//= CStringChecker.cpp - Checks calls to C string functions --------*- C++ -*-// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// // // This defines CStringChecker, which is an assortment of checks on calls // to functions in . // //===----------------------------------------------------------------------===// #include "InterCheckerAPI.h" #include "clang/Basic/CharInfo.h" #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.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/CallDescription.h" #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h" #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" #include "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h" #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallString.h" #include "llvm/ADT/StringExtras.h" #include "llvm/Support/raw_ostream.h" using namespace clang; using namespace ento; namespace { struct AnyArgExpr { // FIXME: Remove constructor in C++17 to turn it into an aggregate. AnyArgExpr(const Expr *Expression, unsigned ArgumentIndex) : Expression{Expression}, ArgumentIndex{ArgumentIndex} {} const Expr *Expression; unsigned ArgumentIndex; }; struct SourceArgExpr : AnyArgExpr { using AnyArgExpr::AnyArgExpr; // FIXME: Remove using in C++17. }; struct DestinationArgExpr : AnyArgExpr { using AnyArgExpr::AnyArgExpr; // FIXME: Same. }; struct SizeArgExpr : AnyArgExpr { using AnyArgExpr::AnyArgExpr; // FIXME: Same. }; using ErrorMessage = SmallString<128>; enum class AccessKind { write, read }; static ErrorMessage createOutOfBoundErrorMsg(StringRef FunctionDescription, AccessKind Access) { ErrorMessage Message; llvm::raw_svector_ostream Os(Message); // Function classification like: Memory copy function Os << toUppercase(FunctionDescription.front()) << &FunctionDescription.data()[1]; if (Access == AccessKind::write) { Os << " overflows the destination buffer"; } else { // read access Os << " accesses out-of-bound array element"; } return Message; } enum class ConcatFnKind { none = 0, strcat = 1, strlcat = 2 }; class CStringChecker : public Checker< eval::Call, check::PreStmt, check::LiveSymbols, check::DeadSymbols, check::RegionChanges > { mutable std::unique_ptr BT_Null, BT_Bounds, BT_Overlap, BT_NotCString, BT_AdditionOverflow; mutable const char *CurrentFunctionDescription; public: /// The filter is used to filter out the diagnostics which are not enabled by /// the user. struct CStringChecksFilter { DefaultBool CheckCStringNullArg; DefaultBool CheckCStringOutOfBounds; DefaultBool CheckCStringBufferOverlap; DefaultBool CheckCStringNotNullTerm; CheckerNameRef CheckNameCStringNullArg; CheckerNameRef CheckNameCStringOutOfBounds; CheckerNameRef CheckNameCStringBufferOverlap; CheckerNameRef CheckNameCStringNotNullTerm; }; CStringChecksFilter Filter; static void *getTag() { static int tag; return &tag; } bool evalCall(const CallEvent &Call, CheckerContext &C) const; void checkPreStmt(const DeclStmt *DS, CheckerContext &C) const; void checkLiveSymbols(ProgramStateRef state, SymbolReaper &SR) const; void checkDeadSymbols(SymbolReaper &SR, CheckerContext &C) const; ProgramStateRef checkRegionChanges(ProgramStateRef state, const InvalidatedSymbols *, ArrayRef ExplicitRegions, ArrayRef Regions, const LocationContext *LCtx, const CallEvent *Call) const; typedef void (CStringChecker::*FnCheck)(CheckerContext &, const CallExpr *) const; CallDescriptionMap Callbacks = { {{CDF_MaybeBuiltin, "memcpy", 3}, &CStringChecker::evalMemcpy}, {{CDF_MaybeBuiltin, "mempcpy", 3}, &CStringChecker::evalMempcpy}, {{CDF_MaybeBuiltin, "memcmp", 3}, &CStringChecker::evalMemcmp}, {{CDF_MaybeBuiltin, "memmove", 3}, &CStringChecker::evalMemmove}, {{CDF_MaybeBuiltin, "memset", 3}, &CStringChecker::evalMemset}, {{CDF_MaybeBuiltin, "explicit_memset", 3}, &CStringChecker::evalMemset}, {{CDF_MaybeBuiltin, "strcpy", 2}, &CStringChecker::evalStrcpy}, {{CDF_MaybeBuiltin, "strncpy", 3}, &CStringChecker::evalStrncpy}, {{CDF_MaybeBuiltin, "stpcpy", 2}, &CStringChecker::evalStpcpy}, {{CDF_MaybeBuiltin, "strlcpy", 3}, &CStringChecker::evalStrlcpy}, {{CDF_MaybeBuiltin, "strcat", 2}, &CStringChecker::evalStrcat}, {{CDF_MaybeBuiltin, "strncat", 3}, &CStringChecker::evalStrncat}, {{CDF_MaybeBuiltin, "strlcat", 3}, &CStringChecker::evalStrlcat}, {{CDF_MaybeBuiltin, "strlen", 1}, &CStringChecker::evalstrLength}, {{CDF_MaybeBuiltin, "strnlen", 2}, &CStringChecker::evalstrnLength}, {{CDF_MaybeBuiltin, "strcmp", 2}, &CStringChecker::evalStrcmp}, {{CDF_MaybeBuiltin, "strncmp", 3}, &CStringChecker::evalStrncmp}, {{CDF_MaybeBuiltin, "strcasecmp", 2}, &CStringChecker::evalStrcasecmp}, {{CDF_MaybeBuiltin, "strncasecmp", 3}, &CStringChecker::evalStrncasecmp}, {{CDF_MaybeBuiltin, "strsep", 2}, &CStringChecker::evalStrsep}, {{CDF_MaybeBuiltin, "bcopy", 3}, &CStringChecker::evalBcopy}, {{CDF_MaybeBuiltin, "bcmp", 3}, &CStringChecker::evalMemcmp}, {{CDF_MaybeBuiltin, "bzero", 2}, &CStringChecker::evalBzero}, {{CDF_MaybeBuiltin, "explicit_bzero", 2}, &CStringChecker::evalBzero}, }; // These require a bit of special handling. CallDescription StdCopy{{"std", "copy"}, 3}, StdCopyBackward{{"std", "copy_backward"}, 3}; FnCheck identifyCall(const CallEvent &Call, CheckerContext &C) const; void evalMemcpy(CheckerContext &C, const CallExpr *CE) const; void evalMempcpy(CheckerContext &C, const CallExpr *CE) const; void evalMemmove(CheckerContext &C, const CallExpr *CE) const; void evalBcopy(CheckerContext &C, const CallExpr *CE) const; void evalCopyCommon(CheckerContext &C, const CallExpr *CE, ProgramStateRef state, SizeArgExpr Size, DestinationArgExpr Dest, SourceArgExpr Source, bool Restricted, bool IsMempcpy) const; void evalMemcmp(CheckerContext &C, const CallExpr *CE) const; void evalstrLength(CheckerContext &C, const CallExpr *CE) const; void evalstrnLength(CheckerContext &C, const CallExpr *CE) const; void evalstrLengthCommon(CheckerContext &C, const CallExpr *CE, bool IsStrnlen = false) const; void evalStrcpy(CheckerContext &C, const CallExpr *CE) const; void evalStrncpy(CheckerContext &C, const CallExpr *CE) const; void evalStpcpy(CheckerContext &C, const CallExpr *CE) const; void evalStrlcpy(CheckerContext &C, const CallExpr *CE) const; void evalStrcpyCommon(CheckerContext &C, const CallExpr *CE, bool ReturnEnd, bool IsBounded, ConcatFnKind appendK, bool returnPtr = true) const; void evalStrcat(CheckerContext &C, const CallExpr *CE) const; void evalStrncat(CheckerContext &C, const CallExpr *CE) const; void evalStrlcat(CheckerContext &C, const CallExpr *CE) const; void evalStrcmp(CheckerContext &C, const CallExpr *CE) const; void evalStrncmp(CheckerContext &C, const CallExpr *CE) const; void evalStrcasecmp(CheckerContext &C, const CallExpr *CE) const; void evalStrncasecmp(CheckerContext &C, const CallExpr *CE) const; void evalStrcmpCommon(CheckerContext &C, const CallExpr *CE, bool IsBounded = false, bool IgnoreCase = false) const; void evalStrsep(CheckerContext &C, const CallExpr *CE) const; void evalStdCopy(CheckerContext &C, const CallExpr *CE) const; void evalStdCopyBackward(CheckerContext &C, const CallExpr *CE) const; void evalStdCopyCommon(CheckerContext &C, const CallExpr *CE) const; void evalMemset(CheckerContext &C, const CallExpr *CE) const; void evalBzero(CheckerContext &C, const CallExpr *CE) const; // Utility methods std::pair static assumeZero(CheckerContext &C, ProgramStateRef state, SVal V, QualType Ty); static ProgramStateRef setCStringLength(ProgramStateRef state, const MemRegion *MR, SVal strLength); static SVal getCStringLengthForRegion(CheckerContext &C, ProgramStateRef &state, const Expr *Ex, const MemRegion *MR, bool hypothetical); SVal getCStringLength(CheckerContext &C, ProgramStateRef &state, const Expr *Ex, SVal Buf, bool hypothetical = false) const; const StringLiteral *getCStringLiteral(CheckerContext &C, ProgramStateRef &state, const Expr *expr, SVal val) const; static ProgramStateRef InvalidateBuffer(CheckerContext &C, ProgramStateRef state, const Expr *Ex, SVal V, bool IsSourceBuffer, const Expr *Size); static bool SummarizeRegion(raw_ostream &os, ASTContext &Ctx, const MemRegion *MR); static bool memsetAux(const Expr *DstBuffer, SVal CharE, const Expr *Size, CheckerContext &C, ProgramStateRef &State); // Re-usable checks ProgramStateRef checkNonNull(CheckerContext &C, ProgramStateRef State, AnyArgExpr Arg, SVal l) const; ProgramStateRef CheckLocation(CheckerContext &C, ProgramStateRef state, AnyArgExpr Buffer, SVal Element, AccessKind Access) const; ProgramStateRef CheckBufferAccess(CheckerContext &C, ProgramStateRef State, AnyArgExpr Buffer, SizeArgExpr Size, AccessKind Access) const; ProgramStateRef CheckOverlap(CheckerContext &C, ProgramStateRef state, SizeArgExpr Size, AnyArgExpr First, AnyArgExpr Second) const; void emitOverlapBug(CheckerContext &C, ProgramStateRef state, const Stmt *First, const Stmt *Second) const; void emitNullArgBug(CheckerContext &C, ProgramStateRef State, const Stmt *S, StringRef WarningMsg) const; void emitOutOfBoundsBug(CheckerContext &C, ProgramStateRef State, const Stmt *S, StringRef WarningMsg) const; void emitNotCStringBug(CheckerContext &C, ProgramStateRef State, const Stmt *S, StringRef WarningMsg) const; void emitAdditionOverflowBug(CheckerContext &C, ProgramStateRef State) const; ProgramStateRef checkAdditionOverflow(CheckerContext &C, ProgramStateRef state, NonLoc left, NonLoc right) const; // Return true if the destination buffer of the copy function may be in bound. // Expects SVal of Size to be positive and unsigned. // Expects SVal of FirstBuf to be a FieldRegion. static bool IsFirstBufInBound(CheckerContext &C, ProgramStateRef state, const Expr *FirstBuf, const Expr *Size); }; } //end anonymous namespace REGISTER_MAP_WITH_PROGRAMSTATE(CStringLength, const MemRegion *, SVal) //===----------------------------------------------------------------------===// // Individual checks and utility methods. //===----------------------------------------------------------------------===// std::pair CStringChecker::assumeZero(CheckerContext &C, ProgramStateRef state, SVal V, QualType Ty) { Optional val = V.getAs(); if (!val) return std::pair(state, state); SValBuilder &svalBuilder = C.getSValBuilder(); DefinedOrUnknownSVal zero = svalBuilder.makeZeroVal(Ty); return state->assume(svalBuilder.evalEQ(state, *val, zero)); } ProgramStateRef CStringChecker::checkNonNull(CheckerContext &C, ProgramStateRef State, AnyArgExpr Arg, SVal l) const { // If a previous check has failed, propagate the failure. if (!State) return nullptr; ProgramStateRef stateNull, stateNonNull; std::tie(stateNull, stateNonNull) = assumeZero(C, State, l, Arg.Expression->getType()); if (stateNull && !stateNonNull) { if (Filter.CheckCStringNullArg) { SmallString<80> buf; llvm::raw_svector_ostream OS(buf); assert(CurrentFunctionDescription); OS << "Null pointer passed as " << (Arg.ArgumentIndex + 1) << llvm::getOrdinalSuffix(Arg.ArgumentIndex + 1) << " argument to " << CurrentFunctionDescription; emitNullArgBug(C, stateNull, Arg.Expression, OS.str()); } return nullptr; } // From here on, assume that the value is non-null. assert(stateNonNull); return stateNonNull; } // FIXME: This was originally copied from ArrayBoundChecker.cpp. Refactor? ProgramStateRef CStringChecker::CheckLocation(CheckerContext &C, ProgramStateRef state, AnyArgExpr Buffer, SVal Element, AccessKind Access) const { // If a previous check has failed, propagate the failure. if (!state) return nullptr; // Check for out of bound array element access. const MemRegion *R = Element.getAsRegion(); if (!R) return state; const auto *ER = dyn_cast(R); if (!ER) return state; if (ER->getValueType() != C.getASTContext().CharTy) return state; // Get the size of the array. const auto *superReg = cast(ER->getSuperRegion()); DefinedOrUnknownSVal Size = getDynamicExtent(state, superReg, C.getSValBuilder()); // Get the index of the accessed element. DefinedOrUnknownSVal Idx = ER->getIndex().castAs(); ProgramStateRef StInBound = state->assumeInBound(Idx, Size, true); ProgramStateRef StOutBound = state->assumeInBound(Idx, Size, false); if (StOutBound && !StInBound) { // These checks are either enabled by the CString out-of-bounds checker // explicitly or implicitly by the Malloc checker. // In the latter case we only do modeling but do not emit warning. if (!Filter.CheckCStringOutOfBounds) return nullptr; // Emit a bug report. ErrorMessage Message = createOutOfBoundErrorMsg(CurrentFunctionDescription, Access); emitOutOfBoundsBug(C, StOutBound, Buffer.Expression, Message); return nullptr; } // Array bound check succeeded. From this point forward the array bound // should always succeed. return StInBound; } ProgramStateRef CStringChecker::CheckBufferAccess(CheckerContext &C, ProgramStateRef State, AnyArgExpr Buffer, SizeArgExpr Size, AccessKind Access) const { // If a previous check has failed, propagate the failure. if (!State) return nullptr; SValBuilder &svalBuilder = C.getSValBuilder(); ASTContext &Ctx = svalBuilder.getContext(); QualType SizeTy = Size.Expression->getType(); QualType PtrTy = Ctx.getPointerType(Ctx.CharTy); // Check that the first buffer is non-null. SVal BufVal = C.getSVal(Buffer.Expression); State = checkNonNull(C, State, Buffer, BufVal); if (!State) return nullptr; // If out-of-bounds checking is turned off, skip the rest. if (!Filter.CheckCStringOutOfBounds) return State; // Get the access length and make sure it is known. // FIXME: This assumes the caller has already checked that the access length // is positive. And that it's unsigned. SVal LengthVal = C.getSVal(Size.Expression); Optional Length = LengthVal.getAs(); if (!Length) return State; // Compute the offset of the last element to be accessed: size-1. NonLoc One = svalBuilder.makeIntVal(1, SizeTy).castAs(); SVal Offset = svalBuilder.evalBinOpNN(State, BO_Sub, *Length, One, SizeTy); if (Offset.isUnknown()) return nullptr; NonLoc LastOffset = Offset.castAs(); // Check that the first buffer is sufficiently long. SVal BufStart = svalBuilder.evalCast(BufVal, PtrTy, Buffer.Expression->getType()); if (Optional BufLoc = BufStart.getAs()) { SVal BufEnd = svalBuilder.evalBinOpLN(State, BO_Add, *BufLoc, LastOffset, PtrTy); State = CheckLocation(C, State, Buffer, BufEnd, Access); // If the buffer isn't large enough, abort. if (!State) return nullptr; } // Large enough or not, return this state! return State; } ProgramStateRef CStringChecker::CheckOverlap(CheckerContext &C, ProgramStateRef state, SizeArgExpr Size, AnyArgExpr First, AnyArgExpr Second) const { if (!Filter.CheckCStringBufferOverlap) return state; // Do a simple check for overlap: if the two arguments are from the same // buffer, see if the end of the first is greater than the start of the second // or vice versa. // If a previous check has failed, propagate the failure. if (!state) return nullptr; ProgramStateRef stateTrue, stateFalse; // Get the buffer values and make sure they're known locations. const LocationContext *LCtx = C.getLocationContext(); SVal firstVal = state->getSVal(First.Expression, LCtx); SVal secondVal = state->getSVal(Second.Expression, LCtx); Optional firstLoc = firstVal.getAs(); if (!firstLoc) return state; Optional secondLoc = secondVal.getAs(); if (!secondLoc) return state; // Are the two values the same? SValBuilder &svalBuilder = C.getSValBuilder(); std::tie(stateTrue, stateFalse) = state->assume(svalBuilder.evalEQ(state, *firstLoc, *secondLoc)); if (stateTrue && !stateFalse) { // If the values are known to be equal, that's automatically an overlap. emitOverlapBug(C, stateTrue, First.Expression, Second.Expression); return nullptr; } // assume the two expressions are not equal. assert(stateFalse); state = stateFalse; // Which value comes first? QualType cmpTy = svalBuilder.getConditionType(); SVal reverse = svalBuilder.evalBinOpLL(state, BO_GT, *firstLoc, *secondLoc, cmpTy); Optional reverseTest = reverse.getAs(); if (!reverseTest) return state; std::tie(stateTrue, stateFalse) = state->assume(*reverseTest); if (stateTrue) { if (stateFalse) { // If we don't know which one comes first, we can't perform this test. return state; } else { // Switch the values so that firstVal is before secondVal. std::swap(firstLoc, secondLoc); // Switch the Exprs as well, so that they still correspond. std::swap(First, Second); } } // Get the length, and make sure it too is known. SVal LengthVal = state->getSVal(Size.Expression, LCtx); Optional Length = LengthVal.getAs(); if (!Length) return state; // Convert the first buffer's start address to char*. // Bail out if the cast fails. ASTContext &Ctx = svalBuilder.getContext(); QualType CharPtrTy = Ctx.getPointerType(Ctx.CharTy); SVal FirstStart = svalBuilder.evalCast(*firstLoc, CharPtrTy, First.Expression->getType()); Optional FirstStartLoc = FirstStart.getAs(); if (!FirstStartLoc) return state; // Compute the end of the first buffer. Bail out if THAT fails. SVal FirstEnd = svalBuilder.evalBinOpLN(state, BO_Add, *FirstStartLoc, *Length, CharPtrTy); Optional FirstEndLoc = FirstEnd.getAs(); if (!FirstEndLoc) return state; // Is the end of the first buffer past the start of the second buffer? SVal Overlap = svalBuilder.evalBinOpLL(state, BO_GT, *FirstEndLoc, *secondLoc, cmpTy); Optional OverlapTest = Overlap.getAs(); if (!OverlapTest) return state; std::tie(stateTrue, stateFalse) = state->assume(*OverlapTest); if (stateTrue && !stateFalse) { // Overlap! emitOverlapBug(C, stateTrue, First.Expression, Second.Expression); return nullptr; } // assume the two expressions don't overlap. assert(stateFalse); return stateFalse; } void CStringChecker::emitOverlapBug(CheckerContext &C, ProgramStateRef state, const Stmt *First, const Stmt *Second) const { ExplodedNode *N = C.generateErrorNode(state); if (!N) return; if (!BT_Overlap) BT_Overlap.reset(new BugType(Filter.CheckNameCStringBufferOverlap, categories::UnixAPI, "Improper arguments")); // Generate a report for this bug. auto report = std::make_unique( *BT_Overlap, "Arguments must not be overlapping buffers", N); report->addRange(First->getSourceRange()); report->addRange(Second->getSourceRange()); C.emitReport(std::move(report)); } void CStringChecker::emitNullArgBug(CheckerContext &C, ProgramStateRef State, const Stmt *S, StringRef WarningMsg) const { if (ExplodedNode *N = C.generateErrorNode(State)) { if (!BT_Null) BT_Null.reset(new BuiltinBug( Filter.CheckNameCStringNullArg, categories::UnixAPI, "Null pointer argument in call to byte string function")); BuiltinBug *BT = static_cast(BT_Null.get()); auto Report = std::make_unique(*BT, WarningMsg, N); Report->addRange(S->getSourceRange()); if (const auto *Ex = dyn_cast(S)) bugreporter::trackExpressionValue(N, Ex, *Report); C.emitReport(std::move(Report)); } } void CStringChecker::emitOutOfBoundsBug(CheckerContext &C, ProgramStateRef State, const Stmt *S, StringRef WarningMsg) const { if (ExplodedNode *N = C.generateErrorNode(State)) { if (!BT_Bounds) BT_Bounds.reset(new BuiltinBug( Filter.CheckCStringOutOfBounds ? Filter.CheckNameCStringOutOfBounds : Filter.CheckNameCStringNullArg, "Out-of-bound array access", "Byte string function accesses out-of-bound array element")); BuiltinBug *BT = static_cast(BT_Bounds.get()); // FIXME: It would be nice to eventually make this diagnostic more clear, // e.g., by referencing the original declaration or by saying *why* this // reference is outside the range. auto Report = std::make_unique(*BT, WarningMsg, N); Report->addRange(S->getSourceRange()); C.emitReport(std::move(Report)); } } void CStringChecker::emitNotCStringBug(CheckerContext &C, ProgramStateRef State, const Stmt *S, StringRef WarningMsg) const { if (ExplodedNode *N = C.generateNonFatalErrorNode(State)) { if (!BT_NotCString) BT_NotCString.reset(new BuiltinBug( Filter.CheckNameCStringNotNullTerm, categories::UnixAPI, "Argument is not a null-terminated string.")); auto Report = std::make_unique(*BT_NotCString, WarningMsg, N); Report->addRange(S->getSourceRange()); C.emitReport(std::move(Report)); } } void CStringChecker::emitAdditionOverflowBug(CheckerContext &C, ProgramStateRef State) const { if (ExplodedNode *N = C.generateErrorNode(State)) { if (!BT_NotCString) BT_NotCString.reset( new BuiltinBug(Filter.CheckNameCStringOutOfBounds, "API", "Sum of expressions causes overflow.")); // This isn't a great error message, but this should never occur in real // code anyway -- you'd have to create a buffer longer than a size_t can // represent, which is sort of a contradiction. const char *WarningMsg = "This expression will create a string whose length is too big to " "be represented as a size_t"; auto Report = std::make_unique(*BT_NotCString, WarningMsg, N); C.emitReport(std::move(Report)); } } ProgramStateRef CStringChecker::checkAdditionOverflow(CheckerContext &C, ProgramStateRef state, NonLoc left, NonLoc right) const { // If out-of-bounds checking is turned off, skip the rest. if (!Filter.CheckCStringOutOfBounds) return state; // If a previous check has failed, propagate the failure. if (!state) return nullptr; SValBuilder &svalBuilder = C.getSValBuilder(); BasicValueFactory &BVF = svalBuilder.getBasicValueFactory(); QualType sizeTy = svalBuilder.getContext().getSizeType(); const llvm::APSInt &maxValInt = BVF.getMaxValue(sizeTy); NonLoc maxVal = svalBuilder.makeIntVal(maxValInt); SVal maxMinusRight; if (right.getAs()) { maxMinusRight = svalBuilder.evalBinOpNN(state, BO_Sub, maxVal, right, sizeTy); } else { // Try switching the operands. (The order of these two assignments is // important!) maxMinusRight = svalBuilder.evalBinOpNN(state, BO_Sub, maxVal, left, sizeTy); left = right; } if (Optional maxMinusRightNL = maxMinusRight.getAs()) { QualType cmpTy = svalBuilder.getConditionType(); // If left > max - right, we have an overflow. SVal willOverflow = svalBuilder.evalBinOpNN(state, BO_GT, left, *maxMinusRightNL, cmpTy); ProgramStateRef stateOverflow, stateOkay; std::tie(stateOverflow, stateOkay) = state->assume(willOverflow.castAs()); if (stateOverflow && !stateOkay) { // We have an overflow. Emit a bug report. emitAdditionOverflowBug(C, stateOverflow); return nullptr; } // From now on, assume an overflow didn't occur. assert(stateOkay); state = stateOkay; } return state; } ProgramStateRef CStringChecker::setCStringLength(ProgramStateRef state, const MemRegion *MR, SVal strLength) { assert(!strLength.isUndef() && "Attempt to set an undefined string length"); MR = MR->StripCasts(); switch (MR->getKind()) { case MemRegion::StringRegionKind: // FIXME: This can happen if we strcpy() into a string region. This is // undefined [C99 6.4.5p6], but we should still warn about it. return state; case MemRegion::SymbolicRegionKind: case MemRegion::AllocaRegionKind: case MemRegion::NonParamVarRegionKind: case MemRegion::ParamVarRegionKind: case MemRegion::FieldRegionKind: case MemRegion::ObjCIvarRegionKind: // These are the types we can currently track string lengths for. break; case MemRegion::ElementRegionKind: // FIXME: Handle element regions by upper-bounding the parent region's // string length. return state; default: // Other regions (mostly non-data) can't have a reliable C string length. // For now, just ignore the change. // FIXME: These are rare but not impossible. We should output some kind of // warning for things like strcpy((char[]){'a', 0}, "b"); return state; } if (strLength.isUnknown()) return state->remove(MR); return state->set(MR, strLength); } SVal CStringChecker::getCStringLengthForRegion(CheckerContext &C, ProgramStateRef &state, const Expr *Ex, const MemRegion *MR, bool hypothetical) { if (!hypothetical) { // If there's a recorded length, go ahead and return it. const SVal *Recorded = state->get(MR); if (Recorded) return *Recorded; } // Otherwise, get a new symbol and update the state. SValBuilder &svalBuilder = C.getSValBuilder(); QualType sizeTy = svalBuilder.getContext().getSizeType(); SVal strLength = svalBuilder.getMetadataSymbolVal(CStringChecker::getTag(), MR, Ex, sizeTy, C.getLocationContext(), C.blockCount()); if (!hypothetical) { if (Optional strLn = strLength.getAs()) { // In case of unbounded calls strlen etc bound the range to SIZE_MAX/4 BasicValueFactory &BVF = svalBuilder.getBasicValueFactory(); const llvm::APSInt &maxValInt = BVF.getMaxValue(sizeTy); llvm::APSInt fourInt = APSIntType(maxValInt).getValue(4); const llvm::APSInt *maxLengthInt = BVF.evalAPSInt(BO_Div, maxValInt, fourInt); NonLoc maxLength = svalBuilder.makeIntVal(*maxLengthInt); SVal evalLength = svalBuilder.evalBinOpNN(state, BO_LE, *strLn, maxLength, sizeTy); state = state->assume(evalLength.castAs(), true); } state = state->set(MR, strLength); } return strLength; } SVal CStringChecker::getCStringLength(CheckerContext &C, ProgramStateRef &state, const Expr *Ex, SVal Buf, bool hypothetical) const { const MemRegion *MR = Buf.getAsRegion(); if (!MR) { // If we can't get a region, see if it's something we /know/ isn't a // C string. In the context of locations, the only time we can issue such // a warning is for labels. if (Optional Label = Buf.getAs()) { if (Filter.CheckCStringNotNullTerm) { SmallString<120> buf; llvm::raw_svector_ostream os(buf); assert(CurrentFunctionDescription); os << "Argument to " << CurrentFunctionDescription << " is the address of the label '" << Label->getLabel()->getName() << "', which is not a null-terminated string"; emitNotCStringBug(C, state, Ex, os.str()); } return UndefinedVal(); } // If it's not a region and not a label, give up. return UnknownVal(); } // If we have a region, strip casts from it and see if we can figure out // its length. For anything we can't figure out, just return UnknownVal. MR = MR->StripCasts(); switch (MR->getKind()) { case MemRegion::StringRegionKind: { // Modifying the contents of string regions is undefined [C99 6.4.5p6], // so we can assume that the byte length is the correct C string length. SValBuilder &svalBuilder = C.getSValBuilder(); QualType sizeTy = svalBuilder.getContext().getSizeType(); const StringLiteral *strLit = cast(MR)->getStringLiteral(); return svalBuilder.makeIntVal(strLit->getByteLength(), sizeTy); } case MemRegion::SymbolicRegionKind: case MemRegion::AllocaRegionKind: case MemRegion::NonParamVarRegionKind: case MemRegion::ParamVarRegionKind: case MemRegion::FieldRegionKind: case MemRegion::ObjCIvarRegionKind: return getCStringLengthForRegion(C, state, Ex, MR, hypothetical); case MemRegion::CompoundLiteralRegionKind: // FIXME: Can we track this? Is it necessary? return UnknownVal(); case MemRegion::ElementRegionKind: // FIXME: How can we handle this? It's not good enough to subtract the // offset from the base string length; consider "123\x00567" and &a[5]. return UnknownVal(); default: // Other regions (mostly non-data) can't have a reliable C string length. // In this case, an error is emitted and UndefinedVal is returned. // The caller should always be prepared to handle this case. if (Filter.CheckCStringNotNullTerm) { SmallString<120> buf; llvm::raw_svector_ostream os(buf); assert(CurrentFunctionDescription); os << "Argument to " << CurrentFunctionDescription << " is "; if (SummarizeRegion(os, C.getASTContext(), MR)) os << ", which is not a null-terminated string"; else os << "not a null-terminated string"; emitNotCStringBug(C, state, Ex, os.str()); } return UndefinedVal(); } } const StringLiteral *CStringChecker::getCStringLiteral(CheckerContext &C, ProgramStateRef &state, const Expr *expr, SVal val) const { // Get the memory region pointed to by the val. const MemRegion *bufRegion = val.getAsRegion(); if (!bufRegion) return nullptr; // Strip casts off the memory region. bufRegion = bufRegion->StripCasts(); // Cast the memory region to a string region. const StringRegion *strRegion= dyn_cast(bufRegion); if (!strRegion) return nullptr; // Return the actual string in the string region. return strRegion->getStringLiteral(); } bool CStringChecker::IsFirstBufInBound(CheckerContext &C, ProgramStateRef state, const Expr *FirstBuf, const Expr *Size) { // If we do not know that the buffer is long enough we return 'true'. // Otherwise the parent region of this field region would also get // invalidated, which would lead to warnings based on an unknown state. // Originally copied from CheckBufferAccess and CheckLocation. SValBuilder &svalBuilder = C.getSValBuilder(); ASTContext &Ctx = svalBuilder.getContext(); const LocationContext *LCtx = C.getLocationContext(); QualType sizeTy = Size->getType(); QualType PtrTy = Ctx.getPointerType(Ctx.CharTy); SVal BufVal = state->getSVal(FirstBuf, LCtx); SVal LengthVal = state->getSVal(Size, LCtx); Optional Length = LengthVal.getAs(); if (!Length) return true; // cf top comment. // Compute the offset of the last element to be accessed: size-1. NonLoc One = svalBuilder.makeIntVal(1, sizeTy).castAs(); SVal Offset = svalBuilder.evalBinOpNN(state, BO_Sub, *Length, One, sizeTy); if (Offset.isUnknown()) return true; // cf top comment NonLoc LastOffset = Offset.castAs(); // Check that the first buffer is sufficiently long. SVal BufStart = svalBuilder.evalCast(BufVal, PtrTy, FirstBuf->getType()); Optional BufLoc = BufStart.getAs(); if (!BufLoc) return true; // cf top comment. SVal BufEnd = svalBuilder.evalBinOpLN(state, BO_Add, *BufLoc, LastOffset, PtrTy); // Check for out of bound array element access. const MemRegion *R = BufEnd.getAsRegion(); if (!R) return true; // cf top comment. const ElementRegion *ER = dyn_cast(R); if (!ER) return true; // cf top comment. // FIXME: Does this crash when a non-standard definition // of a library function is encountered? assert(ER->getValueType() == C.getASTContext().CharTy && "IsFirstBufInBound should only be called with char* ElementRegions"); // Get the size of the array. const SubRegion *superReg = cast(ER->getSuperRegion()); DefinedOrUnknownSVal SizeDV = getDynamicExtent(state, superReg, svalBuilder); // Get the index of the accessed element. DefinedOrUnknownSVal Idx = ER->getIndex().castAs(); ProgramStateRef StInBound = state->assumeInBound(Idx, SizeDV, true); return static_cast(StInBound); } ProgramStateRef CStringChecker::InvalidateBuffer(CheckerContext &C, ProgramStateRef state, const Expr *E, SVal V, bool IsSourceBuffer, const Expr *Size) { Optional L = V.getAs(); if (!L) return state; // FIXME: This is a simplified version of what's in CFRefCount.cpp -- it makes // some assumptions about the value that CFRefCount can't. Even so, it should // probably be refactored. if (Optional MR = L->getAs()) { const MemRegion *R = MR->getRegion()->StripCasts(); // Are we dealing with an ElementRegion? If so, we should be invalidating // the super-region. if (const ElementRegion *ER = dyn_cast(R)) { R = ER->getSuperRegion(); // FIXME: What about layers of ElementRegions? } // Invalidate this region. const LocationContext *LCtx = C.getPredecessor()->getLocationContext(); bool CausesPointerEscape = false; RegionAndSymbolInvalidationTraits ITraits; // Invalidate and escape only indirect regions accessible through the source // buffer. if (IsSourceBuffer) { ITraits.setTrait(R->getBaseRegion(), RegionAndSymbolInvalidationTraits::TK_PreserveContents); ITraits.setTrait(R, RegionAndSymbolInvalidationTraits::TK_SuppressEscape); CausesPointerEscape = true; } else { const MemRegion::Kind& K = R->getKind(); if (K == MemRegion::FieldRegionKind) if (Size && IsFirstBufInBound(C, state, E, Size)) { // If destination buffer is a field region and access is in bound, // do not invalidate its super region. ITraits.setTrait( R, RegionAndSymbolInvalidationTraits::TK_DoNotInvalidateSuperRegion); } } return state->invalidateRegions(R, E, C.blockCount(), LCtx, CausesPointerEscape, nullptr, nullptr, &ITraits); } // If we have a non-region value by chance, just remove the binding. // FIXME: is this necessary or correct? This handles the non-Region // cases. Is it ever valid to store to these? return state->killBinding(*L); } bool CStringChecker::SummarizeRegion(raw_ostream &os, ASTContext &Ctx, const MemRegion *MR) { switch (MR->getKind()) { case MemRegion::FunctionCodeRegionKind: { if (const auto *FD = cast(MR)->getDecl()) os << "the address of the function '" << *FD << '\''; else os << "the address of a function"; return true; } case MemRegion::BlockCodeRegionKind: os << "block text"; return true; case MemRegion::BlockDataRegionKind: os << "a block"; return true; case MemRegion::CXXThisRegionKind: case MemRegion::CXXTempObjectRegionKind: os << "a C++ temp object of type " << cast(MR)->getValueType().getAsString(); return true; case MemRegion::NonParamVarRegionKind: os << "a variable of type" << cast(MR)->getValueType().getAsString(); return true; case MemRegion::ParamVarRegionKind: os << "a parameter of type" << cast(MR)->getValueType().getAsString(); return true; case MemRegion::FieldRegionKind: os << "a field of type " << cast(MR)->getValueType().getAsString(); return true; case MemRegion::ObjCIvarRegionKind: os << "an instance variable of type " << cast(MR)->getValueType().getAsString(); return true; default: return false; } } bool CStringChecker::memsetAux(const Expr *DstBuffer, SVal CharVal, const Expr *Size, CheckerContext &C, ProgramStateRef &State) { SVal MemVal = C.getSVal(DstBuffer); SVal SizeVal = C.getSVal(Size); const MemRegion *MR = MemVal.getAsRegion(); if (!MR) return false; // We're about to model memset by producing a "default binding" in the Store. // Our current implementation - RegionStore - doesn't support default bindings // that don't cover the whole base region. So we should first get the offset // and the base region to figure out whether the offset of buffer is 0. RegionOffset Offset = MR->getAsOffset(); const MemRegion *BR = Offset.getRegion(); Optional SizeNL = SizeVal.getAs(); if (!SizeNL) return false; SValBuilder &svalBuilder = C.getSValBuilder(); ASTContext &Ctx = C.getASTContext(); // void *memset(void *dest, int ch, size_t count); // For now we can only handle the case of offset is 0 and concrete char value. if (Offset.isValid() && !Offset.hasSymbolicOffset() && Offset.getOffset() == 0) { // Get the base region's size. DefinedOrUnknownSVal SizeDV = getDynamicExtent(State, BR, svalBuilder); ProgramStateRef StateWholeReg, StateNotWholeReg; std::tie(StateWholeReg, StateNotWholeReg) = State->assume(svalBuilder.evalEQ(State, SizeDV, *SizeNL)); // With the semantic of 'memset()', we should convert the CharVal to // unsigned char. CharVal = svalBuilder.evalCast(CharVal, Ctx.UnsignedCharTy, Ctx.IntTy); ProgramStateRef StateNullChar, StateNonNullChar; std::tie(StateNullChar, StateNonNullChar) = assumeZero(C, State, CharVal, Ctx.UnsignedCharTy); if (StateWholeReg && !StateNotWholeReg && StateNullChar && !StateNonNullChar) { // If the 'memset()' acts on the whole region of destination buffer and // the value of the second argument of 'memset()' is zero, bind the second // argument's value to the destination buffer with 'default binding'. // FIXME: Since there is no perfect way to bind the non-zero character, we // can only deal with zero value here. In the future, we need to deal with // the binding of non-zero value in the case of whole region. State = State->bindDefaultZero(svalBuilder.makeLoc(BR), C.getLocationContext()); } else { // If the destination buffer's extent is not equal to the value of // third argument, just invalidate buffer. State = InvalidateBuffer(C, State, DstBuffer, MemVal, /*IsSourceBuffer*/ false, Size); } if (StateNullChar && !StateNonNullChar) { // If the value of the second argument of 'memset()' is zero, set the // string length of destination buffer to 0 directly. State = setCStringLength(State, MR, svalBuilder.makeZeroVal(Ctx.getSizeType())); } else if (!StateNullChar && StateNonNullChar) { SVal NewStrLen = svalBuilder.getMetadataSymbolVal( CStringChecker::getTag(), MR, DstBuffer, Ctx.getSizeType(), C.getLocationContext(), C.blockCount()); // If the value of second argument is not zero, then the string length // is at least the size argument. SVal NewStrLenGESize = svalBuilder.evalBinOp( State, BO_GE, NewStrLen, SizeVal, svalBuilder.getConditionType()); State = setCStringLength( State->assume(NewStrLenGESize.castAs(), true), MR, NewStrLen); } } else { // If the offset is not zero and char value is not concrete, we can do // nothing but invalidate the buffer. State = InvalidateBuffer(C, State, DstBuffer, MemVal, /*IsSourceBuffer*/ false, Size); } return true; } //===----------------------------------------------------------------------===// // evaluation of individual function calls. //===----------------------------------------------------------------------===// void CStringChecker::evalCopyCommon(CheckerContext &C, const CallExpr *CE, ProgramStateRef state, SizeArgExpr Size, DestinationArgExpr Dest, SourceArgExpr Source, bool Restricted, bool IsMempcpy) const { CurrentFunctionDescription = "memory copy function"; // See if the size argument is zero. const LocationContext *LCtx = C.getLocationContext(); SVal sizeVal = state->getSVal(Size.Expression, LCtx); QualType sizeTy = Size.Expression->getType(); ProgramStateRef stateZeroSize, stateNonZeroSize; std::tie(stateZeroSize, stateNonZeroSize) = assumeZero(C, state, sizeVal, sizeTy); // Get the value of the Dest. SVal destVal = state->getSVal(Dest.Expression, LCtx); // If the size is zero, there won't be any actual memory access, so // just bind the return value to the destination buffer and return. if (stateZeroSize && !stateNonZeroSize) { stateZeroSize = stateZeroSize->BindExpr(CE, LCtx, destVal); C.addTransition(stateZeroSize); return; } // If the size can be nonzero, we have to check the other arguments. if (stateNonZeroSize) { state = stateNonZeroSize; // Ensure the destination is not null. If it is NULL there will be a // NULL pointer dereference. state = checkNonNull(C, state, Dest, destVal); if (!state) return; // Get the value of the Src. SVal srcVal = state->getSVal(Source.Expression, LCtx); // Ensure the source is not null. If it is NULL there will be a // NULL pointer dereference. state = checkNonNull(C, state, Source, srcVal); if (!state) return; // Ensure the accesses are valid and that the buffers do not overlap. state = CheckBufferAccess(C, state, Dest, Size, AccessKind::write); state = CheckBufferAccess(C, state, Source, Size, AccessKind::read); if (Restricted) state = CheckOverlap(C, state, Size, Dest, Source); if (!state) return; // If this is mempcpy, get the byte after the last byte copied and // bind the expr. if (IsMempcpy) { // Get the byte after the last byte copied. SValBuilder &SvalBuilder = C.getSValBuilder(); ASTContext &Ctx = SvalBuilder.getContext(); QualType CharPtrTy = Ctx.getPointerType(Ctx.CharTy); SVal DestRegCharVal = SvalBuilder.evalCast(destVal, CharPtrTy, Dest.Expression->getType()); SVal lastElement = C.getSValBuilder().evalBinOp( state, BO_Add, DestRegCharVal, sizeVal, Dest.Expression->getType()); // If we don't know how much we copied, we can at least // conjure a return value for later. if (lastElement.isUnknown()) lastElement = C.getSValBuilder().conjureSymbolVal(nullptr, CE, LCtx, C.blockCount()); // The byte after the last byte copied is the return value. state = state->BindExpr(CE, LCtx, lastElement); } else { // All other copies return the destination buffer. // (Well, bcopy() has a void return type, but this won't hurt.) state = state->BindExpr(CE, LCtx, destVal); } // Invalidate the destination (regular invalidation without pointer-escaping // the address of the top-level region). // FIXME: Even if we can't perfectly model the copy, we should see if we // can use LazyCompoundVals to copy the source values into the destination. // This would probably remove any existing bindings past the end of the // copied region, but that's still an improvement over blank invalidation. state = InvalidateBuffer(C, state, Dest.Expression, C.getSVal(Dest.Expression), /*IsSourceBuffer*/ false, Size.Expression); // Invalidate the source (const-invalidation without const-pointer-escaping // the address of the top-level region). state = InvalidateBuffer(C, state, Source.Expression, C.getSVal(Source.Expression), /*IsSourceBuffer*/ true, nullptr); C.addTransition(state); } } void CStringChecker::evalMemcpy(CheckerContext &C, const CallExpr *CE) const { // void *memcpy(void *restrict dst, const void *restrict src, size_t n); // The return value is the address of the destination buffer. DestinationArgExpr Dest = {CE->getArg(0), 0}; SourceArgExpr Src = {CE->getArg(1), 1}; SizeArgExpr Size = {CE->getArg(2), 2}; ProgramStateRef State = C.getState(); constexpr bool IsRestricted = true; constexpr bool IsMempcpy = false; evalCopyCommon(C, CE, State, Size, Dest, Src, IsRestricted, IsMempcpy); } void CStringChecker::evalMempcpy(CheckerContext &C, const CallExpr *CE) const { // void *mempcpy(void *restrict dst, const void *restrict src, size_t n); // The return value is a pointer to the byte following the last written byte. DestinationArgExpr Dest = {CE->getArg(0), 0}; SourceArgExpr Src = {CE->getArg(1), 1}; SizeArgExpr Size = {CE->getArg(2), 2}; constexpr bool IsRestricted = true; constexpr bool IsMempcpy = true; evalCopyCommon(C, CE, C.getState(), Size, Dest, Src, IsRestricted, IsMempcpy); } void CStringChecker::evalMemmove(CheckerContext &C, const CallExpr *CE) const { // void *memmove(void *dst, const void *src, size_t n); // The return value is the address of the destination buffer. DestinationArgExpr Dest = {CE->getArg(0), 0}; SourceArgExpr Src = {CE->getArg(1), 1}; SizeArgExpr Size = {CE->getArg(2), 2}; constexpr bool IsRestricted = false; constexpr bool IsMempcpy = false; evalCopyCommon(C, CE, C.getState(), Size, Dest, Src, IsRestricted, IsMempcpy); } void CStringChecker::evalBcopy(CheckerContext &C, const CallExpr *CE) const { // void bcopy(const void *src, void *dst, size_t n); SourceArgExpr Src(CE->getArg(0), 0); DestinationArgExpr Dest = {CE->getArg(1), 1}; SizeArgExpr Size = {CE->getArg(2), 2}; constexpr bool IsRestricted = false; constexpr bool IsMempcpy = false; evalCopyCommon(C, CE, C.getState(), Size, Dest, Src, IsRestricted, IsMempcpy); } void CStringChecker::evalMemcmp(CheckerContext &C, const CallExpr *CE) const { // int memcmp(const void *s1, const void *s2, size_t n); CurrentFunctionDescription = "memory comparison function"; AnyArgExpr Left = {CE->getArg(0), 0}; AnyArgExpr Right = {CE->getArg(1), 1}; SizeArgExpr Size = {CE->getArg(2), 2}; ProgramStateRef State = C.getState(); SValBuilder &Builder = C.getSValBuilder(); const LocationContext *LCtx = C.getLocationContext(); // See if the size argument is zero. SVal sizeVal = State->getSVal(Size.Expression, LCtx); QualType sizeTy = Size.Expression->getType(); ProgramStateRef stateZeroSize, stateNonZeroSize; std::tie(stateZeroSize, stateNonZeroSize) = assumeZero(C, State, sizeVal, sizeTy); // If the size can be zero, the result will be 0 in that case, and we don't // have to check either of the buffers. if (stateZeroSize) { State = stateZeroSize; State = State->BindExpr(CE, LCtx, Builder.makeZeroVal(CE->getType())); C.addTransition(State); } // If the size can be nonzero, we have to check the other arguments. if (stateNonZeroSize) { State = stateNonZeroSize; // If we know the two buffers are the same, we know the result is 0. // First, get the two buffers' addresses. Another checker will have already // made sure they're not undefined. DefinedOrUnknownSVal LV = State->getSVal(Left.Expression, LCtx).castAs(); DefinedOrUnknownSVal RV = State->getSVal(Right.Expression, LCtx).castAs(); // See if they are the same. ProgramStateRef SameBuffer, NotSameBuffer; std::tie(SameBuffer, NotSameBuffer) = State->assume(Builder.evalEQ(State, LV, RV)); // If the two arguments are the same buffer, we know the result is 0, // and we only need to check one size. if (SameBuffer && !NotSameBuffer) { State = SameBuffer; State = CheckBufferAccess(C, State, Left, Size, AccessKind::read); if (State) { State = SameBuffer->BindExpr(CE, LCtx, Builder.makeZeroVal(CE->getType())); C.addTransition(State); } return; } // If the two arguments might be different buffers, we have to check // the size of both of them. assert(NotSameBuffer); State = CheckBufferAccess(C, State, Right, Size, AccessKind::read); State = CheckBufferAccess(C, State, Left, Size, AccessKind::read); if (State) { // The return value is the comparison result, which we don't know. SVal CmpV = Builder.conjureSymbolVal(nullptr, CE, LCtx, C.blockCount()); State = State->BindExpr(CE, LCtx, CmpV); C.addTransition(State); } } } void CStringChecker::evalstrLength(CheckerContext &C, const CallExpr *CE) const { // size_t strlen(const char *s); evalstrLengthCommon(C, CE, /* IsStrnlen = */ false); } void CStringChecker::evalstrnLength(CheckerContext &C, const CallExpr *CE) const { // size_t strnlen(const char *s, size_t maxlen); evalstrLengthCommon(C, CE, /* IsStrnlen = */ true); } void CStringChecker::evalstrLengthCommon(CheckerContext &C, const CallExpr *CE, bool IsStrnlen) const { CurrentFunctionDescription = "string length function"; ProgramStateRef state = C.getState(); const LocationContext *LCtx = C.getLocationContext(); if (IsStrnlen) { const Expr *maxlenExpr = CE->getArg(1); SVal maxlenVal = state->getSVal(maxlenExpr, LCtx); ProgramStateRef stateZeroSize, stateNonZeroSize; std::tie(stateZeroSize, stateNonZeroSize) = assumeZero(C, state, maxlenVal, maxlenExpr->getType()); // If the size can be zero, the result will be 0 in that case, and we don't // have to check the string itself. if (stateZeroSize) { SVal zero = C.getSValBuilder().makeZeroVal(CE->getType()); stateZeroSize = stateZeroSize->BindExpr(CE, LCtx, zero); C.addTransition(stateZeroSize); } // If the size is GUARANTEED to be zero, we're done! if (!stateNonZeroSize) return; // Otherwise, record the assumption that the size is nonzero. state = stateNonZeroSize; } // Check that the string argument is non-null. AnyArgExpr Arg = {CE->getArg(0), 0}; SVal ArgVal = state->getSVal(Arg.Expression, LCtx); state = checkNonNull(C, state, Arg, ArgVal); if (!state) return; SVal strLength = getCStringLength(C, state, Arg.Expression, ArgVal); // If the argument isn't a valid C string, there's no valid state to // transition to. if (strLength.isUndef()) return; DefinedOrUnknownSVal result = UnknownVal(); // If the check is for strnlen() then bind the return value to no more than // the maxlen value. if (IsStrnlen) { QualType cmpTy = C.getSValBuilder().getConditionType(); // It's a little unfortunate to be getting this again, // but it's not that expensive... const Expr *maxlenExpr = CE->getArg(1); SVal maxlenVal = state->getSVal(maxlenExpr, LCtx); Optional strLengthNL = strLength.getAs(); Optional maxlenValNL = maxlenVal.getAs(); if (strLengthNL && maxlenValNL) { ProgramStateRef stateStringTooLong, stateStringNotTooLong; // Check if the strLength is greater than the maxlen. std::tie(stateStringTooLong, stateStringNotTooLong) = state->assume( C.getSValBuilder() .evalBinOpNN(state, BO_GT, *strLengthNL, *maxlenValNL, cmpTy) .castAs()); if (stateStringTooLong && !stateStringNotTooLong) { // If the string is longer than maxlen, return maxlen. result = *maxlenValNL; } else if (stateStringNotTooLong && !stateStringTooLong) { // If the string is shorter than maxlen, return its length. result = *strLengthNL; } } if (result.isUnknown()) { // If we don't have enough information for a comparison, there's // no guarantee the full string length will actually be returned. // All we know is the return value is the min of the string length // and the limit. This is better than nothing. result = C.getSValBuilder().conjureSymbolVal(nullptr, CE, LCtx, C.blockCount()); NonLoc resultNL = result.castAs(); if (strLengthNL) { state = state->assume(C.getSValBuilder().evalBinOpNN( state, BO_LE, resultNL, *strLengthNL, cmpTy) .castAs(), true); } if (maxlenValNL) { state = state->assume(C.getSValBuilder().evalBinOpNN( state, BO_LE, resultNL, *maxlenValNL, cmpTy) .castAs(), true); } } } else { // This is a plain strlen(), not strnlen(). result = strLength.castAs(); // If we don't know the length of the string, conjure a return // value, so it can be used in constraints, at least. if (result.isUnknown()) { result = C.getSValBuilder().conjureSymbolVal(nullptr, CE, LCtx, C.blockCount()); } } // Bind the return value. assert(!result.isUnknown() && "Should have conjured a value by now"); state = state->BindExpr(CE, LCtx, result); C.addTransition(state); } void CStringChecker::evalStrcpy(CheckerContext &C, const CallExpr *CE) const { // char *strcpy(char *restrict dst, const char *restrict src); evalStrcpyCommon(C, CE, /* ReturnEnd = */ false, /* IsBounded = */ false, /* appendK = */ ConcatFnKind::none); } void CStringChecker::evalStrncpy(CheckerContext &C, const CallExpr *CE) const { // char *strncpy(char *restrict dst, const char *restrict src, size_t n); evalStrcpyCommon(C, CE, /* ReturnEnd = */ false, /* IsBounded = */ true, /* appendK = */ ConcatFnKind::none); } void CStringChecker::evalStpcpy(CheckerContext &C, const CallExpr *CE) const { // char *stpcpy(char *restrict dst, const char *restrict src); evalStrcpyCommon(C, CE, /* ReturnEnd = */ true, /* IsBounded = */ false, /* appendK = */ ConcatFnKind::none); } void CStringChecker::evalStrlcpy(CheckerContext &C, const CallExpr *CE) const { // size_t strlcpy(char *dest, const char *src, size_t size); evalStrcpyCommon(C, CE, /* ReturnEnd = */ true, /* IsBounded = */ true, /* appendK = */ ConcatFnKind::none, /* returnPtr = */ false); } void CStringChecker::evalStrcat(CheckerContext &C, const CallExpr *CE) const { // char *strcat(char *restrict s1, const char *restrict s2); evalStrcpyCommon(C, CE, /* ReturnEnd = */ false, /* IsBounded = */ false, /* appendK = */ ConcatFnKind::strcat); } void CStringChecker::evalStrncat(CheckerContext &C, const CallExpr *CE) const { // char *strncat(char *restrict s1, const char *restrict s2, size_t n); evalStrcpyCommon(C, CE, /* ReturnEnd = */ false, /* IsBounded = */ true, /* appendK = */ ConcatFnKind::strcat); } void CStringChecker::evalStrlcat(CheckerContext &C, const CallExpr *CE) const { // size_t strlcat(char *dst, const char *src, size_t size); // It will append at most size - strlen(dst) - 1 bytes, // NULL-terminating the result. evalStrcpyCommon(C, CE, /* ReturnEnd = */ false, /* IsBounded = */ true, /* appendK = */ ConcatFnKind::strlcat, /* returnPtr = */ false); } void CStringChecker::evalStrcpyCommon(CheckerContext &C, const CallExpr *CE, bool ReturnEnd, bool IsBounded, ConcatFnKind appendK, bool returnPtr) const { if (appendK == ConcatFnKind::none) CurrentFunctionDescription = "string copy function"; else CurrentFunctionDescription = "string concatenation function"; ProgramStateRef state = C.getState(); const LocationContext *LCtx = C.getLocationContext(); // Check that the destination is non-null. DestinationArgExpr Dst = {CE->getArg(0), 0}; SVal DstVal = state->getSVal(Dst.Expression, LCtx); state = checkNonNull(C, state, Dst, DstVal); if (!state) return; // Check that the source is non-null. SourceArgExpr srcExpr = {CE->getArg(1), 1}; SVal srcVal = state->getSVal(srcExpr.Expression, LCtx); state = checkNonNull(C, state, srcExpr, srcVal); if (!state) return; // Get the string length of the source. SVal strLength = getCStringLength(C, state, srcExpr.Expression, srcVal); Optional strLengthNL = strLength.getAs(); // Get the string length of the destination buffer. SVal dstStrLength = getCStringLength(C, state, Dst.Expression, DstVal); Optional dstStrLengthNL = dstStrLength.getAs(); // If the source isn't a valid C string, give up. if (strLength.isUndef()) return; SValBuilder &svalBuilder = C.getSValBuilder(); QualType cmpTy = svalBuilder.getConditionType(); QualType sizeTy = svalBuilder.getContext().getSizeType(); // These two values allow checking two kinds of errors: // - actual overflows caused by a source that doesn't fit in the destination // - potential overflows caused by a bound that could exceed the destination SVal amountCopied = UnknownVal(); SVal maxLastElementIndex = UnknownVal(); const char *boundWarning = nullptr; // FIXME: Why do we choose the srcExpr if the access has no size? // Note that the 3rd argument of the call would be the size parameter. SizeArgExpr SrcExprAsSizeDummy = {srcExpr.Expression, srcExpr.ArgumentIndex}; state = CheckOverlap( C, state, (IsBounded ? SizeArgExpr{CE->getArg(2), 2} : SrcExprAsSizeDummy), Dst, srcExpr); if (!state) return; // If the function is strncpy, strncat, etc... it is bounded. if (IsBounded) { // Get the max number of characters to copy. SizeArgExpr lenExpr = {CE->getArg(2), 2}; SVal lenVal = state->getSVal(lenExpr.Expression, LCtx); // Protect against misdeclared strncpy(). lenVal = svalBuilder.evalCast(lenVal, sizeTy, lenExpr.Expression->getType()); Optional lenValNL = lenVal.getAs(); // If we know both values, we might be able to figure out how much // we're copying. if (strLengthNL && lenValNL) { switch (appendK) { case ConcatFnKind::none: case ConcatFnKind::strcat: { ProgramStateRef stateSourceTooLong, stateSourceNotTooLong; // Check if the max number to copy is less than the length of the src. // If the bound is equal to the source length, strncpy won't null- // terminate the result! std::tie(stateSourceTooLong, stateSourceNotTooLong) = state->assume( svalBuilder .evalBinOpNN(state, BO_GE, *strLengthNL, *lenValNL, cmpTy) .castAs()); if (stateSourceTooLong && !stateSourceNotTooLong) { // Max number to copy is less than the length of the src, so the // actual strLength copied is the max number arg. state = stateSourceTooLong; amountCopied = lenVal; } else if (!stateSourceTooLong && stateSourceNotTooLong) { // The source buffer entirely fits in the bound. state = stateSourceNotTooLong; amountCopied = strLength; } break; } case ConcatFnKind::strlcat: if (!dstStrLengthNL) return; // amountCopied = min (size - dstLen - 1 , srcLen) SVal freeSpace = svalBuilder.evalBinOpNN(state, BO_Sub, *lenValNL, *dstStrLengthNL, sizeTy); if (!freeSpace.getAs()) return; freeSpace = svalBuilder.evalBinOp(state, BO_Sub, freeSpace, svalBuilder.makeIntVal(1, sizeTy), sizeTy); Optional freeSpaceNL = freeSpace.getAs(); // While unlikely, it is possible that the subtraction is // too complex to compute, let's check whether it succeeded. if (!freeSpaceNL) return; SVal hasEnoughSpace = svalBuilder.evalBinOpNN( state, BO_LE, *strLengthNL, *freeSpaceNL, cmpTy); ProgramStateRef TrueState, FalseState; std::tie(TrueState, FalseState) = state->assume(hasEnoughSpace.castAs()); // srcStrLength <= size - dstStrLength -1 if (TrueState && !FalseState) { amountCopied = strLength; } // srcStrLength > size - dstStrLength -1 if (!TrueState && FalseState) { amountCopied = freeSpace; } if (TrueState && FalseState) amountCopied = UnknownVal(); break; } } // We still want to know if the bound is known to be too large. if (lenValNL) { switch (appendK) { case ConcatFnKind::strcat: // For strncat, the check is strlen(dst) + lenVal < sizeof(dst) // Get the string length of the destination. If the destination is // memory that can't have a string length, we shouldn't be copying // into it anyway. if (dstStrLength.isUndef()) return; if (dstStrLengthNL) { maxLastElementIndex = svalBuilder.evalBinOpNN( state, BO_Add, *lenValNL, *dstStrLengthNL, sizeTy); boundWarning = "Size argument is greater than the free space in the " "destination buffer"; } break; case ConcatFnKind::none: case ConcatFnKind::strlcat: // For strncpy and strlcat, this is just checking // that lenVal <= sizeof(dst). // (Yes, strncpy and strncat differ in how they treat termination. // strncat ALWAYS terminates, but strncpy doesn't.) // We need a special case for when the copy size is zero, in which // case strncpy will do no work at all. Our bounds check uses n-1 // as the last element accessed, so n == 0 is problematic. ProgramStateRef StateZeroSize, StateNonZeroSize; std::tie(StateZeroSize, StateNonZeroSize) = assumeZero(C, state, *lenValNL, sizeTy); // If the size is known to be zero, we're done. if (StateZeroSize && !StateNonZeroSize) { if (returnPtr) { StateZeroSize = StateZeroSize->BindExpr(CE, LCtx, DstVal); } else { if (appendK == ConcatFnKind::none) { // strlcpy returns strlen(src) StateZeroSize = StateZeroSize->BindExpr(CE, LCtx, strLength); } else { // strlcat returns strlen(src) + strlen(dst) SVal retSize = svalBuilder.evalBinOp( state, BO_Add, strLength, dstStrLength, sizeTy); StateZeroSize = StateZeroSize->BindExpr(CE, LCtx, retSize); } } C.addTransition(StateZeroSize); return; } // Otherwise, go ahead and figure out the last element we'll touch. // We don't record the non-zero assumption here because we can't // be sure. We won't warn on a possible zero. NonLoc one = svalBuilder.makeIntVal(1, sizeTy).castAs(); maxLastElementIndex = svalBuilder.evalBinOpNN(state, BO_Sub, *lenValNL, one, sizeTy); boundWarning = "Size argument is greater than the length of the " "destination buffer"; break; } } } else { // The function isn't bounded. The amount copied should match the length // of the source buffer. amountCopied = strLength; } assert(state); // This represents the number of characters copied into the destination // buffer. (It may not actually be the strlen if the destination buffer // is not terminated.) SVal finalStrLength = UnknownVal(); SVal strlRetVal = UnknownVal(); if (appendK == ConcatFnKind::none && !returnPtr) { // strlcpy returns the sizeof(src) strlRetVal = strLength; } // If this is an appending function (strcat, strncat...) then set the // string length to strlen(src) + strlen(dst) since the buffer will // ultimately contain both. if (appendK != ConcatFnKind::none) { // Get the string length of the destination. If the destination is memory // that can't have a string length, we shouldn't be copying into it anyway. if (dstStrLength.isUndef()) return; if (appendK == ConcatFnKind::strlcat && dstStrLengthNL && strLengthNL) { strlRetVal = svalBuilder.evalBinOpNN(state, BO_Add, *strLengthNL, *dstStrLengthNL, sizeTy); } Optional amountCopiedNL = amountCopied.getAs(); // If we know both string lengths, we might know the final string length. if (amountCopiedNL && dstStrLengthNL) { // Make sure the two lengths together don't overflow a size_t. state = checkAdditionOverflow(C, state, *amountCopiedNL, *dstStrLengthNL); if (!state) return; finalStrLength = svalBuilder.evalBinOpNN(state, BO_Add, *amountCopiedNL, *dstStrLengthNL, sizeTy); } // If we couldn't get a single value for the final string length, // we can at least bound it by the individual lengths. if (finalStrLength.isUnknown()) { // Try to get a "hypothetical" string length symbol, which we can later // set as a real value if that turns out to be the case. finalStrLength = getCStringLength(C, state, CE, DstVal, true); assert(!finalStrLength.isUndef()); if (Optional finalStrLengthNL = finalStrLength.getAs()) { if (amountCopiedNL && appendK == ConcatFnKind::none) { // we overwrite dst string with the src // finalStrLength >= srcStrLength SVal sourceInResult = svalBuilder.evalBinOpNN( state, BO_GE, *finalStrLengthNL, *amountCopiedNL, cmpTy); state = state->assume(sourceInResult.castAs(), true); if (!state) return; } if (dstStrLengthNL && appendK != ConcatFnKind::none) { // we extend the dst string with the src // finalStrLength >= dstStrLength SVal destInResult = svalBuilder.evalBinOpNN(state, BO_GE, *finalStrLengthNL, *dstStrLengthNL, cmpTy); state = state->assume(destInResult.castAs(), true); if (!state) return; } } } } else { // Otherwise, this is a copy-over function (strcpy, strncpy, ...), and // the final string length will match the input string length. finalStrLength = amountCopied; } SVal Result; if (returnPtr) { // The final result of the function will either be a pointer past the last // copied element, or a pointer to the start of the destination buffer. Result = (ReturnEnd ? UnknownVal() : DstVal); } else { if (appendK == ConcatFnKind::strlcat || appendK == ConcatFnKind::none) //strlcpy, strlcat Result = strlRetVal; else Result = finalStrLength; } assert(state); // If the destination is a MemRegion, try to check for a buffer overflow and // record the new string length. if (Optional dstRegVal = DstVal.getAs()) { QualType ptrTy = Dst.Expression->getType(); // If we have an exact value on a bounded copy, use that to check for // overflows, rather than our estimate about how much is actually copied. if (Optional maxLastNL = maxLastElementIndex.getAs()) { SVal maxLastElement = svalBuilder.evalBinOpLN(state, BO_Add, *dstRegVal, *maxLastNL, ptrTy); state = CheckLocation(C, state, Dst, maxLastElement, AccessKind::write); if (!state) return; } // Then, if the final length is known... if (Optional knownStrLength = finalStrLength.getAs()) { SVal lastElement = svalBuilder.evalBinOpLN(state, BO_Add, *dstRegVal, *knownStrLength, ptrTy); // ...and we haven't checked the bound, we'll check the actual copy. if (!boundWarning) { state = CheckLocation(C, state, Dst, lastElement, AccessKind::write); if (!state) return; } // If this is a stpcpy-style copy, the last element is the return value. if (returnPtr && ReturnEnd) Result = lastElement; } // Invalidate the destination (regular invalidation without pointer-escaping // the address of the top-level region). This must happen before we set the // C string length because invalidation will clear the length. // FIXME: Even if we can't perfectly model the copy, we should see if we // can use LazyCompoundVals to copy the source values into the destination. // This would probably remove any existing bindings past the end of the // string, but that's still an improvement over blank invalidation. state = InvalidateBuffer(C, state, Dst.Expression, *dstRegVal, /*IsSourceBuffer*/ false, nullptr); // Invalidate the source (const-invalidation without const-pointer-escaping // the address of the top-level region). state = InvalidateBuffer(C, state, srcExpr.Expression, srcVal, /*IsSourceBuffer*/ true, nullptr); // Set the C string length of the destination, if we know it. if (IsBounded && (appendK == ConcatFnKind::none)) { // strncpy is annoying in that it doesn't guarantee to null-terminate // the result string. If the original string didn't fit entirely inside // the bound (including the null-terminator), we don't know how long the // result is. if (amountCopied != strLength) finalStrLength = UnknownVal(); } state = setCStringLength(state, dstRegVal->getRegion(), finalStrLength); } assert(state); if (returnPtr) { // If this is a stpcpy-style copy, but we were unable to check for a buffer // overflow, we still need a result. Conjure a return value. if (ReturnEnd && Result.isUnknown()) { Result = svalBuilder.conjureSymbolVal(nullptr, CE, LCtx, C.blockCount()); } } // Set the return value. state = state->BindExpr(CE, LCtx, Result); C.addTransition(state); } void CStringChecker::evalStrcmp(CheckerContext &C, const CallExpr *CE) const { //int strcmp(const char *s1, const char *s2); evalStrcmpCommon(C, CE, /* IsBounded = */ false, /* IgnoreCase = */ false); } void CStringChecker::evalStrncmp(CheckerContext &C, const CallExpr *CE) const { //int strncmp(const char *s1, const char *s2, size_t n); evalStrcmpCommon(C, CE, /* IsBounded = */ true, /* IgnoreCase = */ false); } void CStringChecker::evalStrcasecmp(CheckerContext &C, const CallExpr *CE) const { //int strcasecmp(const char *s1, const char *s2); evalStrcmpCommon(C, CE, /* IsBounded = */ false, /* IgnoreCase = */ true); } void CStringChecker::evalStrncasecmp(CheckerContext &C, const CallExpr *CE) const { //int strncasecmp(const char *s1, const char *s2, size_t n); evalStrcmpCommon(C, CE, /* IsBounded = */ true, /* IgnoreCase = */ true); } void CStringChecker::evalStrcmpCommon(CheckerContext &C, const CallExpr *CE, bool IsBounded, bool IgnoreCase) const { CurrentFunctionDescription = "string comparison function"; ProgramStateRef state = C.getState(); const LocationContext *LCtx = C.getLocationContext(); // Check that the first string is non-null AnyArgExpr Left = {CE->getArg(0), 0}; SVal LeftVal = state->getSVal(Left.Expression, LCtx); state = checkNonNull(C, state, Left, LeftVal); if (!state) return; // Check that the second string is non-null. AnyArgExpr Right = {CE->getArg(1), 1}; SVal RightVal = state->getSVal(Right.Expression, LCtx); state = checkNonNull(C, state, Right, RightVal); if (!state) return; // Get the string length of the first string or give up. SVal LeftLength = getCStringLength(C, state, Left.Expression, LeftVal); if (LeftLength.isUndef()) return; // Get the string length of the second string or give up. SVal RightLength = getCStringLength(C, state, Right.Expression, RightVal); if (RightLength.isUndef()) return; // If we know the two buffers are the same, we know the result is 0. // First, get the two buffers' addresses. Another checker will have already // made sure they're not undefined. DefinedOrUnknownSVal LV = LeftVal.castAs(); DefinedOrUnknownSVal RV = RightVal.castAs(); // See if they are the same. SValBuilder &svalBuilder = C.getSValBuilder(); DefinedOrUnknownSVal SameBuf = svalBuilder.evalEQ(state, LV, RV); ProgramStateRef StSameBuf, StNotSameBuf; std::tie(StSameBuf, StNotSameBuf) = state->assume(SameBuf); // If the two arguments might be the same buffer, we know the result is 0, // and we only need to check one size. if (StSameBuf) { StSameBuf = StSameBuf->BindExpr(CE, LCtx, svalBuilder.makeZeroVal(CE->getType())); C.addTransition(StSameBuf); // If the two arguments are GUARANTEED to be the same, we're done! if (!StNotSameBuf) return; } assert(StNotSameBuf); state = StNotSameBuf; // At this point we can go about comparing the two buffers. // For now, we only do this if they're both known string literals. // Attempt to extract string literals from both expressions. const StringLiteral *LeftStrLiteral = getCStringLiteral(C, state, Left.Expression, LeftVal); const StringLiteral *RightStrLiteral = getCStringLiteral(C, state, Right.Expression, RightVal); bool canComputeResult = false; SVal resultVal = svalBuilder.conjureSymbolVal(nullptr, CE, LCtx, C.blockCount()); if (LeftStrLiteral && RightStrLiteral) { StringRef LeftStrRef = LeftStrLiteral->getString(); StringRef RightStrRef = RightStrLiteral->getString(); if (IsBounded) { // Get the max number of characters to compare. const Expr *lenExpr = CE->getArg(2); SVal lenVal = state->getSVal(lenExpr, LCtx); // If the length is known, we can get the right substrings. if (const llvm::APSInt *len = svalBuilder.getKnownValue(state, lenVal)) { // Create substrings of each to compare the prefix. LeftStrRef = LeftStrRef.substr(0, (size_t)len->getZExtValue()); RightStrRef = RightStrRef.substr(0, (size_t)len->getZExtValue()); canComputeResult = true; } } else { // This is a normal, unbounded strcmp. canComputeResult = true; } if (canComputeResult) { // Real strcmp stops at null characters. size_t s1Term = LeftStrRef.find('\0'); if (s1Term != StringRef::npos) LeftStrRef = LeftStrRef.substr(0, s1Term); size_t s2Term = RightStrRef.find('\0'); if (s2Term != StringRef::npos) RightStrRef = RightStrRef.substr(0, s2Term); // Use StringRef's comparison methods to compute the actual result. int compareRes = IgnoreCase ? LeftStrRef.compare_insensitive(RightStrRef) : LeftStrRef.compare(RightStrRef); // The strcmp function returns an integer greater than, equal to, or less // than zero, [c11, p7.24.4.2]. if (compareRes == 0) { resultVal = svalBuilder.makeIntVal(compareRes, CE->getType()); } else { DefinedSVal zeroVal = svalBuilder.makeIntVal(0, CE->getType()); // Constrain strcmp's result range based on the result of StringRef's // comparison methods. BinaryOperatorKind op = (compareRes == 1) ? BO_GT : BO_LT; SVal compareWithZero = svalBuilder.evalBinOp(state, op, resultVal, zeroVal, svalBuilder.getConditionType()); DefinedSVal compareWithZeroVal = compareWithZero.castAs(); state = state->assume(compareWithZeroVal, true); } } } state = state->BindExpr(CE, LCtx, resultVal); // Record this as a possible path. C.addTransition(state); } void CStringChecker::evalStrsep(CheckerContext &C, const CallExpr *CE) const { // char *strsep(char **stringp, const char *delim); // Verify whether the search string parameter matches the return type. SourceArgExpr SearchStrPtr = {CE->getArg(0), 0}; QualType CharPtrTy = SearchStrPtr.Expression->getType()->getPointeeType(); if (CharPtrTy.isNull() || CE->getType().getUnqualifiedType() != CharPtrTy.getUnqualifiedType()) return; CurrentFunctionDescription = "strsep()"; ProgramStateRef State = C.getState(); const LocationContext *LCtx = C.getLocationContext(); // Check that the search string pointer is non-null (though it may point to // a null string). SVal SearchStrVal = State->getSVal(SearchStrPtr.Expression, LCtx); State = checkNonNull(C, State, SearchStrPtr, SearchStrVal); if (!State) return; // Check that the delimiter string is non-null. AnyArgExpr DelimStr = {CE->getArg(1), 1}; SVal DelimStrVal = State->getSVal(DelimStr.Expression, LCtx); State = checkNonNull(C, State, DelimStr, DelimStrVal); if (!State) return; SValBuilder &SVB = C.getSValBuilder(); SVal Result; if (Optional SearchStrLoc = SearchStrVal.getAs()) { // Get the current value of the search string pointer, as a char*. Result = State->getSVal(*SearchStrLoc, CharPtrTy); // Invalidate the search string, representing the change of one delimiter // character to NUL. State = InvalidateBuffer(C, State, SearchStrPtr.Expression, Result, /*IsSourceBuffer*/ false, nullptr); // Overwrite the search string pointer. The new value is either an address // further along in the same string, or NULL if there are no more tokens. State = State->bindLoc(*SearchStrLoc, SVB.conjureSymbolVal(getTag(), CE, LCtx, CharPtrTy, C.blockCount()), LCtx); } else { assert(SearchStrVal.isUnknown()); // Conjure a symbolic value. It's the best we can do. Result = SVB.conjureSymbolVal(nullptr, CE, LCtx, C.blockCount()); } // Set the return value, and finish. State = State->BindExpr(CE, LCtx, Result); C.addTransition(State); } // These should probably be moved into a C++ standard library checker. void CStringChecker::evalStdCopy(CheckerContext &C, const CallExpr *CE) const { evalStdCopyCommon(C, CE); } void CStringChecker::evalStdCopyBackward(CheckerContext &C, const CallExpr *CE) const { evalStdCopyCommon(C, CE); } void CStringChecker::evalStdCopyCommon(CheckerContext &C, const CallExpr *CE) const { if (!CE->getArg(2)->getType()->isPointerType()) return; ProgramStateRef State = C.getState(); const LocationContext *LCtx = C.getLocationContext(); // template // _OutputIterator // copy(_InputIterator __first, _InputIterator __last, // _OutputIterator __result) // Invalidate the destination buffer const Expr *Dst = CE->getArg(2); SVal DstVal = State->getSVal(Dst, LCtx); State = InvalidateBuffer(C, State, Dst, DstVal, /*IsSource=*/false, /*Size=*/nullptr); SValBuilder &SVB = C.getSValBuilder(); SVal ResultVal = SVB.conjureSymbolVal(nullptr, CE, LCtx, C.blockCount()); State = State->BindExpr(CE, LCtx, ResultVal); C.addTransition(State); } void CStringChecker::evalMemset(CheckerContext &C, const CallExpr *CE) const { // void *memset(void *s, int c, size_t n); CurrentFunctionDescription = "memory set function"; DestinationArgExpr Buffer = {CE->getArg(0), 0}; AnyArgExpr CharE = {CE->getArg(1), 1}; SizeArgExpr Size = {CE->getArg(2), 2}; ProgramStateRef State = C.getState(); // See if the size argument is zero. const LocationContext *LCtx = C.getLocationContext(); SVal SizeVal = C.getSVal(Size.Expression); QualType SizeTy = Size.Expression->getType(); ProgramStateRef ZeroSize, NonZeroSize; std::tie(ZeroSize, NonZeroSize) = assumeZero(C, State, SizeVal, SizeTy); // Get the value of the memory area. SVal BufferPtrVal = C.getSVal(Buffer.Expression); // If the size is zero, there won't be any actual memory access, so // just bind the return value to the buffer and return. if (ZeroSize && !NonZeroSize) { ZeroSize = ZeroSize->BindExpr(CE, LCtx, BufferPtrVal); C.addTransition(ZeroSize); return; } // Ensure the memory area is not null. // If it is NULL there will be a NULL pointer dereference. State = checkNonNull(C, NonZeroSize, Buffer, BufferPtrVal); if (!State) return; State = CheckBufferAccess(C, State, Buffer, Size, AccessKind::write); if (!State) return; // According to the values of the arguments, bind the value of the second // argument to the destination buffer and set string length, or just // invalidate the destination buffer. if (!memsetAux(Buffer.Expression, C.getSVal(CharE.Expression), Size.Expression, C, State)) return; State = State->BindExpr(CE, LCtx, BufferPtrVal); C.addTransition(State); } void CStringChecker::evalBzero(CheckerContext &C, const CallExpr *CE) const { CurrentFunctionDescription = "memory clearance function"; DestinationArgExpr Buffer = {CE->getArg(0), 0}; SizeArgExpr Size = {CE->getArg(1), 1}; SVal Zero = C.getSValBuilder().makeZeroVal(C.getASTContext().IntTy); ProgramStateRef State = C.getState(); // See if the size argument is zero. SVal SizeVal = C.getSVal(Size.Expression); QualType SizeTy = Size.Expression->getType(); ProgramStateRef StateZeroSize, StateNonZeroSize; std::tie(StateZeroSize, StateNonZeroSize) = assumeZero(C, State, SizeVal, SizeTy); // If the size is zero, there won't be any actual memory access, // In this case we just return. if (StateZeroSize && !StateNonZeroSize) { C.addTransition(StateZeroSize); return; } // Get the value of the memory area. SVal MemVal = C.getSVal(Buffer.Expression); // Ensure the memory area is not null. // If it is NULL there will be a NULL pointer dereference. State = checkNonNull(C, StateNonZeroSize, Buffer, MemVal); if (!State) return; State = CheckBufferAccess(C, State, Buffer, Size, AccessKind::write); if (!State) return; if (!memsetAux(Buffer.Expression, Zero, Size.Expression, C, State)) return; C.addTransition(State); } //===----------------------------------------------------------------------===// // The driver method, and other Checker callbacks. //===----------------------------------------------------------------------===// CStringChecker::FnCheck CStringChecker::identifyCall(const CallEvent &Call, CheckerContext &C) const { const auto *CE = dyn_cast_or_null(Call.getOriginExpr()); if (!CE) return nullptr; const FunctionDecl *FD = dyn_cast_or_null(Call.getDecl()); if (!FD) return nullptr; if (StdCopy.matches(Call)) return &CStringChecker::evalStdCopy; if (StdCopyBackward.matches(Call)) return &CStringChecker::evalStdCopyBackward; // Pro-actively check that argument types are safe to do arithmetic upon. // We do not want to crash if someone accidentally passes a structure // into, say, a C++ overload of any of these functions. We could not check // that for std::copy because they may have arguments of other types. for (auto I : CE->arguments()) { QualType T = I->getType(); if (!T->isIntegralOrEnumerationType() && !T->isPointerType()) return nullptr; } const FnCheck *Callback = Callbacks.lookup(Call); if (Callback) return *Callback; return nullptr; } bool CStringChecker::evalCall(const CallEvent &Call, CheckerContext &C) const { FnCheck Callback = identifyCall(Call, C); // If the callee isn't a string function, let another checker handle it. if (!Callback) return false; // Check and evaluate the call. const auto *CE = cast(Call.getOriginExpr()); (this->*Callback)(C, CE); // If the evaluate call resulted in no change, chain to the next eval call // handler. // Note, the custom CString evaluation calls assume that basic safety // properties are held. However, if the user chooses to turn off some of these // checks, we ignore the issues and leave the call evaluation to a generic // handler. return C.isDifferent(); } void CStringChecker::checkPreStmt(const DeclStmt *DS, CheckerContext &C) const { // Record string length for char a[] = "abc"; ProgramStateRef state = C.getState(); for (const auto *I : DS->decls()) { const VarDecl *D = dyn_cast(I); if (!D) continue; // FIXME: Handle array fields of structs. if (!D->getType()->isArrayType()) continue; const Expr *Init = D->getInit(); if (!Init) continue; if (!isa(Init)) continue; Loc VarLoc = state->getLValue(D, C.getLocationContext()); const MemRegion *MR = VarLoc.getAsRegion(); if (!MR) continue; SVal StrVal = C.getSVal(Init); assert(StrVal.isValid() && "Initializer string is unknown or undefined"); DefinedOrUnknownSVal strLength = getCStringLength(C, state, Init, StrVal).castAs(); state = state->set(MR, strLength); } C.addTransition(state); } ProgramStateRef CStringChecker::checkRegionChanges(ProgramStateRef state, const InvalidatedSymbols *, ArrayRef ExplicitRegions, ArrayRef Regions, const LocationContext *LCtx, const CallEvent *Call) const { CStringLengthTy Entries = state->get(); if (Entries.isEmpty()) return state; llvm::SmallPtrSet Invalidated; llvm::SmallPtrSet SuperRegions; // First build sets for the changed regions and their super-regions. for (ArrayRef::iterator I = Regions.begin(), E = Regions.end(); I != E; ++I) { const MemRegion *MR = *I; Invalidated.insert(MR); SuperRegions.insert(MR); while (const SubRegion *SR = dyn_cast(MR)) { MR = SR->getSuperRegion(); SuperRegions.insert(MR); } } CStringLengthTy::Factory &F = state->get_context(); // Then loop over the entries in the current state. for (CStringLengthTy::iterator I = Entries.begin(), E = Entries.end(); I != E; ++I) { const MemRegion *MR = I.getKey(); // Is this entry for a super-region of a changed region? if (SuperRegions.count(MR)) { Entries = F.remove(Entries, MR); continue; } // Is this entry for a sub-region of a changed region? const MemRegion *Super = MR; while (const SubRegion *SR = dyn_cast(Super)) { Super = SR->getSuperRegion(); if (Invalidated.count(Super)) { Entries = F.remove(Entries, MR); break; } } } return state->set(Entries); } void CStringChecker::checkLiveSymbols(ProgramStateRef state, SymbolReaper &SR) const { // Mark all symbols in our string length map as valid. CStringLengthTy Entries = state->get(); for (CStringLengthTy::iterator I = Entries.begin(), E = Entries.end(); I != E; ++I) { SVal Len = I.getData(); for (SymExpr::symbol_iterator si = Len.symbol_begin(), se = Len.symbol_end(); si != se; ++si) SR.markInUse(*si); } } void CStringChecker::checkDeadSymbols(SymbolReaper &SR, CheckerContext &C) const { ProgramStateRef state = C.getState(); CStringLengthTy Entries = state->get(); if (Entries.isEmpty()) return; CStringLengthTy::Factory &F = state->get_context(); for (CStringLengthTy::iterator I = Entries.begin(), E = Entries.end(); I != E; ++I) { SVal Len = I.getData(); if (SymbolRef Sym = Len.getAsSymbol()) { if (SR.isDead(Sym)) Entries = F.remove(Entries, I.getKey()); } } state = state->set(Entries); C.addTransition(state); } void ento::registerCStringModeling(CheckerManager &Mgr) { Mgr.registerChecker(); } bool ento::shouldRegisterCStringModeling(const CheckerManager &mgr) { return true; } #define REGISTER_CHECKER(name) \ void ento::register##name(CheckerManager &mgr) { \ CStringChecker *checker = mgr.getChecker(); \ checker->Filter.Check##name = true; \ checker->Filter.CheckName##name = mgr.getCurrentCheckerName(); \ } \ \ bool ento::shouldRegister##name(const CheckerManager &mgr) { return true; } REGISTER_CHECKER(CStringNullArg) REGISTER_CHECKER(CStringOutOfBounds) REGISTER_CHECKER(CStringBufferOverlap) REGISTER_CHECKER(CStringNotNullTerm)