dfilter: fix memleaks with functions and slice operator

Running tools/dfilter-test.py with LSan enabled resulted in 38 test
failures due to memory leaks from "fvalue_new". Problematic dfilters:
- Return values from functions, e.g. `len(data.data) > 8` (instruction
  CALL_FUNCTION invoking functions from epan/dfilter/dfunctions.c)
- Slice operator: `data.data[1:2] == aa:bb` (function mk_range)

These values end up in "registers", but as some values (from READ_TREE)
reference the proto tree, a new tracking flag ("owns_memory") is added.

Add missing tests for some functions and try to improve documentation.

Change-Id: I28e8cf872675d0a81ea7aa5fac7398257de3f47b
Reviewed-on: https://code.wireshark.org/review/27132
Petri-Dish: Peter Wu <peter@lekensteyn.nl>
Reviewed-by: Peter Wu <peter@lekensteyn.nl>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>

3 files changed, 28 insertions, 7 deletions

diff --git a/epan/dfilter/dfilter-int.h b/epan/dfilter/dfilter-int.h
index 785f5a3315..9d53353954 100644
--- a/epan/dfilter/dfilter-int.h
+++ b/epan/dfilter/dfilter-int.h
@@ -23,6 +23,7 @@ struct epan_dfilter {
 	guint		max_registers;
 	GList		**registers;
 	gboolean	*attempted_load;
+	gboolean	*owns_memory;
 	int		*interesting_fields;
 	int		num_interesting_fields;
 	GPtrArray	*deprecated;
diff --git a/epan/dfilter/dfilter.c b/epan/dfilter/dfilter.c
index a975f84e84..c323ca5266 100644
--- a/epan/dfilter/dfilter.c
+++ b/epan/dfilter/dfilter.c
@@ -133,11 +133,10 @@ dfilter_free(dfilter_t *df)
 
 	g_free(df->interesting_fields);
 
-	/* clear registers */
-	for (i = 0; i < df->max_registers; i++) {
-		if (df->registers[i]) {
-			g_list_free(df->registers[i]);
-		}
+	/* Clear registers with constant values (as set by dfvm_init_const).
+	 * Other registers were cleared on RETURN by free_register_overhead. */
+	for (i = df->num_registers; i < df->max_registers; i++) {
+		g_list_free(df->registers[i]);
 	}
 
 	if (df->deprecated) {
@@ -150,6 +149,7 @@ dfilter_free(dfilter_t *df)
 
 	g_free(df->registers);
 	g_free(df->attempted_load);
+	g_free(df->owns_memory);
 	g_free(df);
 }
 
@@ -350,6 +350,7 @@ dfilter_compile(const gchar *text, dfilter_t **dfp, gchar **err_msg)
 		dfilter->max_registers = dfw->next_register;
 		dfilter->registers = g_new0(GList*, dfilter->max_registers);
 		dfilter->attempted_load = g_new0(gboolean, dfilter->max_registers);
+		dfilter->owns_memory = g_new0(gboolean, dfilter->max_registers);
 
 		/* Initialize constants */
 		dfvm_init_const(dfilter);
diff --git a/epan/dfilter/dfvm.c b/epan/dfilter/dfvm.c
index f93fd50edf..322ca05812 100644
--- a/epan/dfilter/dfvm.c
+++ b/epan/dfilter/dfvm.c
@@ -331,14 +331,19 @@ read_tree(dfilter_t *df, proto_tree *tree, header_field_info *hfinfo, int reg)
 	}
 
 	df->registers[reg] = fvalues;
+	// These values are referenced only, do not try to free it later.
+	df->owns_memory[reg] = FALSE;
 	return TRUE;
 }
 
 
+/* Put a constant value in a register. These will not be cleared by
+ * free_register_overhead. */
 static gboolean
 put_fvalue(dfilter_t *df, fvalue_t *fv, int reg)
 {
 	df->registers[reg] = g_list_append(NULL, fv);
+	df->owns_memory[reg] = FALSE;
 	return TRUE;
 }
 
@@ -396,8 +401,15 @@ any_in_range(dfilter_t *df, int reg1, int reg2, int reg3)
 }
 
 
-/* Free the list nodes w/o freeing the memory that each
- * list node points to. */
+static void
+free_owned_register(gpointer data, gpointer user_data _U_)
+{
+	fvalue_t *value = (fvalue_t *)data;
+	FVALUE_FREE(value);
+}
+
+/* Clear registers that were populated during evaluation (leaving constants
+ * intact). If we created the values, then these will be freed as well. */
 static void
 free_register_overhead(dfilter_t* df)
 {
@@ -406,6 +418,10 @@ free_register_overhead(dfilter_t* df)
 	for (i = 0; i < df->num_registers; i++) {
 		df->attempted_load[i] = FALSE;
 		if (df->registers[i]) {
+			if (df->owns_memory[i]) {
+				g_list_foreach(df->registers[i], free_owned_register, NULL);
+				df->owns_memory[i] = FALSE;
+			}
 			g_list_free(df->registers[i]);
 			df->registers[i] = NULL;
 		}
@@ -437,6 +453,7 @@ mk_range(dfilter_t *df, int from_reg, int to_reg, drange_t *d_range)
 	}
 
 	df->registers[to_reg] = to_list;
+	df->owns_memory[to_reg] = TRUE;
 }
 
 
@@ -499,6 +516,8 @@ dfvm_apply(dfilter_t *df, proto_tree *tree)
 				}
 				accum = arg1->value.funcdef->function(param1, param2,
 						&df->registers[arg2->value.numeric]);
+				// functions create a new value, so own it.
+				df->owns_memory[arg2->value.numeric] = TRUE;
 				break;
 
 			case MK_RANGE: