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clang-1
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clang-1/lib/Checker/MallocChecker.cpp

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//=== MallocChecker.cpp - A malloc/free checker -------------------*- C++ -*--//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines malloc/free checker, which checks for potential memory
// leaks, double free, and use-after-free problems.
//
//===----------------------------------------------------------------------===//
#include "GRExprEngineExperimentalChecks.h"
#include "clang/Checker/BugReporter/BugType.h"
#include "clang/Checker/PathSensitive/CheckerVisitor.h"
#include "clang/Checker/PathSensitive/GRState.h"
#include "clang/Checker/PathSensitive/GRStateTrait.h"
#include "clang/Checker/PathSensitive/SymbolManager.h"
#include "llvm/ADT/ImmutableMap.h"
using namespace clang;
namespace {
class RefState {
enum Kind { AllocateUnchecked, AllocateFailed, Released, Escaped } K;
const Stmt *S;
public:
RefState(Kind k, const Stmt *s) : K(k), S(s) {}
bool isAllocated() const { return K == AllocateUnchecked; }
bool isReleased() const { return K == Released; }
bool isEscaped() const { return K == Escaped; }
bool operator==(const RefState &X) const {
return K == X.K && S == X.S;
}
static RefState getAllocateUnchecked(const Stmt *s) {
return RefState(AllocateUnchecked, s);
}
static RefState getAllocateFailed() {
return RefState(AllocateFailed, 0);
}
static RefState getReleased(const Stmt *s) { return RefState(Released, s); }
static RefState getEscaped(const Stmt *s) { return RefState(Escaped, s); }
void Profile(llvm::FoldingSetNodeID &ID) const {
ID.AddInteger(K);
ID.AddPointer(S);
}
};
class RegionState {};
class MallocChecker : public CheckerVisitor<MallocChecker> {
BuiltinBug *BT_DoubleFree;
BuiltinBug *BT_Leak;
BuiltinBug *BT_UseFree;
IdentifierInfo *II_malloc, *II_free, *II_realloc;
public:
MallocChecker()
: BT_DoubleFree(0), BT_Leak(0), BT_UseFree(0),
II_malloc(0), II_free(0), II_realloc(0) {}
static void *getTag();
bool EvalCallExpr(CheckerContext &C, const CallExpr *CE);
void EvalDeadSymbols(CheckerContext &C,const Stmt *S,SymbolReaper &SymReaper);
void EvalEndPath(GREndPathNodeBuilder &B, void *tag, GRExprEngine &Eng);
void PreVisitReturnStmt(CheckerContext &C, const ReturnStmt *S);
const GRState *EvalAssume(const GRState *state, SVal Cond, bool Assumption);
void VisitLocation(CheckerContext &C, const Stmt *S, SVal l);
private:
void MallocMem(CheckerContext &C, const CallExpr *CE);
const GRState *MallocMemAux(CheckerContext &C, const CallExpr *CE,
const Expr *SizeEx, const GRState *state);
void FreeMem(CheckerContext &C, const CallExpr *CE);
const GRState *FreeMemAux(CheckerContext &C, const CallExpr *CE,
const GRState *state);
void ReallocMem(CheckerContext &C, const CallExpr *CE);
};
} // end anonymous namespace
typedef llvm::ImmutableMap<SymbolRef, RefState> RegionStateTy;
namespace clang {
template <>
struct GRStateTrait<RegionState>
: public GRStatePartialTrait<llvm::ImmutableMap<SymbolRef, RefState> > {
static void *GDMIndex() { return MallocChecker::getTag(); }
};
}
void clang::RegisterMallocChecker(GRExprEngine &Eng) {
Eng.registerCheck(new MallocChecker());
}
void *MallocChecker::getTag() {
static int x;
return &x;
}
bool MallocChecker::EvalCallExpr(CheckerContext &C, const CallExpr *CE) {
const GRState *state = C.getState();
const Expr *Callee = CE->getCallee();
SVal L = state->getSVal(Callee);
const FunctionDecl *FD = L.getAsFunctionDecl();
if (!FD)
return false;
ASTContext &Ctx = C.getASTContext();
if (!II_malloc)
II_malloc = &Ctx.Idents.get("malloc");
if (!II_free)
II_free = &Ctx.Idents.get("free");
if (!II_realloc)
II_realloc = &Ctx.Idents.get("realloc");
if (FD->getIdentifier() == II_malloc) {
MallocMem(C, CE);
return true;
}
if (FD->getIdentifier() == II_free) {
FreeMem(C, CE);
return true;
}
if (FD->getIdentifier() == II_realloc) {
ReallocMem(C, CE);
return true;
}
return false;
}
void MallocChecker::MallocMem(CheckerContext &C, const CallExpr *CE) {
const GRState *state = MallocMemAux(C, CE, CE->getArg(0), C.getState());
C.addTransition(state);
}
const GRState *MallocChecker::MallocMemAux(CheckerContext &C,
const CallExpr *CE,
const Expr *SizeEx,
const GRState *state) {
unsigned Count = C.getNodeBuilder().getCurrentBlockCount();
ValueManager &ValMgr = C.getValueManager();
SVal RetVal = ValMgr.getConjuredSymbolVal(NULL, CE, CE->getType(), Count);
SVal Size = state->getSVal(SizeEx);
state = C.getEngine().getStoreManager().setExtent(state, RetVal.getAsRegion(),
Size);
state = state->BindExpr(CE, RetVal);
SymbolRef Sym = RetVal.getAsLocSymbol();
assert(Sym);
// Set the symbol's state to Allocated.
return state->set<RegionState>(Sym, RefState::getAllocateUnchecked(CE));
}
void MallocChecker::FreeMem(CheckerContext &C, const CallExpr *CE) {
const GRState *state = FreeMemAux(C, CE, C.getState());
if (state)
C.addTransition(state);
}
const GRState *MallocChecker::FreeMemAux(CheckerContext &C, const CallExpr *CE,
const GRState *state) {
SVal ArgVal = state->getSVal(CE->getArg(0));
// If ptr is NULL, no operation is preformed.
if (ArgVal.isZeroConstant())
return state;
SymbolRef Sym = ArgVal.getAsLocSymbol();
assert(Sym);
const RefState *RS = state->get<RegionState>(Sym);
// If the symbol has not been tracked, return. This is possible when free() is
// called on a pointer that does not get its pointee directly from malloc().
// Full support of this requires inter-procedural analysis.
if (!RS)
return state;
// Check double free.
if (RS->isReleased()) {
ExplodedNode *N = C.GenerateSink();
if (N) {
if (!BT_DoubleFree)
BT_DoubleFree = new BuiltinBug("Double free",
"Try to free a memory block that has been released");
// FIXME: should find where it's freed last time.
BugReport *R = new BugReport(*BT_DoubleFree,
BT_DoubleFree->getDescription(), N);
C.EmitReport(R);
}
return NULL;
}
// Normal free.
return state->set<RegionState>(Sym, RefState::getReleased(CE));
}
void MallocChecker::ReallocMem(CheckerContext &C, const CallExpr *CE) {
const GRState *state = C.getState();
const Expr *Arg0 = CE->getArg(0);
DefinedOrUnknownSVal Arg0Val=cast<DefinedOrUnknownSVal>(state->getSVal(Arg0));
ValueManager &ValMgr = C.getValueManager();
SValuator &SVator = C.getSValuator();
DefinedOrUnknownSVal PtrEQ = SVator.EvalEQ(state, Arg0Val, ValMgr.makeNull());
// If the ptr is NULL, the call is equivalent to malloc(size).
if (const GRState *stateEqual = state->Assume(PtrEQ, true)) {
// Hack: set the NULL symbolic region to released to suppress false warning.
// In the future we should add more states for allocated regions, e.g.,
// CheckedNull, CheckedNonNull.
SymbolRef Sym = Arg0Val.getAsLocSymbol();
if (Sym)
stateEqual = stateEqual->set<RegionState>(Sym, RefState::getReleased(CE));
const GRState *stateMalloc = MallocMemAux(C, CE, CE->getArg(1), stateEqual);
C.addTransition(stateMalloc);
}
if (const GRState *stateNotEqual = state->Assume(PtrEQ, false)) {
const Expr *Arg1 = CE->getArg(1);
DefinedOrUnknownSVal Arg1Val =
cast<DefinedOrUnknownSVal>(stateNotEqual->getSVal(Arg1));
DefinedOrUnknownSVal SizeZero = SVator.EvalEQ(stateNotEqual, Arg1Val,
ValMgr.makeIntValWithPtrWidth(0, false));
if (const GRState *stateSizeZero = stateNotEqual->Assume(SizeZero, true)) {
const GRState *stateFree = FreeMemAux(C, CE, stateSizeZero);
if (stateFree)
C.addTransition(stateFree->BindExpr(CE, UndefinedVal(), true));
}
if (const GRState *stateSizeNotZero=stateNotEqual->Assume(SizeZero,false)) {
const GRState *stateFree = FreeMemAux(C, CE, stateSizeNotZero);
if (stateFree) {
// FIXME: We should copy the content of the original buffer.
const GRState *stateRealloc = MallocMemAux(C, CE, CE->getArg(1),
stateFree);
C.addTransition(stateRealloc);
}
}
}
}
void MallocChecker::EvalDeadSymbols(CheckerContext &C, const Stmt *S,
SymbolReaper &SymReaper) {
for (SymbolReaper::dead_iterator I = SymReaper.dead_begin(),
E = SymReaper.dead_end(); I != E; ++I) {
SymbolRef Sym = *I;
const GRState *state = C.getState();
const RefState *RS = state->get<RegionState>(Sym);
if (!RS)
return;
if (RS->isAllocated()) {
ExplodedNode *N = C.GenerateSink();
if (N) {
if (!BT_Leak)
BT_Leak = new BuiltinBug("Memory leak",
"Allocated memory never released. Potential memory leak.");
// FIXME: where it is allocated.
BugReport *R = new BugReport(*BT_Leak, BT_Leak->getDescription(), N);
C.EmitReport(R);
}
}
}
}
void MallocChecker::EvalEndPath(GREndPathNodeBuilder &B, void *tag,
GRExprEngine &Eng) {
SaveAndRestore<bool> OldHasGen(B.HasGeneratedNode);
const GRState *state = B.getState();
typedef llvm::ImmutableMap<SymbolRef, RefState> SymMap;
SymMap M = state->get<RegionState>();
for (SymMap::iterator I = M.begin(), E = M.end(); I != E; ++I) {
RefState RS = I->second;
if (RS.isAllocated()) {
ExplodedNode *N = B.generateNode(state, tag, B.getPredecessor());
if (N) {
if (!BT_Leak)
BT_Leak = new BuiltinBug("Memory leak",
"Allocated memory never released. Potential memory leak.");
BugReport *R = new BugReport(*BT_Leak, BT_Leak->getDescription(), N);
Eng.getBugReporter().EmitReport(R);
}
}
}
}
void MallocChecker::PreVisitReturnStmt(CheckerContext &C, const ReturnStmt *S) {
const Expr *RetE = S->getRetValue();
if (!RetE)
return;
const GRState *state = C.getState();
SymbolRef Sym = state->getSVal(RetE).getAsSymbol();
if (!Sym)
return;
const RefState *RS = state->get<RegionState>(Sym);
if (!RS)
return;
// FIXME: check other cases.
if (RS->isAllocated())
state = state->set<RegionState>(Sym, RefState::getEscaped(S));
C.addTransition(state);
}
const GRState *MallocChecker::EvalAssume(const GRState *state, SVal Cond,
bool Assumption) {
// If a symblic region is assumed to NULL, set its state to AllocateFailed.
// FIXME: should also check symbols assumed to non-null.
RegionStateTy RS = state->get<RegionState>();
for (RegionStateTy::iterator I = RS.begin(), E = RS.end(); I != E; ++I) {
if (state->getSymVal(I.getKey()))
state = state->set<RegionState>(I.getKey(),RefState::getAllocateFailed());
}
return state;
}
// Check if the location is a freed symbolic region.
void MallocChecker::VisitLocation(CheckerContext &C, const Stmt *S, SVal l) {
SymbolRef Sym = l.getLocSymbolInBase();
if (Sym) {
const RefState *RS = C.getState()->get<RegionState>(Sym);
if (RS)
if (RS->isReleased()) {
ExplodedNode *N = C.GenerateSink();
if (!BT_UseFree)
BT_UseFree = new BuiltinBug("Use dynamically allocated memory after"
" it is freed.");
BugReport *R = new BugReport(*BT_UseFree, BT_UseFree->getDescription(),
N);
C.EmitReport(R);
}
}
}
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