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 int get_strlen_from_string(struct expression *expr, struct range_list **rl)
 166 {
 167         sval_t sval;
 168         int len;
 169
 170         len = expr->string->length;
 171         sval = sval_type_val(&int_ctype, len - 1);
 172         *rl = alloc_rl(sval, sval);
 173         return 1;
 174 }
 175
 176
 177 static int get_strlen_from_state(struct expression *expr, struct range_list **rl)
 178 {
 179         struct smatch_state *state;
 180
 181         state = get_state_expr(my_strlen_id, expr);
 182         if (!state)
 183                 return 0;
 184         *rl = estate_rl(state);
 185         return 1;
 186 }
 187
 188 static int get_strlen_from_equiv(struct expression *expr, struct range_list **rl)
 189 {
 190         struct smatch_state *state;
 191
 192         state = get_state_expr(my_equiv_id, expr);
 193         if (!state || !state->data)
 194                 return 0;
 195         if (!get_implied_rl((struct expression *)state->data, rl))
 196                 return 0;
 197         return 1;
 198 }
 199
 200 /*
 201  * This returns the strlen() without the NUL char.
 202  */
 203 int get_implied_strlen(struct expression *expr, struct range_list **rl)
 204 {
 205
 206         *rl = NULL;
 207
 208         expr = strip_expr(expr);
 209         if (expr->type == EXPR_STRING)
 210                 return get_strlen_from_string(expr, rl);
 211
 212         if (get_strlen_from_state(expr, rl))
 213                 return 1;
 214         if (get_strlen_from_equiv(expr, rl))
 215                 return 1;
 216         return 0;
 217 }
 218
 219 int get_size_from_strlen(struct expression *expr)
 220 {
 221         struct range_list *rl;
 222         sval_t max;
 223
 224         if (!get_implied_strlen(expr, &rl))
 225                 return 0;
 226         max = rl_max(rl);
 227         if (sval_is_negative(max) || sval_is_max(max))
 228                 return 0;
 229
 230         return max.value + 1; /* add one because strlen doesn't include the NULL */
 231 }
 232
 233 void set_param_strlen(const char *name, struct symbol *sym, char *key, char *value)
 234 {
 235         struct range_list *rl = NULL;
 236         struct smatch_state *state;
 237         char fullname[256];
 238
 239         if (strncmp(key, "$", 1) != 0)
 240                 return;
 241
 242         snprintf(fullname, 256, "%s%s", name, key + 1);
 243
 244         str_to_rl(&int_ctype, value, &rl);
 245         if (!rl || is_whole_rl(rl))
 246                 return;
 247         state = alloc_estate_rl(rl);
 248         set_state(my_strlen_id, fullname, sym, state);
 249 }
 250
 251 static void match_call(struct expression *expr)
 252 {
 253         struct expression *arg;
 254         struct range_list *rl;
 255         int i;
 256
 257         i = 0;
 258         FOR_EACH_PTR(expr->args, arg) {
 259                 if (!get_implied_strlen(arg, &rl))
 260                         continue;
 261                 if (!is_whole_rl(rl))
 262                         sql_insert_caller_info(expr, STR_LEN, i, "$", show_rl(rl));
 263                 i++;
 264         } END_FOR_EACH_PTR(arg);
 265 }
 266
 267 static void struct_member_callback(struct expression *call, int param, char *printed_name, struct sm_state *sm)
 268 {
 269         if (sm->state == &merged)
 270                 return;
 271         sql_insert_caller_info(call, STR_LEN, param, printed_name, sm->state->name);
 272 }
 273
 274 void register_strlen(int id)
 275 {
 276         my_strlen_id = id;
 277
 278         add_unmatched_state_hook(my_strlen_id, &unmatched_strlen_state);
 279
 280         select_caller_info_hook(set_param_strlen, STR_LEN);
 281         add_hook(&match_string_assignment, ASSIGNMENT_HOOK);
 282
 283         add_modification_hook(my_strlen_id, &set_strlen_undefined);
 284         add_merge_hook(my_strlen_id, &merge_estates);
 285         add_hook(&match_call, FUNCTION_CALL_HOOK);
 286         add_member_info_callback(my_strlen_id, struct_member_callback);
 287         add_hook(&match_strlen_condition, CONDITION_HOOK);
 288 }
 289
 290 void register_strlen_equiv(int id)
 291 {
 292         my_equiv_id = id;
 293         add_function_assign_hook("strlen", &match_strlen, NULL);
 294         add_modification_hook(my_equiv_id, &set_strlen_equiv_undefined);
 295 }
 296