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      1 //=== StackAddrEscapeChecker.cpp ----------------------------------*- C++ -*--//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file defines stack address leak checker, which checks if an invalid
     11 // stack address is stored into a global or heap location. See CERT DCL30-C.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "ClangSACheckers.h"
     16 #include "clang/AST/ExprCXX.h"
     17 #include "clang/Basic/SourceManager.h"
     18 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
     19 #include "clang/StaticAnalyzer/Core/Checker.h"
     20 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
     21 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
     22 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
     23 #include "llvm/ADT/SmallString.h"
     24 #include "llvm/Support/raw_ostream.h"
     25 using namespace clang;
     26 using namespace ento;
     27 
     28 namespace {
     29 class StackAddrEscapeChecker : public Checker< check::PreStmt<ReturnStmt>,
     30                                                check::EndFunction > {
     31   mutable OwningPtr<BuiltinBug> BT_stackleak;
     32   mutable OwningPtr<BuiltinBug> BT_returnstack;
     33 
     34 public:
     35   void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
     36   void checkEndFunction(CheckerContext &Ctx) const;
     37 private:
     38   void EmitStackError(CheckerContext &C, const MemRegion *R,
     39                       const Expr *RetE) const;
     40   static SourceRange genName(raw_ostream &os, const MemRegion *R,
     41                              ASTContext &Ctx);
     42 };
     43 }
     44 
     45 SourceRange StackAddrEscapeChecker::genName(raw_ostream &os, const MemRegion *R,
     46                                             ASTContext &Ctx) {
     47     // Get the base region, stripping away fields and elements.
     48   R = R->getBaseRegion();
     49   SourceManager &SM = Ctx.getSourceManager();
     50   SourceRange range;
     51   os << "Address of ";
     52 
     53   // Check if the region is a compound literal.
     54   if (const CompoundLiteralRegion* CR = dyn_cast<CompoundLiteralRegion>(R)) {
     55     const CompoundLiteralExpr *CL = CR->getLiteralExpr();
     56     os << "stack memory associated with a compound literal "
     57           "declared on line "
     58         << SM.getExpansionLineNumber(CL->getLocStart())
     59         << " returned to caller";
     60     range = CL->getSourceRange();
     61   }
     62   else if (const AllocaRegion* AR = dyn_cast<AllocaRegion>(R)) {
     63     const Expr *ARE = AR->getExpr();
     64     SourceLocation L = ARE->getLocStart();
     65     range = ARE->getSourceRange();
     66     os << "stack memory allocated by call to alloca() on line "
     67        << SM.getExpansionLineNumber(L);
     68   }
     69   else if (const BlockDataRegion *BR = dyn_cast<BlockDataRegion>(R)) {
     70     const BlockDecl *BD = BR->getCodeRegion()->getDecl();
     71     SourceLocation L = BD->getLocStart();
     72     range = BD->getSourceRange();
     73     os << "stack-allocated block declared on line "
     74        << SM.getExpansionLineNumber(L);
     75   }
     76   else if (const VarRegion *VR = dyn_cast<VarRegion>(R)) {
     77     os << "stack memory associated with local variable '"
     78        << VR->getString() << '\'';
     79     range = VR->getDecl()->getSourceRange();
     80   }
     81   else if (const CXXTempObjectRegion *TOR = dyn_cast<CXXTempObjectRegion>(R)) {
     82     QualType Ty = TOR->getValueType().getLocalUnqualifiedType();
     83     os << "stack memory associated with temporary object of type '";
     84     Ty.print(os, Ctx.getPrintingPolicy());
     85     os << "'";
     86     range = TOR->getExpr()->getSourceRange();
     87   }
     88   else {
     89     llvm_unreachable("Invalid region in ReturnStackAddressChecker.");
     90   }
     91 
     92   return range;
     93 }
     94 
     95 void StackAddrEscapeChecker::EmitStackError(CheckerContext &C, const MemRegion *R,
     96                                           const Expr *RetE) const {
     97   ExplodedNode *N = C.generateSink();
     98 
     99   if (!N)
    100     return;
    101 
    102   if (!BT_returnstack)
    103    BT_returnstack.reset(
    104                  new BuiltinBug("Return of address to stack-allocated memory"));
    105 
    106   // Generate a report for this bug.
    107   SmallString<512> buf;
    108   llvm::raw_svector_ostream os(buf);
    109   SourceRange range = genName(os, R, C.getASTContext());
    110   os << " returned to caller";
    111   BugReport *report = new BugReport(*BT_returnstack, os.str(), N);
    112   report->addRange(RetE->getSourceRange());
    113   if (range.isValid())
    114     report->addRange(range);
    115 
    116   C.emitReport(report);
    117 }
    118 
    119 void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
    120                                           CheckerContext &C) const {
    121 
    122   const Expr *RetE = RS->getRetValue();
    123   if (!RetE)
    124     return;
    125   RetE = RetE->IgnoreParens();
    126 
    127   const LocationContext *LCtx = C.getLocationContext();
    128   SVal V = C.getState()->getSVal(RetE, LCtx);
    129   const MemRegion *R = V.getAsRegion();
    130 
    131   if (!R)
    132     return;
    133 
    134   const StackSpaceRegion *SS =
    135     dyn_cast_or_null<StackSpaceRegion>(R->getMemorySpace());
    136 
    137   if (!SS)
    138     return;
    139 
    140   // Return stack memory in an ancestor stack frame is fine.
    141   const StackFrameContext *CurFrame = LCtx->getCurrentStackFrame();
    142   const StackFrameContext *MemFrame = SS->getStackFrame();
    143   if (MemFrame != CurFrame)
    144     return;
    145 
    146   // Automatic reference counting automatically copies blocks.
    147   if (C.getASTContext().getLangOpts().ObjCAutoRefCount &&
    148       isa<BlockDataRegion>(R))
    149     return;
    150 
    151   // Returning a record by value is fine. (In this case, the returned
    152   // expression will be a copy-constructor, possibly wrapped in an
    153   // ExprWithCleanups node.)
    154   if (const ExprWithCleanups *Cleanup = dyn_cast<ExprWithCleanups>(RetE))
    155     RetE = Cleanup->getSubExpr();
    156   if (isa<CXXConstructExpr>(RetE) && RetE->getType()->isRecordType())
    157     return;
    158 
    159   EmitStackError(C, R, RetE);
    160 }
    161 
    162 void StackAddrEscapeChecker::checkEndFunction(CheckerContext &Ctx) const {
    163   ProgramStateRef state = Ctx.getState();
    164 
    165   // Iterate over all bindings to global variables and see if it contains
    166   // a memory region in the stack space.
    167   class CallBack : public StoreManager::BindingsHandler {
    168   private:
    169     CheckerContext &Ctx;
    170     const StackFrameContext *CurSFC;
    171   public:
    172     SmallVector<std::pair<const MemRegion*, const MemRegion*>, 10> V;
    173 
    174     CallBack(CheckerContext &CC) :
    175       Ctx(CC),
    176       CurSFC(CC.getLocationContext()->getCurrentStackFrame())
    177     {}
    178 
    179     bool HandleBinding(StoreManager &SMgr, Store store,
    180                        const MemRegion *region, SVal val) {
    181 
    182       if (!isa<GlobalsSpaceRegion>(region->getMemorySpace()))
    183         return true;
    184 
    185       const MemRegion *vR = val.getAsRegion();
    186       if (!vR)
    187         return true;
    188 
    189       // Under automated retain release, it is okay to assign a block
    190       // directly to a global variable.
    191       if (Ctx.getASTContext().getLangOpts().ObjCAutoRefCount &&
    192           isa<BlockDataRegion>(vR))
    193         return true;
    194 
    195       if (const StackSpaceRegion *SSR =
    196           dyn_cast<StackSpaceRegion>(vR->getMemorySpace())) {
    197         // If the global variable holds a location in the current stack frame,
    198         // record the binding to emit a warning.
    199         if (SSR->getStackFrame() == CurSFC)
    200           V.push_back(std::make_pair(region, vR));
    201       }
    202 
    203       return true;
    204     }
    205   };
    206 
    207   CallBack cb(Ctx);
    208   state->getStateManager().getStoreManager().iterBindings(state->getStore(),cb);
    209 
    210   if (cb.V.empty())
    211     return;
    212 
    213   // Generate an error node.
    214   ExplodedNode *N = Ctx.addTransition(state);
    215   if (!N)
    216     return;
    217 
    218   if (!BT_stackleak)
    219     BT_stackleak.reset(
    220       new BuiltinBug("Stack address stored into global variable",
    221                      "Stack address was saved into a global variable. "
    222                      "This is dangerous because the address will become "
    223                      "invalid after returning from the function"));
    224 
    225   for (unsigned i = 0, e = cb.V.size(); i != e; ++i) {
    226     // Generate a report for this bug.
    227     SmallString<512> buf;
    228     llvm::raw_svector_ostream os(buf);
    229     SourceRange range = genName(os, cb.V[i].second, Ctx.getASTContext());
    230     os << " is still referred to by the global variable '";
    231     const VarRegion *VR = cast<VarRegion>(cb.V[i].first->getBaseRegion());
    232     os << *VR->getDecl()
    233        << "' upon returning to the caller.  This will be a dangling reference";
    234     BugReport *report = new BugReport(*BT_stackleak, os.str(), N);
    235     if (range.isValid())
    236       report->addRange(range);
    237 
    238     Ctx.emitReport(report);
    239   }
    240 }
    241 
    242 void ento::registerStackAddrEscapeChecker(CheckerManager &mgr) {
    243   mgr.registerChecker<StackAddrEscapeChecker>();
    244 }
    245