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