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 check_dereference_name_sym(char *name, struct symbol *sym)
 101 {
 102         struct sm_state *sm;
 103         struct sm_state *tmp;
 104
 105         sm = get_sm_state(my_id, name, sym);
 106         if (!sm)
 107                 return;
 108         if (is_ignored(my_id, sm->name, sm->sym))
 109                 return;
 110         if (implied_not_equal_name_sym(name, sym, 0))
 111                 return;
 112
 113         FOR_EACH_PTR(sm->possible, tmp) {
 114                 if (tmp->state == &merged)
 115                         continue;
 116                 if (tmp->state == &ok)
 117                         continue;
 118                 add_ignore(my_id, sm->name, sm->sym);
 119                 if (tmp->state == &null) {
 120                         if (option_spammy)
 121                                 sm_msg("error: potential NULL dereference '%s'.", tmp->name);
 122                         return;
 123                 }
 124                 if (tmp->state == &uninitialized) {
 125                         if (option_spammy)
 126                                 sm_msg("error: potentially dereferencing uninitialized '%s'.", tmp->name);
 127                         return;
 128                 }
 129                 sm_msg("error: potential null dereference '%s'.  (%s returns null)",
 130                         tmp->name, tmp->state->name);
 131                 return;
 132         } END_FOR_EACH_PTR(tmp);
 133 }
 134
 135 static void match_dereferences(struct expression *expr)
 136 {
 137         if (expr->type != EXPR_PREOP)
 138                 return;
 139         check_dereference(expr->unop);
 140 }
 141
 142 static void match_pointer_as_array(struct expression *expr)
 143 {
 144         if (!is_array(expr))
 145                 return;
 146         check_dereference(expr->unop->left);
 147 }
 148
 149 static void set_param_dereferenced(struct expression *arg, char *key, char *unused)
 150 {
 151         struct symbol *sym;
 152         char *name;
 153
 154         name = get_variable_from_key(arg, key, &sym);
 155         if (!name || !sym)
 156                 goto free;
 157
 158         check_dereference_name_sym(name, sym);
 159 free:
 160         free_string(name);
 161 }
 162
 163 static void match_declarations(struct symbol *sym)
 164 {
 165         const char *name;
 166
 167         if ((get_base_type(sym))->type == SYM_ARRAY)
 168                 return;
 169
 170         if (!sym->ident)
 171                 return;
 172         name = sym->ident->name;
 173         if (!sym->initializer) {
 174                 set_state(my_id, name, sym, &uninitialized);
 175                 scoped_state(my_id, name, sym);
 176         }
 177 }
 178
 179 static void match_assign(struct expression *expr)
 180 {
 181         struct statement *stmt;
 182
 183         if (!is_zero(expr->right))
 184                 return;
 185
 186         FOR_EACH_PTR_REVERSE(big_statement_stack, stmt) {
 187                 if (stmt->type == STMT_DECLARATION)
 188                         return;
 189                 break;
 190         } END_FOR_EACH_PTR_REVERSE(stmt);
 191
 192         set_state_expr(my_id, expr->left, &null);
 193 }
 194
 195 static void match_condition(struct expression *expr)
 196 {
 197         if (expr->type == EXPR_ASSIGNMENT) {
 198                 match_condition(expr->right);
 199                 match_condition(expr->left);
 200         }
 201         if (!get_state_expr(my_id, expr))
 202                 return;
 203         set_true_false_states_expr(my_id, expr, &ok, NULL);
 204 }
 205
 206 static int called_with_no_fail(struct expression *call, int param)
 207 {
 208         struct expression *arg;
 209         sval_t sval;
 210
 211         if (param == -1)
 212                 return 0;
 213         call = strip_expr(call);
 214         if (call->type != EXPR_CALL)
 215                 return 0;
 216         arg = get_argument_from_call_expr(call->args, param);
 217         if (get_value(arg, &sval) && (sval.uvalue & __GFP_NOFAIL))
 218                 return 1;
 219         return 0;
 220 }
 221
 222 static void match_assign_returns_null(const char *fn, struct expression *expr, void *_gfp)
 223 {
 224         struct smatch_state *state;
 225         int gfp_param = PTR_INT(_gfp);
 226
 227         if (called_with_no_fail(expr->right, gfp_param))
 228                 return;
 229         state = alloc_my_state(fn);
 230         set_state_expr(my_id, expr->left, state);
 231 }
 232
 233 static void register_allocation_funcs(void)
 234 {
 235         struct token *token;
 236         const char *func;
 237         int arg;
 238
 239         token = get_tokens_file("kernel.allocation_funcs_gfp");
 240         if (!token)
 241                 return;
 242         if (token_type(token) != TOKEN_STREAMBEGIN)
 243                 return;
 244         token = token->next;
 245         while (token_type(token) != TOKEN_STREAMEND) {
 246                 if (token_type(token) != TOKEN_IDENT)
 247                         return;
 248                 func = show_ident(token->ident);
 249                 token = token->next;
 250                 if (token_type(token) == TOKEN_IDENT)
 251                         arg = -1;
 252                 else if (token_type(token) == TOKEN_NUMBER)
 253                         arg = atoi(token->number);
 254                 else
 255                         return;
 256                 add_function_assign_hook(func, &match_assign_returns_null, INT_PTR(arg));
 257                 token = token->next;
 258         }
 259         clear_token_alloc();
 260 }
 261
 262 void check_deref(int id)
 263 {
 264         my_id = id;
 265
 266         add_unmatched_state_hook(my_id, &unmatched_state);
 267         add_modification_hook(my_id, &is_ok);
 268         add_hook(&match_dereferences, DEREF_HOOK);
 269         add_hook(&match_pointer_as_array, OP_HOOK);
 270         select_call_implies_hook(DEREFERENCE, &set_param_dereferenced);
 271         add_hook(&match_condition, CONDITION_HOOK);
 272         add_hook(&match_declarations, DECLARATION_HOOK);
 273         add_hook(&match_assign, ASSIGNMENT_HOOK);
 274         if (option_project == PROJ_KERNEL)
 275                 register_allocation_funcs();
 276 }