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()
  *

main/pbx.c

@@ -7281,6 +7281,81 @@ static char *handle_show_switches(struct ast_cli_entry *e, int cmd, struct ast_c
 	return CLI_SUCCESS;
 }
 
+#if 0
+/* This code can be used to test if the system survives running out of memory.
+ * It might be an idea to put this in only if ENABLE_AUTODESTRUCT_TESTS is enabled.
+ *
+ * If you want to test this, these Linux sysctl flags might be appropriate:
+ *   vm.overcommit_memory = 2
+ *   vm.swappiness = 0
+ *
+ * <@Corydon76-home> I envision 'core eat disk space' and 'core eat file descriptors' now
+ * <@mjordan> egads
+ * <@mjordan> it's literally the 'big red' auto-destruct button
+ * <@mjordan> if you were wondering who even builds such a thing.... well, now you know
+ * ...
+ * <@Corydon76-home> What about if they lived only if you defined TEST_FRAMEWORK?  Shouldn't have those on production machines
+ * <@mjordan> I think accompanied with an update to one of our README files that "no, really, TEST_FRAMEWORK isn't for you", I'd be fine
+ */
+static char *handle_eat_memory(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
+{
+	void **blocks;
+	int blocks_pos = 0;
+	const int blocks_max = 50000;
+	long long int allocated = 0;
+	int sizes[] = {
+		100 * 1024 * 1024,
+		100 * 1024,
+		2 * 1024,
+		400,
+		0
+	};
+	int i;
+
+	switch (cmd) {
+	case CLI_INIT:
+		/* To do: add method to free memory again? 5 minutes? */
+		e->command = "core eat memory";
+		e->usage =
+			"Usage: core eat memory\n"
+			"       Eats all available memory so you can test if the system survives\n";
+		return NULL;
+	case CLI_GENERATE:
+		return NULL;
+	}
+
+	blocks = ast_malloc(sizeof(void*) * blocks_max);
+	if (!blocks) {
+		ast_log(LOG_ERROR, "Already out of mem?\n");
+		return CLI_SUCCESS;
+	}
+
+	for (i = 0; sizes[i]; ++i) {
+		int alloc_size = sizes[i];
+		ast_log(LOG_WARNING, "Allocating %d sized blocks (got %d blocks already)\n", alloc_size, blocks_pos);
+		while (1) {
+			void *block;
+			if (blocks_pos >= blocks_max) {
+				ast_log(LOG_ERROR, "Memory buffer too small? Run me again :)\n");
+				break;
+			}
+
+			block = ast_malloc(alloc_size);
+			if (!block) {
+				break;
+			}
+
+			blocks[blocks_pos++] = block;
+			allocated += alloc_size;
+		}
+	}
+
+	/* No freeing of the mem! */
+	ast_log(LOG_WARNING, "Allocated %lld bytes total!\n", allocated);
+	return CLI_SUCCESS;
+}
+#endif
+
 static char *handle_show_applications(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
 {
 	struct ast_app *aa;
@@ -8162,6 +8237,9 @@ static char *handle_unset_extenpatternmatchnew(struct ast_cli_entry *e, int cmd,
  * CLI entries for upper commands ...
  */
 static struct ast_cli_entry pbx_cli[] = {
+#if 0
+	AST_CLI_DEFINE(handle_eat_memory, "Eats all available memory"),
+#endif
 	AST_CLI_DEFINE(handle_show_applications, "Shows registered dialplan applications"),
 	AST_CLI_DEFINE(handle_show_functions, "Shows registered dialplan functions"),
 	AST_CLI_DEFINE(handle_show_switches, "Show alternative switches"),

main/utils.c

@@ -74,6 +74,8 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 static char base64[64];
 static char b2a[256];
 
+void *_ast_mem_backtrace_buffer[_AST_MEM_BACKTRACE_BUFLEN];
+
 AST_THREADSTORAGE(inet_ntoa_buf);
 
 #if !defined(HAVE_GETHOSTBYNAME_R_5) && !defined(HAVE_GETHOSTBYNAME_R_6)