smatch_strlen.c

   1 /*
   2  * Copyright (C) 2013 Oracle.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
  16  */
  17
  18 #include <stdlib.h>
  19 #include <errno.h>
  20 #include "parse.h"
  21 #include "smatch.h"
  22 #include "smatch_slist.h"
  23 #include "smatch_extra.h"
  24
  25 #define UNKNOWN_SIZE (-1)
  26
  27 static int my_strlen_id;
  28 /*
  29  * The trick with the my_equiv_id is that if we have:
  30  * foo = strlen(bar);
  31  * We don't know at that point what the strlen() is but we know it's equivalent
  32  * to "foo" so maybe we can find the value of "foo" later.
  33  */
  34 static int my_equiv_id;
  35
  36 static struct smatch_state *size_to_estate(int size)
  37 {
  38         sval_t sval;
  39
  40         sval.type = &int_ctype;
  41         sval.value = size;
  42
  43         return alloc_estate_sval(sval);
  44 }
  45
  46 static struct smatch_state *unmatched_strlen_state(struct sm_state *sm)
  47 {
  48         return size_to_estate(UNKNOWN_SIZE);
  49 }
  50
  51 static void set_strlen_undefined(struct sm_state *sm, struct expression *mod_expr)
  52 {
  53         set_state(sm->owner, sm->name, sm->sym, size_to_estate(UNKNOWN_SIZE));
  54 }
  55
  56 static void set_strlen_equiv_undefined(struct sm_state *sm, struct expression *mod_expr)
  57 {
  58         set_state(sm->owner, sm->name, sm->sym, &undefined);
  59 }
  60
  61 static void match_string_assignment(struct expression *expr)
  62 {
  63         struct range_list *rl;
  64
  65         if (expr->op != '=')
  66                 return;
  67         if (!get_implied_strlen(expr->right, &rl))
  68                 return;
  69         set_state_expr(my_strlen_id, expr->left, alloc_estate_rl(clone_rl(rl)));
  70 }
  71
  72 static void match_strlen(const char *fn, struct expression *expr, void *unused)
  73 {
  74         struct expression *right;
  75         struct expression *str;
  76         struct expression *len_expr;
  77         char *len_name;
  78         struct smatch_state *state;
  79
  80         right = strip_expr(expr->right);
  81         str = get_argument_from_call_expr(right->args, 0);
  82         len_expr = strip_expr(expr->left);
  83
  84         len_name = expr_to_var(len_expr);
  85         if (!len_name)
  86                 return;
  87
  88         state = __alloc_smatch_state(0);
  89         state->name = len_name;
  90         state->data = len_expr;
  91
  92         set_state_expr(my_equiv_id, str, state);
  93 }
  94
  95 static void match_strlen_condition(struct expression *expr)
  96 {
  97         struct expression *left;
  98         struct expression *right;
  99         struct expression *str = NULL;
 100         int strlen_left = 0;
 101         int strlen_right = 0;
 102         sval_t sval;
 103         struct smatch_state *true_state = NULL;
 104         struct smatch_state *false_state = NULL;
 105         int op;
 106
 107         if (expr->type != EXPR_COMPARE)
 108                 return;
 109
 110         left = strip_expr(expr->left);
 111         right = strip_expr(expr->right);
 112
 113         if (left->type == EXPR_CALL && sym_name_is("strlen", left->fn)) {
 114                 str = get_argument_from_call_expr(left->args, 0);
 115                 strlen_left = 1;
 116         }
 117         if (right->type == EXPR_CALL && sym_name_is("strlen", right->fn)) {
 118                 str = get_argument_from_call_expr(right->args, 0);
 119                 strlen_right = 1;
 120         }
 121
 122         if (!strlen_left && !strlen_right)
 123                 return;
 124         if (strlen_left && strlen_right)
 125                 return;
 126
 127         op = expr->op;
 128         if (strlen_left) {
 129                 if (!get_value(right, &sval))
 130                         return;
 131         } else {
 132                 op = flip_comparison(op);
 133                 if (!get_value(left, &sval))
 134                         return;
 135         }
 136
 137         switch (op) {
 138         case '<':
 139         case SPECIAL_UNSIGNED_LT:
 140                 true_state = size_to_estate(sval.value - 1);
 141                 break;
 142         case SPECIAL_LTE:
 143         case SPECIAL_UNSIGNED_LTE:
 144                 true_state = size_to_estate(sval.value);
 145                 break;
 146         case SPECIAL_EQUAL:
 147                 true_state = size_to_estate(sval.value);
 148                 break;
 149         case SPECIAL_NOTEQUAL:
 150                 false_state = size_to_estate(sval.value);
 151                 break;
 152         case SPECIAL_GTE:
 153         case SPECIAL_UNSIGNED_GTE:
 154                 false_state = size_to_estate(sval.value - 1);
 155                 break;
 156         case '>':
 157         case SPECIAL_UNSIGNED_GT:
 158                 false_state = size_to_estate(sval.value);
 159                 break;
 160         }
 161
 162         set_true_false_states_expr(my_strlen_id, str, true_state, false_state);
 163 }
 164
 165 static void match_snprintf(const char *fn, struct expression *expr, void *unused)
 166 {
 167         struct expression *dest;
 168         struct expression *dest_size_expr;
 169         sval_t limit_size;
 170
 171         dest = get_argument_from_call_expr(expr->args, 0);
 172         dest_size_expr = get_argument_from_call_expr(expr->args, 1);
 173
 174         if (!get_implied_value(dest_size_expr, &limit_size))
 175                 return;
 176
 177         if (limit_size.value <= 0)
 178                 return;
 179
 180         set_state_expr(my_strlen_id, dest, size_to_estate(limit_size.value - 1));
 181 }
 182
 183 static void match_strlcpycat(const char *fn, struct expression *expr, void *unused)
 184 {
 185         struct expression *dest;
 186         struct expression *src;
 187         struct expression *limit_expr;
 188         int src_len;
 189         sval_t limit;
 190
 191         dest = get_argument_from_call_expr(expr->args, 0);
 192         src = get_argument_from_call_expr(expr->args, 1);
 193         limit_expr = get_argument_from_call_expr(expr->args, 2);
 194
 195         src_len = get_size_from_strlen(src);
 196
 197         if (!get_implied_max(limit_expr, &limit))
 198                 return;
 199         if (limit.value < 0 || limit.value > INT_MAX)
 200                 return;
 201         if (src_len != 0 && strcmp(fn, "strcpy") == 0 && src_len < limit.value)
 202                 limit.value = src_len;
 203
 204         set_state_expr(my_strlen_id, dest, size_to_estate(limit.value - 1));
 205 }
 206
 207 static void match_strcpy(const char *fn, struct expression *expr, void *unused)
 208 {
 209         struct expression *dest;
 210         struct expression *src;
 211         int src_len;
 212
 213         dest = get_argument_from_call_expr(expr->args, 0);
 214         src = get_argument_from_call_expr(expr->args, 1);
 215
 216         src_len = get_size_from_strlen(src);
 217         if (src_len == 0)
 218                 return;
 219
 220         set_state_expr(my_strlen_id, dest, size_to_estate(src_len - 1));
 221 }
 222
 223 static int get_strlen_from_string(struct expression *expr, struct range_list **rl)
 224 {
 225         sval_t sval;
 226         int len;
 227
 228         len = expr->string->length;
 229         sval = sval_type_val(&int_ctype, len - 1);
 230         *rl = alloc_rl(sval, sval);
 231         return 1;
 232 }
 233
 234
 235 static int get_strlen_from_state(struct expression *expr, struct range_list **rl)
 236 {
 237         struct smatch_state *state;
 238
 239         state = get_state_expr(my_strlen_id, expr);
 240         if (!state)
 241                 return 0;
 242         *rl = estate_rl(state);
 243         return 1;
 244 }
 245
 246 static int get_strlen_from_equiv(struct expression *expr, struct range_list **rl)
 247 {
 248         struct smatch_state *state;
 249
 250         state = get_state_expr(my_equiv_id, expr);
 251         if (!state || !state->data)
 252                 return 0;
 253         if (!get_implied_rl((struct expression *)state->data, rl))
 254                 return 0;
 255         return 1;
 256 }
 257
 258 /*
 259  * This returns the strlen() without the NUL char.
 260  */
 261 int get_implied_strlen(struct expression *expr, struct range_list **rl)
 262 {
 263
 264         *rl = NULL;
 265
 266         expr = strip_expr(expr);
 267         if (expr->type == EXPR_STRING)
 268                 return get_strlen_from_string(expr, rl);
 269
 270         if (get_strlen_from_state(expr, rl))
 271                 return 1;
 272         if (get_strlen_from_equiv(expr, rl))
 273                 return 1;
 274         return 0;
 275 }
 276
 277 int get_size_from_strlen(struct expression *expr)
 278 {
 279         struct range_list *rl;
 280         sval_t max;
 281
 282         if (!get_implied_strlen(expr, &rl))
 283                 return 0;
 284         max = rl_max(rl);
 285         if (sval_is_negative(max) || sval_is_max(max))
 286                 return 0;
 287
 288         return max.value + 1; /* add one because strlen doesn't include the NULL */
 289 }
 290
 291 void set_param_strlen(const char *name, struct symbol *sym, char *key, char *value)
 292 {
 293         struct range_list *rl = NULL;
 294         struct smatch_state *state;
 295         char fullname[256];
 296
 297         if (strncmp(key, "$", 1) != 0)
 298                 return;
 299
 300         snprintf(fullname, 256, "%s%s", name, key + 1);
 301
 302         str_to_rl(&int_ctype, value, &rl);
 303         if (!rl || is_whole_rl(rl))
 304                 return;
 305         state = alloc_estate_rl(rl);
 306         set_state(my_strlen_id, fullname, sym, state);
 307 }
 308
 309 static void match_call(struct expression *expr)
 310 {
 311         struct expression *arg;
 312         struct range_list *rl;
 313         int i;
 314
 315         i = 0;
 316         FOR_EACH_PTR(expr->args, arg) {
 317                 if (!get_implied_strlen(arg, &rl))
 318                         continue;
 319                 if (!is_whole_rl(rl))
 320                         sql_insert_caller_info(expr, STR_LEN, i, "$", show_rl(rl));
 321                 i++;
 322         } END_FOR_EACH_PTR(arg);
 323 }
 324
 325 static void struct_member_callback(struct expression *call, int param, char *printed_name, struct sm_state *sm)
 326 {
 327         if (sm->state == &merged)
 328                 return;
 329         sql_insert_caller_info(call, STR_LEN, param, printed_name, sm->state->name);
 330 }
 331
 332 void register_strlen(int id)
 333 {
 334         my_strlen_id = id;
 335
 336         set_dynamic_states(my_strlen_id);
 337
 338         add_unmatched_state_hook(my_strlen_id, &unmatched_strlen_state);
 339
 340         select_caller_info_hook(set_param_strlen, STR_LEN);
 341         add_hook(&match_string_assignment, ASSIGNMENT_HOOK);
 342
 343         add_modification_hook(my_strlen_id, &set_strlen_undefined);
 344         add_merge_hook(my_strlen_id, &merge_estates);
 345         add_hook(&match_call, FUNCTION_CALL_HOOK);
 346         add_member_info_callback(my_strlen_id, struct_member_callback);
 347         add_hook(&match_strlen_condition, CONDITION_HOOK);
 348
 349         add_function_hook("snprintf", &match_snprintf, NULL);
 350
 351         add_function_hook("strlcpy", &match_strlcpycat, NULL);
 352         add_function_hook("strlcat", &match_strlcpycat, NULL);
 353         add_function_hook("strcpy", &match_strcpy, NULL);
 354 }
 355
 356 void register_strlen_equiv(int id)
 357 {
 358         my_equiv_id = id;
 359         set_dynamic_states(my_equiv_id);
 360         add_function_assign_hook("strlen", &match_strlen, NULL);
 361         add_modification_hook(my_equiv_id, &set_strlen_equiv_undefined);
 362 }
 363