check_check_deref.c

   1 /*
   2  * Copyright (C) 2010 Dan Carpenter.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
  16  */
  17
  18 /*
  19  * This is like check_deref_check.c except that it complains about code like:
  20  * if (a)
  21  *        a->foo = 42;
  22  * a->bar = 7;
  23  *
  24  * Of course, Smatch has complained about these for forever but the problem is
  25  * the old scripts were too messy and complicated and generated too many false
  26  * positives.
  27  *
  28  * This check is supposed to be simpler because it only looks for one kind of
  29  * null dereference bug instead of every kind.  It also gets rid of the false
  30  * positives caused by the checks that happen inside macros.
  31  *
  32  */
  33
  34 #include "smatch.h"
  35 #include "smatch_slist.h"
  36 #include "smatch_extra.h"
  37
  38 static int my_id;
  39
  40 STATE(null);
  41 STATE(ok);
  42
  43 static void is_ok(struct sm_state *sm, struct expression *mod_expr)
  44 {
  45         set_state(my_id, sm->name, sm->sym, &ok);
  46 }
  47
  48 static int get_checked_line_var_sym(char *name, struct symbol *sym)
  49 {
  50         struct sm_state *sm;
  51         struct sm_state *tmp;
  52
  53         sm = get_sm_state(my_id, name, sym);
  54         if (!sm)
  55                 return 0;
  56         if (is_ignored(my_id, sm->name, sm->sym))
  57                 return 0;
  58         if (implied_not_equal_name_sym(name, sym, 0))
  59                 return 0;
  60
  61         FOR_EACH_PTR(sm->possible, tmp) {
  62                 if (tmp->state == &merged)
  63                         continue;
  64                 if (tmp->state == &ok)
  65                         continue;
  66                 if (tmp->state == &null)
  67                         return tmp->line;
  68         } END_FOR_EACH_PTR(tmp);
  69
  70         return 0;
  71 }
  72
  73 static int get_checked_line(struct expression *expr)
  74 {
  75         char *name;
  76         struct symbol *sym;
  77         int line = 0;
  78
  79         name = expr_to_var_sym(expr, &sym);
  80         if (!name || !sym)
  81                 goto free;
  82         line = get_checked_line_var_sym(name, sym);
  83 free:
  84         free_string(name);
  85         return line;
  86 }
  87
  88 static void deref_hook(struct expression *expr)
  89 {
  90         char *name;
  91         struct symbol *sym;
  92         struct range_list *rl;
  93         int line;
  94
  95         if (__in_fake_assign || __in_fake_parameter_assign)
  96                 return;
  97
  98         line = get_checked_line(expr);
  99         if (!line)
 100                 return;
 101
 102         get_absolute_rl(expr, &rl);
 103         if (!rl_has_sval(rl, sval_type_val(rl_type(rl), 0)))
 104                 return;
 105
 106         name = expr_to_var_sym(expr, &sym);
 107         if (!name || !sym)
 108                 goto free;
 109
 110         sm_error("we previously assumed '%s' could be null (see line %d)",
 111                name, line);
 112
 113         add_ignore(my_id, name, sym);
 114 free:
 115         free_string(name);
 116 }
 117
 118 static void match_condition(struct expression *expr)
 119 {
 120         struct smatch_state *true_state = NULL;
 121         char *name;
 122
 123         name = get_macro_name(expr->pos);
 124         if (name &&
 125             (strcmp(name, "likely") != 0 && strcmp(name, "unlikely") != 0))
 126                 return;
 127
 128         if (!is_pointer(expr))
 129                 return;
 130
 131         if (expr->type == EXPR_ASSIGNMENT) {
 132                 match_condition(expr->right);
 133                 match_condition(expr->left);
 134         }
 135
 136         if (implied_not_equal(expr, 0))
 137                 return;
 138
 139         if (get_state_expr(my_id, expr))
 140                 true_state = &ok;
 141
 142         set_true_false_states_expr(my_id, expr, true_state, &null);
 143 }
 144
 145 void check_check_deref(int id)
 146 {
 147         my_id = id;
 148
 149         add_modification_hook(my_id, &is_ok);
 150         add_hook(&match_condition, CONDITION_HOOK);
 151         add_dereference_hook(deref_hook);
 152 }