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)
  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                         sm_msg("error: potential NULL dereference '%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 set_param_dereferenced(struct expression *arg, char *unused)
 105 {
 106         check_dereference(arg);
 107 }
 108
 109 static void match_declarations(struct symbol *sym)
 110 {
 111         const char *name;
 112
 113         if ((get_base_type(sym))->type == SYM_ARRAY)
 114                 return;
 115
 116         name = sym->ident->name;
 117         if (!sym->initializer) {
 118                 set_state(my_id, name, sym, &uninitialized);
 119                 scoped_state(my_id, name, sym);
 120         }
 121 }
 122
 123 static void match_assign(struct expression *expr)
 124 {
 125         if (is_zero(expr->right)) {
 126                 set_state_expr(my_id, expr->left, &null);
 127                 return;
 128         }
 129 }
 130
 131 static void match_condition(struct expression *expr)
 132 {
 133         if (expr->type == EXPR_ASSIGNMENT) {
 134                 match_condition(expr->right);
 135                 match_condition(expr->left);
 136         }
 137         if (!get_state_expr(my_id, expr))
 138                 return;
 139         set_true_false_states_expr(my_id, expr, &ok, NULL);
 140 }
 141
 142 static int called_with_no_fail(struct expression *call, int param)
 143 {
 144         struct expression *arg;
 145         sval_t sval;
 146
 147         if (param == -1)
 148                 return 0;
 149         call = strip_expr(call);
 150         if (call->type != EXPR_CALL)
 151                 return 0;
 152         arg = get_argument_from_call_expr(call->args, param);
 153         if (get_value(arg, &sval) && (sval.uvalue & __GFP_NOFAIL))
 154                 return 1;
 155         return 0;
 156 }
 157
 158 static void match_assign_returns_null(const char *fn, struct expression *expr, void *_gfp)
 159 {
 160         struct smatch_state *state;
 161         int gfp_param = PTR_INT(_gfp);
 162
 163         if (called_with_no_fail(expr->right, gfp_param))
 164                 return;
 165         state = alloc_my_state(fn);
 166         set_state_expr(my_id, expr->left, state);
 167 }
 168
 169 static void register_allocation_funcs(void)
 170 {
 171         struct token *token;
 172         const char *func;
 173         int arg;
 174
 175         token = get_tokens_file("kernel.allocation_funcs_gfp");
 176         if (!token)
 177                 return;
 178         if (token_type(token) != TOKEN_STREAMBEGIN)
 179                 return;
 180         token = token->next;
 181         while (token_type(token) != TOKEN_STREAMEND) {
 182                 if (token_type(token) != TOKEN_IDENT)
 183                         return;
 184                 func = show_ident(token->ident);
 185                 token = token->next;
 186                 if (token_type(token) == TOKEN_IDENT)
 187                         arg = -1;
 188                 else if (token_type(token) == TOKEN_NUMBER)
 189                         arg = atoi(token->number);
 190                 else
 191                         return;
 192                 add_function_assign_hook(func, &match_assign_returns_null, INT_PTR(arg));
 193                 token = token->next;
 194         }
 195         clear_token_alloc();
 196 }
 197
 198 void check_deref(int id)
 199 {
 200         my_id = id;
 201
 202         add_unmatched_state_hook(my_id, &unmatched_state);
 203         add_modification_hook(my_id, &is_ok);
 204         add_hook(&match_dereferences, DEREF_HOOK);
 205         add_hook(&match_pointer_as_array, OP_HOOK);
 206         add_db_fn_call_callback(DEREFERENCE, &set_param_dereferenced);
 207         add_hook(&match_condition, CONDITION_HOOK);
 208         add_hook(&match_declarations, DECLARATION_HOOK);
 209         add_hook(&match_assign, ASSIGNMENT_HOOK);
 210         if (option_project == PROJ_KERNEL)
 211                 register_allocation_funcs();
 212 }