StackAddrLeakChecker.cpp

//=== StackAddrLeakChecker.cpp ------------------------------------*- 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 stack address leak checker, which checks if an invalid 
// stack address is stored into a global or heap location. See CERT DCL30-C.
//
//===----------------------------------------------------------------------===//

#include "GRExprEngineInternalChecks.h"
#include "clang/Checker/BugReporter/BugType.h"
#include "clang/Checker/PathSensitive/CheckerVisitor.h"
#include "clang/Checker/PathSensitive/GRState.h"
#include "clang/Basic/SourceManager.h"
#include "llvm/ADT/SmallString.h"
using namespace clang;

namespace {
class StackAddrLeakChecker : public CheckerVisitor<StackAddrLeakChecker> {
  BuiltinBug *BT_stackleak;
  BuiltinBug *BT_returnstack;

public:
  StackAddrLeakChecker() : BT_stackleak(0), BT_returnstack(0) {}
  static void *getTag() {
    static int x;
    return &x;
  }
  void PreVisitReturnStmt(CheckerContext &C, const ReturnStmt *RS);
  void EvalEndPath(GREndPathNodeBuilder &B, void *tag, GRExprEngine &Eng);
private:
  void EmitStackError(CheckerContext &C, const MemRegion *R, const Expr *RetE);
};
}

void clang::RegisterStackAddrLeakChecker(GRExprEngine &Eng) {
  Eng.registerCheck(new StackAddrLeakChecker());
}
void StackAddrLeakChecker::EmitStackError(CheckerContext &C, const MemRegion *R,
                                          const Expr *RetE) {
  ExplodedNode *N = C.GenerateSink();

  if (!N)
    return;

  if (!BT_returnstack)
   BT_returnstack=new BuiltinBug("Return of address to stack-allocated memory");

  // Generate a report for this bug.
  llvm::SmallString<512> buf;
  llvm::raw_svector_ostream os(buf);
  SourceRange range;

  // Get the base region, stripping away fields and elements.
  R = R->getBaseRegion();

  // Check if the region is a compound literal.
  if (const CompoundLiteralRegion* CR = dyn_cast<CompoundLiteralRegion>(R)) { 
    const CompoundLiteralExpr* CL = CR->getLiteralExpr();
    os << "Address of stack memory associated with a compound literal "
      "declared on line "
       << C.getSourceManager().getInstantiationLineNumber(CL->getLocStart())
       << " returned to caller";    
    range = CL->getSourceRange();
  }
  else if (const AllocaRegion* AR = dyn_cast<AllocaRegion>(R)) {
    const Expr* ARE = AR->getExpr();
    SourceLocation L = ARE->getLocStart();
    range = ARE->getSourceRange();    
    os << "Address of stack memory allocated by call to alloca() on line "
       << C.getSourceManager().getInstantiationLineNumber(L)
       << " returned to caller";
  }
  else if (const BlockDataRegion *BR = dyn_cast<BlockDataRegion>(R)) {
    const BlockDecl *BD = BR->getCodeRegion()->getDecl();
    SourceLocation L = BD->getLocStart();
    range = BD->getSourceRange();
    os << "Address of stack-allocated block declared on line "
       << C.getSourceManager().getInstantiationLineNumber(L)
       << " returned to caller";
  }
  else if (const VarRegion *VR = dyn_cast<VarRegion>(R)) {
    os << "Address of stack memory associated with local variable '"
       << VR->getString() << "' returned";
    range = VR->getDecl()->getSourceRange();
  }
  else {
    assert(false && "Invalid region in ReturnStackAddressChecker.");
    return;
  }

  RangedBugReport *report = new RangedBugReport(*BT_returnstack, os.str(), N);
  report->addRange(RetE->getSourceRange());
  if (range.isValid())
    report->addRange(range);

  C.EmitReport(report);
}	

void StackAddrLeakChecker::PreVisitReturnStmt(CheckerContext &C,
                                              const ReturnStmt *RS) {
  
  const Expr *RetE = RS->getRetValue();
  if (!RetE)
    return;
 
  SVal V = C.getState()->getSVal(RetE);
  const MemRegion *R = V.getAsRegion();

  if (!R || !R->hasStackStorage())
    return;  
  
  if (R->hasStackStorage()) {
    EmitStackError(C, R, RetE);
    return;
  }
}

void StackAddrLeakChecker::EvalEndPath(GREndPathNodeBuilder &B, void *tag,
                                       GRExprEngine &Eng) {
  SaveAndRestore<bool> OldHasGen(B.HasGeneratedNode);
  const GRState *state = B.getState();
  TranslationUnitDecl *TU = Eng.getContext().getTranslationUnitDecl();

  // Check each global variable if it contains a MemRegionVal of a stack
  // variable declared in the function we are leaving.
  for (DeclContext::decl_iterator I = TU->decls_begin(), E = TU->decls_end();
       I != E; ++I) {
    if (VarDecl *VD = dyn_cast<VarDecl>(*I)) {
      const LocationContext *LCtx = B.getPredecessor()->getLocationContext();
      Loc L = state->getLValue(VD, LCtx);
      SVal V = state->getSVal(L);
      if (loc::MemRegionVal *RV = dyn_cast<loc::MemRegionVal>(&V)) {
        const MemRegion *R = RV->getRegion();

        if (const StackSpaceRegion *SSR = 
                              dyn_cast<StackSpaceRegion>(R->getMemorySpace())) {
          const StackFrameContext *ValSFC = SSR->getStackFrame();
          const StackFrameContext *CurSFC = LCtx->getCurrentStackFrame();
          // If the global variable holds a location in the current stack frame,
          // emit a warning.
          if (ValSFC == CurSFC) {
            // The variable is declared in the function scope which we are 
            // leaving. Keeping this variable's address in a global variable
            // is dangerous.

            // FIXME: better warning location.
            
            ExplodedNode *N = B.generateNode(state, tag, B.getPredecessor());
            if (N) {
              if (!BT_stackleak)
                BT_stackleak = new BuiltinBug("Stack address leak",
                        "Stack address was saved into a global variable. "
                        "is dangerous because the address will become invalid "
                        "after returning from the function.");
              BugReport *R = new BugReport(*BT_stackleak, 
                                           BT_stackleak->getDescription(), N);
              Eng.getBugReporter().EmitReport(R);
            }
          }
        }
      }
    }
  }
}