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 = malloc(sizeof(*state));
  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(const char *name, struct symbol *sym, struct expression *expr, void *unused)
  52 {
  53         set_state(my_id, name, 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                         sm_msg("error: potential null derefence '%s'.", tmp->name);
  78                         return;
  79                 }
  80                 if (tmp->state == &uninitialized) {
  81                         sm_msg("error: potentially derefencing uninitialized '%s'.", tmp->name);
  82                         return;
  83                 }
  84                 sm_msg("error: potential null dereference '%s'.  (%s returns null)",
  85                         tmp->name, tmp->state->name);
  86                 return;
  87         } END_FOR_EACH_PTR(tmp);
  88 }
  89
  90 static void match_dereferences(struct expression *expr)
  91 {
  92         if (expr->type != EXPR_PREOP)
  93                 return;
  94         check_dereference(expr->unop);
  95 }
  96
  97 static void match_pointer_as_array(struct expression *expr)
  98 {
  99         if (!is_array(expr))
 100                 return;
 101         check_dereference(expr->unop->left);
 102 }
 103
 104 static void match_declarations(struct symbol *sym)
 105 {
 106         const char *name;
 107
 108         if ((get_base_type(sym))->type == SYM_ARRAY)
 109                 return;
 110
 111         name = sym->ident->name;
 112         if (!sym->initializer) {
 113                 set_state(my_id, name, sym, &uninitialized);
 114                 scoped_state(my_id, name, sym);
 115         }
 116 }
 117
 118 static void match_assign(struct expression *expr)
 119 {
 120         if (is_zero(expr->right)) {
 121                 set_state_expr(my_id, expr->left, &null);
 122                 return;
 123         }
 124 }
 125
 126 static void match_condition(struct expression *expr)
 127 {
 128         if (expr->type == EXPR_ASSIGNMENT) {
 129                 match_condition(expr->right);
 130                 match_condition(expr->left);
 131         }
 132         if (!get_state_expr(my_id, expr))
 133                 return;
 134         set_true_false_states_expr(my_id, expr, &ok, NULL);
 135 }
 136
 137 static int called_with_no_fail(struct expression *call, int param)
 138 {
 139         struct expression *arg;
 140         long long val;
 141
 142         if (param == -1)
 143                 return 0;
 144         call = strip_expr(call);
 145         if (call->type != EXPR_CALL)
 146                 return 0;
 147         arg = get_argument_from_call_expr(call->args, param);
 148         if (get_value(arg, &val) && (val & __GFP_NOFAIL))
 149                 return 1;
 150         return 0;
 151 }
 152
 153 static void match_assign_returns_null(const char *fn, struct expression *expr, void *_gfp)
 154 {
 155         struct smatch_state *state;
 156         int gfp_param = PTR_INT(_gfp);
 157
 158         if (called_with_no_fail(expr->right, gfp_param))
 159                 return;
 160         state = alloc_my_state(fn);
 161         set_state_expr(my_id, expr->left, state);
 162 }
 163
 164 static void register_allocation_funcs(void)
 165 {
 166         struct token *token;
 167         const char *func;
 168         int arg;
 169
 170         token = get_tokens_file("kernel.allocation_funcs_gfp");
 171         if (!token)
 172                 return;
 173         if (token_type(token) != TOKEN_STREAMBEGIN)
 174                 return;
 175         token = token->next;
 176         while (token_type(token) != TOKEN_STREAMEND) {
 177                 if (token_type(token) != TOKEN_IDENT)
 178                         return;
 179                 func = show_ident(token->ident);
 180                 token = token->next;
 181                 if (token_type(token) == TOKEN_IDENT)
 182                         arg = -1;
 183                 else if (token_type(token) == TOKEN_NUMBER)
 184                         arg = atoi(token->number);
 185                 else
 186                         return;
 187                 add_function_assign_hook(func, &match_assign_returns_null, INT_PTR(arg));
 188                 token = token->next;
 189         }
 190         clear_token_alloc();
 191 }
 192
 193 void check_deref(int id)
 194 {
 195         my_id = id;
 196
 197         add_unmatched_state_hook(my_id, &unmatched_state);
 198         set_default_modification_hook(my_id, &is_ok);
 199         add_hook(&match_dereferences, DEREF_HOOK);
 200         add_hook(&match_pointer_as_array, OP_HOOK);
 201         add_hook(&match_condition, CONDITION_HOOK);
 202         add_hook(&match_declarations, DECLARATION_HOOK);
 203         add_hook(&match_assign, ASSIGNMENT_HOOK);
 204         if (option_project == PROJ_KERNEL)
 205                 register_allocation_funcs();
 206 }