check_redundant_null_check.c

   1 /*
   2  * Copyright (C) 2009 Dan Carpenter.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
  16  */
  17
  18 /*
  19  * Some functions are designed to handle NULL values but people always
  20  * do stuff like:  if (foo) kfree(foo);
  21  * The if check is unneeded and a waste of precious CPU cycles.  Also a
  22  * little bit messy.
  23  *
  24  * List of wine functions taken from Michael Stefaniuc's
  25  * redundant_null_check.pl
  26  *
  27  * This test is not the prettiest.  Smatch has a feature where it
  28  * simplifies comparisons to zero and I wanted to take advantage of
  29  * that, but that also makes things a bit complicated.
  30  *
  31  * We work backwards.  When we hit a kfree() we ask was the last statement
  32  * an if statement, and was the last comparison checking the pointer we
  33  * are about to free?  If all three answers are yes, then print a message.
  34  *
  35  */
  36
  37 #include "smatch.h"
  38
  39 static int my_id;
  40
  41 static struct statement *this_statement = NULL;
  42 static struct statement *previous_statement = NULL;
  43 static struct expression *previous_condition = NULL;
  44
  45 static const char *wine_funcs[] = {
  46         "HeapFree",
  47         "RtlFreeHeap",
  48         "SysFreeString",
  49         "CryptMemFree",
  50         "DllFreeSplMem",
  51         "FreeEnvironmentStringsA",
  52         "Free",
  53         "GdipFree",
  54         "I_RpcFree",
  55         "ldap_memfreeA",
  56         "ldap_memfreeW",
  57         "LsaFreeMemory",
  58         "MyFree",
  59         "SetupTermDefaultQueueCallback",
  60 };
  61
  62 static void dont_check(const char *fn, struct expression *expr, void *unused)
  63 {
  64         struct expression *arg;
  65         char *name = NULL;
  66         char *condition_name = NULL;
  67
  68         if (!previous_statement || !previous_condition || previous_statement->type != STMT_IF)
  69                 return;
  70         if (previous_statement->if_false)
  71                 return;
  72         if (previous_statement->if_true->type != STMT_EXPRESSION)
  73                 return;
  74
  75         arg = get_argument_from_call_expr(expr->args, 0);
  76         name = expr_to_var(arg);
  77         if (!name)
  78                 goto free;
  79         condition_name = expr_to_var(previous_condition);
  80         if (!condition_name)
  81                 goto free;
  82         if (!strcmp(name, condition_name))
  83                 sm_msg("info: redundant null check on %s calling %s()", name, fn);
  84
  85 free:
  86         free_string(name);
  87         free_string(condition_name);
  88 }
  89
  90 static void match_statement(struct statement *stmt)
  91 {
  92         if (stmt->type == STMT_COMPOUND)
  93                 return;
  94         previous_statement = this_statement;
  95         this_statement = stmt;
  96 }
  97
  98 static void match_condition(struct expression *expr)
  99 {
 100         previous_condition = expr;
 101 }
 102
 103 void check_redundant_null_check(int id)
 104 {
 105         my_id = id;
 106         int i;
 107
 108         add_hook(&match_statement, STMT_HOOK);
 109         add_hook(&match_condition, CONDITION_HOOK);
 110         add_function_hook("free", &dont_check, NULL);
 111         if (option_project == PROJ_KERNEL) {
 112                 add_function_hook("kfree", &dont_check, NULL);
 113         } else if (option_project == PROJ_WINE) {
 114                 for (i = 0; i < ARRAY_SIZE(wine_funcs); i++) {
 115                         add_function_hook(wine_funcs[i], &dont_check, NULL);
 116                 }
 117         }
 118 }