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
  78         FOR_EACH_PTR(sm->possible, tmp) {
  79                 if (tmp->state == &merged)
  80                         continue;
  81                 if (tmp->state == &ok)
  82                         continue;
  83                 add_ignore(my_id, sm->name, sm->sym);
  84                 if (tmp->state == &null) {
  85                         if (option_spammy)
  86                                 sm_msg("error: potential NULL dereference '%s'.", tmp->name);
  87                         return;
  88                 }
  89                 if (tmp->state == &uninitialized) {
  90                         if (option_spammy)
  91                                 sm_msg("error: potentially dereferencing uninitialized '%s'.", tmp->name);
  92                         return;
  93                 }
  94                 sm_msg("error: potential null dereference '%s'.  (%s returns null)",
  95                         tmp->name, tmp->state->name);
  96                 return;
  97         } END_FOR_EACH_PTR(tmp);
  98 }
  99
 100 static void match_dereferences(struct expression *expr)
 101 {
 102         if (expr->type != EXPR_PREOP)
 103                 return;
 104         check_dereference(expr->unop);
 105 }
 106
 107 static void match_pointer_as_array(struct expression *expr)
 108 {
 109         if (!is_array(expr))
 110                 return;
 111         check_dereference(expr->unop->left);
 112 }
 113
 114 static void set_param_dereferenced(struct expression *arg, char *unused)
 115 {
 116         check_dereference(arg);
 117 }
 118
 119 static void match_declarations(struct symbol *sym)
 120 {
 121         const char *name;
 122
 123         if ((get_base_type(sym))->type == SYM_ARRAY)
 124                 return;
 125
 126         if (!sym->ident)
 127                 return;
 128         name = sym->ident->name;
 129         if (!sym->initializer) {
 130                 set_state(my_id, name, sym, &uninitialized);
 131                 scoped_state(my_id, name, sym);
 132         }
 133 }
 134
 135 static void match_assign(struct expression *expr)
 136 {
 137         struct statement *stmt;
 138
 139         if (!is_zero(expr->right))
 140                 return;
 141
 142         FOR_EACH_PTR_REVERSE(big_statement_stack, stmt) {
 143                 if (stmt->type == STMT_DECLARATION)
 144                         return;
 145                 break;
 146         } END_FOR_EACH_PTR_REVERSE(stmt);
 147
 148         set_state_expr(my_id, expr->left, &null);
 149 }
 150
 151 static void match_condition(struct expression *expr)
 152 {
 153         if (expr->type == EXPR_ASSIGNMENT) {
 154                 match_condition(expr->right);
 155                 match_condition(expr->left);
 156         }
 157         if (!get_state_expr(my_id, expr))
 158                 return;
 159         set_true_false_states_expr(my_id, expr, &ok, NULL);
 160 }
 161
 162 static int called_with_no_fail(struct expression *call, int param)
 163 {
 164         struct expression *arg;
 165         sval_t sval;
 166
 167         if (param == -1)
 168                 return 0;
 169         call = strip_expr(call);
 170         if (call->type != EXPR_CALL)
 171                 return 0;
 172         arg = get_argument_from_call_expr(call->args, param);
 173         if (get_value(arg, &sval) && (sval.uvalue & __GFP_NOFAIL))
 174                 return 1;
 175         return 0;
 176 }
 177
 178 static void match_assign_returns_null(const char *fn, struct expression *expr, void *_gfp)
 179 {
 180         struct smatch_state *state;
 181         int gfp_param = PTR_INT(_gfp);
 182
 183         if (called_with_no_fail(expr->right, gfp_param))
 184                 return;
 185         state = alloc_my_state(fn);
 186         set_state_expr(my_id, expr->left, state);
 187 }
 188
 189 static void register_allocation_funcs(void)
 190 {
 191         struct token *token;
 192         const char *func;
 193         int arg;
 194
 195         token = get_tokens_file("kernel.allocation_funcs_gfp");
 196         if (!token)
 197                 return;
 198         if (token_type(token) != TOKEN_STREAMBEGIN)
 199                 return;
 200         token = token->next;
 201         while (token_type(token) != TOKEN_STREAMEND) {
 202                 if (token_type(token) != TOKEN_IDENT)
 203                         return;
 204                 func = show_ident(token->ident);
 205                 token = token->next;
 206                 if (token_type(token) == TOKEN_IDENT)
 207                         arg = -1;
 208                 else if (token_type(token) == TOKEN_NUMBER)
 209                         arg = atoi(token->number);
 210                 else
 211                         return;
 212                 add_function_assign_hook(func, &match_assign_returns_null, INT_PTR(arg));
 213                 token = token->next;
 214         }
 215         clear_token_alloc();
 216 }
 217
 218 void check_deref(int id)
 219 {
 220         my_id = id;
 221
 222         add_unmatched_state_hook(my_id, &unmatched_state);
 223         add_modification_hook(my_id, &is_ok);
 224         add_hook(&match_dereferences, DEREF_HOOK);
 225         add_hook(&match_pointer_as_array, OP_HOOK);
 226         select_call_implies_hook(DEREFERENCE, &set_param_dereferenced);
 227         add_hook(&match_condition, CONDITION_HOOK);
 228         add_hook(&match_declarations, DECLARATION_HOOK);
 229         add_hook(&match_assign, ASSIGNMENT_HOOK);
 230         if (option_project == PROJ_KERNEL)
 231                 register_allocation_funcs();
 232 }