lib/Checker/MallocChecker.cpp

//=== 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();

  // Various cases could lead to non-symbol values here.
  if (!Sym)
    return state;

  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);
      }
  }
}