//==--- 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/BugReporter/BugType.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/CheckerManager.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/raw_ostream.h"
using namespace clang;
using namespace ento;
namespace {
class MacOSKeychainAPIChecker : public Checker<check::PreStmt<CallExpr>,
check::PostStmt<CallExpr>,
check::DeadSymbols> {
mutable std::unique_ptr<BugType> BT;
public:
/// AllocationState is a part of the checker specific state together with the
/// MemRegion corresponding to the allocated data.
struct AllocationState {
/// The index of the allocator function.
unsigned int AllocatorIdx;
SymbolRef Region;
AllocationState(const Expr *E, unsigned int Idx, SymbolRef R) :
AllocatorIdx(Idx),
Region(R) {}
bool operator==(const AllocationState &X) const {
return (AllocatorIdx == X.AllocatorIdx &&
Region == X.Region);
}
void Profile(llvm::FoldingSetNodeID &ID) const {
ID.AddInteger(AllocatorIdx);
ID.AddPointer(Region);
}
};
void checkPreStmt(const CallExpr *S, CheckerContext &C) const;
void checkPostStmt(const CallExpr *S, CheckerContext &C) const;
void checkDeadSymbols(SymbolReaper &SR, CheckerContext &C) const;
private:
typedef std::pair<SymbolRef, const AllocationState*> AllocationPair;
typedef SmallVector<AllocationPair, 2> AllocationPairVec;
enum APIKind {
/// Denotes functions tracked by this checker.
ValidAPI = 0,
/// The functions commonly/mistakenly used in place of the given API.
ErrorAPI = 1,
/// The functions which may allocate the data. These are tracked to reduce
/// the false alarm rate.
PossibleAPI = 2
};
/// 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;
APIKind Kind;
};
static const unsigned InvalidIdx = 100000;
static const unsigned FunctionsToTrackSize = 8;
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.
static unsigned getTrackedFunctionIndex(StringRef Name, bool IsAllocator);
inline void initBugType() const {
if (!BT)
BT.reset(new BugType(this, "Improper use of SecKeychain API",
"API Misuse (Apple)"));
}
void generateDeallocatorMismatchReport(const AllocationPair &AP,
const Expr *ArgExpr,
CheckerContext &C) const;
/// Find the allocation site for Sym on the path leading to the node N.
const ExplodedNode *getAllocationNode(const ExplodedNode *N, SymbolRef Sym,
CheckerContext &C) const;
BugReport *generateAllocatedDataNotReleasedReport(const AllocationPair &AP,
ExplodedNode *N,
CheckerContext &C) const;
/// Check if RetSym evaluates to an error value in the current state.
bool definitelyReturnedError(SymbolRef RetSym,
ProgramStateRef State,
SValBuilder &Builder,
bool noError = false) const;
/// Check if RetSym evaluates to a NoErr value in the current state.
bool definitelyDidnotReturnError(SymbolRef RetSym,
ProgramStateRef State,
SValBuilder &Builder) const {
return definitelyReturnedError(RetSym, State, Builder, true);
}
/// Mark an AllocationPair interesting for diagnostic reporting.
void markInteresting(BugReport *R, const AllocationPair &AP) const {
R->markInteresting(AP.first);
R->markInteresting(AP.second->Region);
}
/// The bug visitor which allows us to print extra diagnostics along the
/// BugReport path. For example, showing the allocation site of the leaked
/// region.
class SecKeychainBugVisitor
: public BugReporterVisitorImpl<SecKeychainBugVisitor> {
protected:
// The allocated region symbol tracked by the main analysis.
SymbolRef Sym;
public:
SecKeychainBugVisitor(SymbolRef S) : Sym(S) {}
~SecKeychainBugVisitor() override {}
void Profile(llvm::FoldingSetNodeID &ID) const override {
static int X = 0;
ID.AddPointer(&X);
ID.AddPointer(Sym);
}
PathDiagnosticPiece *VisitNode(const ExplodedNode *N,
const ExplodedNode *PrevN,
BugReporterContext &BRC,
BugReport &BR) override;
};
};
}
/// ProgramState traits to store the currently allocated (and not yet freed)
/// symbols. This is a map from the allocated content symbol to the
/// corresponding AllocationState.
REGISTER_MAP_WITH_PROGRAMSTATE(AllocatedData,
SymbolRef,
MacOSKeychainAPIChecker::AllocationState)
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, ValidAPI}, // 0
{"SecKeychainFindGenericPassword", 6, 3, ValidAPI}, // 1
{"SecKeychainFindInternetPassword", 13, 3, ValidAPI}, // 2
{"SecKeychainItemFreeContent", 1, InvalidIdx, ValidAPI}, // 3
{"SecKeychainItemCopyAttributesAndData", 5, 5, ValidAPI}, // 4
{"SecKeychainItemFreeAttributesAndData", 1, InvalidIdx, ValidAPI}, // 5
{"free", 0, InvalidIdx, ErrorAPI}, // 6
{"CFStringCreateWithBytesNoCopy", 1, InvalidIdx, PossibleAPI}, // 7
};
unsigned MacOSKeychainAPIChecker::getTrackedFunctionIndex(StringRef Name,
bool IsAllocator) {
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 bool isBadDeallocationArgument(const MemRegion *Arg) {
if (!Arg)
return false;
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) {
ProgramStateRef State = C.getState();
SVal ArgV = State->getSVal(Expr, C.getLocationContext());
if (Optional<loc::MemRegionVal> X = ArgV.getAs<loc::MemRegionVal>()) {
StoreManager& SM = C.getStoreManager();
SymbolRef sym = SM.getBinding(State->getStore(), *X).getAsLocSymbol();
if (sym)
return sym;
}
return nullptr;
}
// When checking for error code, we need to consider the following cases:
// 1) noErr / [0]
// 2) someErr / [1, inf]
// 3) unknown
// If noError, returns true iff (1).
// If !noError, returns true iff (2).
bool MacOSKeychainAPIChecker::definitelyReturnedError(SymbolRef RetSym,
ProgramStateRef State,
SValBuilder &Builder,
bool noError) const {
DefinedOrUnknownSVal NoErrVal = Builder.makeIntVal(NoErr,
Builder.getSymbolManager().getType(RetSym));
DefinedOrUnknownSVal NoErr = Builder.evalEQ(State, NoErrVal,
nonloc::SymbolVal(RetSym));
ProgramStateRef ErrState = State->assume(NoErr, noError);
if (ErrState == State) {
return true;
}
return false;
}
// Report deallocator mismatch. Remove the region from tracking - reporting a
// missing free error after this one is redundant.
void MacOSKeychainAPIChecker::
generateDeallocatorMismatchReport(const AllocationPair &AP,
const Expr *ArgExpr,
CheckerContext &C) const {
ProgramStateRef State = C.getState();
State = State->remove<AllocatedData>(AP.first);
ExplodedNode *N = C.addTransition(State);
if (!N)
return;
initBugType();
SmallString<80> sbuf;
llvm::raw_svector_ostream os(sbuf);
unsigned int PDeallocIdx =
FunctionsToTrack[AP.second->AllocatorIdx].DeallocatorIdx;
os << "Deallocator doesn't match the allocator: '"
<< FunctionsToTrack[PDeallocIdx].Name << "' should be used.";
BugReport *Report = new BugReport(*BT, os.str(), N);
Report->addVisitor(llvm::make_unique<SecKeychainBugVisitor>(AP.first));
Report->addRange(ArgExpr->getSourceRange());
markInteresting(Report, AP);
C.emitReport(Report);
}
void MacOSKeychainAPIChecker::checkPreStmt(const CallExpr *CE,
CheckerContext &C) const {
unsigned idx = InvalidIdx;
ProgramStateRef State = C.getState();
const FunctionDecl *FD = C.getCalleeDecl(CE);
if (!FD || FD->getKind() != Decl::Function)
return;
StringRef funName = C.getCalleeName(FD);
if (funName.empty())
return;
// If it is a call to an allocator function, it could be a double allocation.
idx = getTrackedFunctionIndex(funName, true);
if (idx != InvalidIdx) {
unsigned paramIdx = FunctionsToTrack[idx].Param;
if (CE->getNumArgs() <= paramIdx)
return;
const Expr *ArgExpr = CE->getArg(paramIdx);
if (SymbolRef V = getAsPointeeSymbol(ArgExpr, C))
if (const AllocationState *AS = State->get<AllocatedData>(V)) {
if (!definitelyReturnedError(AS->Region, State, C.getSValBuilder())) {
// Remove the value from the state. The new symbol will be added for
// tracking when the second allocator is processed in checkPostStmt().
State = State->remove<AllocatedData>(V);
ExplodedNode *N = C.addTransition(State);
if (!N)
return;
initBugType();
SmallString<128> sbuf;
llvm::raw_svector_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
<< "'.";
BugReport *Report = new BugReport(*BT, os.str(), N);
Report->addVisitor(llvm::make_unique<SecKeychainBugVisitor>(V));
Report->addRange(ArgExpr->getSourceRange());
Report->markInteresting(AS->Region);
C.emitReport(Report);
}
}
return;
}
// Is it a call to one of deallocator functions?
idx = getTrackedFunctionIndex(funName, false);
if (idx == InvalidIdx)
return;
unsigned paramIdx = FunctionsToTrack[idx].Param;
if (CE->getNumArgs() <= paramIdx)
return;
// Check the argument to the deallocator.
const Expr *ArgExpr = CE->getArg(paramIdx);
SVal ArgSVal = State->getSVal(ArgExpr, C.getLocationContext());
// Undef is reported by another checker.
if (ArgSVal.isUndef())
return;
SymbolRef ArgSM = ArgSVal.getAsLocSymbol();
// If the argument is coming from the heap, globals, or unknown, do not
// report it.
bool RegionArgIsBad = false;
if (!ArgSM) {
if (!isBadDeallocationArgument(ArgSVal.getAsRegion()))
return;
RegionArgIsBad = true;
}
// Is the argument to the call being tracked?
const AllocationState *AS = State->get<AllocatedData>(ArgSM);
if (!AS && FunctionsToTrack[idx].Kind != ValidAPI) {
return;
}
// If trying to free data which has not been allocated yet, report as a bug.
// TODO: We might want a more precise diagnostic for double free
// (that would involve tracking all the freed symbols in the checker state).
if (!AS || RegionArgIsBad) {
// It is possible that this is a false positive - the argument might
// have entered as an enclosing function parameter.
if (isEnclosingFunctionParam(ArgExpr))
return;
ExplodedNode *N = C.addTransition(State);
if (!N)
return;
initBugType();
BugReport *Report = new BugReport(*BT,
"Trying to free data which has not been allocated.", N);
Report->addRange(ArgExpr->getSourceRange());
if (AS)
Report->markInteresting(AS->Region);
C.emitReport(Report);
return;
}
// Process functions which might deallocate.
if (FunctionsToTrack[idx].Kind == PossibleAPI) {
if (funName == "CFStringCreateWithBytesNoCopy") {
const Expr *DeallocatorExpr = CE->getArg(5)->IgnoreParenCasts();
// NULL ~ default deallocator, so warn.
if (DeallocatorExpr->isNullPointerConstant(C.getASTContext(),
Expr::NPC_ValueDependentIsNotNull)) {
const AllocationPair AP = std::make_pair(ArgSM, AS);
generateDeallocatorMismatchReport(AP, ArgExpr, C);
return;
}
// One of the default allocators, so warn.
if (const DeclRefExpr *DE = dyn_cast<DeclRefExpr>(DeallocatorExpr)) {
StringRef DeallocatorName = DE->getFoundDecl()->getName();
if (DeallocatorName == "kCFAllocatorDefault" ||
DeallocatorName == "kCFAllocatorSystemDefault" ||
DeallocatorName == "kCFAllocatorMalloc") {
const AllocationPair AP = std::make_pair(ArgSM, AS);
generateDeallocatorMismatchReport(AP, ArgExpr, C);
return;
}
// If kCFAllocatorNull, which does not deallocate, we still have to
// find the deallocator.
if (DE->getFoundDecl()->getName() == "kCFAllocatorNull")
return;
}
// In all other cases, assume the user supplied a correct deallocator
// that will free memory so stop tracking.
State = State->remove<AllocatedData>(ArgSM);
C.addTransition(State);
return;
}
llvm_unreachable("We know of no other possible APIs.");
}
// The call is deallocating a value we previously allocated, so remove it
// from the next state.
State = State->remove<AllocatedData>(ArgSM);
// Check if the proper deallocator is used.
unsigned int PDeallocIdx = FunctionsToTrack[AS->AllocatorIdx].DeallocatorIdx;
if (PDeallocIdx != idx || (FunctionsToTrack[idx].Kind == ErrorAPI)) {
const AllocationPair AP = std::make_pair(ArgSM, AS);
generateDeallocatorMismatchReport(AP, ArgExpr, C);
return;
}
// If the buffer can be null and the return status can be an error,
// report a bad call to free.
if (State->assume(ArgSVal.castAs<DefinedSVal>(), false) &&
!definitelyDidnotReturnError(AS->Region, State, C.getSValBuilder())) {
ExplodedNode *N = C.addTransition(State);
if (!N)
return;
initBugType();
BugReport *Report = new BugReport(*BT,
"Only call free if a valid (non-NULL) buffer was returned.", N);
Report->addVisitor(llvm::make_unique<SecKeychainBugVisitor>(ArgSM));
Report->addRange(ArgExpr->getSourceRange());
Report->markInteresting(AS->Region);
C.emitReport(Report);
return;
}
C.addTransition(State);
}
void MacOSKeychainAPIChecker::checkPostStmt(const CallExpr *CE,
CheckerContext &C) const {
ProgramStateRef State = C.getState();
const FunctionDecl *FD = C.getCalleeDecl(CE);
if (!FD || FD->getKind() != Decl::Function)
return;
StringRef funName = C.getCalleeName(FD);
// If a value has been allocated, add it to the set for tracking.
unsigned idx = getTrackedFunctionIndex(funName, true);
if (idx == InvalidIdx)
return;
const Expr *ArgExpr = CE->getArg(FunctionsToTrack[idx].Param);
// If the argument entered as an enclosing function parameter, skip it to
// avoid false positives.
if (isEnclosingFunctionParam(ArgExpr) &&
C.getLocationContext()->getParent() == nullptr)
return;
if (SymbolRef V = getAsPointeeSymbol(ArgExpr, C)) {
// If the argument points to something that's not a symbolic region, it
// can be:
// - unknown (cannot reason about it)
// - undefined (already reported by other checker)
// - constant (null - should not be tracked,
// other constant will generate a compiler warning)
// - goto (should be reported by other checker)
// The call return value symbol should stay alive for as long as the
// allocated value symbol, since our diagnostics depend on the value
// returned by the call. Ex: Data should only be freed if noErr was
// returned during allocation.)
SymbolRef RetStatusSymbol =
State->getSVal(CE, C.getLocationContext()).getAsSymbol();
C.getSymbolManager().addSymbolDependency(V, RetStatusSymbol);
// Track the allocated value in the checker state.
State = State->set<AllocatedData>(V, AllocationState(ArgExpr, idx,
RetStatusSymbol));
assert(State);
C.addTransition(State);
}
}
// TODO: This logic is the same as in Malloc checker.
const ExplodedNode *
MacOSKeychainAPIChecker::getAllocationNode(const ExplodedNode *N,
SymbolRef Sym,
CheckerContext &C) const {
const LocationContext *LeakContext = N->getLocationContext();
// Walk the ExplodedGraph backwards and find the first node that referred to
// the tracked symbol.
const ExplodedNode *AllocNode = N;
while (N) {
if (!N->getState()->get<AllocatedData>(Sym))
break;
// Allocation node, is the last node in the current or parent context in
// which the symbol was tracked.
const LocationContext *NContext = N->getLocationContext();
if (NContext == LeakContext ||
NContext->isParentOf(LeakContext))
AllocNode = N;
N = N->pred_empty() ? nullptr : *(N->pred_begin());
}
return AllocNode;
}
BugReport *MacOSKeychainAPIChecker::
generateAllocatedDataNotReleasedReport(const AllocationPair &AP,
ExplodedNode *N,
CheckerContext &C) const {
const ADFunctionInfo &FI = FunctionsToTrack[AP.second->AllocatorIdx];
initBugType();
SmallString<70> sbuf;
llvm::raw_svector_ostream os(sbuf);
os << "Allocated data is not released: missing a call to '"
<< FunctionsToTrack[FI.DeallocatorIdx].Name << "'.";
// Most bug reports are cached at the location where they occurred.
// With leaks, we want to unique them by the location where they were
// allocated, and only report a single path.
PathDiagnosticLocation LocUsedForUniqueing;
const ExplodedNode *AllocNode = getAllocationNode(N, AP.first, C);
const Stmt *AllocStmt = nullptr;
ProgramPoint P = AllocNode->getLocation();
if (Optional<CallExitEnd> Exit = P.getAs<CallExitEnd>())
AllocStmt = Exit->getCalleeContext()->getCallSite();
else if (Optional<clang::PostStmt> PS = P.getAs<clang::PostStmt>())
AllocStmt = PS->getStmt();
if (AllocStmt)
LocUsedForUniqueing = PathDiagnosticLocation::createBegin(AllocStmt,
C.getSourceManager(),
AllocNode->getLocationContext());
BugReport *Report = new BugReport(*BT, os.str(), N, LocUsedForUniqueing,
AllocNode->getLocationContext()->getDecl());
Report->addVisitor(llvm::make_unique<SecKeychainBugVisitor>(AP.first));
markInteresting(Report, AP);
return Report;
}
void MacOSKeychainAPIChecker::checkDeadSymbols(SymbolReaper &SR,
CheckerContext &C) const {
ProgramStateRef State = C.getState();
AllocatedDataTy ASet = State->get<AllocatedData>();
if (ASet.isEmpty())
return;
bool Changed = false;
AllocationPairVec Errors;
for (AllocatedDataTy::iterator I = ASet.begin(), E = ASet.end(); I != E; ++I) {
if (SR.isLive(I->first))
continue;
Changed = true;
State = State->remove<AllocatedData>(I->first);
// If the allocated symbol is null or if the allocation call might have
// returned an error, do not report.
ConstraintManager &CMgr = State->getConstraintManager();
ConditionTruthVal AllocFailed = CMgr.isNull(State, I.getKey());
if (AllocFailed.isConstrainedTrue() ||
definitelyReturnedError(I->second.Region, State, C.getSValBuilder()))
continue;
Errors.push_back(std::make_pair(I->first, &I->second));
}
if (!Changed) {
// Generate the new, cleaned up state.
C.addTransition(State);
return;
}
static CheckerProgramPointTag Tag(this, "DeadSymbolsLeak");
ExplodedNode *N = C.addTransition(C.getState(), C.getPredecessor(), &Tag);
// Generate the error reports.
for (AllocationPairVec::iterator I = Errors.begin(), E = Errors.end();
I != E; ++I) {
C.emitReport(generateAllocatedDataNotReleasedReport(*I, N, C));
}
// Generate the new, cleaned up state.
C.addTransition(State, N);
}
PathDiagnosticPiece *MacOSKeychainAPIChecker::SecKeychainBugVisitor::VisitNode(
const ExplodedNode *N,
const ExplodedNode *PrevN,
BugReporterContext &BRC,
BugReport &BR) {
const AllocationState *AS = N->getState()->get<AllocatedData>(Sym);
if (!AS)
return nullptr;
const AllocationState *ASPrev = PrevN->getState()->get<AllocatedData>(Sym);
if (ASPrev)
return nullptr;
// (!ASPrev && AS) ~ We started tracking symbol in node N, it must be the
// allocation site.
const CallExpr *CE =
cast<CallExpr>(N->getLocation().castAs<StmtPoint>().getStmt());
const FunctionDecl *funDecl = CE->getDirectCallee();
assert(funDecl && "We do not support indirect function calls as of now.");
StringRef funName = funDecl->getName();
// Get the expression of the corresponding argument.
unsigned Idx = getTrackedFunctionIndex(funName, true);
assert(Idx != InvalidIdx && "This should be a call to an allocator.");
const Expr *ArgExpr = CE->getArg(FunctionsToTrack[Idx].Param);
PathDiagnosticLocation Pos(ArgExpr, BRC.getSourceManager(),
N->getLocationContext());
return new PathDiagnosticEventPiece(Pos, "Data is allocated here.");
}
void ento::registerMacOSKeychainAPIChecker(CheckerManager &mgr) {
mgr.registerChecker<MacOSKeychainAPIChecker>();
}