check_check_deref.c

/*
 * Copyright (C) 2010 Dan Carpenter.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
 */

/*
 * This is like check_deref_check.c except that it complains about code like:
 * if (a)
 *        a->foo = 42;
 * a->bar = 7;
 *
 * Of course, Smatch has complained about these for forever but the problem is
 * the old scripts were too messy and complicated and generated too many false
 * positives.
 *
 * This check is supposed to be simpler because it only looks for one kind of
 * null dereference bug instead of every kind.  It also gets rid of the false
 * positives caused by the checks that happen inside macros.
 *
 */

#include "smatch.h"
#include "smatch_slist.h"
#include "smatch_extra.h"

static int my_id;

STATE(null);
STATE(ok);

static void is_ok(struct sm_state *sm, struct expression *mod_expr)
{
	set_state(my_id, sm->name, sm->sym, &ok);
}

static int get_checked_line_var_sym(char *name, struct symbol *sym)
{
	struct sm_state *sm;
	struct sm_state *tmp;

	sm = get_sm_state(my_id, name, sym);
	if (!sm)
		return 0;
	if (is_ignored(my_id, sm->name, sm->sym))
		return 0;
	if (implied_not_equal_name_sym(name, sym, 0))
		return 0;

	FOR_EACH_PTR(sm->possible, tmp) {
		if (tmp->state == &merged)
			continue;
		if (tmp->state == &ok)
			continue;
		if (tmp->state == &null)
			return tmp->line;
	} END_FOR_EACH_PTR(tmp);

	return 0;
}

static int get_checked_line(struct expression *expr)
{
	char *name;
	struct symbol *sym;
	int line = 0;

	name = expr_to_var_sym(expr, &sym);
	if (!name || !sym)
		goto free;
	line = get_checked_line_var_sym(name, sym);
free:
	free_string(name);
	return line;
}

static void deref_hook(struct expression *expr)
{
	char *name;
	struct symbol *sym;
	struct range_list *rl;
	int line;

	if (__in_fake_assign || __in_fake_parameter_assign)
		return;

	line = get_checked_line(expr);
	if (!line)
		return;

	get_absolute_rl(expr, &rl);
	if (!rl_has_sval(rl, sval_type_val(rl_type(rl), 0)))
		return;

	name = expr_to_var_sym(expr, &sym);
	if (!name || !sym)
		goto free;

	sm_error("we previously assumed '%s' could be null (see line %d)",
	       name, line);

	add_ignore(my_id, name, sym);
free:
	free_string(name);
}

static void match_condition(struct expression *expr)
{
	struct smatch_state *true_state = NULL;
	char *name;

	name = get_macro_name(expr->pos);
	if (name &&
	    (strcmp(name, "likely") != 0 && strcmp(name, "unlikely") != 0))
		return;

	if (!is_pointer(expr))
		return;

	if (expr->type == EXPR_ASSIGNMENT) {
		match_condition(expr->right);
		match_condition(expr->left);
	}

	if (implied_not_equal(expr, 0))
		return;

	if (get_state_expr(my_id, expr))
		true_state = &ok;

	set_true_false_states_expr(my_id, expr, true_state, &null);
}

void check_check_deref(int id)
{
	my_id = id;

	add_modification_hook(my_id, &is_ok);
	add_hook(&match_condition, CONDITION_HOOK);
	add_dereference_hook(deref_hook);
}