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         long long val;
  52         struct expression *tmp;
  53         int step = 0;
  54         int dot_ops = 0;
  55
  56         if (!get_implied_value(offset, &val))
  57                 return 0;
  58         if (get_array_size(array) != val)
  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                 return 0;
  77         } END_FOR_EACH_PTR_REVERSE(tmp);
  78         return 0;
  79 }
  80
  81 static void array_check(struct expression *expr)
  82 {
  83         struct expression *array_expr;
  84         int array_size;
  85         struct expression *offset;
  86         long long max;
  87         char *name;
  88
  89         expr = strip_expr(expr);
  90         if (!is_array(expr))
  91                 return;
  92
  93         array_expr = strip_parens(expr->unop->left);
  94         array_size = get_array_size(array_expr);
  95         if (!array_size || array_size == 1)
  96                 return;
  97
  98         offset = get_array_offset(expr);
  99         if (!get_fuzzy_max(offset, &max)) {
 100                 if (getting_address())
 101                         return;
 102                 set_state_expr(my_used_id, offset, alloc_state_num(array_size));
 103         } else if (array_size <= max) {
 104                 const char *level = "error";
 105
 106                 if (getting_address())
 107                         level = "warn";
 108
 109                 if (definitely_just_used_as_limiter(array_expr, offset))
 110                         return;
 111
 112                 if (!option_spammy) {
 113                         struct smatch_state *state;
 114
 115                         state = get_state_expr(SMATCH_EXTRA, offset);
 116                         if (state && is_whole_range(state))
 117                                 return;
 118                 }
 119
 120                 name = get_variable_from_expr_complex(array_expr, NULL);
 121                 /* Blast.  Smatch can't figure out glibc's strcmp __strcmp_cg()
 122                  * so it prints an error every time you compare to a string
 123                  * literal array with 4 or less chars.
 124                  */
 125                 if (name && strcmp(name, "__s1") && strcmp(name, "__s2")) {
 126                         sm_msg("%s: buffer overflow '%s' %d <= %lld",
 127                                 level, name, array_size, max);
 128                 }
 129                 free_string(name);
 130         }
 131 }
 132
 133 static void match_condition(struct expression *expr)
 134 {
 135         int left;
 136         long long val;
 137         struct state_list *slist;
 138         struct sm_state *tmp;
 139         int boundary;
 140
 141         if (!expr || expr->type != EXPR_COMPARE)
 142                 return;
 143         if (get_macro_name(expr->pos))
 144                 return;
 145         if (get_implied_value(expr->left, &val))
 146                 left = 1;
 147         else if (get_implied_value(expr->right, &val))
 148                 left = 0;
 149         else
 150                 return;
 151
 152         if (left)
 153                 slist = get_possible_states_expr(my_used_id, expr->right);
 154         else
 155                 slist = get_possible_states_expr(my_used_id, expr->left);
 156         if (!slist)
 157                 return;
 158         FOR_EACH_PTR(slist, tmp) {
 159                 if (tmp->state == &merged || tmp->state == &undefined)
 160                         continue;
 161                 boundary = PTR_INT(tmp->state->data);
 162                 boundary -= val;
 163                 if (boundary < 1 && boundary > -1) {
 164                         char *name;
 165
 166                         name = get_variable_from_expr((left ? expr->right : expr->left), NULL);
 167                         sm_msg("error: testing array offset '%s' after use.", name);
 168                         return;
 169                 }
 170         } END_FOR_EACH_PTR(tmp);
 171 }
 172
 173 static void match_strcpy(const char *fn, struct expression *expr, void *unused)
 174 {
 175         struct expression *dest;
 176         struct expression *data;
 177         char *dest_name = NULL;
 178         char *data_name = NULL;
 179         int dest_size;
 180         int data_size;
 181
 182         dest = get_argument_from_call_expr(expr->args, 0);
 183         data = get_argument_from_call_expr(expr->args, 1);
 184         dest_size = get_array_size_bytes(dest);
 185         data_size = get_array_size_bytes(data);
 186
 187         if (!dest_size)
 188                 return;
 189
 190         /* If the size of both arrays is known and the destination
 191          * buffer is larger than the source buffer, we're okay.
 192          */
 193         if (data_size && dest_size >= data_size)
 194                 return;
 195
 196         dest_name = get_variable_from_expr_complex(dest, NULL);
 197         data_name = get_variable_from_expr_complex(data, NULL);
 198
 199         if (data_size)
 200                 sm_msg("error: %s() '%s' too large for '%s' (%d vs %d)",
 201                         fn, data_name, dest_name, data_size, dest_size);
 202         else if (option_spammy)
 203                 sm_msg("warn: %s() '%s' of unknown size might be too large for '%s'",
 204                         fn, data_name, dest_name);
 205
 206         free_string(dest_name);
 207         free_string(data_name);
 208 }
 209
 210 static void match_snprintf(const char *fn, struct expression *expr, void *unused)
 211 {
 212         struct expression *dest;
 213         struct expression *dest_size_expr;
 214         struct expression *format_string;
 215         struct expression *data;
 216         char *data_name = NULL;
 217         int dest_size;
 218         long long limit_size;
 219         char *format;
 220         int data_size;
 221
 222         dest = get_argument_from_call_expr(expr->args, 0);
 223         dest_size_expr = get_argument_from_call_expr(expr->args, 1);
 224         format_string = get_argument_from_call_expr(expr->args, 2);
 225         data = get_argument_from_call_expr(expr->args, 3);
 226
 227         dest_size = get_array_size_bytes(dest);
 228         if (!get_implied_value(dest_size_expr, &limit_size))
 229                 return;
 230         if (dest_size && dest_size < limit_size)
 231                 sm_msg("error: snprintf() is printing too much %lld vs %d", limit_size, dest_size);
 232         format = get_variable_from_expr(format_string, NULL);
 233         if (!format)
 234                 return;
 235         if (strcmp(format, "\"%s\""))
 236                 goto free;
 237         data_name = get_variable_from_expr_complex(data, NULL);
 238         data_size = get_array_size_bytes(data);
 239         if (limit_size < data_size)
 240                 sm_msg("error: snprintf() chops off the last chars of '%s': %d vs %lld",
 241                        data_name, data_size, limit_size);
 242 free:
 243         free_string(data_name);
 244         free_string(format);
 245 }
 246
 247 static void match_sprintf(const char *fn, struct expression *expr, void *unused)
 248 {
 249         struct expression *dest;
 250         struct expression *format_string;
 251         struct expression *data;
 252         char *data_name = NULL;
 253         int dest_size;
 254         char *format;
 255         int data_size;
 256
 257         dest = get_argument_from_call_expr(expr->args, 0);
 258         format_string = get_argument_from_call_expr(expr->args, 1);
 259         data = get_argument_from_call_expr(expr->args, 2);
 260
 261         dest_size = get_array_size_bytes(dest);
 262         if (!dest_size)
 263                 return;
 264         format = get_variable_from_expr(format_string, NULL);
 265         if (!format)
 266                 return;
 267         if (strcmp(format, "\"%s\""))
 268                 goto free;
 269         data_name = get_variable_from_expr_complex(data, NULL);
 270         data_size = get_array_size_bytes(data);
 271         if (dest_size < data_size)
 272                 sm_msg("error: sprintf() copies too much data from '%s': %d vs %d",
 273                        data_name, data_size, dest_size);
 274 free:
 275         free_string(data_name);
 276         free_string(format);
 277 }
 278
 279 static void match_limited(const char *fn, struct expression *expr, void *_limiter)
 280 {
 281         struct limiter *limiter = (struct limiter *)_limiter;
 282         struct expression *dest;
 283         struct expression *data;
 284         char *dest_name = NULL;
 285         long long needed;
 286         int has;
 287
 288         dest = get_argument_from_call_expr(expr->args, limiter->buf_arg);
 289         data = get_argument_from_call_expr(expr->args, limiter->limit_arg);
 290         if (!get_fuzzy_max(data, &needed))
 291                 return;
 292         has = get_array_size_bytes(dest);
 293         if (!has)
 294                 return;
 295         if (has >= needed)
 296                 return;
 297
 298         dest_name = get_variable_from_expr_complex(dest, NULL);
 299         sm_msg("error: %s() '%s' too small (%d vs %lld)", fn, dest_name, has, needed);
 300         free_string(dest_name);
 301 }
 302
 303 static void register_funcs_from_file(void)
 304 {
 305         char name[256];
 306         struct token *token;
 307         const char *func;
 308         int size, buf;
 309         struct limiter *limiter;
 310
 311         snprintf(name, 256, "%s.sizeof_param", option_project_str);
 312         name[255] = '\0';
 313         token = get_tokens_file(name);
 314         if (!token)
 315                 return;
 316         if (token_type(token) != TOKEN_STREAMBEGIN)
 317                 return;
 318         token = token->next;
 319         while (token_type(token) != TOKEN_STREAMEND) {
 320                 if (token_type(token) != TOKEN_IDENT)
 321                         return;
 322                 func = show_ident(token->ident);
 323
 324                 token = token->next;
 325                 if (token_type(token) != TOKEN_NUMBER)
 326                         return;
 327                 size = atoi(token->number);
 328
 329                 token = token->next;
 330                 if (token_type(token) != TOKEN_NUMBER)
 331                         return;
 332                 buf = atoi(token->number);
 333
 334                 limiter = malloc(sizeof(*limiter));
 335                 limiter->limit_arg = size;
 336                 limiter->buf_arg = buf;
 337
 338                 add_function_hook(func, &match_limited, limiter);
 339
 340                 token = token->next;
 341         }
 342         clear_token_alloc();
 343 }
 344
 345 void check_overflow(int id)
 346 {
 347         my_used_id = id;
 348         register_funcs_from_file();
 349         add_hook(&match_function_def, FUNC_DEF_HOOK);
 350         add_hook(&array_check, OP_HOOK);
 351         add_hook(&match_condition, CONDITION_HOOK);
 352         add_function_hook("strcpy", &match_strcpy, NULL);
 353         add_function_hook("snprintf", &match_snprintf, NULL);
 354         add_function_hook("sprintf", &match_sprintf, NULL);
 355         add_function_hook("memcmp", &match_limited, &b0_l2);
 356         add_function_hook("memcmp", &match_limited, &b1_l2);
 357         add_modification_hook(my_used_id, &delete);
 358         if (option_project == PROJ_KERNEL) {
 359                 add_function_hook("copy_to_user", &match_limited, &b0_l2);
 360                 add_function_hook("copy_to_user", &match_limited, &b1_l2);
 361                 add_function_hook("_copy_to_user", &match_limited, &b0_l2);
 362                 add_function_hook("_copy_to_user", &match_limited, &b1_l2);
 363                 add_function_hook("__copy_to_user", &match_limited, &b0_l2);
 364                 add_function_hook("__copy_to_user", &match_limited, &b1_l2);
 365                 add_function_hook("copy_from_user", &match_limited, &b0_l2);
 366                 add_function_hook("copy_from_user", &match_limited, &b1_l2);
 367                 add_function_hook("_copy_from_user", &match_limited, &b0_l2);
 368                 add_function_hook("_copy_from_user", &match_limited, &b1_l2);
 369                 add_function_hook("__copy_from_user", &match_limited, &b0_l2);
 370                 add_function_hook("__copy_from_user", &match_limited, &b1_l2);
 371         }
 372 }