libroot/malloc: Make the guarded heap handle bogus pointers better.

* Check if the area is a stack, and panic() if so.

 * Check names before accessing any area, and don't try
   to do anything with areas that we didn't create.

Makes frees pointing to stack data have much more useful
diagnostics than just "generic segfault".

src/system/libroot/posix/malloc/debug/guarded_heap.cpp

@@ -714,6 +714,15 @@ guarded_heap_area_allocation_for(void* address, area_id& allocationArea)
 	if (get_area_info(allocationArea, &areaInfo) != B_OK)
 		return NULL;
 
+	if ((areaInfo.protection & B_STACK_AREA) != 0) {
+		panic("tried to free %p which is in a stack area (%d)",
+			address, allocationArea);
+		return NULL;
+	}
+
+	if (strncmp(areaInfo.name, "guarded_heap", strlen("guarded_heap")) != 0)
+		return NULL;
+
 	guarded_heap_page* page = (guarded_heap_page*)areaInfo.address;
 	if (page->flags != (GUARDED_HEAP_PAGE_FLAG_USED
 			| GUARDED_HEAP_PAGE_FLAG_FIRST | GUARDED_HEAP_PAGE_FLAG_AREA)) {