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 void check_dereference(struct expression *expr)
  49 {
  50         struct sm_state *sm;
  51         struct sm_state *tmp;
  52
  53         expr = strip_expr(expr);
  54         if (getting_address())
  55                 return;
  56         sm = get_sm_state_expr(my_id, expr);
  57         if (!sm)
  58                 return;
  59         if (is_ignored(my_id, sm->name, sm->sym))
  60                 return;
  61         if (implied_not_equal(expr, 0))
  62                 return;
  63
  64         FOR_EACH_PTR(sm->possible, tmp) {
  65                 if (tmp->state == &merged)
  66                         continue;
  67                 if (tmp->state == &ok)
  68                         continue;
  69                 if (tmp->state == &null) {
  70                         sm_msg("error: we previously assumed '%s' could be null (see line %d)",
  71                                tmp->name, tmp->line);
  72                         add_ignore(my_id, sm->name, sm->sym);
  73                         return;
  74                 }
  75         } END_FOR_EACH_PTR(tmp);
  76 }
  77
  78 static void check_dereference_name_sym(char *name, struct symbol *sym)
  79 {
  80         struct sm_state *sm;
  81         struct sm_state *tmp;
  82
  83         sm = get_sm_state(my_id, name, sym);
  84         if (!sm)
  85                 return;
  86         if (is_ignored(my_id, sm->name, sm->sym))
  87                 return;
  88         if (implied_not_equal_name_sym(name, sym, 0))
  89                 return;
  90
  91         FOR_EACH_PTR(sm->possible, tmp) {
  92                 if (tmp->state == &merged)
  93                         continue;
  94                 if (tmp->state == &ok)
  95                         continue;
  96                 if (tmp->state == &null) {
  97                         sm_msg("error: we previously assumed '%s' could be null (see line %d)",
  98                                tmp->name, tmp->line);
  99                         add_ignore(my_id, sm->name, sm->sym);
 100                         return;
 101                 }
 102         } END_FOR_EACH_PTR(tmp);
 103 }
 104
 105 static void match_dereferences(struct expression *expr)
 106 {
 107         if (expr->type != EXPR_PREOP)
 108                 return;
 109         check_dereference(expr->unop);
 110 }
 111
 112 static void match_pointer_as_array(struct expression *expr)
 113 {
 114         if (!is_array(expr))
 115                 return;
 116         check_dereference(get_array_base(expr));
 117 }
 118
 119 static void set_param_dereferenced(struct expression *arg, char *key, char *unused)
 120 {
 121         struct symbol *sym;
 122         char *name;
 123
 124         name = get_variable_from_key(arg, key, &sym);
 125         if (!name || !sym)
 126                 goto free;
 127
 128         check_dereference_name_sym(name, sym);
 129 free:
 130         free_string(name);
 131 }
 132
 133 static void match_condition(struct expression *expr)
 134 {
 135         if (get_macro_name(expr->pos))
 136                 return;
 137
 138         if (expr->type == EXPR_ASSIGNMENT) {
 139                 match_condition(expr->right);
 140                 match_condition(expr->left);
 141         }
 142         set_true_false_states_expr(my_id, expr, &ok, &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_dereferences, DEREF_HOOK);
 151         add_hook(&match_pointer_as_array, OP_HOOK);
 152         select_call_implies_hook(DEREFERENCE, &set_param_dereferenced);
 153         add_hook(&match_condition, CONDITION_HOOK);
 154 }