check_deref.c

   1 /*
   2  * sparse/check_deref.c
   3  *
   4  * Copyright (C) 2010 Dan Carpenter.
   5  *
   6  * Licensed under the Open Software License version 1.1
   7  *
   8  */
   9
  10 /*
  11  * There was a previous null dereference test but it was too confusing and
  12  * difficult to debug.  This test is much simpler in its goals and scope.
  13  *
  14  * This test only complains about:
  15  * 1) dereferencing uninitialized variables
  16  * 2) dereferencing variables which were assigned as null.
  17  * 3) dereferencing variables which were assigned a function the returns
  18  *    null.
  19  *
  20  * If we dereference something then we complain if any of those three
  21  * are possible.
  22  *
  23  */
  24
  25 #include "smatch.h"
  26 #include "smatch_slist.h"
  27 #include "smatch_extra.h"
  28
  29 static int my_id;
  30
  31 #define __GFP_NOFAIL 0x800
  32
  33 STATE(null);
  34 STATE(ok);
  35 STATE(uninitialized);
  36
  37 static struct smatch_state *alloc_my_state(const char *name)
  38 {
  39         struct smatch_state *state;
  40
  41         state = __alloc_smatch_state(0);
  42         state->name = name;
  43         return state;
  44 }
  45
  46 static struct smatch_state *unmatched_state(struct sm_state *sm)
  47 {
  48         return &ok;
  49 }
  50
  51 static void is_ok(struct sm_state *sm, struct expression *mod_expr)
  52 {
  53         set_state(my_id, sm->name, sm->sym, &ok);
  54 }
  55
  56 static void check_dereference(struct expression *expr)
  57 {
  58         struct sm_state *sm;
  59         struct sm_state *tmp;
  60
  61         expr = strip_expr(expr);
  62         sm = get_sm_state_expr(my_id, expr);
  63         if (!sm)
  64                 return;
  65         if (is_ignored(my_id, sm->name, sm->sym))
  66                 return;
  67         if (implied_not_equal(expr, 0))
  68                 return;
  69
  70         FOR_EACH_PTR(sm->possible, tmp) {
  71                 if (tmp->state == &merged)
  72                         continue;
  73                 if (tmp->state == &ok)
  74                         continue;
  75                 add_ignore(my_id, sm->name, sm->sym);
  76                 if (tmp->state == &null) {
  77                         if (option_spammy)
  78                                 sm_msg("error: potential NULL dereference '%s'.", tmp->name);
  79                         return;
  80                 }
  81                 if (tmp->state == &uninitialized) {
  82                         if (option_spammy)
  83                                 sm_msg("error: potentially dereferencing uninitialized '%s'.", tmp->name);
  84                         return;
  85                 }
  86                 sm_msg("error: potential null dereference '%s'.  (%s returns null)",
  87                         tmp->name, tmp->state->name);
  88                 return;
  89         } END_FOR_EACH_PTR(tmp);
  90 }
  91
  92 static void match_dereferences(struct expression *expr)
  93 {
  94         if (expr->type != EXPR_PREOP)
  95                 return;
  96         check_dereference(expr->unop);
  97 }
  98
  99 static void match_pointer_as_array(struct expression *expr)
 100 {
 101         if (!is_array(expr))
 102                 return;
 103         check_dereference(expr->unop->left);
 104 }
 105
 106 static void set_param_dereferenced(struct expression *arg, char *unused)
 107 {
 108         check_dereference(arg);
 109 }
 110
 111 static void match_declarations(struct symbol *sym)
 112 {
 113         const char *name;
 114
 115         if ((get_base_type(sym))->type == SYM_ARRAY)
 116                 return;
 117
 118         if (!sym->ident)
 119                 return;
 120         name = sym->ident->name;
 121         if (!sym->initializer) {
 122                 set_state(my_id, name, sym, &uninitialized);
 123                 scoped_state(my_id, name, sym);
 124         }
 125 }
 126
 127 static void match_assign(struct expression *expr)
 128 {
 129         struct statement *stmt;
 130
 131         if (!is_zero(expr->right))
 132                 return;
 133
 134         FOR_EACH_PTR_REVERSE(big_statement_stack, stmt) {
 135                 if (stmt->type == STMT_DECLARATION)
 136                         return;
 137                 break;
 138         } END_FOR_EACH_PTR_REVERSE(stmt);
 139
 140         set_state_expr(my_id, expr->left, &null);
 141 }
 142
 143 static void match_condition(struct expression *expr)
 144 {
 145         if (expr->type == EXPR_ASSIGNMENT) {
 146                 match_condition(expr->right);
 147                 match_condition(expr->left);
 148         }
 149         if (!get_state_expr(my_id, expr))
 150                 return;
 151         set_true_false_states_expr(my_id, expr, &ok, NULL);
 152 }
 153
 154 static int called_with_no_fail(struct expression *call, int param)
 155 {
 156         struct expression *arg;
 157         sval_t sval;
 158
 159         if (param == -1)
 160                 return 0;
 161         call = strip_expr(call);
 162         if (call->type != EXPR_CALL)
 163                 return 0;
 164         arg = get_argument_from_call_expr(call->args, param);
 165         if (get_value(arg, &sval) && (sval.uvalue & __GFP_NOFAIL))
 166                 return 1;
 167         return 0;
 168 }
 169
 170 static void match_assign_returns_null(const char *fn, struct expression *expr, void *_gfp)
 171 {
 172         struct smatch_state *state;
 173         int gfp_param = PTR_INT(_gfp);
 174
 175         if (called_with_no_fail(expr->right, gfp_param))
 176                 return;
 177         state = alloc_my_state(fn);
 178         set_state_expr(my_id, expr->left, state);
 179 }
 180
 181 static void register_allocation_funcs(void)
 182 {
 183         struct token *token;
 184         const char *func;
 185         int arg;
 186
 187         token = get_tokens_file("kernel.allocation_funcs_gfp");
 188         if (!token)
 189                 return;
 190         if (token_type(token) != TOKEN_STREAMBEGIN)
 191                 return;
 192         token = token->next;
 193         while (token_type(token) != TOKEN_STREAMEND) {
 194                 if (token_type(token) != TOKEN_IDENT)
 195                         return;
 196                 func = show_ident(token->ident);
 197                 token = token->next;
 198                 if (token_type(token) == TOKEN_IDENT)
 199                         arg = -1;
 200                 else if (token_type(token) == TOKEN_NUMBER)
 201                         arg = atoi(token->number);
 202                 else
 203                         return;
 204                 add_function_assign_hook(func, &match_assign_returns_null, INT_PTR(arg));
 205                 token = token->next;
 206         }
 207         clear_token_alloc();
 208 }
 209
 210 void check_deref(int id)
 211 {
 212         my_id = id;
 213
 214         add_unmatched_state_hook(my_id, &unmatched_state);
 215         add_modification_hook(my_id, &is_ok);
 216         add_hook(&match_dereferences, DEREF_HOOK);
 217         add_hook(&match_pointer_as_array, OP_HOOK);
 218         select_call_implies_hook(DEREFERENCE, &set_param_dereferenced);
 219         add_hook(&match_condition, CONDITION_HOOK);
 220         add_hook(&match_declarations, DECLARATION_HOOK);
 221         add_hook(&match_assign, ASSIGNMENT_HOOK);
 222         if (option_project == PROJ_KERNEL)
 223                 register_allocation_funcs();
 224 }