmime-multipart.c
@@ -775,22 +775,10 @@ g_mime_multipart_get_boundary (GMimeMultipart *multipart)
        return GMIME_MULTIPART_GET_CLASS (multipart)->get_boundary (multipart);
 }
 
-
-static void
-multipart_foreach (GMimeMultipart *multipart, GMimeObjectForeachFunc callback, gpointer user_data)
-{
+typedef struct _GMimeForeachData {
+       GMimeObject *parent;
        GMimeObject *part;
-       guint i;
-       
-       for (i = 0; i < multipart->children->len; i++) {
-               part = (GMimeObject *) multipart->children->pdata[i];
-               callback ((GMimeObject *) multipart, part, user_data);
-               
-               if (GMIME_IS_MULTIPART (part))
-                       multipart_foreach ((GMimeMultipart *) part, callback, user_data);
-       }
-}
-
+} GMimeForeachData;
 
 /**
  * g_mime_multipart_foreach: 
@@ -804,10 +792,42 @@ multipart_foreach (GMimeMultipart *multipart, GMimeObjectForeachFunc callback, g
 void
 g_mime_multipart_foreach (GMimeMultipart *multipart, GMimeObjectForeachFunc callback, gpointer user_data)
 {
+       GMimeForeachData *tmp;
+       GQueue *queue;
+       guint i;
        g_return_if_fail (GMIME_IS_MULTIPART (multipart));
        g_return_if_fail (callback != NULL);
        
-       multipart_foreach (multipart, callback, user_data);
+       tmp = g_malloc (sizeof (GMimeForeachData));
+       queue = g_queue_new ();
+
+       tmp->parent = (GMimeObject *) multipart;
+       tmp->part = (GMimeObject *) multipart;
+
+       g_queue_push_tail (queue, tmp);
+
+       while ((tmp = (GMimeForeachData *) g_queue_pop_head (queue))) {
+               GMimeObject *parent = tmp->parent;
+               GMimeObject *part = tmp->part;
+
+               g_free (tmp);
+               if (part != parent)
+                       callback (parent, part, user_data);
+
+               if (GMIME_IS_MULTIPART (part)) {
+                       multipart = (GMimeMultipart *) part;
+                       i = multipart->children->len;
+                       while (i > 0) {
+                               tmp = g_malloc (sizeof (GMimeForeachData));
+                               tmp->parent = part;
+                               tmp->part = (GMimeObject *) multipart->children->pdata[--i];
+
+                               g_queue_push_head (queue, tmp);
+                       }
+               }
+       }
+
+       g_queue_free (queue);
 }