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cppcheck/lib/checknullpointer.cpp

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/*
* Cppcheck - A tool for static C/C++ code analysis
* Copyright (C) 2007-2019 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 "astutils.h"
#include "errorlogger.h"
#include "library.h"
#include "settings.h"
#include "symboldatabase.h"
#include "token.h"
#include "tokenize.h"
#include "utils.h"
#include <algorithm>
#include <cctype>
#include <cstddef>
#include <set>
//---------------------------------------------------------------------------
// Register this check class (by creating a static instance of it)
namespace {
CheckNullPointer instance;
}
static const CWE CWE476(476U); // NULL Pointer Dereference
static const CWE CWE682(682U); // Incorrect Calculation
//---------------------------------------------------------------------------
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
*/
void CheckNullPointer::parseFunctionCall(const Token &tok, std::list<const Token *> &var, const Library *library)
{
if (Token::Match(&tok, "%name% ( )") || !tok.tokAt(2))
return;
const std::vector<const Token *> args = getArguments(&tok);
if (library || tok.function() != nullptr) {
for (int argnr = 1; argnr <= args.size(); ++argnr) {
const Token *param = args[argnr - 1];
if (library && library->isnullargbad(&tok, argnr) && checkNullpointerFunctionCallPlausibility(tok.function(), argnr))
var.push_back(param);
else if (tok.function()) {
const Variable* argVar = tok.function()->getArgumentVar(argnr-1);
if (argVar && argVar->isStlStringType() && !argVar->isArrayOrPointer())
var.push_back(param);
}
}
}
if (library && library->formatstr_function(&tok)) {
const int formatStringArgNr = library->formatstr_argno(&tok);
if (formatStringArgNr < 0 || formatStringArgNr >= args.size())
return;
// 1st parameter..
if (Token::Match(&tok, "snprintf|vsnprintf|fnprintf|vfnprintf") && args.size() > 1 && !(args[1] && args[1]->hasKnownIntValue() && args[1]->getKnownIntValue() == 0)) // Only if length (second parameter) is not zero
var.push_back(args[0]);
if (args[formatStringArgNr]->tokType() != Token::eString)
return;
const std::string &formatString = args[formatStringArgNr]->strValue();
int argnr = formatStringArgNr + 1;
const bool scan = library->formatstr_scan(&tok);
bool percent = false;
for (std::string::const_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
argnr++;
}
++i;
if (i == formatString.end())
return;
}
if (_continue)
continue;
if (argnr < args.size() && (*i == 'n' || *i == 's' || scan))
var.push_back(args[argnr]);
if (*i != 'm') // %m is a non-standard glibc extension that requires no parameter
argnr++;
}
}
}
}
namespace {
const std::set<std::string> stl_stream = {
"fstream", "ifstream", "iostream", "istream",
"istringstream", "ofstream", "ostream", "ostringstream",
"stringstream", "wistringstream", "wostringstream", "wstringstream"
};
}
/**
* 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) const
{
return isPointerDeRef(tok, unknown, mSettings);
}
bool CheckNullPointer::isPointerDeRef(const Token *tok, bool &unknown, const Settings *settings)
{
unknown = false;
// Is pointer used as function parameter?
if (Token::Match(tok->previous(), "[(,] %name% [,)]") && settings) {
const Token *ftok = tok->previous();
while (ftok && ftok->str() != "(") {
if (ftok->str() == ")")
ftok = ftok->link();
ftok = ftok->previous();
}
if (ftok && ftok->previous()) {
std::list<const Token *> varlist;
parseFunctionCall(*ftok->previous(), varlist, &settings->library);
if (std::find(varlist.begin(), varlist.end(), tok) != varlist.end()) {
return true;
}
}
}
const Token* parent = tok->astParent();
if (!parent)
return false;
if (parent->str() == "." && parent->astOperand2() == tok)
return isPointerDeRef(parent, unknown, settings);
const 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->isUnaryOp("*") && !Token::Match(parent->tokAt(-2), "sizeof|decltype|typeof"))
return true;
// array access
if (firstOperand && 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->isUnaryOp("&"))
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, "%name% ("))
return true;
if (Token::Match(tok, "%var% = %var% .") &&
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(), "%name% (") && 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()
{
if (!mSettings->isEnabled(Settings::WARNING))
return;
const SymbolDatabase* const symbolDatabase = mTokenizer->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 (const Scope &forScope : symbolDatabase->scopeList) {
const Token* const tok1 = forScope.classDef;
// search for a "for" scope..
if (forScope.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% . %name%")) {
// 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());
if (Token::Match(tok2->tokAt(-2), "%varid% ?", varid))
continue;
// Check usage of dereferenced variable in the loop..
// TODO: Move this to ValueFlow
for (const Scope *innerScope : forScope.nestedList) {
if (innerScope->type != Scope::eWhile)
continue;
// TODO: are there false negatives for "while ( %varid% ||"
if (Token::Match(innerScope->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 = innerScope->bodyStart; tok4; tok4 = tok4->next()) {
if (tok4 == forScope.bodyEnd) {
const ValueFlow::Value v(innerScope->classDef, 0LL);
nullPointerError(tok1, var->name(), &v, false);
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;
}
}
}
}
}
}
}
static bool isNullablePointer(const Token* tok, const Settings* settings)
{
if (!tok)
return false;
if (astIsPointer(tok))
return true;
if (astIsSmartPointer(tok))
return true;
if (Token::simpleMatch(tok, "."))
return isNullablePointer(tok->astOperand2(), settings);
if (const Variable* var = tok->variable()) {
return (var->isPointer() || var->isSmartPointer());
}
return false;
}
void CheckNullPointer::nullPointerByDeRefAndChec()
{
const bool printInconclusive = (mSettings->inconclusive);
for (const Token *tok = mTokenizer->tokens(); tok; tok = tok->next()) {
if (Token::Match(tok, "sizeof|decltype|typeid|typeof (")) {
tok = tok->next()->link();
continue;
}
if (Token::Match(tok, "%num%|%char%|%str%"))
continue;
if (!isNullablePointer(tok, mSettings))
continue;
// Can pointer be NULL?
const ValueFlow::Value *value = tok->getValue(0);
if (!value)
continue;
if (!printInconclusive && value->isInconclusive())
continue;
// Pointer dereference.
bool unknown = false;
if (!isPointerDeRef(tok,unknown)) {
if (unknown)
nullPointerError(tok, tok->expressionString(), value, true);
continue;
}
nullPointerError(tok, tok->expressionString(), value, value->isInconclusive());
}
}
void CheckNullPointer::nullPointer()
{
nullPointerLinkedList();
nullPointerByDeRefAndChec();
}
namespace {
const std::set<std::string> stl_istream = {
"fstream", "ifstream", "iostream", "istream",
"istringstream", "stringstream", "wistringstream", "wstringstream"
};
}
/** Dereferencing null constant (simplified token list) */
void CheckNullPointer::nullConstantDereference()
{
const SymbolDatabase *symbolDatabase = mTokenizer->getSymbolDatabase();
for (const Scope * scope : symbolDatabase->functionScopes) {
if (scope->function == nullptr || !scope->function->hasBody()) // We only look for functions with a body
continue;
const Token *tok = scope->bodyStart;
if (scope->function->isConstructor())
tok = scope->function->token; // Check initialization list
for (; tok != scope->bodyEnd; 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(), "!!. %name% (") && (tok->previous()->str() != "::" || tok->strAt(-2) == "std")) {
if (Token::Match(tok->tokAt(2), "0|NULL|nullptr )") && 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, &mSettings->library);
// is one of the var items a NULL pointer?
for (const Token *vartok : var) {
if (vartok->hasKnownIntValue() && vartok->getKnownIntValue() == 0)
nullPointerError(vartok);
}
}
} else if (Token::Match(tok, "std :: string|wstring ( 0|NULL|nullptr )"))
nullPointerError(tok);
else if (Token::Match(tok->previous(), "::|. %name% (")) {
const std::vector<const Token *> &args = getArguments(tok);
for (int argnr = 0; argnr < args.size(); ++argnr) {
const Token *argtok = args[argnr];
if (!argtok->hasKnownIntValue())
continue;
if (argtok->values().front().intvalue != 0)
continue;
if (mSettings->library.isnullargbad(tok, argnr+1))
nullPointerError(argtok);
}
}
else if (Token::Match(tok->previous(), ">> 0|NULL|nullptr")) { // 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_istream))
nullPointerError(tok);
}
}
const Variable *ovar = nullptr;
const Token *tokNull = nullptr;
if (Token::Match(tok, "0|NULL|nullptr ==|!=|>|>=|<|<= %var%")) {
if (!Token::Match(tok->tokAt(3),".|[")) {
ovar = tok->tokAt(2)->variable();
tokNull = tok;
}
} else if (Token::Match(tok, "%var% ==|!=|>|>=|<|<= 0|NULL|nullptr") ||
Token::Match(tok, "%var% =|+ 0|NULL|nullptr )|]|,|;|+")) {
ovar = tok->variable();
tokNull = tok->tokAt(2);
}
if (ovar && !ovar->isPointer() && !ovar->isArray() && ovar->isStlStringType() && tokNull && tokNull->originalName() != "'\\0'")
nullPointerError(tokNull);
}
}
}
void CheckNullPointer::nullPointerError(const Token *tok, const std::string &varname, const ValueFlow::Value *value, bool inconclusive)
{
const std::string errmsgcond("$symbol:" + varname + '\n' + ValueFlow::eitherTheConditionIsRedundant(value ? value->condition : nullptr) + " or there is possible null pointer dereference: $symbol.");
const std::string errmsgdefarg("$symbol:" + varname + "\nPossible null pointer dereference if the default parameter value is used: $symbol");
if (!tok) {
reportError(tok, Severity::error, "nullPointer", "Null pointer dereference", CWE476, false);
reportError(tok, Severity::warning, "nullPointerDefaultArg", errmsgdefarg, CWE476, false);
reportError(tok, Severity::warning, "nullPointerRedundantCheck", errmsgcond, CWE476, false);
return;
}
if (!value) {
reportError(tok, Severity::error, "nullPointer", "Null pointer dereference", CWE476, inconclusive);
return;
}
if (!mSettings->isEnabled(value, inconclusive))
return;
const ErrorPath errorPath = getErrorPath(tok, value, "Null pointer dereference");
if (value->condition) {
reportError(errorPath, Severity::warning, "nullPointerRedundantCheck", errmsgcond, CWE476, inconclusive || value->isInconclusive());
} else if (value->defaultArg) {
reportError(errorPath, Severity::warning, "nullPointerDefaultArg", errmsgdefarg, CWE476, inconclusive || value->isInconclusive());
} else {
std::string errmsg;
errmsg = std::string(value->isKnown() ? "Null" : "Possible null") + " pointer dereference";
if (!varname.empty())
errmsg = "$symbol:" + varname + '\n' + errmsg + ": $symbol";
reportError(errorPath,
value->isKnown() ? Severity::error : Severity::warning,
"nullPointer",
errmsg,
CWE476, inconclusive || value->isInconclusive());
}
}
void CheckNullPointer::arithmetic()
{
const SymbolDatabase *symbolDatabase = mTokenizer->getSymbolDatabase();
for (const Scope * scope : symbolDatabase->functionScopes) {
for (const Token* tok = scope->bodyStart->next(); tok != scope->bodyEnd; tok = tok->next()) {
if (!Token::Match(tok, "-|+|+=|-=|++|--"))
continue;
const Token *pointerOperand;
const Token *numericOperand;
if (tok->astOperand1() && tok->astOperand1()->valueType() && tok->astOperand1()->valueType()->pointer != 0) {
pointerOperand = tok->astOperand1();
numericOperand = tok->astOperand2();
} else if (tok->astOperand2() && tok->astOperand2()->valueType() && tok->astOperand2()->valueType()->pointer != 0) {
pointerOperand = tok->astOperand2();
numericOperand = tok->astOperand1();
} else
continue;
if (numericOperand && numericOperand->valueType() && !numericOperand->valueType()->isIntegral())
continue;
MathLib::bigint checkValue = 0;
// When using an assign op, the value read from
// valueflow has already been updated, so instead of
// checking for zero we check that the value is equal
// to RHS
if (tok->astOperand2() && tok->astOperand2()->hasKnownIntValue()) {
if (tok->str() == "-=")
checkValue -= tok->astOperand2()->values().front().intvalue;
else if (tok->str() == "+=")
checkValue = tok->astOperand2()->values().front().intvalue;
}
const ValueFlow::Value *value = pointerOperand->getValue(checkValue);
if (!value)
continue;
if (!mSettings->inconclusive && value->isInconclusive())
continue;
if (value->condition && !mSettings->isEnabled(Settings::WARNING))
continue;
if (value->condition)
redundantConditionWarning(tok, value, value->condition, value->isInconclusive());
else
pointerArithmeticError(tok, value, value->isInconclusive());
}
}
}
static std::string arithmeticTypeString(const Token *tok)
{
if (tok && tok->str()[0] == '-')
return "subtraction";
else if (tok && tok->str()[0] == '+')
return "addition";
else
return "arithmetic";
}
void CheckNullPointer::pointerArithmeticError(const Token* tok, const ValueFlow::Value *value, bool inconclusive)
{
std::string arithmetic = arithmeticTypeString(tok);
std::string errmsg;
if (tok && tok->str()[0] == '-') {
errmsg = "Overflow in pointer arithmetic, NULL pointer is subtracted.";
} else {
errmsg = "Pointer " + arithmetic + " with NULL pointer.";
}
const ErrorPath errorPath = getErrorPath(tok, value, "Null pointer " + arithmetic);
reportError(errorPath,
Severity::error,
"nullPointerArithmetic",
errmsg,
CWE682,
inconclusive);
}
void CheckNullPointer::redundantConditionWarning(const Token* tok, const ValueFlow::Value *value, const Token *condition, bool inconclusive)
{
std::string arithmetic = arithmeticTypeString(tok);
std::string errmsg;
if (tok && tok->str()[0] == '-') {
errmsg = ValueFlow::eitherTheConditionIsRedundant(condition) + " or there is overflow in pointer " + arithmetic + ".";
} else {
errmsg = ValueFlow::eitherTheConditionIsRedundant(condition) + " or there is pointer arithmetic with NULL pointer.";
}
const ErrorPath errorPath = getErrorPath(tok, value, "Null pointer " + arithmetic);
reportError(errorPath,
Severity::warning,
"nullPointerArithmeticRedundantCheck",
errmsg,
CWE682,
inconclusive);
}
std::string CheckNullPointer::MyFileInfo::toString() const
{
return CTU::toString(unsafeUsage);
}
static bool isUnsafeUsage(const Check *check, const Token *vartok, MathLib::bigint *value)
{
(void)value;
const CheckNullPointer *checkNullPointer = dynamic_cast<const CheckNullPointer *>(check);
bool unknown = false;
return checkNullPointer && checkNullPointer->isPointerDeRef(vartok, unknown);
}
Check::FileInfo *CheckNullPointer::getFileInfo(const Tokenizer *tokenizer, const Settings *settings) const
{
CheckNullPointer check(tokenizer, settings, nullptr);
const std::list<CTU::FileInfo::UnsafeUsage> &unsafeUsage = CTU::getUnsafeUsage(tokenizer, settings, &check, ::isUnsafeUsage);
if (unsafeUsage.empty())
return nullptr;
MyFileInfo *fileInfo = new MyFileInfo;
fileInfo->unsafeUsage = unsafeUsage;
return fileInfo;
}
Check::FileInfo * CheckNullPointer::loadFileInfoFromXml(const tinyxml2::XMLElement *xmlElement) const
{
const std::list<CTU::FileInfo::UnsafeUsage> &unsafeUsage = CTU::loadUnsafeUsageListFromXml(xmlElement);
if (unsafeUsage.empty())
return nullptr;
MyFileInfo *fileInfo = new MyFileInfo;
fileInfo->unsafeUsage = unsafeUsage;
return fileInfo;
}
bool CheckNullPointer::analyseWholeProgram(const CTU::FileInfo *ctu, const std::list<Check::FileInfo*> &fileInfo, const Settings& settings, ErrorLogger &errorLogger)
{
if (!ctu)
return false;
bool foundErrors = false;
(void)settings; // This argument is unused
const std::map<std::string, std::list<const CTU::FileInfo::CallBase *>> callsMap = ctu->getCallsMap();
for (Check::FileInfo *fi1 : fileInfo) {
const MyFileInfo *fi = dynamic_cast<MyFileInfo*>(fi1);
if (!fi)
continue;
for (const CTU::FileInfo::UnsafeUsage &unsafeUsage : fi->unsafeUsage) {
for (int warning = 0; warning <= 1; warning++) {
if (warning == 1 && !settings.isEnabled(Settings::WARNING))
break;
const std::list<ErrorLogger::ErrorMessage::FileLocation> &locationList =
ctu->getErrorPath(CTU::FileInfo::InvalidValueType::null,
unsafeUsage,
callsMap,
"Dereferencing argument ARG that is null",
nullptr,
warning);
if (locationList.empty())
continue;
const ErrorLogger::ErrorMessage errmsg(locationList,
emptyString,
warning ? Severity::warning : Severity::error,
"Null pointer dereference: " + unsafeUsage.myArgumentName,
"ctunullpointer",
CWE476, false);
errorLogger.reportErr(errmsg);
foundErrors = true;
break;
}
}
}
return foundErrors;
}
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