Prevent heap alloc functions from running out of stack space.

When asterisk has run out of memory (for whatever reason), the alloc
function logs a message. Logging requires memory. A recipe for
infinite recursion.

Stop the recursion by comparing the function call depth for sane values
before attempting another OOM log message.

Review: https://reviewboard.asterisk.org/r/2743/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@396822 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/utils.h

@@ -25,6 +25,7 @@
 
 #include "asterisk/network.h"
 
+#include <execinfo.h>
 #include <time.h>	/* we want to override localtime_r */
 #include <unistd.h>
 #include <string.h>
@@ -483,8 +484,24 @@ static void ast_free_ptr(void *ptr)
 
 #ifndef __AST_DEBUG_MALLOC
 
+/* This buffer is in static memory. We never intend to read it,
+ * nor do we care about multiple threads writing to it at the
+ * same time. We only want to know if we're recursing too deep
+ * already. 60 entries should be more than enough. Function call
+ * depth rarely exceeds 20 or so. */
+#define _AST_MEM_BACKTRACE_BUFLEN 60
+extern void *_ast_mem_backtrace_buffer[_AST_MEM_BACKTRACE_BUFLEN];
+
 #define MALLOC_FAILURE_MSG \
-	ast_log(LOG_ERROR, "Memory Allocation Failure in function %s at line %d of %s\n", func, lineno, file);
+	{ \
+		/* Ok, this sucks. But if we're already out of mem, we don't \
+		 * want the logger to create infinite recursion (and a crash). */ \
+		if (backtrace(_ast_mem_backtrace_buffer, _AST_MEM_BACKTRACE_BUFLEN) < \
+				_AST_MEM_BACKTRACE_BUFLEN) { \
+			ast_log(LOG_ERROR, "Memory Allocation Failure in function %s at line %d of %s\n", func, lineno, file); \
+		} \
+	}
+
 /*!
  * \brief A wrapper for malloc()
  *