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)
  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 common_false_positives(char *name)
  84 {
  85         if (!name)
  86                 return 0;
  87
  88         /* Smatch can't figure out glibc's strcmp __strcmp_cg()
  89          * so it prints an error every time you compare to a string
  90          * literal array with 4 or less chars.
  91          */
  92         if (strcmp(name, "__s1") == 0 || strcmp(name, "__s2") == 0)
  93                 return 1;
  94
  95         /*
  96          * passing WORK_CPU_UNBOUND is idiomatic but Smatch doesn't understand
  97          * how it's used so it causes a bunch of false positives.
  98          */
  99         if (option_project == PROJ_KERNEL &&
 100             strcmp(name, "__per_cpu_offset") == 0)
 101                 return 1;
 102         return 0;
 103 }
 104
 105 static void array_check(struct expression *expr)
 106 {
 107         struct expression *array_expr;
 108         int array_size;
 109         struct expression *offset;
 110         sval_t max;
 111         char *name;
 112
 113         expr = strip_expr(expr);
 114         if (!is_array(expr))
 115                 return;
 116
 117         array_expr = strip_parens(expr->unop->left);
 118         array_size = get_array_size(array_expr);
 119         if (!array_size || array_size == 1)
 120                 return;
 121
 122         offset = get_array_offset(expr);
 123         if (!get_fuzzy_max(offset, &max)) {
 124                 if (getting_address())
 125                         return;
 126                 set_state_expr(my_used_id, offset, alloc_state_num(array_size));
 127         } else if (array_size <= max.value) {
 128                 const char *level = "error";
 129
 130                 if (getting_address())
 131                         level = "warn";
 132
 133                 if (definitely_just_used_as_limiter(array_expr, offset))
 134                         return;
 135
 136                 if (!option_spammy) {
 137                         struct smatch_state *state;
 138
 139                         state = get_state_expr(SMATCH_EXTRA, offset);
 140                         if (state && estate_is_whole(state))
 141                                 return;
 142                 }
 143
 144                 name = expr_to_str(array_expr);
 145                 if (!common_false_positives(name)) {
 146                         sm_msg("%s: buffer overflow '%s' %d <= %s",
 147                                 level, name, array_size, sval_to_str(max));
 148                 }
 149                 free_string(name);
 150         }
 151 }
 152
 153 static void match_condition(struct expression *expr)
 154 {
 155         int left;
 156         sval_t sval;
 157         struct state_list *slist;
 158         struct sm_state *tmp;
 159         int boundary;
 160
 161         if (!expr || expr->type != EXPR_COMPARE)
 162                 return;
 163         if (get_macro_name(expr->pos))
 164                 return;
 165         if (get_implied_value(expr->left, &sval))
 166                 left = 1;
 167         else if (get_implied_value(expr->right, &sval))
 168                 left = 0;
 169         else
 170                 return;
 171
 172         if (left)
 173                 slist = get_possible_states_expr(my_used_id, expr->right);
 174         else
 175                 slist = get_possible_states_expr(my_used_id, expr->left);
 176         if (!slist)
 177                 return;
 178         FOR_EACH_PTR(slist, tmp) {
 179                 if (tmp->state == &merged || tmp->state == &undefined)
 180                         continue;
 181                 boundary = PTR_INT(tmp->state->data);
 182                 boundary -= sval.value;
 183                 if (boundary < 1 && boundary > -1) {
 184                         char *name;
 185
 186                         name = expr_to_var(left ? expr->right : expr->left);
 187                         sm_msg("error: testing array offset '%s' after use.", name);
 188                         return;
 189                 }
 190         } END_FOR_EACH_PTR(tmp);
 191 }
 192
 193 static void match_strcpy(const char *fn, struct expression *expr, void *unused)
 194 {
 195         struct expression *dest;
 196         struct expression *data;
 197         char *dest_name = NULL;
 198         char *data_name = NULL;
 199         int dest_size;
 200         int data_size;
 201
 202         dest = get_argument_from_call_expr(expr->args, 0);
 203         data = get_argument_from_call_expr(expr->args, 1);
 204         dest_size = get_array_size_bytes(dest);
 205         data_size = get_array_size_bytes(data);
 206
 207         if (!dest_size)
 208                 return;
 209
 210         /* If the size of both arrays is known and the destination
 211          * buffer is larger than the source buffer, we're okay.
 212          */
 213         if (data_size && dest_size >= data_size)
 214                 return;
 215
 216         dest_name = expr_to_str(dest);
 217         data_name = expr_to_str(data);
 218
 219         if (data_size)
 220                 sm_msg("error: %s() '%s' too large for '%s' (%d vs %d)",
 221                         fn, data_name, dest_name, data_size, dest_size);
 222         else if (option_spammy)
 223                 sm_msg("warn: %s() '%s' of unknown size might be too large for '%s'",
 224                         fn, data_name, dest_name);
 225
 226         free_string(dest_name);
 227         free_string(data_name);
 228 }
 229
 230 static void match_snprintf(const char *fn, struct expression *expr, void *unused)
 231 {
 232         struct expression *dest;
 233         struct expression *dest_size_expr;
 234         struct expression *format_string;
 235         struct expression *data;
 236         char *data_name = NULL;
 237         int dest_size;
 238         sval_t limit_size;
 239         char *format;
 240         int data_size;
 241
 242         dest = get_argument_from_call_expr(expr->args, 0);
 243         dest_size_expr = get_argument_from_call_expr(expr->args, 1);
 244         format_string = get_argument_from_call_expr(expr->args, 2);
 245         data = get_argument_from_call_expr(expr->args, 3);
 246
 247         dest_size = get_array_size_bytes(dest);
 248         if (!get_implied_value(dest_size_expr, &limit_size))
 249                 return;
 250         if (dest_size && dest_size < limit_size.value)
 251                 sm_msg("error: snprintf() is printing too much %s vs %d",
 252                        sval_to_str(limit_size), dest_size);
 253         format = expr_to_var(format_string);
 254         if (!format)
 255                 return;
 256         if (strcmp(format, "\"%s\""))
 257                 goto free;
 258         data_name = expr_to_str(data);
 259         data_size = get_array_size_bytes(data);
 260         if (limit_size.value < data_size)
 261                 sm_msg("error: snprintf() chops off the last chars of '%s': %d vs %s",
 262                        data_name, data_size, sval_to_str(limit_size));
 263 free:
 264         free_string(data_name);
 265         free_string(format);
 266 }
 267
 268 static void match_sprintf(const char *fn, struct expression *expr, void *unused)
 269 {
 270         struct expression *dest;
 271         struct expression *format_string;
 272         struct expression *data;
 273         char *data_name = NULL;
 274         int dest_size;
 275         char *format;
 276         int data_size;
 277
 278         dest = get_argument_from_call_expr(expr->args, 0);
 279         format_string = get_argument_from_call_expr(expr->args, 1);
 280         data = get_argument_from_call_expr(expr->args, 2);
 281
 282         dest_size = get_array_size_bytes(dest);
 283         if (!dest_size)
 284                 return;
 285         format = expr_to_var(format_string);
 286         if (!format)
 287                 return;
 288         if (strcmp(format, "\"%s\""))
 289                 goto free;
 290         data_name = expr_to_str(data);
 291         data_size = get_array_size_bytes(data);
 292         if (dest_size < data_size)
 293                 sm_msg("error: sprintf() copies too much data from '%s': %d vs %d",
 294                        data_name, data_size, dest_size);
 295 free:
 296         free_string(data_name);
 297         free_string(format);
 298 }
 299
 300 static void match_limited(const char *fn, struct expression *expr, void *_limiter)
 301 {
 302         struct limiter *limiter = (struct limiter *)_limiter;
 303         struct expression *dest;
 304         struct expression *data;
 305         char *dest_name = NULL;
 306         sval_t needed;
 307         int has;
 308
 309         dest = get_argument_from_call_expr(expr->args, limiter->buf_arg);
 310         data = get_argument_from_call_expr(expr->args, limiter->limit_arg);
 311         if (!get_fuzzy_max(data, &needed))
 312                 return;
 313         has = get_array_size_bytes(dest);
 314         if (!has)
 315                 return;
 316         if (has >= needed.value)
 317                 return;
 318
 319         dest_name = expr_to_str(dest);
 320         sm_msg("error: %s() '%s' too small (%d vs %s)", fn, dest_name, has, sval_to_str(needed));
 321         free_string(dest_name);
 322 }
 323
 324 static void db_returns_buf_size(struct expression *expr, int param, char *unused, char *math)
 325 {
 326         struct expression *call;
 327         struct symbol *type;
 328         int bytes;
 329         sval_t sval;
 330
 331         if (expr->type != EXPR_ASSIGNMENT)
 332                 return;
 333         call = strip_expr(expr->right);
 334         type = get_pointer_type(expr->left);
 335
 336         if (!parse_call_math(call, math, &sval) || sval.value == 0)
 337                 return;
 338         if (!type)
 339                 return;
 340         bytes = bits_to_bytes(type->bit_size);
 341         if (bytes <= 0)
 342                 return;
 343         if (sval.uvalue >= bytes)
 344                 return;
 345         sm_msg("error: not allocating enough data %d vs %s", bytes, sval_to_str(sval));
 346 }
 347
 348 static void register_funcs_from_file(void)
 349 {
 350         char name[256];
 351         struct token *token;
 352         const char *func;
 353         int size, buf;
 354         struct limiter *limiter;
 355
 356         snprintf(name, 256, "%s.sizeof_param", option_project_str);
 357         name[255] = '\0';
 358         token = get_tokens_file(name);
 359         if (!token)
 360                 return;
 361         if (token_type(token) != TOKEN_STREAMBEGIN)
 362                 return;
 363         token = token->next;
 364         while (token_type(token) != TOKEN_STREAMEND) {
 365                 if (token_type(token) != TOKEN_IDENT)
 366                         return;
 367                 func = show_ident(token->ident);
 368
 369                 token = token->next;
 370                 if (token_type(token) != TOKEN_NUMBER)
 371                         return;
 372                 size = atoi(token->number);
 373
 374                 token = token->next;
 375                 if (token_type(token) != TOKEN_NUMBER)
 376                         return;
 377                 buf = atoi(token->number);
 378
 379                 limiter = malloc(sizeof(*limiter));
 380                 limiter->limit_arg = size;
 381                 limiter->buf_arg = buf;
 382
 383                 add_function_hook(func, &match_limited, limiter);
 384
 385                 token = token->next;
 386         }
 387         clear_token_alloc();
 388 }
 389
 390 void check_overflow(int id)
 391 {
 392         my_used_id = id;
 393         register_funcs_from_file();
 394         add_hook(&match_function_def, FUNC_DEF_HOOK);
 395         add_hook(&array_check, OP_HOOK);
 396         add_hook(&match_condition, CONDITION_HOOK);
 397         add_function_hook("strcpy", &match_strcpy, NULL);
 398         add_function_hook("snprintf", &match_snprintf, NULL);
 399         add_function_hook("sprintf", &match_sprintf, NULL);
 400         add_function_hook("memcmp", &match_limited, &b0_l2);
 401         add_function_hook("memcmp", &match_limited, &b1_l2);
 402         add_db_return_states_callback(BUF_SIZE, &db_returns_buf_size);
 403         add_modification_hook(my_used_id, &delete);
 404         if (option_project == PROJ_KERNEL) {
 405                 add_function_hook("copy_to_user", &match_limited, &b0_l2);
 406                 add_function_hook("copy_to_user", &match_limited, &b1_l2);
 407                 add_function_hook("_copy_to_user", &match_limited, &b0_l2);
 408                 add_function_hook("_copy_to_user", &match_limited, &b1_l2);
 409                 add_function_hook("__copy_to_user", &match_limited, &b0_l2);
 410                 add_function_hook("__copy_to_user", &match_limited, &b1_l2);
 411                 add_function_hook("copy_from_user", &match_limited, &b0_l2);
 412                 add_function_hook("copy_from_user", &match_limited, &b1_l2);
 413                 add_function_hook("_copy_from_user", &match_limited, &b0_l2);
 414                 add_function_hook("_copy_from_user", &match_limited, &b1_l2);
 415                 add_function_hook("__copy_from_user", &match_limited, &b0_l2);
 416                 add_function_hook("__copy_from_user", &match_limited, &b1_l2);
 417         }
 418 }