minix/external/bsd/llvm/dist/clang/lib/StaticAnalyzer/Checkers/DereferenceChecker.cpp

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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/BugReporter/BugType.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/CheckerManager.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/raw_ostream.h"
using namespace clang;
using namespace ento;
namespace {
class DereferenceChecker
: public Checker< check::Location,
check::Bind,
EventDispatcher<ImplicitNullDerefEvent> > {
mutable OwningPtr<BuiltinBug> BT_null;
mutable OwningPtr<BuiltinBug> BT_undef;
void reportBug(ProgramStateRef State, const Stmt *S, CheckerContext &C,
bool IsBind = false) const;
public:
void checkLocation(SVal location, bool isLoad, const Stmt* S,
CheckerContext &C) const;
void checkBind(SVal L, SVal V, const Stmt *S, CheckerContext &C) const;
static void AddDerefSource(raw_ostream &os,
SmallVectorImpl<SourceRange> &Ranges,
const Expr *Ex, const ProgramState *state,
const LocationContext *LCtx,
bool loadedFrom = false);
};
} // end anonymous namespace
void
DereferenceChecker::AddDerefSource(raw_ostream &os,
SmallVectorImpl<SourceRange> &Ranges,
const Expr *Ex,
const ProgramState *state,
const LocationContext *LCtx,
bool loadedFrom) {
Ex = Ex->IgnoreParenLValueCasts();
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());
}
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;
}
case Stmt::ObjCIvarRefExprClass: {
const ObjCIvarRefExpr *IV = cast<ObjCIvarRefExpr>(Ex);
os << " (" << (loadedFrom ? "loaded from" : "via")
<< " ivar '" << IV->getDecl()->getName() << "')";
SourceLocation L = IV->getLocation();
Ranges.push_back(SourceRange(L, L));
break;
}
}
}
void DereferenceChecker::reportBug(ProgramStateRef State, const Stmt *S,
CheckerContext &C, bool IsBind) const {
// Generate an error node.
ExplodedNode *N = C.generateSink(State);
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;
llvm::raw_svector_ostream os(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();
if (IsBind) {
if (const BinaryOperator *BO = dyn_cast<BinaryOperator>(S)) {
if (BO->isAssignmentOp())
S = BO->getRHS();
} else if (const DeclStmt *DS = dyn_cast<DeclStmt>(S)) {
assert(DS->isSingleDecl() && "We process decls one by one");
if (const VarDecl *VD = dyn_cast<VarDecl>(DS->getSingleDecl()))
if (const Expr *Init = VD->getAnyInitializer())
S = Init;
}
}
switch (S->getStmtClass()) {
case Stmt::ArraySubscriptExprClass: {
os << "Array access";
const ArraySubscriptExpr *AE = cast<ArraySubscriptExpr>(S);
AddDerefSource(os, Ranges, AE->getBase()->IgnoreParenCasts(),
State.getPtr(), N->getLocationContext());
os << " results in a null pointer dereference";
break;
}
case Stmt::UnaryOperatorClass: {
os << "Dereference of null pointer";
const UnaryOperator *U = cast<UnaryOperator>(S);
AddDerefSource(os, Ranges, U->getSubExpr()->IgnoreParens(),
State.getPtr(), N->getLocationContext(), true);
break;
}
case Stmt::MemberExprClass: {
const MemberExpr *M = cast<MemberExpr>(S);
if (M->isArrow() || bugreporter::isDeclRefExprToReference(M->getBase())) {
os << "Access to field '" << M->getMemberNameInfo()
<< "' results in a dereference of a null pointer";
AddDerefSource(os, Ranges, M->getBase()->IgnoreParenCasts(),
State.getPtr(), N->getLocationContext(), true);
}
break;
}
case Stmt::ObjCIvarRefExprClass: {
const ObjCIvarRefExpr *IV = cast<ObjCIvarRefExpr>(S);
os << "Access to instance variable '" << *IV->getDecl()
<< "' results in a dereference of a null pointer";
AddDerefSource(os, Ranges, IV->getBase()->IgnoreParenCasts(),
State.getPtr(), N->getLocationContext(), true);
break;
}
default:
break;
}
os.flush();
BugReport *report =
new BugReport(*BT_null,
buf.empty() ? BT_null->getDescription() : buf.str(),
N);
bugreporter::trackNullOrUndefValue(N, bugreporter::getDerefExpr(S), *report);
for (SmallVectorImpl<SourceRange>::iterator
I = Ranges.begin(), E = Ranges.end(); I!=E; ++I)
report->addRange(*I);
C.emitReport(report);
}
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);
bugreporter::trackNullOrUndefValue(N, bugreporter::getDerefExpr(S),
*report);
C.emitReport(report);
}
return;
}
DefinedOrUnknownSVal location = l.castAs<DefinedOrUnknownSVal>();
// Check for null dereferences.
if (!location.getAs<Loc>())
return;
ProgramStateRef state = C.getState();
ProgramStateRef notNullState, nullState;
llvm::tie(notNullState, nullState) = state->assume(location);
// The explicit NULL case.
if (nullState) {
if (!notNullState) {
reportBug(nullState, S, C);
return;
}
// 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 DereferenceChecker::checkBind(SVal L, SVal V, const Stmt *S,
CheckerContext &C) const {
// If we're binding to a reference, check if the value is known to be null.
if (V.isUndef())
return;
const MemRegion *MR = L.getAsRegion();
const TypedValueRegion *TVR = dyn_cast_or_null<TypedValueRegion>(MR);
if (!TVR)
return;
if (!TVR->getValueType()->isReferenceType())
return;
ProgramStateRef State = C.getState();
ProgramStateRef StNonNull, StNull;
llvm::tie(StNonNull, StNull) =
State->assume(V.castAs<DefinedOrUnknownSVal>());
if (StNull) {
if (!StNonNull) {
reportBug(StNull, S, C, /*isBind=*/true);
return;
}
// At this point the value could be either null or non-null.
// Record this as an "implicit" null dereference.
if (ExplodedNode *N = C.generateSink(StNull)) {
ImplicitNullDerefEvent event = { V, /*isLoad=*/true, N,
&C.getBugReporter() };
dispatchEvent(event);
}
}
// Unlike a regular null dereference, initializing a reference with a
// dereferenced null pointer does not actually cause a runtime exception in
// Clang's implementation of references.
//
// int &r = *p; // safe??
// if (p != NULL) return; // uh-oh
// r = 5; // trap here
//
// The standard says this is invalid as soon as we try to create a "null
// reference" (there is no such thing), but turning this into an assumption
// that 'p' is never null will not match our actual runtime behavior.
// So we do not record this assumption, allowing us to warn on the last line
// of this example.
//
// We do need to add a transition because we may have generated a sink for
// the "implicit" null dereference.
C.addTransition(State, this);
}
void ento::registerDereferenceChecker(CheckerManager &mgr) {
mgr.registerChecker<DereferenceChecker>();
}