/*
* Cppcheck - A tool for static C/C++ code analysis
* Copyright (C) 2007-2018 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/>.
*/
//---------------------------------------------------------------------------
// Auto variables checks
//---------------------------------------------------------------------------
#include "checkautovariables.h"
#include "astutils.h"
#include "errorlogger.h"
#include "library.h"
#include "settings.h"
#include "symboldatabase.h"
#include "token.h"
#include "tokenize.h"
#include "valueflow.h"
#include <cstddef>
#include <list>
//---------------------------------------------------------------------------
// Register this check class into cppcheck by creating a static instance of it..
namespace {
CheckAutoVariables instance;
}
static const CWE CWE398(398U); // Indicator of Poor Code Quality
static const CWE CWE562(562U); // Return of Stack Variable Address
static const CWE CWE590(590U); // Free of Memory not on the Heap
static bool isPtrArg(const Token *tok)
{
const Variable *var = tok->variable();
return (var && var->isArgument() && var->isPointer());
}
static bool isGlobalPtr(const Token *tok)
{
const Variable *var = tok->variable();
return (var && var->isGlobal() && var->isPointer());
}
static bool isArrayArg(const Token *tok)
{
const Variable *var = tok->variable();
return (var && var->isArgument() && var->isArray());
}
static bool isRefPtrArg(const Token *tok)
{
const Variable *var = tok->variable();
return (var && var->isArgument() && var->isReference() && var->isPointer());
}
static bool isNonReferenceArg(const Token *tok)
{
const Variable *var = tok->variable();
return (var && var->isArgument() && !var->isReference() && (var->isPointer() || var->typeStartToken()->isStandardType() || var->type()));
}
static bool isAutoVar(const Token *tok)
{
const Variable *var = tok->variable();
if (!var || !var->isLocal() || var->isStatic())
return false;
if (var->isReference()) {
// address of reference variable can be taken if the address
// of the variable it points at is not a auto-var
// TODO: check what the reference variable references.
return false;
}
if (Token::Match(tok, "%name% .|::")) {
do {
tok = tok->tokAt(2);
} while (Token::Match(tok, "%name% .|::"));
if (Token::Match(tok, "%name% ("))
return false;
}
return true;
}
static bool isAutoVarArray(const Token *tok)
{
if (!tok)
return false;
// &x[..]
if (tok->str() == "&" && Token::simpleMatch(tok->astOperand1(), "[") && !tok->astOperand2())
return isAutoVarArray(tok->astOperand1()->astOperand1());
// x+y
if (tok->str() == "+")
return isAutoVarArray(tok->astOperand1()) || isAutoVarArray(tok->astOperand2());
// x-intexpr
if (tok->str() == "-")
return isAutoVarArray(tok->astOperand1()) &&
tok->astOperand2() &&
tok->astOperand2()->valueType() &&
tok->astOperand2()->valueType()->isIntegral();
const Variable *var = tok->variable();
if (!var)
return false;
// Variable
if (var->isLocal() && !var->isStatic() && var->isArray() && !var->isPointer())
return true;
// ValueFlow
if (var->isPointer() && !var->isArgument()) {
for (std::list<ValueFlow::Value>::const_iterator it = tok->values().begin(); it != tok->values().end(); ++it) {
const ValueFlow::Value &val = *it;
if (val.isTokValue() && isAutoVarArray(val.tokvalue))
return true;
}
}
return false;
}
// Verification that we really take the address of a local variable
static bool checkRvalueExpression(const Token * const vartok)
{
const Variable * const var = vartok->variable();
if (var == nullptr)
return false;
if (Token::Match(vartok->previous(), "& %name% [") && var->isPointer())
return false;
const Token * const next = vartok->next();
// &a.b[0]
if (Token::Match(vartok, "%name% . %var% [") && !var->isPointer()) {
const Variable *var2 = next->next()->variable();
return var2 && !var2->isPointer();
}
return ((next->str() != "." || (!var->isPointer() && (!var->isClass() || var->type()))) && next->strAt(2) != ".");
}
static bool variableIsUsedInScope(const Token* start, unsigned int varId, const Scope *scope)
{
if (!start) // Ticket #5024
return false;
for (const Token *tok = start; tok && tok != scope->classEnd; tok = tok->next()) {
if (tok->varId() == varId)
return true;
const Scope::ScopeType scopeType = tok->scope()->type;
if (scopeType == Scope::eFor || scopeType == Scope::eDo || scopeType == Scope::eWhile) // In case of loops, better checking would be necessary
return true;
if (Token::simpleMatch(tok, "asm ("))
return true;
}
return false;
}
void CheckAutoVariables::assignFunctionArg()
{
const bool printStyle = _settings->isEnabled(Settings::STYLE);
const bool printWarning = _settings->isEnabled(Settings::WARNING);
if (!printStyle && !printWarning)
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];
for (const Token *tok = scope->classStart; tok && tok != scope->classEnd; tok = tok->next()) {
// TODO: What happens if this is removed?
if (tok->astParent())
continue;
if (!Token::Match(tok, "=|++|--") || !Token::Match(tok->astOperand1(), "%var%"))
continue;
const Token* const vartok = tok->astOperand1();
if (isNonReferenceArg(vartok) &&
!Token::Match(vartok->next(), "= %varid% ;", vartok->varId()) &&
!variableIsUsedInScope(Token::findsimplematch(vartok->next(), ";"), vartok->varId(), scope) &&
!Token::findsimplematch(vartok, "goto", scope->classEnd)) {
if (vartok->variable()->isPointer() && printWarning)
errorUselessAssignmentPtrArg(vartok);
else if (printStyle)
errorUselessAssignmentArg(vartok);
}
}
}
}
static bool reassignedGlobalPointer(const Token *vartok, unsigned int pointerVarId)
{
const Token * const end = vartok->variable()->typeStartToken()->scope()->classEnd;
for (const Token *tok2 = vartok; tok2 != nullptr && tok2 != end; tok2 = tok2->next()) {
if (Token::Match(tok2, "%varid% =", pointerVarId))
return true;
if (Token::Match(tok2, "%name% (") && !Token::simpleMatch(tok2->linkAt(1), ") {")) {
// Bailout: possibly written
// TODO: check if it is written
return true;
}
}
return false;
}
void CheckAutoVariables::autoVariables()
{
const bool printInconclusive = _settings->inconclusive;
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];
for (const Token *tok = scope->classStart; tok && tok != scope->classEnd; tok = tok->next()) {
// Critical assignment
if (Token::Match(tok, "[;{}] %var% = & %var%") && isRefPtrArg(tok->next()) && isAutoVar(tok->tokAt(4))) {
if (checkRvalueExpression(tok->tokAt(4)))
errorAutoVariableAssignment(tok->next(), false);
} else if (Token::Match(tok, "[;{}] * %var% = & %var%") && isPtrArg(tok->tokAt(2)) && isAutoVar(tok->tokAt(5))) {
if (checkRvalueExpression(tok->tokAt(5)))
errorAutoVariableAssignment(tok->next(), false);
} else if (_settings->isEnabled(Settings::WARNING) && Token::Match(tok, "[;{}] %var% = &| %var% ;") && isGlobalPtr(tok->next())) {
const Token * const pointer = tok->next();
if (isAutoVarArray(tok->tokAt(3))) {
const Token * const array = tok->tokAt(3);
if (!reassignedGlobalPointer(array, pointer->varId()))
errorAssignAddressOfLocalArrayToGlobalPointer(pointer, array);
} else if (isAutoVar(tok->tokAt(4))) {
const Token * const variable = tok->tokAt(4);
if (!reassignedGlobalPointer(variable, pointer->varId()))
errorAssignAddressOfLocalVariableToGlobalPointer(pointer, variable);
}
} else if (Token::Match(tok, "[;{}] %var% . %var% = & %var%")) {
// TODO: check if the parameter is only changed temporarily (#2969)
if (printInconclusive && isPtrArg(tok->next())) {
const Token * const var2tok = tok->tokAt(6);
if (isAutoVar(var2tok) && checkRvalueExpression(var2tok))
errorAutoVariableAssignment(tok->next(), true);
}
tok = tok->tokAt(6);
} else if (Token::Match(tok, "[;{}] %var% . %var% = %var% ;")) {
// TODO: check if the parameter is only changed temporarily (#2969)
if (printInconclusive && isPtrArg(tok->next())) {
if (isAutoVarArray(tok->tokAt(5)))
errorAutoVariableAssignment(tok->next(), true);
}
tok = tok->tokAt(5);
} else if (Token::Match(tok, "[;{}] * %var% = %var% ;")) {
const Variable * var1 = tok->tokAt(2)->variable();
if (var1 && var1->isArgument() && Token::Match(var1->nameToken()->tokAt(-3), "%type% * *")) {
if (isAutoVarArray(tok->tokAt(4)))
errorAutoVariableAssignment(tok->next(), false);
}
tok = tok->tokAt(4);
} else if (Token::Match(tok, "[;{}] %var% [") && Token::Match(tok->linkAt(2), "] = & %var%") &&
(isPtrArg(tok->next()) || isArrayArg(tok->next())) && isAutoVar(tok->linkAt(2)->tokAt(3))) {
const Token* const varTok = tok->linkAt(2)->tokAt(3);
if (checkRvalueExpression(varTok))
errorAutoVariableAssignment(tok->next(), false);
}
// Critical return
else if (Token::Match(tok, "return %var% ;") && isAutoVar(tok->next())) {
const std::list<ValueFlow::Value> &values = tok->next()->values();
const ValueFlow::Value *value = nullptr;
for (std::list<ValueFlow::Value>::const_iterator it = values.begin(); it != values.end(); ++it) {
if (!it->isTokValue())
continue;
if (!_settings->inconclusive && it->isInconclusive())
continue;
if (!Token::Match(it->tokvalue->previous(), "= & %var%"))
continue;
if (!isAutoVar(it->tokvalue->next()))
continue;
if (!value || value->isInconclusive())
value = &(*it);
}
if (value)
errorReturnAddressToAutoVariable(tok, value);
}
else if (Token::Match(tok, "return & %var% ;")) {
const Token* varTok = tok->tokAt(2);
if (isAutoVar(varTok))
errorReturnAddressToAutoVariable(tok);
else if (varTok->varId()) {
const Variable * var1 = varTok->variable();
if (var1 && var1->isArgument() && var1->typeEndToken()->str() != "&")
errorReturnAddressOfFunctionParameter(tok, varTok->str());
}
}
// Invalid pointer deallocation
else if ((Token::Match(tok, "%name% ( %var% ) ;") && _settings->library.dealloc(tok)) ||
(_tokenizer->isCPP() && Token::Match(tok, "delete [| ]| (| %var% !!["))) {
tok = Token::findmatch(tok->next(), "%var%");
if (isAutoVarArray(tok))
errorInvalidDeallocation(tok);
} else if ((Token::Match(tok, "%name% ( & %var% ) ;") && _settings->library.dealloc(tok)) ||
(_tokenizer->isCPP() && Token::Match(tok, "delete [| ]| (| & %var% !!["))) {
tok = Token::findmatch(tok->next(), "%var%");
if (isAutoVar(tok))
errorInvalidDeallocation(tok);
}
}
}
}
//---------------------------------------------------------------------------
void CheckAutoVariables::returnPointerToLocalArray()
{
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)
continue;
const Token *tok = scope->function->tokenDef;
// have we reached a function that returns a pointer
if (tok->previous() && tok->previous()->str() == "*") {
for (const Token *tok2 = scope->classStart->next(); tok2 && tok2 != scope->classEnd; tok2 = tok2->next()) {
// Return pointer to local array variable..
if (tok2 ->str() == "return" && isAutoVarArray(tok2->astOperand1())) {
errorReturnPointerToLocalArray(tok2);
}
}
}
}
}
void CheckAutoVariables::errorReturnAddressToAutoVariable(const Token *tok)
{
reportError(tok, Severity::error, "returnAddressOfAutoVariable", "Address of an auto-variable returned.", CWE562, false);
}
void CheckAutoVariables::errorReturnAddressToAutoVariable(const Token *tok, const ValueFlow::Value *value)
{
reportError(tok, Severity::error, "returnAddressOfAutoVariable", "Address of auto-variable '" + value->tokvalue->astOperand1()->expressionString() + "' returned", CWE562, false);
}
void CheckAutoVariables::errorReturnPointerToLocalArray(const Token *tok)
{
reportError(tok, Severity::error, "returnLocalVariable", "Pointer to local array variable returned.", CWE562, false);
}
void CheckAutoVariables::errorAutoVariableAssignment(const Token *tok, bool inconclusive)
{
if (!inconclusive) {
reportError(tok, Severity::error, "autoVariables",
"Address of local auto-variable assigned to a function parameter.\n"
"Dangerous assignment - the function parameter is assigned the address of a local "
"auto-variable. Local auto-variables are reserved from the stack which "
"is freed when the function ends. So the pointer to a local variable "
"is invalid after the function ends.", CWE562, false);
} else {
reportError(tok, Severity::error, "autoVariables",
"Address of local auto-variable assigned to a function parameter.\n"
"Function parameter is assigned the address of a local auto-variable. "
"Local auto-variables are reserved from the stack which is freed when "
"the function ends. The address is invalid after the function ends and it "
"might 'leak' from the function through the parameter.",
CWE562,
true);
}
}
void CheckAutoVariables::errorAssignAddressOfLocalArrayToGlobalPointer(const Token *pointer, const Token *array)
{
const std::string pointerName = pointer ? pointer->str() : std::string("pointer");
const std::string arrayName = array ? array->str() : std::string("array");
reportError(pointer, Severity::warning, "autoVariablesAssignGlobalPointer",
"Address of local array " + arrayName + " is assigned to global pointer " + pointerName +" and not reassigned before " + arrayName + " goes out of scope.", CWE562, false);
}
void CheckAutoVariables::errorAssignAddressOfLocalVariableToGlobalPointer(const Token *pointer, const Token *variable)
{
const std::string pointerName = pointer ? pointer->str() : std::string("pointer");
const std::string variableName = variable ? variable->str() : std::string("variable");
reportError(pointer, Severity::warning, "autoVariablesAssignGlobalPointer",
"Address of local variable " + variableName + " is assigned to global pointer " + pointerName +" and not reassigned before " + variableName + " goes out of scope.", CWE562, false);
}
void CheckAutoVariables::errorReturnAddressOfFunctionParameter(const Token *tok, const std::string &varname)
{
reportError(tok, Severity::error, "returnAddressOfFunctionParameter",
"Address of function parameter '" + varname + "' returned.\n"
"Address of the function parameter '" + varname + "' becomes invalid after the function exits because "
"function parameters are stored on the stack which is freed when the function exits. Thus the returned "
"value is invalid.", CWE562, false);
}
void CheckAutoVariables::errorUselessAssignmentArg(const Token *tok)
{
reportError(tok,
Severity::style,
"uselessAssignmentArg",
"Assignment of function parameter has no effect outside the function.", CWE398, false);
}
void CheckAutoVariables::errorUselessAssignmentPtrArg(const Token *tok)
{
reportError(tok,
Severity::warning,
"uselessAssignmentPtrArg",
"Assignment of function parameter has no effect outside the function. Did you forget dereferencing it?", CWE398, false);
}
//---------------------------------------------------------------------------
// return temporary?
bool CheckAutoVariables::returnTemporary(const Token *tok)
{
bool func = false; // Might it be a function call?
bool retref = false; // is there such a function that returns a reference?
bool retvalue = false; // is there such a function that returns a value?
const Function *function = tok->function();
if (function) {
// Ticket #5478: Only functions or operator equal might return a temporary
if (function->type != Function::eOperatorEqual && function->type != Function::eFunction)
return false;
retref = function->tokenDef->strAt(-1) == "&";
if (!retref) {
const Token *start = function->retDef;
if (start->str() == "const")
start = start->next();
if (start->str() == "::")
start = start->next();
if (Token::simpleMatch(start, "std ::")) {
if (start->strAt(3) != "<" || !Token::simpleMatch(start->linkAt(3), "> ::"))
retvalue = true;
else
retref = true; // Assume that a reference is returned
} else {
if (start->type())
retvalue = true;
else
retref = true;
}
}
func = true;
}
if (!func && tok->type())
return true;
return (!retref && retvalue);
}
//---------------------------------------------------------------------------
static bool astHasAutoResult(const Token *tok)
{
if (tok->astOperand1() && !astHasAutoResult(tok->astOperand1()))
return false;
if (tok->astOperand2() && !astHasAutoResult(tok->astOperand2()))
return false;
if (tok->isOp()) {
if (tok->tokType() == Token::eIncDecOp)
return false;
if ((tok->str() == "<<" || tok->str() == ">>") && tok->astOperand1()) {
const Token* tok2 = tok->astOperand1();
while (tok2 && tok2->str() == "*" && !tok2->astOperand2())
tok2 = tok2->astOperand1();
return tok2 && tok2->variable() && !tok2->variable()->isClass() && !tok2->variable()->isStlType(); // Class or unknown type on LHS: Assume it is a stream
}
return true;
}
if (tok->isLiteral())
return true;
if (tok->isName()) {
// TODO: check function calls, struct members, arrays, etc also
if (!tok->variable())
return false;
if (tok->variable()->isStlType())
return true;
if (tok->variable()->isClass() || tok->variable()->isPointer() || tok->variable()->isReference()) // TODO: Properly handle pointers/references to classes in symbol database
return false;
return true;
}
return false;
}
void CheckAutoVariables::returnReference()
{
if (_tokenizer->isC())
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)
continue;
const Token *tok = scope->function->tokenDef;
// have we reached a function that returns a reference?
if (tok->previous() && tok->previous()->str() == "&") {
for (const Token *tok2 = scope->classStart->next(); tok2 && tok2 != scope->classEnd; tok2 = tok2->next()) {
if (!tok2->scope()->isExecutable()) {
tok2 = tok2->scope()->classEnd;
if (!tok2)
break;
continue;
}
// Skip over lambdas
const Token *lambdaEndToken = findLambdaEndToken(tok2);
if (lambdaEndToken)
tok2 = lambdaEndToken->next();
if (tok2->str() == "(")
tok2 = tok2->link();
if (tok2->str() != "return")
continue;
// return..
if (Token::Match(tok2, "return %var% ;")) {
// is the returned variable a local variable?
if (isAutoVar(tok2->next())) {
const Variable *var1 = tok2->next()->variable();
// If reference variable is used, check what it references
if (Token::Match(var1->nameToken(), "%var% [=(]")) {
const Token *tok3 = var1->nameToken()->tokAt(2);
if (!Token::Match(tok3, "%var% [);.]"))
continue;
// Only report error if variable that is referenced is
// a auto variable
if (!isAutoVar(tok3))
continue;
}
// report error..
errorReturnReference(tok2);
}
}
// return reference to temporary..
else if (Token::Match(tok2, "return %name% (") &&
Token::simpleMatch(tok2->linkAt(2), ") ;")) {
if (returnTemporary(tok2->next())) {
// report error..
errorReturnTempReference(tok2);
}
}
// Return reference to a literal or the result of a calculation
else if (tok2->astOperand1() && (tok2->astOperand1()->isCalculation() || tok2->next()->isLiteral()) && astHasAutoResult(tok2->astOperand1())) {
errorReturnTempReference(tok2);
}
}
}
}
}
void CheckAutoVariables::errorReturnReference(const Token *tok)
{
reportError(tok, Severity::error, "returnReference", "Reference to auto variable returned.", CWE562, false);
}
void CheckAutoVariables::errorReturnTempReference(const Token *tok)
{
reportError(tok, Severity::error, "returnTempReference", "Reference to temporary returned.", CWE562, false);
}
void CheckAutoVariables::errorInvalidDeallocation(const Token *tok)
{
reportError(tok,
Severity::error,
"autovarInvalidDeallocation",
"Deallocation of an auto-variable results in undefined behaviour.\n"
"The deallocation of an auto-variable results in undefined behaviour. You should only free memory "
"that has been allocated dynamically.", CWE590, false);
}