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//=== StackAddrEscapeChecker.cpp ----------------------------------*- C++ -*--//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file defines stack address leak checker, which checks if an invalid
// stack address is stored into a global or heap location. See CERT DCL30-C.
#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
#include "clang/AST/ExprCXX.h"
#include "clang/Basic/SourceManager.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/CallEvent.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/raw_ostream.h"
using namespace clang;
using namespace ento;
namespace {
class StackAddrEscapeChecker
: public Checker<check::PreCall, check::PreStmt<ReturnStmt>,
check::EndFunction> {
mutable IdentifierInfo *dispatch_semaphore_tII;
mutable std::unique_ptr<BuiltinBug> BT_stackleak;
mutable std::unique_ptr<BuiltinBug> BT_returnstack;
mutable std::unique_ptr<BuiltinBug> BT_capturedstackasync;
mutable std::unique_ptr<BuiltinBug> BT_capturedstackret;
enum CheckKind {
DefaultBool ChecksEnabled[CK_NumCheckKinds];
void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
void checkEndFunction(const ReturnStmt *RS, CheckerContext &Ctx) const;
void checkReturnedBlockCaptures(const BlockDataRegion &B,
CheckerContext &C) const;
void checkAsyncExecutedBlockCaptures(const BlockDataRegion &B,
CheckerContext &C) const;
void EmitStackError(CheckerContext &C, const MemRegion *R,
const Expr *RetE) const;
bool isSemaphoreCaptured(const BlockDecl &B) const;
static SourceRange genName(raw_ostream &os, const MemRegion *R,
ASTContext &Ctx);
static SmallVector<const MemRegion *, 4>
getCapturedStackRegions(const BlockDataRegion &B, CheckerContext &C);
static bool isArcManagedBlock(const MemRegion *R, CheckerContext &C);
static bool isNotInCurrentFrame(const MemRegion *R, CheckerContext &C);
} // namespace
SourceRange StackAddrEscapeChecker::genName(raw_ostream &os, const MemRegion *R,
ASTContext &Ctx) {
// Get the base region, stripping away fields and elements.
R = R->getBaseRegion();
SourceManager &SM = Ctx.getSourceManager();
SourceRange range;
os << "Address of ";
// Check if the region is a compound literal.
if (const auto *CR = dyn_cast<CompoundLiteralRegion>(R)) {
const CompoundLiteralExpr *CL = CR->getLiteralExpr();
os << "stack memory associated with a compound literal "
"declared on line "
<< SM.getExpansionLineNumber(CL->getBeginLoc()) << " returned to caller";
range = CL->getSourceRange();
} else if (const auto *AR = dyn_cast<AllocaRegion>(R)) {
const Expr *ARE = AR->getExpr();
SourceLocation L = ARE->getBeginLoc();
range = ARE->getSourceRange();
os << "stack memory allocated by call to alloca() on line "
<< SM.getExpansionLineNumber(L);
} else if (const auto *BR = dyn_cast<BlockDataRegion>(R)) {
const BlockDecl *BD = BR->getCodeRegion()->getDecl();
SourceLocation L = BD->getBeginLoc();
range = BD->getSourceRange();
os << "stack-allocated block declared on line "
<< SM.getExpansionLineNumber(L);
} else if (const auto *VR = dyn_cast<VarRegion>(R)) {
os << "stack memory associated with local variable '" << VR->getString()
<< '\'';
range = VR->getDecl()->getSourceRange();
} else if (const auto *TOR = dyn_cast<CXXTempObjectRegion>(R)) {
QualType Ty = TOR->getValueType().getLocalUnqualifiedType();
os << "stack memory associated with temporary object of type '";
Ty.print(os, Ctx.getPrintingPolicy());
os << "'";
range = TOR->getExpr()->getSourceRange();
} else {
llvm_unreachable("Invalid region in ReturnStackAddressChecker.");
return range;
bool StackAddrEscapeChecker::isArcManagedBlock(const MemRegion *R,
CheckerContext &C) {
assert(R && "MemRegion should not be null");
return C.getASTContext().getLangOpts().ObjCAutoRefCount &&
bool StackAddrEscapeChecker::isNotInCurrentFrame(const MemRegion *R,
CheckerContext &C) {
const StackSpaceRegion *S = cast<StackSpaceRegion>(R->getMemorySpace());
return S->getStackFrame() != C.getStackFrame();
bool StackAddrEscapeChecker::isSemaphoreCaptured(const BlockDecl &B) const {
if (!dispatch_semaphore_tII)
dispatch_semaphore_tII = &B.getASTContext().Idents.get("dispatch_semaphore_t");
for (const auto &C : B.captures()) {
const auto *T = C.getVariable()->getType()->getAs<TypedefType>();
if (T && T->getDecl()->getIdentifier() == dispatch_semaphore_tII)
return true;
return false;
SmallVector<const MemRegion *, 4>
StackAddrEscapeChecker::getCapturedStackRegions(const BlockDataRegion &B,
CheckerContext &C) {
SmallVector<const MemRegion *, 4> Regions;
BlockDataRegion::referenced_vars_iterator I = B.referenced_vars_begin();
BlockDataRegion::referenced_vars_iterator E = B.referenced_vars_end();
for (; I != E; ++I) {
SVal Val = C.getState()->getSVal(I.getCapturedRegion());
const MemRegion *Region = Val.getAsRegion();
if (Region && isa<StackSpaceRegion>(Region->getMemorySpace()))
return Regions;
void StackAddrEscapeChecker::EmitStackError(CheckerContext &C,
const MemRegion *R,
const Expr *RetE) const {
ExplodedNode *N = C.generateNonFatalErrorNode();
if (!N)
if (!BT_returnstack)
BT_returnstack = std::make_unique<BuiltinBug>(
this, "Return of address to stack-allocated memory");
// Generate a report for this bug.
SmallString<128> buf;
llvm::raw_svector_ostream os(buf);
SourceRange range = genName(os, R, C.getASTContext());
os << " returned to caller";
auto report =
std::make_unique<PathSensitiveBugReport>(*BT_returnstack, os.str(), N);
if (range.isValid())
void StackAddrEscapeChecker::checkAsyncExecutedBlockCaptures(
const BlockDataRegion &B, CheckerContext &C) const {
// There is a not-too-uncommon idiom
// where a block passed to dispatch_async captures a semaphore
// and then the thread (which called dispatch_async) is blocked on waiting
// for the completion of the execution of the block
// via dispatch_semaphore_wait. To avoid false-positives (for now)
// we ignore all the blocks which have captured
// a variable of the type "dispatch_semaphore_t".
if (isSemaphoreCaptured(*B.getDecl()))
for (const MemRegion *Region : getCapturedStackRegions(B, C)) {
// The block passed to dispatch_async may capture another block
// created on the stack. However, there is no leak in this situaton,
// no matter if ARC or no ARC is enabled:
// dispatch_async copies the passed "outer" block (via Block_copy)
// and if the block has captured another "inner" block,
// the "inner" block will be copied as well.
if (isa<BlockDataRegion>(Region))
ExplodedNode *N = C.generateNonFatalErrorNode();
if (!N)
if (!BT_capturedstackasync)
BT_capturedstackasync = std::make_unique<BuiltinBug>(
this, "Address of stack-allocated memory is captured");
SmallString<128> Buf;
llvm::raw_svector_ostream Out(Buf);
SourceRange Range = genName(Out, Region, C.getASTContext());
Out << " is captured by an asynchronously-executed block";
auto Report = std::make_unique<PathSensitiveBugReport>(
*BT_capturedstackasync, Out.str(), N);
if (Range.isValid())
void StackAddrEscapeChecker::checkReturnedBlockCaptures(
const BlockDataRegion &B, CheckerContext &C) const {
for (const MemRegion *Region : getCapturedStackRegions(B, C)) {
if (isArcManagedBlock(Region, C) || isNotInCurrentFrame(Region, C))
ExplodedNode *N = C.generateNonFatalErrorNode();
if (!N)
if (!BT_capturedstackret)
BT_capturedstackret = std::make_unique<BuiltinBug>(
this, "Address of stack-allocated memory is captured");
SmallString<128> Buf;
llvm::raw_svector_ostream Out(Buf);
SourceRange Range = genName(Out, Region, C.getASTContext());
Out << " is captured by a returned block";
auto Report = std::make_unique<PathSensitiveBugReport>(*BT_capturedstackret,
Out.str(), N);
if (Range.isValid())
void StackAddrEscapeChecker::checkPreCall(const CallEvent &Call,
CheckerContext &C) const {
if (!ChecksEnabled[CK_StackAddrAsyncEscapeChecker])
if (!Call.isGlobalCFunction("dispatch_after") &&
for (unsigned Idx = 0, NumArgs = Call.getNumArgs(); Idx < NumArgs; ++Idx) {
if (const BlockDataRegion *B = dyn_cast_or_null<BlockDataRegion>(
checkAsyncExecutedBlockCaptures(*B, C);
void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
CheckerContext &C) const {
if (!ChecksEnabled[CK_StackAddrEscapeChecker])
const Expr *RetE = RS->getRetValue();
if (!RetE)
RetE = RetE->IgnoreParens();
SVal V = C.getSVal(RetE);
const MemRegion *R = V.getAsRegion();
if (!R)
if (const BlockDataRegion *B = dyn_cast<BlockDataRegion>(R))
checkReturnedBlockCaptures(*B, C);
if (!isa<StackSpaceRegion>(R->getMemorySpace()) ||
isNotInCurrentFrame(R, C) || isArcManagedBlock(R, C))
// Returning a record by value is fine. (In this case, the returned
// expression will be a copy-constructor, possibly wrapped in an
// ExprWithCleanups node.)
if (const ExprWithCleanups *Cleanup = dyn_cast<ExprWithCleanups>(RetE))
RetE = Cleanup->getSubExpr();
if (isa<CXXConstructExpr>(RetE) && RetE->getType()->isRecordType())
// The CK_CopyAndAutoreleaseBlockObject cast causes the block to be copied
// so the stack address is not escaping here.
if (auto *ICE = dyn_cast<ImplicitCastExpr>(RetE)) {
if (isa<BlockDataRegion>(R) &&
ICE->getCastKind() == CK_CopyAndAutoreleaseBlockObject) {
EmitStackError(C, R, RetE);
void StackAddrEscapeChecker::checkEndFunction(const ReturnStmt *RS,
CheckerContext &Ctx) const {
if (!ChecksEnabled[CK_StackAddrEscapeChecker])
ProgramStateRef State = Ctx.getState();
// Iterate over all bindings to global variables and see if it contains
// a memory region in the stack space.
class CallBack : public StoreManager::BindingsHandler {
CheckerContext &Ctx;
const StackFrameContext *CurSFC;
SmallVector<std::pair<const MemRegion *, const MemRegion *>, 10> V;
CallBack(CheckerContext &CC) : Ctx(CC), CurSFC(CC.getStackFrame()) {}
bool HandleBinding(StoreManager &SMgr, Store S, const MemRegion *Region,
SVal Val) override {
if (!isa<GlobalsSpaceRegion>(Region->getMemorySpace()))
return true;
const MemRegion *VR = Val.getAsRegion();
if (VR && isa<StackSpaceRegion>(VR->getMemorySpace()) &&
!isArcManagedBlock(VR, Ctx) && !isNotInCurrentFrame(VR, Ctx))
V.emplace_back(Region, VR);
return true;
CallBack Cb(Ctx);
if (Cb.V.empty())
// Generate an error node.
ExplodedNode *N = Ctx.generateNonFatalErrorNode(State);
if (!N)
if (!BT_stackleak)
BT_stackleak = std::make_unique<BuiltinBug>(
this, "Stack address stored into global variable",
"Stack address was saved into a global variable. "
"This is dangerous because the address will become "
"invalid after returning from the function");
for (const auto &P : Cb.V) {
// Generate a report for this bug.
SmallString<128> Buf;
llvm::raw_svector_ostream Out(Buf);
SourceRange Range = genName(Out, P.second, Ctx.getASTContext());
Out << " is still referred to by the ";
if (isa<StaticGlobalSpaceRegion>(P.first->getMemorySpace()))
Out << "static";
Out << "global";
Out << " variable '";
const VarRegion *VR = cast<VarRegion>(P.first->getBaseRegion());
Out << *VR->getDecl()
<< "' upon returning to the caller. This will be a dangling reference";
auto Report =
std::make_unique<PathSensitiveBugReport>(*BT_stackleak, Out.str(), N);
if (Range.isValid())
void ento::registerStackAddrEscapeBase(CheckerManager &mgr) {
bool ento::shouldRegisterStackAddrEscapeBase(const LangOptions &LO) {
return true;
#define REGISTER_CHECKER(name) \
void ento::register##name(CheckerManager &Mgr) { \
StackAddrEscapeChecker *Chk = \
Mgr.getChecker<StackAddrEscapeChecker>(); \
Chk->ChecksEnabled[StackAddrEscapeChecker::CK_##name] = true; \
} \
bool ento::shouldRegister##name(const LangOptions &LO) { \
return true; \