check_deref.c

   1 /*
   2  * Copyright (C) 2010 Dan Carpenter.
   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 /*
  19  * There was a previous null dereference test but it was too confusing and
  20  * difficult to debug.  This test is much simpler in its goals and scope.
  21  *
  22  * This test only complains about:
  23  * 1) dereferencing uninitialized variables
  24  * 2) dereferencing variables which were assigned as null.
  25  * 3) dereferencing variables which were assigned a function the returns
  26  *    null.
  27  *
  28  * If we dereference something then we complain if any of those three
  29  * are possible.
  30  *
  31  */
  32
  33 #include "smatch.h"
  34 #include "smatch_slist.h"
  35 #include "smatch_extra.h"
  36
  37 static int my_id;
  38
  39 #define __GFP_NOFAIL 0x800
  40
  41 STATE(null);
  42 STATE(ok);
  43 STATE(uninitialized);
  44
  45 static struct smatch_state *alloc_my_state(const char *name)
  46 {
  47         struct smatch_state *state;
  48
  49         state = __alloc_smatch_state(0);
  50         state->name = name;
  51         return state;
  52 }
  53
  54 static struct smatch_state *unmatched_state(struct sm_state *sm)
  55 {
  56         return &ok;
  57 }
  58
  59 static void is_ok(struct sm_state *sm, struct expression *mod_expr)
  60 {
  61         set_state(my_id, sm->name, sm->sym, &ok);
  62 }
  63
  64 static void check_dereference(struct expression *expr)
  65 {
  66         struct sm_state *sm;
  67         struct sm_state *tmp;
  68
  69         expr = strip_expr(expr);
  70         sm = get_sm_state_expr(my_id, expr);
  71         if (!sm)
  72                 return;
  73         if (is_ignored(my_id, sm->name, sm->sym))
  74                 return;
  75         if (implied_not_equal(expr, 0))
  76                 return;
  77         if (is_impossible_path())
  78                 return;
  79
  80         FOR_EACH_PTR(sm->possible, tmp) {
  81                 if (tmp->state == &merged)
  82                         continue;
  83                 if (tmp->state == &ok)
  84                         continue;
  85                 add_ignore(my_id, sm->name, sm->sym);
  86                 if (tmp->state == &null) {
  87                         if (option_spammy)
  88                                 sm_msg("error: potential NULL dereference '%s'.", tmp->name);
  89                         return;
  90                 }
  91                 if (tmp->state == &uninitialized) {
  92                         if (option_spammy)
  93                                 sm_msg("error: potentially dereferencing uninitialized '%s'.", tmp->name);
  94                         return;
  95                 }
  96                 sm_msg("error: potential null dereference '%s'.  (%s returns null)",
  97                         tmp->name, tmp->state->name);
  98                 return;
  99         } END_FOR_EACH_PTR(tmp);
 100 }
 101
 102 static void check_dereference_name_sym(char *name, struct symbol *sym)
 103 {
 104         struct sm_state *sm;
 105         struct sm_state *tmp;
 106
 107         sm = get_sm_state(my_id, name, sym);
 108         if (!sm)
 109                 return;
 110         if (is_ignored(my_id, sm->name, sm->sym))
 111                 return;
 112         if (implied_not_equal_name_sym(name, sym, 0))
 113                 return;
 114         if (is_impossible_path())
 115                 return;
 116
 117         FOR_EACH_PTR(sm->possible, tmp) {
 118                 if (tmp->state == &merged)
 119                         continue;
 120                 if (tmp->state == &ok)
 121                         continue;
 122                 add_ignore(my_id, sm->name, sm->sym);
 123                 if (tmp->state == &null) {
 124                         if (option_spammy)
 125                                 sm_msg("error: potential NULL dereference '%s'.", tmp->name);
 126                         return;
 127                 }
 128                 if (tmp->state == &uninitialized) {
 129                         if (option_spammy)
 130                                 sm_msg("error: potentially dereferencing uninitialized '%s'.", tmp->name);
 131                         return;
 132                 }
 133                 sm_msg("error: potential null dereference '%s'.  (%s returns null)",
 134                         tmp->name, tmp->state->name);
 135                 return;
 136         } END_FOR_EACH_PTR(tmp);
 137 }
 138
 139 static void match_dereferences(struct expression *expr)
 140 {
 141         if (expr->type != EXPR_PREOP)
 142                 return;
 143         check_dereference(expr->unop);
 144 }
 145
 146 static void match_pointer_as_array(struct expression *expr)
 147 {
 148         if (!is_array(expr))
 149                 return;
 150         check_dereference(get_array_base(expr));
 151 }
 152
 153 static void set_param_dereferenced(struct expression *arg, char *key, char *unused)
 154 {
 155         struct symbol *sym;
 156         char *name;
 157
 158         name = get_variable_from_key(arg, key, &sym);
 159         if (!name || !sym)
 160                 goto free;
 161
 162         check_dereference_name_sym(name, sym);
 163 free:
 164         free_string(name);
 165 }
 166
 167 static void match_declarations(struct symbol *sym)
 168 {
 169         const char *name;
 170
 171         if ((get_base_type(sym))->type == SYM_ARRAY)
 172                 return;
 173
 174         if (!sym->ident)
 175                 return;
 176         name = sym->ident->name;
 177         if (!sym->initializer) {
 178                 set_state(my_id, name, sym, &uninitialized);
 179                 scoped_state(my_id, name, sym);
 180         }
 181 }
 182
 183 static void match_assign(struct expression *expr)
 184 {
 185         struct statement *stmt;
 186
 187         if (!is_zero(expr->right))
 188                 return;
 189
 190         FOR_EACH_PTR_REVERSE(big_statement_stack, stmt) {
 191                 if (stmt->type == STMT_DECLARATION)
 192                         return;
 193                 break;
 194         } END_FOR_EACH_PTR_REVERSE(stmt);
 195
 196         set_state_expr(my_id, expr->left, &null);
 197 }
 198
 199 static void match_condition(struct expression *expr)
 200 {
 201         if (expr->type == EXPR_ASSIGNMENT) {
 202                 match_condition(expr->right);
 203                 match_condition(expr->left);
 204         }
 205         if (!get_state_expr(my_id, expr))
 206                 return;
 207         set_true_false_states_expr(my_id, expr, &ok, NULL);
 208 }
 209
 210 static int called_with_no_fail(struct expression *call, int param)
 211 {
 212         struct expression *arg;
 213         sval_t sval;
 214
 215         if (param == -1)
 216                 return 0;
 217         call = strip_expr(call);
 218         if (call->type != EXPR_CALL)
 219                 return 0;
 220         arg = get_argument_from_call_expr(call->args, param);
 221         if (get_value(arg, &sval) && (sval.uvalue & __GFP_NOFAIL))
 222                 return 1;
 223         return 0;
 224 }
 225
 226 static void match_assign_returns_null(const char *fn, struct expression *expr, void *_gfp)
 227 {
 228         struct smatch_state *state;
 229         int gfp_param = PTR_INT(_gfp);
 230
 231         if (called_with_no_fail(expr->right, gfp_param))
 232                 return;
 233         state = alloc_my_state(fn);
 234         set_state_expr(my_id, expr->left, state);
 235 }
 236
 237 static void register_allocation_funcs(void)
 238 {
 239         struct token *token;
 240         const char *func;
 241         int arg;
 242
 243         token = get_tokens_file("kernel.allocation_funcs_gfp");
 244         if (!token)
 245                 return;
 246         if (token_type(token) != TOKEN_STREAMBEGIN)
 247                 return;
 248         token = token->next;
 249         while (token_type(token) != TOKEN_STREAMEND) {
 250                 if (token_type(token) != TOKEN_IDENT)
 251                         return;
 252                 func = show_ident(token->ident);
 253                 token = token->next;
 254                 if (token_type(token) == TOKEN_IDENT)
 255                         arg = -1;
 256                 else if (token_type(token) == TOKEN_NUMBER)
 257                         arg = atoi(token->number);
 258                 else
 259                         return;
 260                 add_function_assign_hook(func, &match_assign_returns_null, INT_PTR(arg));
 261                 token = token->next;
 262         }
 263         clear_token_alloc();
 264 }
 265
 266 void check_deref(int id)
 267 {
 268         my_id = id;
 269
 270         add_unmatched_state_hook(my_id, &unmatched_state);
 271         add_modification_hook(my_id, &is_ok);
 272         add_hook(&match_dereferences, DEREF_HOOK);
 273         add_hook(&match_pointer_as_array, OP_HOOK);
 274         select_call_implies_hook(DEREFERENCE, &set_param_dereferenced);
 275         add_hook(&match_condition, CONDITION_HOOK);
 276         add_hook(&match_declarations, DECLARATION_HOOK);
 277         add_hook(&match_assign, ASSIGNMENT_HOOK);
 278         if (option_project == PROJ_KERNEL)
 279                 register_allocation_funcs();
 280 }