check_free.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  * check_memory() is getting too big and messy.
  20  *
  21  */
  22
  23 #include <string.h>
  24 #include "smatch.h"
  25 #include "smatch_slist.h"
  26
  27 static int my_id;
  28
  29 STATE(freed);
  30 STATE(ok);
  31
  32 static void ok_to_use(struct sm_state *sm, struct expression *mod_expr)
  33 {
  34         if (sm->state != &ok)
  35                 set_state(my_id, sm->name, sm->sym, &ok);
  36 }
  37
  38 static void pre_merge_hook(struct sm_state *sm)
  39 {
  40         if (is_impossible_path())
  41                 set_state(my_id, sm->name, sm->sym, &ok);
  42 }
  43
  44 static int is_freed(struct expression *expr)
  45 {
  46         struct sm_state *sm;
  47
  48         sm = get_sm_state_expr(my_id, expr);
  49         if (sm && slist_has_state(sm->possible, &freed))
  50                 return 1;
  51         return 0;
  52 }
  53
  54 static void match_symbol(struct expression *expr)
  55 {
  56         struct expression *parent;
  57         char *name;
  58
  59         if (is_impossible_path())
  60                 return;
  61
  62         parent = expr_get_parent_expr(expr);
  63         while (parent && parent->type == EXPR_PREOP && parent->op == '(')
  64                 parent = expr_get_parent_expr(parent);
  65         if (parent && parent->type == EXPR_PREOP && parent->op == '&')
  66                 return;
  67
  68         if (!is_freed(expr))
  69                 return;
  70         name = expr_to_var(expr);
  71         sm_msg("warn: '%s' was already freed.", name);
  72         free_string(name);
  73 }
  74
  75 static void match_dereferences(struct expression *expr)
  76 {
  77         char *name;
  78
  79         if (expr->type != EXPR_PREOP)
  80                 return;
  81
  82         if (is_impossible_path())
  83                 return;
  84
  85         expr = strip_expr(expr->unop);
  86         if (!is_freed(expr))
  87                 return;
  88         name = expr_to_var(expr);
  89         sm_msg("error: dereferencing freed memory '%s'", name);
  90         set_state_expr(my_id, expr, &ok);
  91         free_string(name);
  92 }
  93
  94 static int ignored_params[16];
  95
  96 static void set_ignored_params(struct expression *call)
  97 {
  98         struct expression *arg;
  99         const char *p;
 100         int i;
 101
 102         memset(&ignored_params, 0, sizeof(ignored_params));
 103
 104         i = -1;
 105         FOR_EACH_PTR(call->args, arg) {
 106                 i++;
 107                 if (arg->type != EXPR_STRING)
 108                         continue;
 109                 goto found;
 110         } END_FOR_EACH_PTR(arg);
 111
 112         return;
 113
 114 found:
 115         i++;
 116         p = arg->string->data;
 117         while ((p = strchr(p, '%'))) {
 118                 if (i >= ARRAY_SIZE(ignored_params))
 119                         return;
 120                 p++;
 121                 if (*p == '%') {
 122                         p++;
 123                         continue;
 124                 }
 125                 if (*p == '.')
 126                         p++;
 127                 if (*p == '*')
 128                         i++;
 129                 if (*p == 'p')
 130                         ignored_params[i] = 1;
 131                 i++;
 132         }
 133 }
 134
 135 static int is_free_func(struct expression *fn)
 136 {
 137         char *name;
 138         int ret = 0;
 139
 140         name = expr_to_str(fn);
 141         if (!name)
 142                 return 0;
 143         if (strstr(name, "free"))
 144                 ret = 1;
 145         free_string(name);
 146
 147         return ret;
 148 }
 149
 150 static void match_call(struct expression *expr)
 151 {
 152         struct expression *arg;
 153         char *name;
 154         int i;
 155
 156         if (is_impossible_path())
 157                 return;
 158
 159         set_ignored_params(expr);
 160
 161         i = -1;
 162         FOR_EACH_PTR(expr->args, arg) {
 163                 i++;
 164                 if (!is_pointer(arg))
 165                         continue;
 166                 if (!is_freed(arg))
 167                         continue;
 168                 if (ignored_params[i])
 169                         continue;
 170
 171                 name = expr_to_var(arg);
 172                 if (is_free_func(expr->fn))
 173                         sm_msg("error: double free of '%s'", name);
 174                 else
 175                         sm_msg("warn: passing freed memory '%s'", name);
 176                 set_state_expr(my_id, arg, &ok);
 177                 free_string(name);
 178         } END_FOR_EACH_PTR(arg);
 179 }
 180
 181 static void match_return(struct expression *expr)
 182 {
 183         char *name;
 184
 185         if (is_impossible_path())
 186                 return;
 187
 188         if (!expr)
 189                 return;
 190         if (!is_freed(expr))
 191                 return;
 192
 193         name = expr_to_var(expr);
 194         sm_msg("warn: returning freed memory '%s'", name);
 195         set_state_expr(my_id, expr, &ok);
 196         free_string(name);
 197 }
 198
 199 static void match_free(const char *fn, struct expression *expr, void *param)
 200 {
 201         struct expression *arg;
 202
 203         if (is_impossible_path())
 204                 return;
 205
 206         arg = get_argument_from_call_expr(expr->args, PTR_INT(param));
 207         if (!arg)
 208                 return;
 209         if (is_freed(arg)) {
 210                 char *name = expr_to_var(arg);
 211
 212                 sm_msg("error: double free of '%s'", name);
 213                 free_string(name);
 214         }
 215         set_state_expr(my_id, arg, &freed);
 216 }
 217
 218 static void set_param_freed(struct expression *call, struct expression *arg, char *key, char *unused)
 219 {
 220         struct symbol *sym;
 221         char *name;
 222
 223         name = get_variable_from_key(arg, key, &sym);
 224         if (!name || !sym)
 225                 goto free;
 226
 227         set_state(my_id, name, sym, &freed);
 228 free:
 229         free_string(name);
 230 }
 231
 232 int parent_is_free_var_sym(const char *name, struct symbol *sym)
 233 {
 234         char buf[256];
 235         char *start;
 236         char *end;
 237         struct smatch_state *state;
 238
 239         strncpy(buf, name, sizeof(buf) - 1);
 240         buf[sizeof(buf) - 1] = '\0';
 241
 242         start = &buf[0];
 243         while ((*start == '&'))
 244                 start++;
 245
 246         while ((end = strrchr(start, '-'))) {
 247                 *end = '\0';
 248                 state = __get_state(my_id, start, sym);
 249                 if (state == &freed)
 250                         return 1;
 251         }
 252         return 0;
 253 }
 254
 255 int parent_is_free(struct expression *expr)
 256 {
 257         struct symbol *sym;
 258         char *var;
 259         int ret = 0;
 260
 261         expr = strip_expr(expr);
 262         var = expr_to_var_sym(expr, &sym);
 263         if (!var || !sym)
 264                 goto free;
 265         ret = parent_is_free_var_sym(var, sym);
 266 free:
 267         free_string(var);
 268         return ret;
 269 }
 270
 271 void check_free(int id)
 272 {
 273         my_id = id;
 274
 275         if (option_project == PROJ_KERNEL) {
 276                 add_function_hook("kfree", &match_free, INT_PTR(0));
 277                 add_function_hook("kmem_cache_free", &match_free, INT_PTR(1));
 278         } else {
 279                 add_function_hook("free", &match_free, INT_PTR(0));
 280         }
 281
 282         if (option_spammy)
 283                 add_hook(&match_symbol, SYM_HOOK);
 284         add_hook(&match_dereferences, DEREF_HOOK);
 285         add_hook(&match_call, FUNCTION_CALL_HOOK);
 286         add_hook(&match_return, RETURN_HOOK);
 287
 288         add_modification_hook(my_id, &ok_to_use);
 289         select_call_implies_hook(PARAM_FREED, &set_param_freed);
 290         add_pre_merge_hook(my_id, &pre_merge_hook);
 291 }