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cppcheck/lib/checknullpointer.cpp

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/*
* Cppcheck - A tool for static C/C++ code analysis
* Copyright (C) 2007-2015 Daniel Marjamäki and Cppcheck team.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
//---------------------------------------------------------------------------
#include "checknullpointer.h"
#include "mathlib.h"
#include "symboldatabase.h"
#include <cctype>
//---------------------------------------------------------------------------
// Register this check class (by creating a static instance of it)
namespace {
CheckNullPointer instance;
}
//---------------------------------------------------------------------------
static bool checkNullpointerFunctionCallPlausibility(const Function* func, unsigned int arg)
{
return !func || (func->argCount() >= arg && func->getArgumentVar(arg - 1) && func->getArgumentVar(arg - 1)->isPointer());
}
/**
* @brief parse a function call and extract information about variable usage
* @param tok first token
* @param var variables that the function read / write.
* @param library --library files data
* @param value 0 => invalid with null pointers as parameter.
* 1-.. => only invalid with uninitialized data.
*/
void CheckNullPointer::parseFunctionCall(const Token &tok, std::list<const Token *> &var, const Library *library, unsigned char value)
{
if (Token::Match(&tok, "%var% ( )") || !tok.tokAt(2))
return;
const Token* firstParam = tok.tokAt(2);
const Token* secondParam = firstParam->nextArgument();
// 1st parameter..
if ((Token::Match(firstParam, "%var% ,|)") && firstParam->varId() > 0) ||
(value == 0 && Token::Match(firstParam, "0|NULL ,|)"))) {
if (value == 0 && Token::Match(&tok, "snprintf|vsnprintf|fnprintf|vfnprintf") && secondParam && secondParam->str() != "0") // Only if length (second parameter) is not zero
var.push_back(firstParam);
else if (value == 0 && library != nullptr && library->isnullargbad(&tok, 1) && checkNullpointerFunctionCallPlausibility(tok.function(), 1))
var.push_back(firstParam);
else if (value == 1 && library != nullptr && library->isuninitargbad(&tok, 1))
var.push_back(firstParam);
}
// 2nd parameter..
if ((value == 0 && Token::Match(secondParam, "0|NULL ,|)")) || (secondParam && secondParam->varId() > 0 && Token::Match(secondParam->next(),"[,)]"))) {
if (value == 0 && library != nullptr && library->isnullargbad(&tok, 2) && checkNullpointerFunctionCallPlausibility(tok.function(), 2))
var.push_back(secondParam);
else if (value == 1 && library != nullptr && library->isuninitargbad(&tok, 2))
var.push_back(secondParam);
}
if (Token::Match(&tok, "printf|sprintf|snprintf|fprintf|fnprintf|scanf|sscanf|fscanf|wprintf|swprintf|fwprintf|wscanf|swscanf|fwscanf")) {
const Token* argListTok = 0; // Points to first va_list argument
std::string formatString;
bool scan = Token::Match(&tok, "scanf|sscanf|fscanf|wscanf|swscanf|fwscanf");
if (Token::Match(&tok, "printf|scanf|wprintf|wscanf ( %str%")) {
formatString = firstParam->strValue();
argListTok = secondParam;
} else if (Token::Match(&tok, "sprintf|fprintf|sscanf|fscanf|fwprintf|fwscanf|swscanf")) {
const Token* formatStringTok = secondParam; // Find second parameter (format string)
if (formatStringTok && formatStringTok->type() == Token::eString) {
argListTok = formatStringTok->nextArgument(); // Find third parameter (first argument of va_args)
formatString = formatStringTok->strValue();
}
} else if (Token::Match(&tok, "snprintf|fnprintf|swprintf") && secondParam) {
const Token* formatStringTok = secondParam->nextArgument(); // Find third parameter (format string)
if (formatStringTok && formatStringTok->type() == Token::eString) {
argListTok = formatStringTok->nextArgument(); // Find fourth parameter (first argument of va_args)
formatString = formatStringTok->strValue();
}
}
if (argListTok) {
bool percent = false;
for (std::string::iterator i = formatString.begin(); i != formatString.end(); ++i) {
if (*i == '%') {
percent = !percent;
} else if (percent) {
percent = false;
bool _continue = false;
while (!std::isalpha((unsigned char)*i)) {
if (*i == '*') {
if (scan)
_continue = true;
else
argListTok = argListTok->nextArgument();
}
++i;
if (!argListTok || i == formatString.end())
return;
}
if (_continue)
continue;
if ((*i == 'n' || *i == 's' || scan) && (!scan || value == 0)) {
if ((value == 0 && argListTok->str() == "0") || (argListTok->varId() > 0 && Token::Match(argListTok,"%var% [,)]"))) {
var.push_back(argListTok);
}
}
if (*i != 'm') // %m is a non-standard glibc extension that requires no parameter
argListTok = argListTok->nextArgument(); // Find next argument
if (!argListTok)
break;
}
}
}
}
}
/**
* Is there a pointer dereference? Everything that should result in
* a nullpointer dereference error message will result in a true
* return value. If it's unknown if the pointer is dereferenced false
* is returned.
* @param tok token for the pointer
* @param unknown it is not known if there is a pointer dereference (could be reported as a debug message)
* @return true => there is a dereference
*/
bool CheckNullPointer::isPointerDeRef(const Token *tok, bool &unknown)
{
// THIS ARRAY MUST BE ORDERED ALPHABETICALLY
static const char* const stl_stream [] = {
"fstream", "ifstream", "iostream", "istream",
"istringstream", "ofstream", "ostream", "ostringstream",
"stringstream", "wistringstream", "wostringstream", "wstringstream"
};
unknown = false;
const Token* parent = tok->astParent();
if (!parent)
return false;
bool firstOperand = parent->astOperand1() == tok;
while (parent->str() == "(" && (parent->astOperand2() == nullptr && parent->strAt(1) != ")")) { // Skip over casts
parent = parent->astParent();
if (!parent)
return false;
}
// Dereferencing pointer..
if (parent->str() == "*" && !parent->astOperand2() && !Token::Match(parent->tokAt(-2), "sizeof|decltype|typeof"))
return true;
// array access
if (parent->str() == "[" && (!parent->astParent() || parent->astParent()->str() != "&"))
return true;
// address of member variable / array element
const Token *parent2 = parent;
while (Token::Match(parent2, "[|."))
parent2 = parent2->astParent();
if (parent2 != parent && parent2 && parent2->str() == "&" && !parent2->astOperand2())
return false;
// read/write member variable
if (firstOperand && parent->str() == "." && (!parent->astParent() || parent->astParent()->str() != "&")) {
if (!parent->astParent() || parent->astParent()->str() != "(" || parent->astParent() == tok->previous())
return true;
unknown = true;
return false;
}
if (Token::Match(tok, "%var% ("))
return true;
if (Token::Match(tok, "%var% = %var% .") &&
tok->varId() > 0 &&
tok->varId() == tok->tokAt(2)->varId())
return true;
// std::string dereferences nullpointers
if (Token::Match(parent->tokAt(-3), "std :: string|wstring (") && tok->strAt(1) == ")")
return true;
if (Token::Match(parent->previous(), "%var% (") && tok->strAt(1) == ")") {
const Variable* var = tok->tokAt(-2)->variable();
if (var && !var->isPointer() && !var->isArray() && var->isStlStringType())
return true;
}
// streams dereference nullpointers
if (Token::Match(parent, "<<|>>") && !firstOperand) {
const Variable* var = tok->variable();
if (var && var->isPointer() && Token::Match(var->typeStartToken(), "char|wchar_t")) { // Only outputting or reading to char* can cause problems
const Token* tok2 = parent; // Find start of statement
for (; tok2; tok2 = tok2->previous()) {
if (Token::Match(tok2->previous(), ";|{|}|:"))
break;
}
if (Token::Match(tok2, "std :: cout|cin|cerr"))
return true;
if (tok2 && tok2->varId() != 0) {
const Variable* var2 = tok2->variable();
if (var2 && var2->isStlType(stl_stream))
return true;
}
}
}
const Variable *ovar = nullptr;
if (Token::Match(parent, "+|==|!=") || (parent->str() == "=" && !firstOperand)) {
if (parent->astOperand1() == tok && parent->astOperand2())
ovar = parent->astOperand2()->variable();
else if (parent->astOperand1() && parent->astOperand2() == tok)
ovar = parent->astOperand1()->variable();
}
if (ovar && !ovar->isPointer() && !ovar->isArray() && ovar->isStlStringType())
return true;
// assume that it's not a dereference (no false positives)
return false;
}
void CheckNullPointer::nullPointerLinkedList()
{
const SymbolDatabase* const symbolDatabase = _tokenizer->getSymbolDatabase();
// looping through items in a linked list in a inner loop.
// Here is an example:
// for (const Token *tok = tokens; tok; tok = tok->next) {
// if (tok->str() == "hello")
// tok = tok->next; // <- tok might become a null pointer!
// }
for (std::list<Scope>::const_iterator i = symbolDatabase->scopeList.begin(); i != symbolDatabase->scopeList.end(); ++i) {
const Token* const tok1 = i->classDef;
// search for a "for" scope..
if (i->type != Scope::eFor || !tok1)
continue;
// is there any dereferencing occurring in the for statement
const Token* end2 = tok1->linkAt(1);
for (const Token *tok2 = tok1->tokAt(2); tok2 != end2; tok2 = tok2->next()) {
// Dereferencing a variable inside the "for" parentheses..
if (Token::Match(tok2, "%var% . %var%")) {
// Is this variable a pointer?
const Variable *var = tok2->variable();
if (!var || !var->isPointer())
continue;
// Variable id for dereferenced variable
const unsigned int varid(tok2->varId());
// We don't support variables without a varid
if (varid == 0)
continue;
if (Token::Match(tok2->tokAt(-2), "%varid% ?", varid))
continue;
// Check usage of dereferenced variable in the loop..
for (std::list<Scope*>::const_iterator j = i->nestedList.begin(); j != i->nestedList.end(); ++j) {
Scope* scope = *j;
if (scope->type != Scope::eWhile)
continue;
// TODO: are there false negatives for "while ( %varid% ||"
if (Token::Match(scope->classDef->next(), "( %varid% &&|)", varid)) {
// Make sure there is a "break" or "return" inside the loop.
// Without the "break" a null pointer could be dereferenced in the
// for statement.
for (const Token *tok4 = scope->classStart; tok4; tok4 = tok4->next()) {
if (tok4 == i->classEnd) {
nullPointerError(tok1, var->name(), scope->classDef);
break;
}
// There is a "break" or "return" inside the loop.
// TODO: there can be false negatives. There could still be
// execution paths that are not properly terminated
else if (tok4->str() == "break" || tok4->str() == "return")
break;
}
}
}
}
}
}
}
void CheckNullPointer::nullPointerByDeRefAndChec()
{
for (const Token *tok = _tokenizer->tokens(); tok; tok = tok->next()) {
const Variable *var = tok->variable();
if (!var || !var->isPointer() || tok == var->nameToken())
continue;
// Can pointer be NULL?
const ValueFlow::Value *value = tok->getValue(0);
if (!value)
continue;
if (!_settings->inconclusive && value->inconclusive)
continue;
// Is pointer used as function parameter?
if (Token::Match(tok->previous(), "[(,] %var% [,)]")) {
const Token *ftok = tok->previous();
while (ftok && ftok->str() != "(") {
if (ftok->str() == ")")
ftok = ftok->link();
ftok = ftok->previous();
}
if (!ftok || !ftok->previous())
continue;
std::list<const Token *> varlist;
parseFunctionCall(*ftok->previous(), varlist, &_settings->library, 0);
if (std::find(varlist.begin(), varlist.end(), tok) != varlist.end()) {
if (value->condition == nullptr)
nullPointerError(tok, tok->str());
else if (_settings->isEnabled("warning"))
nullPointerError(tok, tok->str(), value->condition, value->inconclusive);
}
continue;
}
// Pointer dereference.
bool unknown = false;
if (!isPointerDeRef(tok,unknown)) {
if (_settings->inconclusive && unknown) {
if (value->condition == nullptr)
nullPointerError(tok, tok->str(), true);
else
nullPointerError(tok, tok->str(), value->condition, true);
}
continue;
}
if (value->condition == nullptr)
nullPointerError(tok, tok->str(), value->inconclusive);
else if (_settings->isEnabled("warning"))
nullPointerError(tok, tok->str(), value->condition, value->inconclusive);
}
}
void CheckNullPointer::nullPointer()
{
nullPointerLinkedList();
nullPointerByDeRefAndChec();
nullPointerDefaultArgument();
}
/** Dereferencing null constant (simplified token list) */
void CheckNullPointer::nullConstantDereference()
{
const SymbolDatabase *symbolDatabase = _tokenizer->getSymbolDatabase();
// THIS ARRAY MUST BE ORDERED ALPHABETICALLY
static const char* const stl_stream[] = {
"fstream", "ifstream", "iostream", "istream",
"istringstream", "stringstream", "wistringstream", "wstringstream"
};
const std::size_t functions = symbolDatabase->functionScopes.size();
for (std::size_t i = 0; i < functions; ++i) {
const Scope * scope = symbolDatabase->functionScopes[i];
if (scope->function == 0 || !scope->function->hasBody()) // We only look for functions with a body
continue;
const Token *tok = scope->classStart;
if (scope->function && scope->function->isConstructor())
tok = scope->function->token; // Check initialization list
for (; tok != scope->classEnd; tok = tok->next()) {
if (Token::Match(tok, "sizeof|decltype|typeid|typeof ("))
tok = tok->next()->link();
else if (Token::simpleMatch(tok, "* 0")) {
if (Token::Match(tok->previous(), "return|throw|;|{|}|:|[|(|,") || tok->previous()->isOp()) {
nullPointerError(tok);
}
}
else if (Token::Match(tok, "0 [") && (tok->previous()->str() != "&" || !Token::Match(tok->next()->link()->next(), "[.(]")))
nullPointerError(tok);
else if (Token::Match(tok->previous(), "!!. %var% (") && (tok->previous()->str() != "::" || tok->strAt(-2) == "std")) {
if (Token::simpleMatch(tok->tokAt(2), "0 )") && tok->varId()) { // constructor call
const Variable *var = tok->variable();
if (var && !var->isPointer() && !var->isArray() && var->isStlStringType())
nullPointerError(tok);
} else { // function call
std::list<const Token *> var;
parseFunctionCall(*tok, var, &_settings->library, 0);
// is one of the var items a NULL pointer?
for (std::list<const Token *>::const_iterator it = var.begin(); it != var.end(); ++it) {
if (Token::Match(*it, "0|NULL [,)]")) {
nullPointerError(*it);
}
}
}
} else if (Token::Match(tok, "std :: string|wstring ( 0 )"))
nullPointerError(tok);
else if (Token::simpleMatch(tok->previous(), ">> 0")) { // Only checking input stream operations is safe here, because otherwise 0 can be an integer as well
const Token* tok2 = tok->previous(); // Find start of statement
for (; tok2; tok2 = tok2->previous()) {
if (Token::Match(tok2->previous(), ";|{|}|:|("))
break;
}
if (tok2 && tok2->previous() && tok2->previous()->str()=="(")
continue;
if (Token::simpleMatch(tok2, "std :: cin"))
nullPointerError(tok);
if (tok2 && tok2->varId() != 0) {
const Variable *var = tok2->variable();
if (var && var->isStlType(stl_stream))
nullPointerError(tok);
}
}
const Variable *ovar = nullptr;
if (Token::Match(tok, "0 ==|!=|>|>=|<|<= %var% !!."))
ovar = tok->tokAt(2)->variable();
else if (Token::Match(tok, "%var% ==|!=|>|>=|<|<= 0"))
ovar = tok->variable();
else if (Token::Match(tok, "%var% =|+ 0 )|]|,|;|+"))
ovar = tok->variable();
if (ovar && !ovar->isPointer() && !ovar->isArray() && ovar->isStlStringType() && tok->tokAt(2)->originalName() != "'\\0'")
nullPointerError(tok);
}
}
}
/**
* @brief If tok is a function call that passes in a pointer such that
* the pointer may be modified, this function will remove that
* pointer from pointerArgs.
*/
void CheckNullPointer::removeAssignedVarFromSet(const Token* tok, std::set<unsigned int>& pointerArgs)
{
// If a pointer's address is passed into a function, stop considering it
if (Token::Match(tok->previous(), "[;{}] %var% (")) {
// Common functions that are known NOT to modify their pointer argument
const char safeFunctions[] = "printf|sprintf|fprintf|vprintf";
const Token* endParen = tok->next()->link();
for (const Token* tok2 = tok->next(); tok2 != endParen; tok2 = tok2->next()) {
if (tok2->isName() && tok2->varId() > 0 && !Token::Match(tok, safeFunctions)) {
pointerArgs.erase(tok2->varId());
}
}
}
}
/**
* @brief Does one part of the check for nullPointer().
* -# default argument that sets a pointer to 0
* -# dereference pointer
*/
void CheckNullPointer::nullPointerDefaultArgument()
{
if (!_settings->isEnabled("warning"))
return;
const SymbolDatabase *symbolDatabase = _tokenizer->getSymbolDatabase();
const std::size_t functions = symbolDatabase->functionScopes.size();
for (std::size_t i = 0; i < functions; ++i) {
const Scope * scope = symbolDatabase->functionScopes[i];
if (scope->function == 0 || !scope->function->hasBody()) // We only look for functions with a body
continue;
// Scan the argument list for default arguments that are pointers and
// which default to a NULL pointer if no argument is specified.
std::set<unsigned int> pointerArgs;
for (const Token *tok = scope->function->arg; tok != scope->function->arg->link(); tok = tok->next()) {
if (Token::Match(tok, "%var% = 0 ,|)") && tok->varId() != 0) {
const Variable *var = tok->variable();
if (var && var->isPointer())
pointerArgs.insert(tok->varId());
}
}
// Report an error if any of the default-NULL arguments are dereferenced
if (!pointerArgs.empty()) {
for (const Token *tok = scope->classStart; tok != scope->classEnd; tok = tok->next()) {
// If we encounter a possible NULL-pointer check, skip over its body
if (tok->str() == "?") { // TODO: Skip this if the condition is unrelated to the variables
// Find end of statement
tok = tok->astOperand2();
while (tok && !Token::Match(tok, ")|;")) {
if (tok->link() && Token::Match(tok, "(|[|<|{"))
tok = tok->link();
tok = tok->next();
}
if (!tok)
break;
} else if (Token::simpleMatch(tok, "if (")) {
bool dependsOnPointer = false;
const Token *endOfCondition = tok->next()->link();
if (!endOfCondition)
continue;
const Token *startOfIfBlock =
Token::simpleMatch(endOfCondition, ") {") ? endOfCondition->next() : nullptr;
if (!startOfIfBlock)
continue;
// If this if() statement may return, it may be a null
// pointer check for the pointers referenced in its condition
const Token *endOfIf = startOfIfBlock->link();
bool isExitOrReturn =
Token::findmatch(startOfIfBlock, "exit|return|throw", endOfIf) != nullptr;
if (Token::Match(tok, "if ( %var% == 0 )")) {
const unsigned int var = tok->tokAt(2)->varId();
if (var > 0 && pointerArgs.count(var) > 0) {
if (isExitOrReturn)
pointerArgs.erase(var);
else
dependsOnPointer = true;
}
} else {
for (const Token *tok2 = tok->next(); tok2 != endOfCondition; tok2 = tok2->next()) {
if (tok2->isName() && tok2->varId() > 0 &&
pointerArgs.count(tok2->varId()) > 0) {
// If the if() depends on a pointer and may return, stop
// considering that pointer because it may be a NULL-pointer
// check that returns if the pointer is NULL.
if (isExitOrReturn)
pointerArgs.erase(tok2->varId());
else
dependsOnPointer = true;
}
}
}
if (dependsOnPointer && endOfIf) {
for (; tok != endOfIf; tok = tok->next()) {
// If a pointer is assigned a new value, stop considering it.
if (Token::Match(tok, "%var% ="))
pointerArgs.erase(tok->varId());
else
removeAssignedVarFromSet(tok, pointerArgs);
}
continue;
}
}
// If there is a noreturn function (e.g. exit()), stop considering the rest of
// this function.
bool unknown = false;
if (Token::Match(tok, "return|throw|exit") ||
(_tokenizer->IsScopeNoReturn(tok, &unknown) && !unknown))
break;
removeAssignedVarFromSet(tok, pointerArgs);
if (tok->varId() == 0 || pointerArgs.count(tok->varId()) == 0)
continue;
// If a pointer is assigned a new value, stop considering it.
if (Token::Match(tok, "%var% ="))
pointerArgs.erase(tok->varId());
// If a pointer dereference is preceded by an && or ||,
// they serve as a sequence point so the dereference
// may not be executed.
if (isPointerDeRef(tok, unknown) && !unknown &&
tok->strAt(-1) != "&&" && tok->strAt(-1) != "||" &&
tok->strAt(-2) != "&&" && tok->strAt(-2) != "||")
nullPointerDefaultArgError(tok, tok->str());
}
}
}
}
void CheckNullPointer::nullPointerError(const Token *tok)
{
reportError(tok, Severity::error, "nullPointer", "Null pointer dereference");
}
void CheckNullPointer::nullPointerError(const Token *tok, const std::string &varname, bool inconclusive)
{
reportError(tok, Severity::error, "nullPointer", "Possible null pointer dereference: " + varname, inconclusive);
}
void CheckNullPointer::nullPointerError(const Token *tok, const std::string &varname, const Token* nullCheck, bool inconclusive)
{
std::list<const Token*> callstack;
callstack.push_back(tok);
callstack.push_back(nullCheck);
const std::string errmsg("Possible null pointer dereference: " + varname + " - otherwise it is redundant to check it against null.");
reportError(callstack, Severity::warning, "nullPointer", errmsg, inconclusive);
}
void CheckNullPointer::nullPointerDefaultArgError(const Token *tok, const std::string &varname)
{
reportError(tok, Severity::warning, "nullPointer", "Possible null pointer dereference if the default parameter value is used: " + varname);
}
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