cppcheck/lib/checkstring.cpp at main · cppcheck-opensource/cppcheck · GitHub

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* Cppcheck - A tool for static C/C++ code analysis

* 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 "checkstring.h"

#include "astutils.h"

#include "errortypes.h"

#include "mathlib.h"

#include "settings.h"

#include "symboldatabase.h"

#include "token.h"

#include "tokenize.h"

#include "utils.h"

#include <cstddef>

#include <list>

#include <vector>

#include <utility>

//---------------------------------------------------------------------------

// CWE ids used:

static const CWE CWE570(570U); // Expression is Always False

static const CWE CWE571(571U); // Expression is Always True

static const CWE CWE595(595U); // Comparison of Object References Instead of Object Contents

static const CWE CWE628(628U); // Function Call with Incorrectly Specified Arguments

static const CWE CWE665(665U); // Improper Initialization

static const CWE CWE758(758U); // Reliance on Undefined, Unspecified, or Implementation-Defined Behavior

//---------------------------------------------------------------------------

// Writing string literal is UB

//---------------------------------------------------------------------------

void CheckStringImpl::stringLiteralWrite()

{

logChecker("CheckString::stringLiteralWrite");

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 (!tok->variable() || !tok->variable()->isPointer())

continue;

const Token *str = tok->getValueTokenMinStrSize(mSettings);

if (!str)

continue;

if (Token::Match(tok, "%var% [") && Token::simpleMatch(tok->linkAt(1), "] ="))

stringLiteralWriteError(tok, str);

else if (Token::Match(tok->previous(), "* %var% ="))

stringLiteralWriteError(tok, str);

}

void CheckStringImpl::stringLiteralWriteError(const Token *tok, const Token *strValue)

{

std::list<const Token*> callstack{ tok };

if (strValue)

callstack.push_back(strValue);

std::string errmsg("Modifying string literal");

if (strValue) {

std::string s = strValue->str();

// 20 is an arbitrary value, the max string length shown in a warning message

if (s.size() > 20U)

s.replace(17, std::string::npos, "..\"");

errmsg += " " + s;

}

errmsg += " directly or indirectly is undefined behaviour.";

reportError(callstack, Severity::error, "stringLiteralWrite", errmsg, CWE758, Certainty::normal);

}

//---------------------------------------------------------------------------

// Check for string comparison involving two static strings.

// if(strcmp("00FF00","00FF00")==0) // <- statement is always true

//---------------------------------------------------------------------------

void CheckStringImpl::checkAlwaysTrueOrFalseStringCompare()

{

if (!mSettings.severity.isEnabled(Severity::warning))

return;

logChecker("CheckString::checkAlwaysTrueOrFalseStringCompare"); // warning

for (const Token* tok = mTokenizer->tokens(); tok; tok = tok->next()) {

if (tok->isName() && tok->strAt(1) == "(" && Token::Match(tok, "memcmp|strncmp|strcmp|stricmp|strverscmp|bcmp|strcmpi|strcasecmp|strncasecmp|strncasecmp_l|strcasecmp_l|wcsncasecmp|wcscasecmp|wmemcmp|wcscmp|wcscasecmp_l|wcsncasecmp_l|wcsncmp|_mbscmp|_mbscmp_l|_memicmp|_memicmp_l|_stricmp|_wcsicmp|wcsicmp|_mbsicmp|_stricmp_l|_wcsicmp_l|_mbsicmp_l")) {

if (Token::Match(tok->tokAt(2), "%str% , %str% ,|)")) {

const std::string &str1 = tok->strAt(2);

const std::string &str2 = tok->strAt(4);

if (!tok->isExpandedMacro() && !tok->tokAt(2)->isExpandedMacro() && !tok->tokAt(4)->isExpandedMacro())

alwaysTrueFalseStringCompareError(tok, str1, str2);

tok = tok->tokAt(5);

} else if (Token::Match(tok->tokAt(2), "%name% , %name% ,|)")) {

const std::string &str1 = tok->strAt(2);

const std::string &str2 = tok->strAt(4);

if (str1 == str2)

alwaysTrueStringVariableCompareError(tok, str1, str2);

tok = tok->tokAt(5);

} else if (Token::Match(tok->tokAt(2), "%name% . c_str ( ) , %name% . c_str ( ) ,|)")) {

const std::string &str1 = tok->strAt(2);

const std::string &str2 = tok->strAt(8);

if (str1 == str2)

alwaysTrueStringVariableCompareError(tok, str1, str2);

tok = tok->tokAt(13);

}

} else if (tok->isName() && Token::Match(tok, "QString :: compare ( %str% , %str% )")) {

const std::string &str1 = tok->strAt(4);

const std::string &str2 = tok->strAt(6);

alwaysTrueFalseStringCompareError(tok, str1, str2);

tok = tok->tokAt(7);

} else if (Token::Match(tok, "!!+ %str% ==|!= %str% !!+")) {

const std::string &str1 = tok->strAt(1);

const std::string &str2 = tok->strAt(3);

alwaysTrueFalseStringCompareError(tok, str1, str2);

tok = tok->tokAt(5);

}

if (!tok)

break;

}

void CheckStringImpl::alwaysTrueFalseStringCompareError(const Token *tok, const std::string& str1, const std::string& str2)

{

constexpr std::size_t stringLen = 10;

const std::string string1 = (str1.size() < stringLen) ? str1 : (str1.substr(0, stringLen-2) + "..");

const std::string string2 = (str2.size() < stringLen) ? str2 : (str2.substr(0, stringLen-2) + "..");

reportError(tok, Severity::warning, "staticStringCompare",

"Unnecessary comparison of static strings.\n"

"The compared strings, '" + string1 + "' and '" + string2 + "', are always " + (str1==str2?"identical":"unequal") + ". "

"Therefore the comparison is unnecessary and looks suspicious.", (str1==str2)?CWE571:CWE570, Certainty::normal);

}

void CheckStringImpl::alwaysTrueStringVariableCompareError(const Token *tok, const std::string& str1, const std::string& str2)

{

reportError(tok, Severity::warning, "stringCompare",

"Comparison of identical string variables.\n"

"The compared strings, '" + str1 + "' and '" + str2 + "', are identical. "

"This could be a logic bug.", CWE571, Certainty::normal);

}

//-----------------------------------------------------------------------------

// Detect "str == '\0'" where "*str == '\0'" is correct.

// Comparing char* with each other instead of using strcmp()

//-----------------------------------------------------------------------------

void CheckStringImpl::checkSuspiciousStringCompare()

{

if (!mSettings.severity.isEnabled(Severity::warning))

return;

logChecker("CheckString::checkSuspiciousStringCompare"); // warning

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 (!tok->isComparisonOp())

continue;

const Token* varTok = tok->astOperand1();

const Token* litTok = tok->astOperand2();

if (!varTok || !litTok) // <- failed to create AST for comparison

continue;

if (Token::Match(varTok, "%char%|%num%|%str%"))

std::swap(varTok, litTok);

else if (!Token::Match(litTok, "%char%|%num%|%str%"))

continue;

if (varTok->isLiteral())

continue;

const ValueType* varType = varTok->valueType();

if (varTok->isCpp() && (!varType || !varType->isIntegral()))

continue;

if (litTok->tokType() == Token::eString) {

if (varTok->isC() || (varType && varType->pointer))

suspiciousStringCompareError(tok, varTok->expressionString(), litTok->isLong());

} else if (litTok->tokType() == Token::eChar && varType && varType->pointer) {

suspiciousStringCompareError_char(tok, varTok->expressionString());

}

void CheckStringImpl::suspiciousStringCompareError(const Token* tok, const std::string& var, bool isLong)

{

const std::string cmpFunc = isLong ? "wcscmp" : "strcmp";

reportError(tok, Severity::warning, "literalWithCharPtrCompare",

"$symbol:" + var + "\nString literal compared with variable '$symbol'. Did you intend to use " + cmpFunc + "() instead?", CWE595, Certainty::normal);

}

void CheckStringImpl::suspiciousStringCompareError_char(const Token* tok, const std::string& var)

{

reportError(tok, Severity::warning, "charLiteralWithCharPtrCompare",

"$symbol:" + var + "\nChar literal compared with pointer '$symbol'. Did you intend to dereference it?", CWE595, Certainty::normal);

}

//---------------------------------------------------------------------------

// Adding C-string and char with operator+

//---------------------------------------------------------------------------

static bool isChar(const Variable* var)

{

return (var && !var->isPointer() && !var->isArray() && (var->typeStartToken()->str() == "char" || var->typeStartToken()->str() == "wchar_t"));

}

void CheckStringImpl::strPlusChar()

{

logChecker("CheckString::strPlusChar");

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 (tok->str() == "+") {

if (tok->astOperand1() && (tok->astOperand1()->tokType() == Token::eString)) { // string literal...

if (tok->astOperand2() && (tok->astOperand2()->tokType() == Token::eChar || isChar(tok->astOperand2()->variable()))) // added to char variable or char constant

strPlusCharError(tok);

}

void CheckStringImpl::strPlusCharError(const Token *tok)

{

std::string charType = "char";

if (tok && tok->astOperand2() && tok->astOperand2()->variable())

charType = tok->astOperand2()->variable()->typeStartToken()->str();

else if (tok && tok->astOperand2() && tok->astOperand2()->tokType() == Token::eChar && tok->astOperand2()->isLong())

charType = "wchar_t";

reportError(tok, Severity::error, "strPlusChar", "Unusual pointer arithmetic. A value of type '" + charType +"' is added to a string literal.", CWE665, Certainty::normal);

}

static bool isMacroUsage(const Token* tok)

{

if (const Token* parent = tok->astParent()) {

while (parent && (parent->isCast() || parent->str() == "&&")) {

if (parent->isExpandedMacro())

return true;

parent = parent->astParent();

}

if (!parent)

return false;

if (parent->isExpandedMacro())

return true;

if (parent->isUnaryOp("!") || parent->isComparisonOp()) {

int argn{};

const Token* ftok = getTokenArgumentFunction(parent, argn);

if (ftok && !ftok->function())

return true;

}

return false;

}

//---------------------------------------------------------------------------

// Implicit casts of string literals to bool

// Comparing string literal with strlen() with wrong length

//---------------------------------------------------------------------------

void CheckStringImpl::checkIncorrectStringCompare()

{

if (!mSettings.severity.isEnabled(Severity::warning))

return;

logChecker("CheckString::checkIncorrectStringCompare"); // warning

const SymbolDatabase *symbolDatabase = mTokenizer->getSymbolDatabase();

for (const Scope * scope : symbolDatabase->functionScopes) {

for (const Token* tok = scope->bodyStart->next(); tok != scope->bodyEnd; tok = tok->next()) {

// skip "assert(str && ..)" and "assert(.. && str)"

if ((endsWith(tok->str(), "assert") || endsWith(tok->str(), "ASSERT")) &&

Token::Match(tok, "%name% (") &&

(Token::Match(tok->tokAt(2), "%str% &&") || Token::Match(tok->linkAt(1)->tokAt(-2), "&& %str% )")))

tok = tok->linkAt(1);

if (Token::simpleMatch(tok, ". substr (") && Token::Match(tok->tokAt(3)->nextArgument(), "%num% )")) {

const MathLib::biguint clen = MathLib::toBigUNumber(tok->linkAt(2)->tokAt(-1));

const Token* begin = tok->previous();

for (;;) { // Find start of statement

while (begin->link() && Token::Match(begin, "]|)|>"))

begin = begin->link()->previous();

if (Token::Match(begin->previous(), ".|::"))

begin = begin->tokAt(-2);

else

break;

}

begin = begin->previous();

const Token* end = tok->linkAt(2)->next();

if (Token::Match(begin->previous(), "%str% ==|!=") && begin->strAt(-2) != "+") {

const std::size_t slen = Token::getStrLength(begin->previous());

if (clen != slen) {

incorrectStringCompareError(tok->next(), "substr", begin->strAt(-1));

}

} else if (Token::Match(end, "==|!= %str% !!+")) {

const std::size_t slen = Token::getStrLength(end->next());

if (clen != slen) {

incorrectStringCompareError(tok->next(), "substr", end->strAt(1));

}

} else if (Token::Match(tok, "%str%|%char%") &&

!Token::Match(tok->next(), "%name%") &&

isUsedAsBool(tok, mSettings) &&

!isMacroUsage(tok))

incorrectStringBooleanError(tok, tok->str());

}

void CheckStringImpl::incorrectStringCompareError(const Token *tok, const std::string& func, const std::string &string)

{

reportError(tok, Severity::warning, "incorrectStringCompare", "$symbol:" + func + "\nString literal " + string + " doesn't match length argument for $symbol().", CWE570, Certainty::normal);

}

void CheckStringImpl::incorrectStringBooleanError(const Token *tok, const std::string& string)

{

const bool charLiteral = isCharLiteral(string);

const std::string literalType = charLiteral ? "char" : "string";

const std::string result = bool_to_string(getCharLiteral(string) != "\\0");

reportError(tok,

Severity::warning,

charLiteral ? "incorrectCharBooleanError" : "incorrectStringBooleanError",

"Conversion of " + literalType + " literal " + string + " to bool always evaluates to " + result + '.', CWE571, Certainty::normal);

}

//---------------------------------------------------------------------------

// always true: strcmp(str,"a")==0 || strcmp(str,"b")

// TODO: Library configuration for string comparison functions

//---------------------------------------------------------------------------

void CheckStringImpl::overlappingStrcmp()

{

if (!mSettings.severity.isEnabled(Severity::warning))

return;

logChecker("CheckString::overlappingStrcmp"); // warning

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 (tok->str() != "||")

continue;

std::list<const Token *> equals0;

std::list<const Token *> notEquals0;

visitAstNodes(tok, [&](const Token * t) {

if (!t)

return ChildrenToVisit::none;

if (t->str() == "||") {

return ChildrenToVisit::op1_and_op2;

}

if (t->str() == "==") {

if (Token::simpleMatch(t->astOperand1(), "(") && Token::simpleMatch(t->astOperand2(), "0"))

equals0.push_back(t->astOperand1());

else if (Token::simpleMatch(t->astOperand2(), "(") && Token::simpleMatch(t->astOperand1(), "0"))

equals0.push_back(t->astOperand2());

return ChildrenToVisit::none;

}

if (t->str() == "!=") {

if (Token::simpleMatch(t->astOperand1(), "(") && Token::simpleMatch(t->astOperand2(), "0"))

notEquals0.push_back(t->astOperand1());

else if (Token::simpleMatch(t->astOperand2(), "(") && Token::simpleMatch(t->astOperand1(), "0"))

notEquals0.push_back(t->astOperand2());

return ChildrenToVisit::none;

}

if (t->str() == "!" && Token::simpleMatch(t->astOperand1(), "("))

equals0.push_back(t->astOperand1());

else if (t->str() == "(")

notEquals0.push_back(t);

return ChildrenToVisit::none;

});

for (const Token *eq0 : equals0) {

for (const Token * ne0 : notEquals0) {

if (!Token::Match(eq0->previous(), "strcmp|wcscmp ("))

continue;

if (!Token::Match(ne0->previous(), "strcmp|wcscmp ("))

continue;

const std::vector<const Token *> args1 = getArguments(eq0->previous());

const std::vector<const Token *> args2 = getArguments(ne0->previous());

if (args1.size() != 2 || args2.size() != 2)

continue;

if (args1[1]->isLiteral() &&

args2[1]->isLiteral() &&

args1[1]->str() != args2[1]->str() &&

isSameExpression(true, args1[0], args2[0], mSettings, true, false))

overlappingStrcmpError(eq0, ne0);

}

void CheckStringImpl::overlappingStrcmpError(const Token *eq0, const Token *ne0)

{

std::string eq0Expr(eq0 ? eq0->expressionString() : std::string("strcmp(x,\"abc\")"));

if (eq0 && eq0->astParent()->str() == "!")

eq0Expr = "!" + eq0Expr;

else

eq0Expr += " == 0";

const std::string ne0Expr = (ne0 ? ne0->expressionString() : std::string("strcmp(x,\"def\")")) + " != 0";

reportError(ne0, Severity::warning, "overlappingStrcmp", "The expression '" + ne0Expr + "' is suspicious. It overlaps '" + eq0Expr + "'.");

}

//---------------------------------------------------------------------------

// Overlapping source and destination passed to sprintf().

// TODO: Library configuration for overlapping arguments

//---------------------------------------------------------------------------

void CheckStringImpl::sprintfOverlappingData()

{

logChecker("CheckString::sprintfOverlappingData");

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, "sprintf|snprintf|swprintf ("))

continue;

const std::vector<const Token *> args = getArguments(tok);

const int formatString = Token::simpleMatch(tok, "sprintf") ? 1 : 2;

for (unsigned int argnr = formatString + 1; argnr < args.size(); ++argnr) {

const Token *dest = args[0];

while (dest->isCast())

dest = dest->astOperand2() ? dest->astOperand2() : dest->astOperand1();

const Token *arg = args[argnr];

if (!arg->valueType() || arg->valueType()->pointer != 1)

continue;

while (arg->isCast())

arg = arg->astOperand2() ? arg->astOperand2() : arg->astOperand1();

const bool same = isSameExpression(false,

dest,

arg,

mSettings,

true,

false);

if (same) {

sprintfOverlappingDataError(tok, args[argnr], arg->expressionString());

}

void CheckStringImpl::sprintfOverlappingDataError(const Token *funcTok, const Token *tok, const std::string &varname)

{

const std::string func = funcTok ? funcTok->str() : "s[n]printf";

reportError(tok, Severity::error, "sprintfOverlappingData",

"$symbol:" + varname + "\n"

"Undefined behavior: Variable '$symbol' is used as parameter and destination in " + func + "().\n" +

"The variable '$symbol' is used both as a parameter and as destination in " +

func + "(). The origin and destination buffers overlap. Quote from glibc (C-library) "

"documentation (http://www.gnu.org/software/libc/manual/html_mono/libc.html#Formatted-Output-Functions): "

"\"If copying takes place between objects that overlap as a result of a call "

"to sprintf() or snprintf(), the results are undefined.\"", CWE628, Certainty::normal);

}

void CheckString::runChecks(const Tokenizer &tokenizer, ErrorLogger& errorLogger)

{

CheckStringImpl checkString(&tokenizer, tokenizer.getSettings(), errorLogger);

// Checks

checkString.strPlusChar();

checkString.checkSuspiciousStringCompare();

checkString.stringLiteralWrite();

checkString.overlappingStrcmp();

checkString.checkIncorrectStringCompare();

checkString.sprintfOverlappingData();

checkString.checkAlwaysTrueOrFalseStringCompare();

}

void CheckString::getErrorMessages(ErrorLogger& errorLogger, const Settings &settings) const

{

CheckStringImpl c(nullptr, settings, errorLogger);

c.stringLiteralWriteError(nullptr, nullptr);

c.sprintfOverlappingDataError(nullptr, nullptr, "varname");

c.strPlusCharError(nullptr);

c.incorrectStringCompareError(nullptr, "substr", "\"Hello World\"");

c.suspiciousStringCompareError(nullptr, "foo", false);

c.suspiciousStringCompareError_char(nullptr, "foo");

c.incorrectStringBooleanError(nullptr, "\"Hello World\"");

c.incorrectStringBooleanError(nullptr, "\'x\'");

c.alwaysTrueFalseStringCompareError(nullptr, "str1", "str2");

c.alwaysTrueStringVariableCompareError(nullptr, "varname1", "varname2");

c.overlappingStrcmpError(nullptr, nullptr);

}

cppcheck/lib/checkstring.cpp at main · cppcheck-opensource/cppcheck · GitHub

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