path: root/lib/StaticAnalyzer/Checkers/MacOSKeychainAPIChecker.cpp

//==--- MacOSKeychainAPIChecker.cpp ------------------------------*- C++ -*-==//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
// This checker flags misuses of KeyChainAPI. In particular, the password data
// allocated/returned by SecKeychainItemCopyContent,
// SecKeychainFindGenericPassword, SecKeychainFindInternetPassword functions has
// to be freed using a call to SecKeychainItemFreeContent.
//===----------------------------------------------------------------------===//

#include "ClangSACheckers.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/CheckerManager.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/GRState.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/GRStateTrait.h"

using namespace clang;
using namespace ento;

namespace {
class MacOSKeychainAPIChecker : public Checker<check::PreStmt<CallExpr>,
                                               check::PreStmt<ReturnStmt>,
                                               check::PostStmt<CallExpr>,
                                               check::EndPath > {
  mutable llvm::OwningPtr<BugType> BT;

public:
  /// AllocationState is a part of the checker specific state together with the
  /// MemRegion corresponding to the allocated data.
  struct AllocationState {
    const Expr *Address;
    /// The index of the allocator function.
    unsigned int AllocatorIdx;
    SymbolRef RetValue;

    AllocationState(const Expr *E, unsigned int Idx, SymbolRef R) :
      Address(E),
      AllocatorIdx(Idx),
      RetValue(R) {}

    bool operator==(const AllocationState &X) const {
      return Address == X.Address;
    }
    void Profile(llvm::FoldingSetNodeID &ID) const {
      ID.AddPointer(Address);
      ID.AddInteger(AllocatorIdx);
    }
  };

  void checkPreStmt(const CallExpr *S, CheckerContext &C) const;
  void checkPreStmt(const ReturnStmt *S, CheckerContext &C) const;
  void checkPostStmt(const CallExpr *S, CheckerContext &C) const;

  void checkEndPath(EndOfFunctionNodeBuilder &B, ExprEngine &Eng) const;

private:
  /// Stores the information about the allocator and deallocator functions -
  /// these are the functions the checker is tracking.
  struct ADFunctionInfo {
    const char* Name;
    unsigned int Param;
    unsigned int DeallocatorIdx;
  };
  static const unsigned InvalidIdx = 100000;
  static const unsigned FunctionsToTrackSize = 6;
  static const ADFunctionInfo FunctionsToTrack[FunctionsToTrackSize];
  /// The value, which represents no error return value for allocator functions.
  static const unsigned NoErr = 0;

  /// Given the function name, returns the index of the allocator/deallocator
  /// function.
  unsigned getTrackedFunctionIndex(StringRef Name, bool IsAllocator) const;

  inline void initBugType() const {
    if (!BT)
      BT.reset(new BugType("Improper use of SecKeychain API", "Mac OS API"));
  }
};
}

/// GRState traits to store the currently allocated (and not yet freed) symbols.
/// This is a map from the allocated content symbol to the corresponding
/// AllocationState.
typedef llvm::ImmutableMap<SymbolRef,
                       MacOSKeychainAPIChecker::AllocationState> AllocatedSetTy;

namespace { struct AllocatedData {}; }
namespace clang { namespace ento {
template<> struct GRStateTrait<AllocatedData>
    :  public GRStatePartialTrait<AllocatedSetTy > {
  static void *GDMIndex() { static int index = 0; return &index; }
};
}}

static bool isEnclosingFunctionParam(const Expr *E) {
  E = E->IgnoreParenCasts();
  if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E)) {
    const ValueDecl *VD = DRE->getDecl();
    if (isa<ImplicitParamDecl>(VD) || isa<ParmVarDecl>(VD))
      return true;
  }
  return false;
}

const MacOSKeychainAPIChecker::ADFunctionInfo
  MacOSKeychainAPIChecker::FunctionsToTrack[FunctionsToTrackSize] = {
    {"SecKeychainItemCopyContent", 4, 3},                       // 0
    {"SecKeychainFindGenericPassword", 6, 3},                   // 1
    {"SecKeychainFindInternetPassword", 13, 3},                 // 2
    {"SecKeychainItemFreeContent", 1, InvalidIdx},              // 3
    {"SecKeychainItemCopyAttributesAndData", 5, 5},             // 4
    {"SecKeychainItemFreeAttributesAndData", 1, InvalidIdx},    // 5
};

unsigned MacOSKeychainAPIChecker::getTrackedFunctionIndex(StringRef Name,
                                                       bool IsAllocator) const {
  for (unsigned I = 0; I < FunctionsToTrackSize; ++I) {
    ADFunctionInfo FI = FunctionsToTrack[I];
    if (FI.Name != Name)
      continue;
    // Make sure the function is of the right type (allocator vs deallocator).
    if (IsAllocator && (FI.DeallocatorIdx == InvalidIdx))
      return InvalidIdx;
    if (!IsAllocator && (FI.DeallocatorIdx != InvalidIdx))
      return InvalidIdx;

    return I;
  }
  // The function is not tracked.
  return InvalidIdx;
}

static SymbolRef getSymbolForRegion(CheckerContext &C,
                                   const MemRegion *R) {
  if (!isa<SymbolicRegion>(R))
    return 0;
  return cast<SymbolicRegion>(R)->getSymbol();
}

static bool isBadDeallocationArgument(const MemRegion *Arg) {
  if (isa<AllocaRegion>(Arg) ||
      isa<BlockDataRegion>(Arg) ||
      isa<TypedRegion>(Arg)) {
    return true;
  }
  return false;
}
/// Given the address expression, retrieve the value it's pointing to. Assume
/// that value is itself an address, and return the corresponding symbol.
static SymbolRef getAsPointeeSymbol(const Expr *Expr,
                                    CheckerContext &C) {
  const GRState *State = C.getState();
  SVal ArgV = State->getSVal(Expr);

  if (const loc::MemRegionVal *X = dyn_cast<loc::MemRegionVal>(&ArgV)) {
    StoreManager& SM = C.getStoreManager();
    const MemRegion *V = SM.Retrieve(State->getStore(), *X).getAsRegion();
    if (V)
      return getSymbolForRegion(C, V);
  }
  return 0;
}

void MacOSKeychainAPIChecker::checkPreStmt(const CallExpr *CE,
                                           CheckerContext &C) const {
  const GRState *State = C.getState();
  const Expr *Callee = CE->getCallee();
  SVal L = State->getSVal(Callee);
  unsigned idx = InvalidIdx;

  const FunctionDecl *funDecl = L.getAsFunctionDecl();
  if (!funDecl)
    return;
  IdentifierInfo *funI = funDecl->getIdentifier();
  if (!funI)
    return;
  StringRef funName = funI->getName();

  // If it is a call to an allocator function, it could be a double allocation.
  idx = getTrackedFunctionIndex(funName, true);
  if (idx != InvalidIdx) {
    const Expr *ArgExpr = CE->getArg(FunctionsToTrack[idx].Param);
    if (SymbolRef V = getAsPointeeSymbol(ArgExpr, C))
      if (const AllocationState *AS = State->get<AllocatedData>(V)) {
        ExplodedNode *N = C.generateSink(State);
        if (!N)
          return;
        initBugType();
        std::string sbuf;
        llvm::raw_string_ostream os(sbuf);
        unsigned int DIdx = FunctionsToTrack[AS->AllocatorIdx].DeallocatorIdx;
        os << "Allocated data should be released before another call to "
           << "the allocator: missing a call to '"
           << FunctionsToTrack[DIdx].Name
           << "'.";
        RangedBugReport *Report = new RangedBugReport(*BT, os.str(), N);
        Report->addRange(ArgExpr->getSourceRange());
        C.EmitReport(Report);
      }
    return;
  }

  // Is it a call to one of deallocator functions?
  idx = getTrackedFunctionIndex(funName, false);
  if (idx == InvalidIdx)
    return;

  // Check the argument to the deallocator.
  const Expr *ArgExpr = CE->getArg(FunctionsToTrack[idx].Param);
  SVal ArgSVal = State->getSVal(ArgExpr);

  // Undef is reported by another checker.
  if