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 bool is_possibly_zero(const char *name, struct symbol *sym)
  65 {
  66         struct sm_state *sm, *tmp;
  67
  68         sm = get_sm_state(SMATCH_EXTRA, name, sym);
  69         if (!sm)
  70                 return false;
  71         FOR_EACH_PTR(sm->possible, tmp) {
  72                 if (!estate_rl(tmp->state))
  73                         continue;
  74                 if (rl_min(estate_rl(tmp->state)).value == 0 &&
  75                     rl_max(estate_rl(tmp->state)).value == 0)
  76                         return true;
  77         } END_FOR_EACH_PTR(tmp);
  78
  79         return false;
  80 }
  81
  82 static void check_dereference(struct expression *expr)
  83 {
  84         struct sm_state *sm;
  85         struct sm_state *tmp;
  86
  87         expr = strip_expr(expr);
  88         if (is_static(expr))
  89                 return;
  90         sm = get_sm_state_expr(my_id, expr);
  91         if (!sm)
  92                 return;
  93         if (is_ignored(my_id, sm->name, sm->sym))
  94                 return;
  95         if (!is_possibly_zero(sm->name, sm->sym))
  96                 return;
  97         if (is_impossible_path())
  98                 return;
  99
 100         FOR_EACH_PTR(sm->possible, tmp) {
 101                 if (tmp->state == &merged)
 102                         continue;
 103                 if (tmp->state == &ok)
 104                         continue;
 105                 add_ignore(my_id, sm->name, sm->sym);
 106                 if (tmp->state == &null)
 107                         return;
 108                 if (tmp->state == &uninitialized)
 109                         return;
 110                 sm_error("potential null dereference '%s'.  (%s returns null)",
 111                         tmp->name, tmp->state->name);
 112                 return;
 113         } END_FOR_EACH_PTR(tmp);
 114 }
 115
 116 static void check_dereference_name_sym(char *name, struct symbol *sym)
 117 {
 118         struct sm_state *sm;
 119         struct sm_state *tmp;
 120
 121         sm = get_sm_state(my_id, name, sym);
 122         if (!sm)
 123                 return;
 124         if (is_ignored(my_id, sm->name, sm->sym))
 125                 return;
 126         if (!is_possibly_zero(sm->name, sm->sym))
 127                 return;
 128         if (is_impossible_path())
 129                 return;
 130
 131         FOR_EACH_PTR(sm->possible, tmp) {
 132                 if (tmp->state == &merged)
 133                         continue;
 134                 if (tmp->state == &ok)
 135                         continue;
 136                 add_ignore(my_id, sm->name, sm->sym);
 137                 if (tmp->state == &null)
 138                         return;
 139                 if (tmp->state == &uninitialized)
 140                         return;
 141                 sm_error("potential null dereference '%s'.  (%s returns null)",
 142                         tmp->name, tmp->state->name);
 143                 return;
 144         } END_FOR_EACH_PTR(tmp);
 145 }
 146
 147 static void match_dereferences(struct expression *expr)
 148 {
 149         if (expr->type != EXPR_PREOP)
 150                 return;
 151         check_dereference(expr->unop);
 152 }
 153
 154 static void match_pointer_as_array(struct expression *expr)
 155 {
 156         if (!is_array(expr))
 157                 return;
 158         check_dereference(get_array_base(expr));
 159 }
 160
 161 static void set_param_dereferenced(struct expression *call, struct expression *arg, char *key, char *unused)
 162 {
 163         struct symbol *sym;
 164         char *name;
 165
 166         name = get_variable_from_key(arg, key, &sym);
 167         if (!name || !sym)
 168                 goto free;
 169
 170         check_dereference_name_sym(name, sym);
 171 free:
 172         free_string(name);
 173 }
 174
 175 static void match_declarations(struct symbol *sym)
 176 {
 177         const char *name;
 178
 179         if ((get_base_type(sym))->type == SYM_ARRAY)
 180                 return;
 181
 182         if (!sym->ident)
 183                 return;
 184         name = sym->ident->name;
 185         if (!sym->initializer) {
 186                 set_state(my_id, name, sym, &uninitialized);
 187                 scoped_state(my_id, name, sym);
 188         }
 189 }
 190
 191 static void match_assign(struct expression *expr)
 192 {
 193         struct statement *stmt;
 194
 195         if (!expr_is_zero(expr->right))
 196                 return;
 197
 198         if (__in_fake_assign)
 199                 return;
 200
 201         stmt = get_current_statement();
 202         if (stmt && stmt->type == STMT_DECLARATION)
 203                 return;
 204
 205         set_state_expr(my_id, expr->left, &null);
 206 }
 207
 208 static void match_assigns_address(struct expression *expr)
 209 {
 210         struct expression *right;
 211
 212         right = strip_expr(expr->right);
 213         if (right->type != EXPR_PREOP || right->op != '&')
 214                 return;
 215         set_state_expr(my_id, right, &ok);
 216 }
 217
 218 static void match_condition(struct expression *expr)
 219 {
 220         if (expr->type == EXPR_ASSIGNMENT) {
 221                 match_condition(expr->right);
 222                 match_condition(expr->left);
 223         }
 224         if (!get_state_expr(my_id, expr))
 225                 return;
 226         set_true_false_states_expr(my_id, expr, &ok, NULL);
 227 }
 228
 229 static int called_with_no_fail(struct expression *call, int param)
 230 {
 231         struct expression *arg;
 232         sval_t sval;
 233
 234         if (param == -1)
 235                 return 0;
 236         call = strip_expr(call);
 237         if (call->type != EXPR_CALL)
 238                 return 0;
 239         arg = get_argument_from_call_expr(call->args, param);
 240         if (get_value(arg, &sval) && (sval.uvalue & __GFP_NOFAIL))
 241                 return 1;
 242         return 0;
 243 }
 244
 245 static void match_assign_returns_null(const char *fn, struct expression *expr, void *_gfp)
 246 {
 247         struct smatch_state *state;
 248         int gfp_param = PTR_INT(_gfp);
 249
 250         if (called_with_no_fail(expr->right, gfp_param))
 251                 return;
 252         state = alloc_my_state(fn);
 253         set_state_expr(my_id, expr->left, state);
 254 }
 255
 256 static void register_allocation_funcs(void)
 257 {
 258         struct token *token;
 259         const char *func;
 260         int arg;
 261
 262         token = get_tokens_file("kernel.allocation_funcs_gfp");
 263         if (!token)
 264                 return;
 265         if (token_type(token) != TOKEN_STREAMBEGIN)
 266                 return;
 267         token = token->next;
 268         while (token_type(token) != TOKEN_STREAMEND) {
 269                 if (token_type(token) != TOKEN_IDENT)
 270                         return;
 271                 func = show_ident(token->ident);
 272                 token = token->next;
 273                 if (token_type(token) == TOKEN_IDENT)
 274                         arg = -1;
 275                 else if (token_type(token) == TOKEN_NUMBER)
 276                         arg = atoi(token->number);
 277                 else
 278                         return;
 279                 add_function_assign_hook(func, &match_assign_returns_null, INT_PTR(arg));
 280                 token = token->next;
 281         }
 282         clear_token_alloc();
 283 }
 284
 285 void check_deref(int id)
 286 {
 287         my_id = id;
 288
 289         add_unmatched_state_hook(my_id, &unmatched_state);
 290         add_modification_hook(my_id, &is_ok);
 291         add_hook(&match_dereferences, DEREF_HOOK);
 292         add_hook(&match_pointer_as_array, OP_HOOK);
 293         select_return_implies_hook(DEREFERENCE, &set_param_dereferenced);
 294         add_hook(&match_condition, CONDITION_HOOK);
 295         add_hook(&match_declarations, DECLARATION_HOOK);
 296         add_hook(&match_assign, ASSIGNMENT_HOOK);
 297         add_hook(&match_assigns_address, ASSIGNMENT_HOOK);
 298         if (option_project == PROJ_KERNEL)
 299                 register_allocation_funcs();
 300 }