check_null_deref.c

   1 /*
   2  * sparse/check_deference.c
   3  *
   4  * Copyright (C) 2006 Dan Carpenter.
   5  *
   6  * Licensed under the Open Software License version 1.1
   7  *
   8  */
   9
  10 #include "token.h"
  11 #include "smatch.h"
  12 #include "smatch_slist.h"
  13
  14 /*
  15  * TODO:  The return_null list of functions should be determined automatically
  16  */
  17 static const char *return_null[] = {
  18         "kmalloc",
  19 };
  20
  21 struct func_n_param {
  22         struct symbol *func;
  23         int param;
  24         int line;
  25 };
  26 ALLOCATOR(func_n_param, "func parameters");
  27 DECLARE_PTR_LIST(param_list, struct func_n_param);
  28
  29 static struct param_list *funcs;
  30 static struct param_list *do_not_call;
  31 static struct param_list *calls;
  32
  33 static int my_id;
  34
  35 STATE(argument);
  36 STATE(arg_nonnull);
  37 STATE(arg_null);
  38 STATE(assumed_nonnull);
  39 STATE(ignore);
  40 STATE(isnull);
  41 STATE(nonnull);
  42
  43 static struct symbol *func_sym;
  44
  45 /*
  46  * merge_func() is to handle assumed_nonnull.
  47  *
  48  * Assumed_nonnull is a funny state.  It's almost the same as
  49  * no state.  Maybe it would be better to delete it completely...
  50  */
  51 static struct smatch_state *merge_func(const char *name, struct symbol *sym,
  52                                        struct smatch_state *s1,
  53                                        struct smatch_state *s2)
  54 {
  55         if (s1 == &ignore || s2 == &ignore)
  56                 return &ignore;
  57         return &merged;
  58
  59 }
  60
  61 static struct smatch_state *unmatched_state(struct sm_state *sm)
  62 {
  63         if (sm->state == &assumed_nonnull)
  64                 return &assumed_nonnull;
  65         return &undefined;
  66 }
  67
  68 static int is_maybe_null_no_arg(const char *name, struct symbol *sym)
  69 {
  70         struct state_list *slist;
  71         struct sm_state *tmp;
  72         int ret = 0;
  73
  74         slist = get_possible_states(name, my_id, sym);
  75         FOR_EACH_PTR(slist, tmp) {
  76                 if (tmp->state == &ignore)
  77                         return 0;
  78                 if (tmp->state == &isnull) {
  79                         SM_DEBUG("is_maybe_null_no_arg() says %s &isnull\n", name);
  80                         ret = 1;
  81                 }
  82                 if (tmp->state == &undefined) {
  83                         SM_DEBUG("is_maybe_null_no_arg() says %s &undefined\n", name);
  84                         ret = 1;
  85                 }
  86         } END_FOR_EACH_PTR(tmp);
  87         return ret;
  88 }
  89
  90
  91 static int is_maybe_null(const char *name, struct symbol *sym)
  92 {
  93         struct state_list *slist;
  94         struct sm_state *tmp;
  95         int ret = 0;
  96
  97         slist = get_possible_states(name, my_id, sym);
  98         FOR_EACH_PTR(slist, tmp) {
  99                 if (tmp->state == &ignore)
 100                         return 0;
 101                 if (tmp->state == &isnull) {
 102                         SM_DEBUG("is_maybe_null() says %s &isnull\n", name);
 103                         ret = 1;
 104                 }
 105                 if (tmp->state == &undefined) {
 106                         SM_DEBUG("is_maybe_null() says %s &undefined\n", name);
 107                         ret = 1;
 108                 }
 109                 if (tmp->state == &arg_null) {
 110                         SM_DEBUG("is_maybe_null() says %s &arg_null\n", name);
 111                         ret = 1;
 112                 }
 113         } END_FOR_EACH_PTR(tmp);
 114         return ret;
 115 }
 116
 117 static int is_maybe_null_arg(char *name, struct symbol *sym)
 118 {
 119         struct state_list *slist;
 120         struct sm_state *tmp;
 121         int maybe_null = 0;
 122
 123         slist = get_possible_states(name, my_id, sym);
 124         FOR_EACH_PTR(slist, tmp) {
 125                 if (tmp->state != &argument && tmp->state != &arg_null &&
 126                     tmp->state != &arg_nonnull && tmp->state !=  &merged &&
 127                     tmp->state != &assumed_nonnull)
 128                         return 0;
 129                 if (tmp->state == &argument || tmp->state == &arg_null)
 130                         maybe_null = 1;
 131         } END_FOR_EACH_PTR(tmp);
 132
 133         /* We really only care about arguments if they are null */
 134         return maybe_null;
 135 }
 136
 137 static struct func_n_param *alloc_func_n_param(struct symbol *func, int param,
 138                                                int line)
 139 {
 140         struct func_n_param *tmp = __alloc_func_n_param(0);
 141
 142         tmp->func = func;
 143         tmp->param = param;
 144         tmp->line = line;
 145         return tmp;
 146 }
 147
 148 static int get_arg_num(struct symbol *sym)
 149 {
 150         struct symbol *arg;
 151         int i = 0;
 152
 153         FOR_EACH_PTR(func_sym->ctype.base_type->arguments, arg) {
 154                 if (arg == sym) {
 155                         return i;
 156                 }
 157                 i++;
 158         } END_FOR_EACH_PTR(arg);
 159         return -1;
 160 }
 161
 162 static void add_do_not_call(struct symbol *sym, int line)
 163 {
 164         struct func_n_param *tmp;
 165         int num = get_arg_num(sym);
 166
 167         FOR_EACH_PTR(do_not_call, tmp) {
 168                 if (tmp->func == func_sym && tmp->param == num)
 169                         return;
 170         } END_FOR_EACH_PTR(tmp);
 171         tmp = alloc_func_n_param(func_sym, num, line);
 172         add_ptr_list(&do_not_call, tmp);
 173 }
 174
 175 static void add_param(struct param_list **list, struct symbol *func, int param,
 176                       int line)
 177 {
 178         struct func_n_param *tmp;
 179
 180         tmp = alloc_func_n_param(func, param, line);
 181         add_ptr_list(list, tmp);
 182 }
 183
 184 static void match_function_def(struct symbol *sym)
 185 {
 186         struct symbol *arg;
 187
 188         func_sym = sym;
 189         add_param(&funcs, sym, 0, 0);
 190         FOR_EACH_PTR(sym->ctype.base_type->arguments, arg) {
 191                 if (!arg->ident) {
 192                         continue;
 193                 }
 194                 set_state(arg->ident->name, my_id, arg, &argument);
 195         } END_FOR_EACH_PTR(arg);
 196 }
 197
 198 static char *get_function_call(struct expression *expr)
 199 {
 200         if (expr->type != EXPR_CALL)
 201                 return NULL;
 202         if (expr->fn->type == EXPR_SYMBOL && expr->fn->symbol)
 203                 return expr->fn->symbol->ident->name;
 204         return NULL;
 205 }
 206
 207 static void match_function_call_after(struct expression *expr)
 208 {
 209         struct expression *tmp;
 210         struct symbol *sym;
 211         char *name;
 212         struct symbol *func = NULL;
 213         int i;
 214
 215         if (expr->fn->type == EXPR_SYMBOL)
 216                 func = expr->fn->symbol;
 217
 218         i = 0;
 219         FOR_EACH_PTR(expr->args, tmp) {
 220                 tmp = strip_expr(tmp);
 221                 if (tmp->op == '&') {
 222                         name = get_variable_from_expr(tmp->unop, &sym);
 223                         if (name) {
 224                                 set_state(name, my_id, sym, &assumed_nonnull);
 225                         }
 226                         free_string(name);
 227                 } else if (func) {
 228                         name = get_variable_from_expr(tmp, &sym);
 229                         if (name && is_maybe_null_no_arg(name, sym))
 230                                 add_param(&calls, func, i, get_lineno());
 231                         free_string(name);
 232                 }
 233                 i++;
 234         } END_FOR_EACH_PTR(tmp);
 235 }
 236
 237 static int check_null_returns(const char *name, struct symbol *sym,
 238                         struct expression *right)
 239 {
 240         int i;
 241         char *func_name;
 242
 243         func_name = get_function_call(right);
 244         if (!func_name)
 245                 return 0;
 246
 247         for(i = 0; i < sizeof(*return_null)/sizeof(return_null[0]); i++) {
 248                 if (!strcmp(func_name, return_null[i])) {
 249                         set_state(name, my_id, sym, &undefined);
 250                         return 1;
 251                 }
 252         }
 253         return 0;
 254 }
 255
 256 static void match_assign(struct expression *expr)
 257 {
 258         struct expression *left, *right;
 259         struct symbol *sym;
 260         char *name;
 261
 262         left = strip_expr(expr->left);
 263         name = get_variable_from_expr(left, &sym);
 264         if (!name)
 265                 return;
 266         right = strip_expr(expr->right);
 267         if (is_zero(right)) {
 268                 set_state(name, my_id, sym, &isnull);
 269                 free_string(name);
 270                 return;
 271         }
 272         if (check_null_returns(name, sym, right)) {
 273                 free_string(name);
 274                 return;
 275         }
 276
 277         /* by default we assume it's assigned something nonnull */
 278         set_state(name, my_id, sym, &assumed_nonnull);
 279         free_string(name);
 280 }
 281
 282 /*
 283  * set_new_true_false_paths() is used in the following conditions
 284  * if (a) { ... if (a) { ... } }
 285  * The problem is that after the second blog a is set to undefined
 286  * even though the second condition is meaning less.  (The second test
 287  * could be a macro for example).
 288  *
 289  * Also, stuff passed to the condition hook is processed behind the scenes
 290  * a bit.  Instead of a condition like (foo == 0) which is true when foo is
 291  * null, we get just (foo) and the true and false states are adjusted later.
 292  * Basically the important thing to remember, is that for us, true is always
 293  * non null and false is always null.
 294  */
 295 static void set_new_true_false_paths(const char *name, struct symbol *sym,
 296         int recently_assigned)
 297 {
 298         struct smatch_state *tmp;
 299
 300         tmp = get_state(name, my_id, sym);
 301
 302         SM_DEBUG("set_new_stuff called at for %s on line %d value='%s'\n",
 303                 name, get_lineno(), show_state(tmp));
 304
 305         if (tmp == &argument) {
 306                 set_true_false_states(name, my_id, sym, &arg_nonnull, &arg_null);
 307                 return;
 308         }
 309
 310         if (!tmp || recently_assigned || is_maybe_null(name, sym)) {
 311                 set_true_false_states(name, my_id, sym, &nonnull, &isnull);
 312                 return;
 313         }
 314 }
 315
 316 static void match_var_null_nonnull(struct expression *expr,
 317                                    int recently_assigned)
 318 {
 319         struct symbol *sym;
 320         char *name;
 321
 322         name = get_variable_from_expr(expr, &sym);
 323         if (!name)
 324                 return;
 325         set_new_true_false_paths(name, sym, recently_assigned);
 326         free_string(name);
 327 }
 328
 329 static void match_condition(struct expression *expr)
 330 {
 331         struct symbol *sym;
 332         char *name;
 333         expr = strip_expr(expr);
 334         switch(expr->type) {
 335         case EXPR_PREOP:
 336         case EXPR_SYMBOL:
 337         case EXPR_DEREF:
 338                 match_var_null_nonnull(expr, 0);
 339                 return;
 340         case EXPR_ASSIGNMENT:
 341                 /*
 342                  * There is a kernel macro that does
 343                  *  for ( ... ; ... || x = NULL ; ) ...
 344                  */
 345                 if (is_zero(expr->right)) {
 346                         name = get_variable_from_expr(expr->left, &sym);
 347                         if (!name)
 348                                 return;
 349                         set_true_false_states(name, my_id, sym, NULL, &isnull);
 350                         free_string(name);
 351                         return;
 352                 }
 353                 match_var_null_nonnull(expr->left, 1);
 354                 return;
 355         }
 356 }
 357
 358 static void match_declarations(struct symbol *sym)
 359 {
 360         const char *name;
 361
 362         if ((get_base_type(sym))->type == SYM_ARRAY) {
 363                 return;
 364         }
 365
 366         name = sym->ident->name;
 367
 368         if (sym->initializer) {
 369                 if (is_zero(sym->initializer)) {
 370                         set_state(name, my_id, sym, &isnull);
 371                         return;
 372                 }
 373                 if (check_null_returns(name, sym, strip_expr(sym->initializer)))
 374                         return;
 375                 set_state(name, my_id, sym, &assumed_nonnull);
 376         } else {
 377                 set_state(name, my_id, sym, &undefined);
 378         }
 379 }
 380
 381 static void match_dereferences(struct expression *expr)
 382 {
 383         char *deref = NULL;
 384         struct symbol *sym = NULL;
 385
 386         if (strcmp(show_special(expr->deref->op), "*"))
 387                 return;
 388
 389         deref = get_variable_from_expr(expr->deref->unop, &sym);
 390         if (!deref)
 391                 return;
 392
 393         if (is_maybe_null_arg(deref, sym)) {
 394                 add_do_not_call(sym, get_lineno());
 395                 set_state(deref, my_id, sym, &assumed_nonnull);
 396         } else if (is_maybe_null(deref, sym)) {
 397                 smatch_msg("error: dereferencing undefined:  '%s'", deref);
 398                 set_state(deref, my_id, sym, &ignore);
 399         }
 400         free_string(deref);
 401 }
 402
 403 static void end_file_processing(void)
 404 {
 405         struct func_n_param *param1, *param2;
 406
 407         // if a function is not static print it out...
 408         FOR_EACH_PTR(do_not_call, param1) {
 409                 if (!(param1->func->ctype.modifiers & MOD_STATIC))
 410                         printf("%s +%d info: unchecked param %s %d\n",
 411                                get_filename(), param1->line,
 412                                param1->func->ident->name, param1->param);
 413         } END_FOR_EACH_PTR(param1);
 414
 415         // if there is an error print it out...
 416         FOR_EACH_PTR(calls, param1) {
 417                 FOR_EACH_PTR(do_not_call, param2) {
 418                         if (param1->func == param2->func &&
 419                             param1->param == param2->param)
 420                                 printf("%s +%d error: cross_func deref %s %d\n",
 421                                        get_filename(), param1->line,
 422                                        param1->func->ident->name,
 423                                        param1->param);
 424                 } END_FOR_EACH_PTR(param2);
 425         } END_FOR_EACH_PTR(param1);
 426
 427         // if someone calls a non-static function print that..
 428         FOR_EACH_PTR(calls, param1) {
 429                 int defined = 0;
 430
 431                 FOR_EACH_PTR(funcs, param2) {
 432                         if (param1->func == param2->func)
 433                                 defined = 1;
 434                 } END_FOR_EACH_PTR(param2);
 435                 if (!defined)
 436                         printf("%s +%d info: undefined param %s %d\n",
 437                                get_filename(), param1->line,
 438                                param1->func->ident->name, param1->param);
 439         } END_FOR_EACH_PTR(param1);
 440 }
 441
 442 void check_null_deref(int id)
 443 {
 444         my_id = id;
 445         add_merge_hook(my_id, &merge_func);
 446         add_unmatched_state_hook(my_id, &unmatched_state);
 447         add_hook(&match_function_def, FUNC_DEF_HOOK);
 448         add_hook(&match_function_call_after, FUNCTION_CALL_HOOK);
 449         add_hook(&match_assign, ASSIGNMENT_HOOK);
 450         add_hook(&match_condition, CONDITION_HOOK);
 451         add_hook(&match_dereferences, DEREF_HOOK);
 452         add_hook(&match_declarations, DECLARATION_HOOK);
 453         add_hook(&end_file_processing, END_FILE_HOOK);
 454 }