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
  28 static int my_id;
  29
  30 #define __GFP_NOFAIL 0x800
  31
  32 STATE(null);
  33 STATE(ok);
  34 STATE(uninitialized);
  35
  36 static struct smatch_state *alloc_my_state(const char *name)
  37 {
  38         struct smatch_state *state;
  39
  40         state = malloc(sizeof(*state));
  41         state->name = name;
  42         return state;
  43 }
  44
  45 static struct smatch_state *unmatched_state(struct sm_state *sm)
  46 {
  47         return &ok;
  48 }
  49
  50 static void is_ok(const char *name, struct symbol *sym, struct expression *expr, void *unused)
  51 {
  52         set_state(my_id, name, sym, &ok);
  53 }
  54
  55 static void check_dereference(struct expression *expr)
  56 {
  57         struct sm_state *sm;
  58         struct sm_state *tmp;
  59
  60         expr = strip_expr(expr);
  61         sm = get_sm_state_expr(my_id, expr);
  62         if (!sm)
  63                 return;
  64         if (is_ignored(my_id, sm->name, sm->sym))
  65                 return;
  66
  67         FOR_EACH_PTR(sm->possible, tmp) {
  68                 if (tmp->state == &merged)
  69                         continue;
  70                 if (tmp->state == &ok)
  71                         continue;
  72                 add_ignore(my_id, sm->name, sm->sym);
  73                 if (tmp->state == &null) {
  74                         sm_msg("error: potential null derefence '%s'.", tmp->name);
  75                         return;
  76                 }
  77                 if (tmp->state == &uninitialized) {
  78                         sm_msg("error: potentially derefencing uninitialized '%s'.", tmp->name);
  79                         return;
  80                 }
  81                 sm_msg("error: potential null dereference '%s'.  (%s returns null)",
  82                         tmp->name, tmp->state->name);
  83                 return;
  84         } END_FOR_EACH_PTR(tmp);
  85 }
  86
  87 static void match_dereferences(struct expression *expr)
  88 {
  89         if (expr->type != EXPR_PREOP)
  90                 return;
  91         check_dereference(expr->unop);
  92 }
  93
  94 static void match_pointer_as_array(struct expression *expr)
  95 {
  96         if (!is_array(expr))
  97                 return;
  98         check_dereference(expr->unop->left);
  99 }
 100
 101 static void match_declarations(struct symbol *sym)
 102 {
 103         const char *name;
 104
 105         if ((get_base_type(sym))->type == SYM_ARRAY)
 106                 return;
 107
 108         name = sym->ident->name;
 109         if (!sym->initializer) {
 110                 set_state(my_id, name, sym, &uninitialized);
 111                 scoped_state(my_id, name, sym);
 112         }
 113 }
 114
 115 static void match_assign(struct expression *expr)
 116 {
 117         if (is_zero(expr->right)) {
 118                 set_state_expr(my_id, expr->left, &null);
 119                 return;
 120         }
 121 }
 122
 123 static void match_condition(struct expression *expr)
 124 {
 125         if (expr->type == EXPR_ASSIGNMENT) {
 126                 match_condition(expr->right);
 127                 match_condition(expr->left);
 128         }
 129         if (!get_state_expr(my_id, expr))
 130                 return;
 131         set_true_false_states_expr(my_id, expr, &ok, NULL);
 132 }
 133
 134 static int called_with_no_fail(struct expression *call, int param)
 135 {
 136         struct expression *arg;
 137         long long val;
 138
 139         if (param == -1)
 140                 return 0;
 141         call = strip_expr(call);
 142         if (call->type != EXPR_CALL)
 143                 return 0;
 144         arg = get_argument_from_call_expr(call->args, param);
 145         if (get_value(arg, &val) && (val & __GFP_NOFAIL))
 146                 return 1;
 147         return 0;
 148 }
 149
 150 static void match_assign_returns_null(const char *fn, struct expression *expr, void *_gfp)
 151 {
 152         struct smatch_state *state;
 153         int gfp_param = (int)_gfp;
 154
 155         if (called_with_no_fail(expr->right, gfp_param))
 156                 return;
 157         state = alloc_my_state(fn);
 158         set_state_expr(my_id, expr->left, state);
 159 }
 160
 161 static void register_allocation_funcs(void)
 162 {
 163         struct token *token;
 164         const char *func;
 165         int arg;
 166
 167         token = get_tokens_file("kernel.allocation_funcs_gfp");
 168         if (!token)
 169                 return;
 170         if (token_type(token) != TOKEN_STREAMBEGIN)
 171                 return;
 172         token = token->next;
 173         while (token_type(token) != TOKEN_STREAMEND) {
 174                 if (token_type(token) != TOKEN_IDENT)
 175                         return;
 176                 func = show_ident(token->ident);
 177                 token = token->next;
 178                 if (token_type(token) == TOKEN_IDENT)
 179                         arg = -1;
 180                 else if (token_type(token) == TOKEN_NUMBER)
 181                         arg = atoi(token->number);
 182                 else
 183                         return;
 184                 add_function_assign_hook(func, &match_assign_returns_null, INT_PTR(arg));
 185                 token = token->next;
 186         }
 187         clear_token_alloc();
 188 }
 189
 190 void check_deref(int id)
 191 {
 192         my_id = id;
 193
 194         add_unmatched_state_hook(my_id, &unmatched_state);
 195         set_default_modification_hook(my_id, &is_ok);
 196         add_hook(&match_dereferences, DEREF_HOOK);
 197         add_hook(&match_pointer_as_array, OP_HOOK);
 198         add_hook(&match_condition, CONDITION_HOOK);
 199         add_hook(&match_declarations, DECLARATION_HOOK);
 200         add_hook(&match_assign, ASSIGNMENT_HOOK);
 201         if (option_project == PROJ_KERNEL)
 202                 register_allocation_funcs();
 203 }