Index: apps/app_macro.c
===================================================================
--- apps/app_macro.c	(revision 60763)
+++ apps/app_macro.c	(working copy)
@@ -161,6 +161,14 @@
 	struct ast_context *c;
 	struct ast_exten *e;
 
+	/* Approximation of log10(pow(2, n - 1)) + 3, which is the number of
+	 * characters needed to print a signed integer of n bits, where n is the
+	 * native pointer size.  Due to integer rounding, this is good for quite
+	 * a long time.
+	 */
+	char stackheadc[sizeof(void *) * 9999 / 4000 + 3];
+	void *stackhead;
+
 	if (ast_strlen_zero(data)) {
 		ast_log(LOG_WARNING, "Macro() requires arguments. See \"show application macro\" for help.\n");
 		return -1;
@@ -181,6 +189,19 @@
 		depth = 0;
 	}
 
+	/* Since people keep finding new ways to overflow the stack with Macro,
+	 * here is a new approach to avoid future crashes -- just count the amount
+	 * of stack used so far and return before we near our limit.
+	 */
+	tmp = pbx_builtin_getvar_helper(chan, "MACRO_STACKHEAD");
+	if (tmp) {
+		sscanf(tmp, "%p", &stackhead);
+	} else {
+		stackhead = &tmp;
+		snprintf(stackheadc, sizeof(stackheadc), "%p", stackhead);
+		pbx_builtin_setvar_helper(chan, "MACRO_STACKHEAD", stackheadc);
+	}
+
 	/* Used for detecting whether to return when a Macro is called from another Macro after hangup */
 	if (strcmp(chan->exten, "h") == 0)
 		pbx_builtin_setvar_helper(chan, "MACRO_IN_HANGUP", "1");
@@ -193,6 +214,17 @@
 		LOCAL_USER_REMOVE(u);
 		return 0;
 	}
+
+	/* 200,000 is an arbitrary number lower than 240k, which is the current
+	 * per-thread stack size.  Also, we abs() the value, so that it doesn't
+	 * matter which way the stack grows (per arch).
+	 */
+	if (abs((long)&tmp - (long)stackhead) > 200000L) {
+		ast_log(LOG_ERROR, "Macro():  you have consumed too much per-thread stack space.  Returning early to avoid a possible crash.\n");
+		LOCAL_USER_REMOVE(u);
+		return 0;
+	}
+
 	snprintf(depthc, sizeof(depthc), "%d", depth + 1);
 	pbx_builtin_setvar_helper(chan, "MACRO_DEPTH", depthc);