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(const char *name, struct symbol *sym, struct expression *expr, void *unused)
  45 {
  46         delete_state(my_used_id, name, sym);
  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                 add_modification_hook_expr(my_used_id, offset, &delete, NULL);
 104         } else if (array_size <= max) {
 105                 const char *level = "error";
 106
 107                 if (getting_address())
 108                         level = "warn";
 109
 110                 if (definitely_just_used_as_limiter(array_expr, offset))
 111                         return;
 112
 113                 if (!option_spammy) {
 114                         struct smatch_state *state;
 115
 116                         state = get_state_expr(SMATCH_EXTRA, offset);
 117                         if (state && is_whole_range(state))
 118                                 return;
 119                 }
 120
 121                 name = get_variable_from_expr_complex(array_expr, NULL);
 122                 /* Blast.  Smatch can't figure out glibc's strcmp __strcmp_cg()
 123                  * so it prints an error every time you compare to a string
 124                  * literal array with 4 or less chars.
 125                  */
 126                 if (name && strcmp(name, "__s1") && strcmp(name, "__s2")) {
 127                         sm_msg("%s: buffer overflow '%s' %d <= %lld",
 128                                 level, name, array_size, max);
 129                 }
 130                 free_string(name);
 131         }
 132 }
 133
 134 static void match_condition(struct expression *expr)
 135 {
 136         int left;
 137         long long val;
 138         struct state_list *slist;
 139         struct sm_state *tmp;
 140         int boundary;
 141
 142         if (!expr || expr->type != EXPR_COMPARE)
 143                 return;
 144         if (get_implied_value(expr->left, &val))
 145                 left = 1;
 146         else if (get_implied_value(expr->right, &val))
 147                 left = 0;
 148         else
 149                 return;
 150
 151         if (left)
 152                 slist = get_possible_states_expr(my_used_id, expr->right);
 153         else
 154                 slist = get_possible_states_expr(my_used_id, expr->left);
 155         if (!slist)
 156                 return;
 157         FOR_EACH_PTR(slist, tmp) {
 158                 if (tmp->state == &merged)
 159                         continue;
 160                 boundary = PTR_INT(tmp->state->data);
 161                 boundary -= val;
 162                 if (boundary < 1 && boundary > -1) {
 163                         char *name;
 164
 165                         name = get_variable_from_expr((left ? expr->right : expr->left), NULL);
 166                         sm_msg("error: testing array offset '%s' after use.", name);
 167                         return;
 168                 }
 169         } END_FOR_EACH_PTR(tmp);
 170 }
 171
 172 static void match_strcpy(const char *fn, struct expression *expr, void *unused)
 173 {
 174         struct expression *dest;
 175         struct expression *data;
 176         char *dest_name = NULL;
 177         char *data_name = NULL;
 178         int dest_size;
 179         int data_size;
 180
 181         dest = get_argument_from_call_expr(expr->args, 0);
 182         data = get_argument_from_call_expr(expr->args, 1);
 183         dest_size = get_array_size_bytes(dest);
 184         data_size = get_array_size_bytes(data);
 185
 186         if (!dest_size)
 187                 return;
 188
 189         /* If the size of both arrays is known and the destination
 190          * buffer is larger than the source buffer, we're okay.
 191          */
 192         if (data_size && dest_size >= data_size)
 193                 return;
 194
 195         dest_name = get_variable_from_expr_complex(dest, NULL);
 196         data_name = get_variable_from_expr_complex(data, NULL);
 197
 198         if (data_size)
 199                 sm_msg("error: %s() '%s' too large for '%s' (%d vs %d)",
 200                         fn, data_name, dest_name, data_size, dest_size);
 201         else if (option_spammy)
 202                 sm_msg("warn: %s() '%s' of unknown size might be too large for '%s'",
 203                         fn, data_name, dest_name);
 204
 205         free_string(dest_name);
 206         free_string(data_name);
 207 }
 208
 209 static void match_snprintf(const char *fn, struct expression *expr, void *unused)
 210 {
 211         struct expression *dest;
 212         struct expression *dest_size_expr;
 213         struct expression *format_string;
 214         struct expression *data;
 215         char *data_name = NULL;
 216         int dest_size;
 217         long long limit_size;
 218         char *format;
 219         int data_size;
 220
 221         dest = get_argument_from_call_expr(expr->args, 0);
 222         dest_size_expr = get_argument_from_call_expr(expr->args, 1);
 223         format_string = get_argument_from_call_expr(expr->args, 2);
 224         data = get_argument_from_call_expr(expr->args, 3);
 225
 226         dest_size = get_array_size_bytes(dest);
 227         if (!get_implied_value(dest_size_expr, &limit_size))
 228                 return;
 229         if (dest_size && dest_size < limit_size)
 230                 sm_msg("error: snprintf() is printing too much %lld vs %d", limit_size, dest_size);
 231         format = get_variable_from_expr(format_string, NULL);
 232         if (!format)
 233                 return;
 234         if (strcmp(format, "\"%s\""))
 235                 goto free;
 236         data_name = get_variable_from_expr_complex(data, NULL);
 237         data_size = get_array_size_bytes(data);
 238         if (limit_size < data_size)
 239                 sm_msg("error: snprintf() chops off the last chars of '%s': %d vs %lld",
 240                        data_name, data_size, limit_size);
 241 free:
 242         free_string(data_name);
 243         free_string(format);
 244 }
 245
 246 static void match_sprintf(const char *fn, struct expression *expr, void *unused)
 247 {
 248         struct expression *dest;
 249         struct expression *format_string;
 250         struct expression *data;
 251         char *data_name = NULL;
 252         int dest_size;
 253         char *format;
 254         int data_size;
 255
 256         dest = get_argument_from_call_expr(expr->args, 0);
 257         format_string = get_argument_from_call_expr(expr->args, 1);
 258         data = get_argument_from_call_expr(expr->args, 2);
 259
 260         dest_size = get_array_size_bytes(dest);
 261         if (!dest_size)
 262                 return;
 263         format = get_variable_from_expr(format_string, NULL);
 264         if (!format)
 265                 return;
 266         if (strcmp(format, "\"%s\""))
 267                 goto free;
 268         data_name = get_variable_from_expr_complex(data, NULL);
 269         data_size = get_array_size_bytes(data);
 270         if (dest_size < data_size)
 271                 sm_msg("error: sprintf() copies too much data from '%s': %d vs %d",
 272                        data_name, data_size, dest_size);
 273 free:
 274         free_string(data_name);
 275         free_string(format);
 276 }
 277
 278 static void match_limited(const char *fn, struct expression *expr, void *_limiter)
 279 {
 280         struct limiter *limiter = (struct limiter *)_limiter;
 281         struct expression *dest;
 282         struct expression *data;
 283         char *dest_name = NULL;
 284         long long needed;
 285         int has;
 286
 287         dest = get_argument_from_call_expr(expr->args, limiter->buf_arg);
 288         data = get_argument_from_call_expr(expr->args, limiter->limit_arg);
 289         if (!get_fuzzy_max(data, &needed))
 290                 return;
 291         has = get_array_size_bytes(dest);
 292         if (!has)
 293                 return;
 294         if (has >= needed)
 295                 return;
 296
 297         dest_name = get_variable_from_expr_complex(dest, NULL);
 298         sm_msg("error: %s() '%s' too small (%d vs %lld)", fn, dest_name, has, needed);
 299         free_string(dest_name);
 300 }
 301
 302 void check_overflow(int id)
 303 {
 304         my_used_id = id;
 305         add_hook(&match_function_def, FUNC_DEF_HOOK);
 306         add_hook(&array_check, OP_HOOK);
 307         add_hook(&match_condition, CONDITION_HOOK);
 308         add_function_hook("strcpy", &match_strcpy, NULL);
 309         add_function_hook("snprintf", &match_snprintf, NULL);
 310         add_function_hook("sprintf", &match_sprintf, NULL);
 311         if (option_project == PROJ_KERNEL) {
 312                 add_function_hook("copy_to_user", &match_limited, &b0_l2);
 313                 add_function_hook("copy_to_user", &match_limited, &b1_l2);
 314                 add_function_hook("_copy_to_user", &match_limited, &b0_l2);
 315                 add_function_hook("_copy_to_user", &match_limited, &b1_l2);
 316                 add_function_hook("__copy_to_user", &match_limited, &b0_l2);
 317                 add_function_hook("__copy_to_user", &match_limited, &b1_l2);
 318                 add_function_hook("copy_from_user", &match_limited, &b0_l2);
 319                 add_function_hook("copy_from_user", &match_limited, &b1_l2);
 320                 add_function_hook("_copy_from_user", &match_limited, &b0_l2);
 321                 add_function_hook("_copy_from_user", &match_limited, &b1_l2);
 322                 add_function_hook("__copy_from_user", &match_limited, &b0_l2);
 323                 add_function_hook("__copy_from_user", &match_limited, &b1_l2);
 324         }
 325 }