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 STATE(null);
  31 STATE(ok);
  32 STATE(uninitialized);
  33
  34 static struct smatch_state *alloc_my_state(const char *name)
  35 {
  36         struct smatch_state *state;
  37
  38         state = malloc(sizeof(*state));
  39         state->name = name;
  40         return state;
  41 }
  42
  43 static struct smatch_state *unmatched_state(struct sm_state *sm)
  44 {
  45         return &ok;
  46 }
  47
  48 static void is_ok(const char *name, struct symbol *sym, struct expression *expr, void *unused)
  49 {
  50         set_state(my_id, name, sym, &ok);
  51 }
  52
  53 static void match_dereferences(struct expression *expr)
  54 {
  55         struct sm_state *sm;
  56         struct sm_state *tmp;
  57
  58         if (expr->type != EXPR_PREOP)
  59                 return;
  60         expr = strip_expr(expr->unop);
  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_declarations(struct symbol *sym)
  88 {
  89         const char *name;
  90
  91         if ((get_base_type(sym))->type == SYM_ARRAY)
  92                 return;
  93
  94         name = sym->ident->name;
  95         if (!sym->initializer) {
  96                 set_state(my_id, name, sym, &uninitialized);
  97                 scoped_state(my_id, name, sym);
  98         }
  99 }
 100
 101 static void match_assign(struct expression *expr)
 102 {
 103         if (is_zero(expr->right)) {
 104                 set_state_expr(my_id, expr->left, &null);
 105                 return;
 106         }
 107 }
 108
 109 static void match_condition(struct expression *expr)
 110 {
 111         if (expr->type == EXPR_ASSIGNMENT) {
 112                 match_condition(expr->right);
 113                 match_condition(expr->left);
 114         }
 115         if (!get_state_expr(my_id, expr))
 116                 return;
 117         set_true_false_states_expr(my_id, expr, &ok, NULL);
 118 }
 119
 120 static void match_assign_returns_null(const char *fn, struct expression *expr, void *unused)
 121 {
 122         struct smatch_state *state;
 123
 124         state = alloc_my_state(fn);
 125         set_state_expr(my_id, expr->left, state);
 126 }
 127
 128 static void register_allocation_funcs(void)
 129 {
 130         struct token *token;
 131         const char *func;
 132
 133         token = get_tokens_file("kernel.allocation_funcs");
 134         if (!token)
 135                 return;
 136         if (token_type(token) != TOKEN_STREAMBEGIN)
 137                 return;
 138         token = token->next;
 139         while (token_type(token) != TOKEN_STREAMEND) {
 140                 if (token_type(token) != TOKEN_IDENT)
 141                         return;
 142                 func = show_ident(token->ident);
 143                 add_function_assign_hook(func, &match_assign_returns_null, NULL);
 144                 token = token->next;
 145         }
 146         clear_token_alloc();
 147 }
 148
 149 void check_deref(int id)
 150 {
 151         my_id = id;
 152
 153         add_unmatched_state_hook(my_id, &unmatched_state);
 154         set_default_modification_hook(my_id, &is_ok);
 155
 156         add_hook(&match_dereferences, DEREF_HOOK);
 157         add_hook(&match_condition, CONDITION_HOOK);
 158         add_hook(&match_declarations, DECLARATION_HOOK);
 159         add_hook(&match_assign, ASSIGNMENT_HOOK);
 160         if (option_project == PROJ_KERNEL)
 161                 register_allocation_funcs();
 162 }