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//== NullDerefChecker.cpp - Null dereference checker ------------*- C++ -*--==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This defines NullDerefChecker, a builtin check in ExprEngine that performs
// checks for null pointers at loads and stores.
//
//===----------------------------------------------------------------------===//
#include "ClangSACheckers.h"
#include "clang/AST/ExprObjC.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/CheckerManager.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
#include "llvm/ADT/SmallString.h"
using namespace clang;
using namespace ento;
namespace {
class DereferenceChecker
: public Checker< check::Location,
EventDispatcher<ImplicitNullDerefEvent> > {
mutable OwningPtr<BuiltinBug> BT_null;
mutable OwningPtr<BuiltinBug> BT_undef;
public:
void checkLocation(SVal location, bool isLoad, const Stmt* S,
CheckerContext &C) const;
static const MemRegion *AddDerefSource(raw_ostream &os,
SmallVectorImpl<SourceRange> &Ranges,
const Expr *Ex, const ProgramState *state,
const LocationContext *LCtx,
bool loadedFrom = false);
};
} // end anonymous namespace
const MemRegion *
DereferenceChecker::AddDerefSource(raw_ostream &os,
SmallVectorImpl<SourceRange> &Ranges,
const Expr *Ex,
const ProgramState *state,
const LocationContext *LCtx,
bool loadedFrom) {
Ex = Ex->IgnoreParenLValueCasts();
const MemRegion *sourceR = 0;
switch (Ex->getStmtClass()) {
default:
break;
case Stmt::DeclRefExprClass: {
const DeclRefExpr *DR = cast<DeclRefExpr>(Ex);
if (const VarDecl *VD = dyn_cast<VarDecl>(DR->getDecl())) {
os << " (" << (loadedFrom ? "loaded from" : "from")
<< " variable '" << VD->getName() << "')";
Ranges.push_back(DR->getSourceRange());
sourceR = state->getLValue(VD, LCtx).getAsRegion();
}
break;
}
case Stmt::MemberExprClass: {
const MemberExpr *ME = cast<MemberExpr>(Ex);
os << " (" << (loadedFrom ? "loaded from" : "via")
<< " field '" << ME->getMemberNameInfo() << "')";
SourceLocation L = ME->getMemberLoc();
Ranges.push_back(SourceRange(L, L));
break;
}
}
return sourceR;
}
void DereferenceChecker::checkLocation(SVal l, bool isLoad, const Stmt* S,
CheckerContext &C) const {
// Check for dereference of an undefined value.
if (l.isUndef()) {
if (ExplodedNode *N = C.generateSink()) {
if (!BT_undef)
BT_undef.reset(new BuiltinBug("Dereference of undefined pointer value"));
BugReport *report =
new BugReport(*BT_undef, BT_undef->getDescription(), N);
report->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N,
bugreporter::GetDerefExpr(N), report));
C.EmitReport(report);
}
return;
}
DefinedOrUnknownSVal location = cast<DefinedOrUnknownSVal>(l);
// Check for null dereferences.
if (!isa<Loc>(location))
return;
ProgramStateRef state = C.getState();
const LocationContext *LCtx = C.getLocationContext();
ProgramStateRef notNullState, nullState;
llvm::tie(notNullState, nullState) = state->assume(location);
// The explicit NULL case.
if (nullState) {
if (!notNullState) {
// Generate an error node.
ExplodedNode *N = C.generateSink(nullState);
if (!N)
return;
// We know that 'location' cannot be non-null. This is what
// we call an "explicit" null dereference.
if (!BT_null)
BT_null.reset(new BuiltinBug("Dereference of null pointer"));
SmallString<100> buf;
SmallVector<SourceRange, 2> Ranges;
// Walk through lvalue casts to get the original expression
// that syntactically caused the load.
if (const Expr *expr = dyn_cast<Expr>(S))
S = expr->IgnoreParenLValueCasts();
const MemRegion *sourceR = 0;
switch (S->getStmtClass()) {
case Stmt::ArraySubscriptExprClass: {
llvm::raw_svector_ostream os(buf);
os << "Array access";
const ArraySubscriptExpr *AE = cast<ArraySubscriptExpr>(S);
sourceR =
AddDerefSource(os, Ranges, AE->getBase()->IgnoreParenCasts(),
state.getPtr(), LCtx);
os << " results in a null pointer dereference";
break;
}
case Stmt::UnaryOperatorClass: {
llvm::raw_svector_ostream os(buf);
os << "Dereference of null pointer";
const UnaryOperator *U = cast<UnaryOperator>(S);
sourceR =
AddDerefSource(os, Ranges, U->getSubExpr()->IgnoreParens(),
state.getPtr(), LCtx, true);
break;
}
case Stmt::MemberExprClass: {
const MemberExpr *M = cast<MemberExpr>(S);
if (M->isArrow()) {
llvm::raw_svector_ostream os(buf);
os << "Access to field '" << M->getMemberNameInfo()
<< "' results in a dereference of a null pointer";
sourceR =
AddDerefSource(os, Ranges, M->getBase()->IgnoreParenCasts(),
state.getPtr(), LCtx, true);
}
break;
}
case Stmt::ObjCIvarRefExprClass: {
const ObjCIvarRefExpr *IV = cast<ObjCIvarRefExpr>(S);
if (const DeclRefExpr *DR =
dyn_cast<DeclRefExpr>(IV->getBase()->IgnoreParenCasts())) {
if (const VarDecl *VD = dyn_cast<VarDecl>(DR->getDecl())) {
llvm::raw_svector_ostream os(buf);
os << "Instance variable access (via '" << VD->getName()
<< "') results in a null pointer dereference";
}
}
Ranges.push_back(IV->getSourceRange());
break;
}
default:
break;
}
BugReport *report =
new BugReport(*BT_null,
buf.empty() ? BT_null->getDescription():buf.str(),
N);
report->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N,
bugreporter::GetDerefExpr(N), report));
for (SmallVectorImpl<SourceRange>::iterator
I = Ranges.begin(), E = Ranges.end(); I!=E; ++I)
report->addRange(*I);
if (sourceR) {
report->markInteresting(sourceR);
report->markInteresting(state->getRawSVal(loc::MemRegionVal(sourceR)));
}
C.EmitReport(report);
return;
}
else {
// Otherwise, we have the case where the location could either be
// null or not-null. Record the error node as an "implicit" null
// dereference.
if (ExplodedNode *N = C.generateSink(nullState)) {
ImplicitNullDerefEvent event = { l, isLoad, N, &C.getBugReporter() };
dispatchEvent(event);
}
}
}
// From this point forward, we know that the location is not null.
C.addTransition(notNullState);
}
void ento::registerDereferenceChecker(CheckerManager &mgr) {
mgr.registerChecker<DereferenceChecker>();
}
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