check_overflow.c

   1 /*
   2  * smatch/check_overflow.c
   3  *
   4  * Copyright (C) 2010 Dan Carpenter.
   5  *
   6  * Licensed under the Open Software License version 1.1
   7  *
   8  */
   9
  10 #include <stdlib.h>
  11 #include "parse.h"
  12 #include "smatch.h"
  13 #include "smatch_slist.h"
  14 #include "smatch_extra.h"
  15
  16 struct bound {
  17         int param;
  18         int size;
  19 };
  20
  21 /*
  22  * This check has two smatch IDs.
  23  * my_used_id - keeps a record of array offsets that have been used.
  24  *              If the code checks that they are within bounds later on,
  25  *              we complain about using an array offset before checking
  26  *              that it is within bounds.
  27  */
  28 static int my_used_id;
  29
  30 static struct symbol *this_func;
  31
  32 static void match_function_def(struct symbol *sym)
  33 {
  34         this_func = sym;
  35 }
  36
  37 struct limiter {
  38         int buf_arg;
  39         int limit_arg;
  40 };
  41 static struct limiter b0_l2 = {0, 2};
  42 static struct limiter b1_l2 = {1, 2};
  43
  44 static void delete(struct sm_state *sm, struct expression *mod_expr)
  45 {
  46         set_state(my_used_id, sm->name, sm->sym, &undefined);
  47 }
  48
  49 static int definitely_just_used_as_limiter(struct expression *array, struct expression *offset)
  50 {
  51         sval_t sval;
  52         struct expression *tmp;
  53         int step = 0;
  54         int dot_ops = 0;
  55
  56         if (!get_implied_value(offset, &sval))
  57                 return 0;
  58         if (get_array_size(array) != sval.value)
  59                 return 0;
  60
  61         FOR_EACH_PTR_REVERSE(big_expression_stack, tmp) {
  62                 if (step == 0) {
  63                         step = 1;
  64                         continue;
  65                 }
  66                 if (tmp->type == EXPR_PREOP && tmp->op == '(')
  67                         continue;
  68                 if (tmp->op == '.' && !dot_ops++)
  69                         continue;
  70                 if (step == 1 && tmp->op == '&') {
  71                         step = 2;
  72                         continue;
  73                 }
  74                 if (step == 2 && tmp->type == EXPR_COMPARE)
  75                         return 1;
  76                 if (step == 2 && tmp->type == EXPR_ASSIGNMENT)
  77                         return 1;
  78                 return 0;
  79         } END_FOR_EACH_PTR_REVERSE(tmp);
  80         return 0;
  81 }
  82
  83 static int get_the_max(struct expression *expr, sval_t *sval)
  84 {
  85         if (get_hard_max(expr, sval))
  86                 return 1;
  87         if (!option_spammy)
  88                 return 0;
  89         if (is_user_data(expr))
  90                 return get_absolute_max(expr, sval);
  91         /* FIXME: get_fuzzy_max() is not working well across function boundaries */
  92         return 0;
  93 }
  94
  95 static int common_false_positives(char *name)
  96 {
  97         if (!name)
  98                 return 0;
  99
 100         /* Smatch can't figure out glibc's strcmp __strcmp_cg()
 101          * so it prints an error every time you compare to a string
 102          * literal array with 4 or less chars.
 103          */
 104         if (strcmp(name, "__s1") == 0 || strcmp(name, "__s2") == 0)
 105                 return 1;
 106
 107         /*
 108          * passing WORK_CPU_UNBOUND is idiomatic but Smatch doesn't understand
 109          * how it's used so it causes a bunch of false positives.
 110          */
 111         if (option_project == PROJ_KERNEL &&
 112             strcmp(name, "__per_cpu_offset") == 0)
 113                 return 1;
 114         return 0;
 115 }
 116
 117 static void array_check(struct expression *expr)
 118 {
 119         struct expression *array_expr;
 120         int array_size;
 121         struct expression *offset;
 122         sval_t max;
 123         char *name;
 124
 125         expr = strip_expr(expr);
 126         if (!is_array(expr))
 127                 return;
 128
 129         array_expr = strip_parens(expr->unop->left);
 130         array_size = get_array_size(array_expr);
 131         if (!array_size || array_size == 1)
 132                 return;
 133
 134         offset = get_array_offset(expr);
 135         if (!get_the_max(offset, &max)) {
 136                 if (getting_address())
 137                         return;
 138                 if (is_capped(offset))
 139                         return;
 140                 set_state_expr(my_used_id, offset, alloc_state_num(array_size));
 141         } else if (array_size <= max.value) {
 142                 const char *level = "error";
 143
 144                 if (getting_address())
 145                         level = "warn";
 146
 147                 if (definitely_just_used_as_limiter(array_expr, offset))
 148                         return;
 149
 150                 if (!option_spammy) {
 151                         struct smatch_state *state;
 152
 153                         state = get_state_expr(SMATCH_EXTRA, offset);
 154                         if (state && estate_is_whole(state))
 155                                 return;
 156                 }
 157
 158                 name = expr_to_str(array_expr);
 159                 if (!common_false_positives(name)) {
 160                         sm_msg("%s: buffer overflow '%s' %d <= %s",
 161                                 level, name, array_size, sval_to_str(max));
 162                 }
 163                 free_string(name);
 164         }
 165 }
 166
 167 static void match_condition(struct expression *expr)
 168 {
 169         int left;
 170         sval_t sval;
 171         struct state_list *slist;
 172         struct sm_state *tmp;
 173         int boundary;
 174
 175         if (!expr || expr->type != EXPR_COMPARE)
 176                 return;
 177         if (get_macro_name(expr->pos))
 178                 return;
 179         if (get_implied_value(expr->left, &sval))
 180                 left = 1;
 181         else if (get_implied_value(expr->right, &sval))
 182                 left = 0;
 183         else
 184                 return;
 185
 186         if (left)
 187                 slist = get_possible_states_expr(my_used_id, expr->right);
 188         else
 189                 slist = get_possible_states_expr(my_used_id, expr->left);
 190         if (!slist)
 191                 return;
 192         FOR_EACH_PTR(slist, tmp) {
 193                 if (tmp->state == &merged || tmp->state == &undefined)
 194                         continue;
 195                 boundary = PTR_INT(tmp->state->data);
 196                 boundary -= sval.value;
 197                 if (boundary < 1 && boundary > -1) {
 198                         char *name;
 199
 200                         name = expr_to_var(left ? expr->right : expr->left);
 201                         sm_msg("error: testing array offset '%s' after use.", name);
 202                         return;
 203                 }
 204         } END_FOR_EACH_PTR(tmp);
 205 }
 206
 207 static void match_strcpy(const char *fn, struct expression *expr, void *unused)
 208 {
 209         struct expression *dest;
 210         struct expression *data;
 211         char *dest_name = NULL;
 212         char *data_name = NULL;
 213         int dest_size;
 214         int data_size;
 215
 216         dest = get_argument_from_call_expr(expr->args, 0);
 217         data = get_argument_from_call_expr(expr->args, 1);
 218         dest_size = get_array_size_bytes(dest);
 219         data_size = get_array_size_bytes(data);
 220
 221         if (!dest_size)
 222                 return;
 223
 224         /* If the size of both arrays is known and the destination
 225          * buffer is larger than the source buffer, we're okay.
 226          */
 227         if (data_size && dest_size >= data_size)
 228                 return;
 229
 230         dest_name = expr_to_str(dest);
 231         data_name = expr_to_str(data);
 232
 233         if (data_size)
 234                 sm_msg("error: %s() '%s' too large for '%s' (%d vs %d)",
 235                         fn, data_name, dest_name, data_size, dest_size);
 236         else if (option_spammy)
 237                 sm_msg("warn: %s() '%s' of unknown size might be too large for '%s'",
 238                         fn, data_name, dest_name);
 239
 240         free_string(dest_name);
 241         free_string(data_name);
 242 }
 243
 244 static void match_snprintf(const char *fn, struct expression *expr, void *unused)
 245 {
 246         struct expression *dest;
 247         struct expression *dest_size_expr;
 248         struct expression *format_string;
 249         struct expression *data;
 250         char *data_name = NULL;
 251         int dest_size;
 252         sval_t limit_size;
 253         char *format;
 254         int data_size;
 255
 256         dest = get_argument_from_call_expr(expr->args, 0);
 257         dest_size_expr = get_argument_from_call_expr(expr->args, 1);
 258         format_string = get_argument_from_call_expr(expr->args, 2);
 259         data = get_argument_from_call_expr(expr->args, 3);
 260
 261         dest_size = get_array_size_bytes(dest);
 262         if (!get_implied_value(dest_size_expr, &limit_size))
 263                 return;
 264         if (dest_size && dest_size < limit_size.value)
 265                 sm_msg("error: snprintf() is printing too much %s vs %d",
 266                        sval_to_str(limit_size), dest_size);
 267         format = expr_to_var(format_string);
 268         if (!format)
 269                 return;
 270         if (strcmp(format, "\"%s\""))
 271                 goto free;
 272         data_name = expr_to_str(data);
 273         data_size = get_array_size_bytes(data);
 274         if (limit_size.value < data_size)
 275                 sm_msg("error: snprintf() chops off the last chars of '%s': %d vs %s",
 276                        data_name, data_size, sval_to_str(limit_size));
 277 free:
 278         free_string(data_name);
 279         free_string(format);
 280 }
 281
 282 static void match_sprintf(const char *fn, struct expression *expr, void *unused)
 283 {
 284         struct expression *dest;
 285         struct expression *format_string;
 286         struct expression *data;
 287         char *data_name = NULL;
 288         int dest_size;
 289         char *format;
 290         int data_size;
 291
 292         dest = get_argument_from_call_expr(expr->args, 0);
 293         format_string = get_argument_from_call_expr(expr->args, 1);
 294         data = get_argument_from_call_expr(expr->args, 2);
 295
 296         dest_size = get_array_size_bytes(dest);
 297         if (!dest_size)
 298                 return;
 299         format = expr_to_var(format_string);
 300         if (!format)
 301                 return;
 302         if (strcmp(format, "\"%s\""))
 303                 goto free;
 304         data_name = expr_to_str(data);
 305         data_size = get_array_size_bytes(data);
 306         if (dest_size < data_size)
 307                 sm_msg("error: sprintf() copies too much data from '%s': %d vs %d",
 308                        data_name, data_size, dest_size);
 309 free:
 310         free_string(data_name);
 311         free_string(format);
 312 }
 313
 314 static void match_limited(const char *fn, struct expression *expr, void *_limiter)
 315 {
 316         struct limiter *limiter = (struct limiter *)_limiter;
 317         struct expression *dest;
 318         struct expression *data;
 319         char *dest_name = NULL;
 320         sval_t needed;
 321         int has;
 322
 323         dest = get_argument_from_call_expr(expr->args, limiter->buf_arg);
 324         data = get_argument_from_call_expr(expr->args, limiter->limit_arg);
 325         if (!get_the_max(data, &needed))
 326                 return;
 327         has = get_array_size_bytes(dest);
 328         if (!has)
 329                 return;
 330         if (has >= needed.value)
 331                 return;
 332
 333         dest_name = expr_to_str(dest);
 334         sm_msg("error: %s() '%s' too small (%d vs %s)", fn, dest_name, has, sval_to_str(needed));
 335         free_string(dest_name);
 336 }
 337
 338 static void db_returns_buf_size(struct expression *expr, int param, char *unused, char *math)
 339 {
 340         struct expression *call;
 341         struct symbol *left_type, *right_type;
 342         int bytes;
 343         sval_t sval;
 344
 345         if (expr->type != EXPR_ASSIGNMENT)
 346                 return;
 347         right_type = get_pointer_type(expr->right);
 348         if (!right_type || right_type->bit_size != -1)
 349                 return;
 350
 351         call = strip_expr(expr->right);
 352         left_type = get_pointer_type(expr->left);
 353
 354         if (!parse_call_math(call, math, &sval) || sval.value == 0)
 355                 return;
 356         if (!left_type)
 357                 return;
 358         bytes = bits_to_bytes(left_type->bit_size);
 359         if (bytes <= 0)
 360                 return;
 361         if (sval.uvalue >= bytes)
 362                 return;
 363         sm_msg("error: not allocating enough data %d vs %s", bytes, sval_to_str(sval));
 364 }
 365
 366 static void register_funcs_from_file(void)
 367 {
 368         char name[256];
 369         struct token *token;
 370         const char *func;
 371         int size, buf;
 372         struct limiter *limiter;
 373
 374         snprintf(name, 256, "%s.sizeof_param", option_project_str);
 375         name[255] = '\0';
 376         token = get_tokens_file(name);
 377         if (!token)
 378                 return;
 379         if (token_type(token) != TOKEN_STREAMBEGIN)
 380                 return;
 381         token = token->next;
 382         while (token_type(token) != TOKEN_STREAMEND) {
 383                 if (token_type(token) != TOKEN_IDENT)
 384                         return;
 385                 func = show_ident(token->ident);
 386
 387                 token = token->next;
 388                 if (token_type(token) != TOKEN_NUMBER)
 389                         return;
 390                 size = atoi(token->number);
 391
 392                 token = token->next;
 393                 if (token_type(token) != TOKEN_NUMBER)
 394                         return;
 395                 buf = atoi(token->number);
 396
 397                 limiter = malloc(sizeof(*limiter));
 398                 limiter->limit_arg = size;
 399                 limiter->buf_arg = buf;
 400
 401                 add_function_hook(func, &match_limited, limiter);
 402
 403                 token = token->next;
 404         }
 405         clear_token_alloc();
 406 }
 407
 408 void check_overflow(int id)
 409 {
 410         my_used_id = id;
 411         register_funcs_from_file();
 412         add_hook(&match_function_def, FUNC_DEF_HOOK);
 413         add_hook(&array_check, OP_HOOK);
 414         add_hook(&match_condition, CONDITION_HOOK);
 415         add_function_hook("strcpy", &match_strcpy, NULL);
 416         add_function_hook("snprintf", &match_snprintf, NULL);
 417         add_function_hook("sprintf", &match_sprintf, NULL);
 418         add_function_hook("memcmp", &match_limited, &b0_l2);
 419         add_function_hook("memcmp", &match_limited, &b1_l2);
 420         select_return_states_hook(BUF_SIZE, &db_returns_buf_size);
 421         add_modification_hook(my_used_id, &delete);
 422         if (option_project == PROJ_KERNEL) {
 423                 add_function_hook("copy_to_user", &match_limited, &b0_l2);
 424                 add_function_hook("copy_to_user", &match_limited, &b1_l2);
 425                 add_function_hook("_copy_to_user", &match_limited, &b0_l2);
 426                 add_function_hook("_copy_to_user", &match_limited, &b1_l2);
 427                 add_function_hook("__copy_to_user", &match_limited, &b0_l2);
 428                 add_function_hook("__copy_to_user", &match_limited, &b1_l2);
 429                 add_function_hook("copy_from_user", &match_limited, &b0_l2);
 430                 add_function_hook("copy_from_user", &match_limited, &b1_l2);
 431                 add_function_hook("_copy_from_user", &match_limited, &b0_l2);
 432                 add_function_hook("_copy_from_user", &match_limited, &b1_l2);
 433                 add_function_hook("__copy_from_user", &match_limited, &b0_l2);
 434                 add_function_hook("__copy_from_user", &match_limited, &b1_l2);
 435         }
 436 }