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//== ObjCContainersChecker.cpp - Path sensitive checker for CFArray *- C++ -*=//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Performs path sensitive checks of Core Foundation static containers like
// CFArray.
// 1) Check for buffer overflows:
// In CFArrayGetArrayAtIndex( myArray, index), if the index is outside the
// index space of theArray (0 to N-1 inclusive (where N is the count of
// theArray), the behavior is undefined.
//
//===----------------------------------------------------------------------===//
#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
#include "clang/AST/ParentMap.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/CheckerManager.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
using namespace clang;
using namespace ento;
namespace {
class ObjCContainersChecker : public Checker< check::PreStmt<CallExpr>,
check::PostStmt<CallExpr>,
check::PointerEscape> {
mutable std::unique_ptr<BugType> BT;
inline void initBugType() const {
if (!BT)
BT.reset(new BugType(this, "CFArray API",
categories::CoreFoundationObjectiveC));
}
inline SymbolRef getArraySym(const Expr *E, CheckerContext &C) const {
SVal ArrayRef = C.getSVal(E);
SymbolRef ArraySym = ArrayRef.getAsSymbol();
return ArraySym;
}
void addSizeInfo(const Expr *Array, const Expr *Size,
CheckerContext &C) const;
public:
/// A tag to id this checker.
static void *getTag() { static int Tag; return &Tag; }
void checkPostStmt(const CallExpr *CE, CheckerContext &C) const;
void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;
ProgramStateRef checkPointerEscape(ProgramStateRef State,
const InvalidatedSymbols &Escaped,
const CallEvent *Call,
PointerEscapeKind Kind) const;
void printState(raw_ostream &OS, ProgramStateRef State,
const char *NL, const char *Sep) const override;
};
} // end anonymous namespace
// ProgramState trait - a map from array symbol to its state.
REGISTER_MAP_WITH_PROGRAMSTATE(ArraySizeMap, SymbolRef, DefinedSVal)
void ObjCContainersChecker::addSizeInfo(const Expr *Array, const Expr *Size,
CheckerContext &C) const {
ProgramStateRef State = C.getState();
SVal SizeV = C.getSVal(Size);
// Undefined is reported by another checker.
if (SizeV.isUnknownOrUndef())
return;
// Get the ArrayRef symbol.
SVal ArrayRef = C.getSVal(Array);
SymbolRef ArraySym = ArrayRef.getAsSymbol();
if (!ArraySym)
return;
C.addTransition(
State->set<ArraySizeMap>(ArraySym, SizeV.castAs<DefinedSVal>()));
}
void ObjCContainersChecker::checkPostStmt(const CallExpr *CE,
CheckerContext &C) const {
StringRef Name = C.getCalleeName(CE);
if (Name.empty() || CE->getNumArgs() < 1)
return;
// Add array size information to the state.
if (Name.equals("CFArrayCreate")) {
if (CE->getNumArgs() < 3)
return;
// Note, we can visit the Create method in the post-visit because
// the CFIndex parameter is passed in by value and will not be invalidated
// by the call.
addSizeInfo(CE, CE->getArg(2), C);
return;
}
if (Name.equals("CFArrayGetCount")) {
addSizeInfo(CE->getArg(0), CE, C);
return;
}
}
void ObjCContainersChecker::checkPreStmt(const CallExpr *CE,
CheckerContext &C) const {
StringRef Name = C.getCalleeName(CE);
if (Name.empty() || CE->getNumArgs() < 2)
return;
// Check the array access.
if (Name.equals("CFArrayGetValueAtIndex")) {
ProgramStateRef State = C.getState();
// Retrieve the size.
// Find out if we saw this array symbol before and have information about
// it.
const Expr *ArrayExpr = CE->getArg(0);
SymbolRef ArraySym = getArraySym(ArrayExpr, C);
if (!ArraySym)
return;
const DefinedSVal *Size = State->get<ArraySizeMap>(ArraySym);
if (!Size)
return;
// Get the index.
const Expr *IdxExpr = CE->getArg(1);
SVal IdxVal = C.getSVal(IdxExpr);
if (IdxVal.isUnknownOrUndef())
return;
DefinedSVal Idx = IdxVal.castAs<DefinedSVal>();
// Now, check if 'Idx in [0, Size-1]'.
const QualType T = IdxExpr->getType();
ProgramStateRef StInBound = State->assumeInBound(Idx, *Size, true, T);
ProgramStateRef StOutBound = State->assumeInBound(Idx, *Size, false, T);
if (StOutBound && !StInBound) {
ExplodedNode *N = C.generateErrorNode(StOutBound);
if (!N)
return;
initBugType();
auto R = std::make_unique<PathSensitiveBugReport>(
*BT, "Index is out of bounds", N);
R->addRange(IdxExpr->getSourceRange());
bugreporter::trackExpressionValue(N, IdxExpr, *R,
{bugreporter::TrackingKind::Thorough,
/*EnableNullFPSuppression=*/false});
C.emitReport(std::move(R));
return;
}
}
}
ProgramStateRef
ObjCContainersChecker::checkPointerEscape(ProgramStateRef State,
const InvalidatedSymbols &Escaped,
const CallEvent *Call,
PointerEscapeKind Kind) const {
for (const auto &Sym : Escaped) {
// When a symbol for a mutable array escapes, we can't reason precisely
// about its size any more -- so remove it from the map.
// Note that we aren't notified here when a CFMutableArrayRef escapes as a
// CFArrayRef. This is because CFArrayRef is typedef'd as a pointer to a
// const-qualified type.
State = State->remove<ArraySizeMap>(Sym);
}
return State;
}
void ObjCContainersChecker::printState(raw_ostream &OS, ProgramStateRef State,
const char *NL, const char *Sep) const {
ArraySizeMapTy Map = State->get<ArraySizeMap>();
if (Map.isEmpty())
return;
OS << Sep << "ObjC container sizes :" << NL;
for (auto I : Map) {
OS << I.first << " : " << I.second << NL;
}
}
/// Register checker.
void ento::registerObjCContainersChecker(CheckerManager &mgr) {
mgr.registerChecker<ObjCContainersChecker>();
}
bool ento::shouldRegisterObjCContainersChecker(const CheckerManager &mgr) {
return true;
}
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