| //= CStringChecker.h - Checks calls to C string functions ----------*- C++ -*-// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This defines CStringChecker, which is an assortment of checks on calls |
| // to functions in <string.h>. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "GRExprEngineExperimentalChecks.h" |
| #include "clang/Checker/BugReporter/BugType.h" |
| #include "clang/Checker/PathSensitive/CheckerVisitor.h" |
| #include "llvm/ADT/StringSwitch.h" |
| |
| using namespace clang; |
| |
| namespace { |
| class CStringChecker : public CheckerVisitor<CStringChecker> { |
| BugType *BT_Null, *BT_Bounds, *BT_Overlap; |
| public: |
| CStringChecker() |
| : BT_Null(0), BT_Bounds(0), BT_Overlap(0) {} |
| static void *getTag() { static int tag; return &tag; } |
| |
| bool EvalCallExpr(CheckerContext &C, const CallExpr *CE); |
| |
| typedef void (CStringChecker::*FnCheck)(CheckerContext &, const CallExpr *); |
| |
| void EvalMemcpy(CheckerContext &C, const CallExpr *CE); |
| void EvalMemmove(CheckerContext &C, const CallExpr *CE); |
| void EvalBcopy(CheckerContext &C, const CallExpr *CE); |
| void EvalCopyCommon(CheckerContext &C, const GRState *state, |
| const Expr *Size, const Expr *Source, const Expr *Dest, |
| bool Restricted = false); |
| |
| void EvalMemcmp(CheckerContext &C, const CallExpr *CE); |
| |
| // Utility methods |
| std::pair<const GRState*, const GRState*> |
| AssumeZero(CheckerContext &C, const GRState *state, SVal V, QualType Ty); |
| |
| const GRState *CheckNonNull(CheckerContext &C, const GRState *state, |
| const Expr *S, SVal l); |
| const GRState *CheckLocation(CheckerContext &C, const GRState *state, |
| const Expr *S, SVal l); |
| const GRState *CheckBufferAccess(CheckerContext &C, const GRState *state, |
| const Expr *Size, |
| const Expr *FirstBuf, |
| const Expr *SecondBuf = NULL); |
| const GRState *CheckOverlap(CheckerContext &C, const GRState *state, |
| const Expr *Size, const Expr *First, |
| const Expr *Second); |
| void EmitOverlapBug(CheckerContext &C, const GRState *state, |
| const Stmt *First, const Stmt *Second); |
| }; |
| } //end anonymous namespace |
| |
| void clang::RegisterCStringChecker(GRExprEngine &Eng) { |
| Eng.registerCheck(new CStringChecker()); |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // Individual checks and utility methods. |
| //===----------------------------------------------------------------------===// |
| |
| std::pair<const GRState*, const GRState*> |
| CStringChecker::AssumeZero(CheckerContext &C, const GRState *state, SVal V, |
| QualType Ty) { |
| DefinedSVal *Val = dyn_cast<DefinedSVal>(&V); |
| if (!Val) |
| return std::pair<const GRState*, const GRState *>(state, state); |
| |
| ValueManager &ValMgr = C.getValueManager(); |
| SValuator &SV = ValMgr.getSValuator(); |
| |
| DefinedOrUnknownSVal Zero = ValMgr.makeZeroVal(Ty); |
| DefinedOrUnknownSVal ValIsZero = SV.EvalEQ(state, *Val, Zero); |
| |
| return state->Assume(ValIsZero); |
| } |
| |
| const GRState *CStringChecker::CheckNonNull(CheckerContext &C, |
| const GRState *state, |
| const Expr *S, SVal l) { |
| // If a previous check has failed, propagate the failure. |
| if (!state) |
| return NULL; |
| |
| const GRState *stateNull, *stateNonNull; |
| llvm::tie(stateNull, stateNonNull) = AssumeZero(C, state, l, S->getType()); |
| |
| if (stateNull && !stateNonNull) { |
| ExplodedNode *N = C.GenerateSink(stateNull); |
| if (!N) |
| return NULL; |
| |
| if (!BT_Null) |
| BT_Null = new BuiltinBug("API", |
| "Null pointer argument in call to byte string function"); |
| |
| // Generate a report for this bug. |
| BuiltinBug *BT = static_cast<BuiltinBug*>(BT_Null); |
| EnhancedBugReport *report = new EnhancedBugReport(*BT, |
| BT->getDescription(), N); |
| |
| report->addRange(S->getSourceRange()); |
| report->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue, S); |
| C.EmitReport(report); |
| return NULL; |
| } |
| |
| // From here on, assume that the value is non-null. |
| assert(stateNonNull); |
| return stateNonNull; |
| } |
| |
| // FIXME: This was originally copied from ArrayBoundChecker.cpp. Refactor? |
| const GRState *CStringChecker::CheckLocation(CheckerContext &C, |
| const GRState *state, |
| const Expr *S, SVal l) { |
| // If a previous check has failed, propagate the failure. |
| if (!state) |
| return NULL; |
| |
| // Check for out of bound array element access. |
| const MemRegion *R = l.getAsRegion(); |
| if (!R) |
| return state; |
| |
| const ElementRegion *ER = dyn_cast<ElementRegion>(R); |
| if (!ER) |
| return state; |
| |
| assert(ER->getValueType(C.getASTContext()) == C.getASTContext().CharTy && |
| "CheckLocation should only be called with char* ElementRegions"); |
| |
| // Get the size of the array. |
| const SubRegion *Super = cast<SubRegion>(ER->getSuperRegion()); |
| ValueManager &ValMgr = C.getValueManager(); |
| SVal Extent = ValMgr.convertToArrayIndex(Super->getExtent(ValMgr)); |
| DefinedOrUnknownSVal Size = cast<DefinedOrUnknownSVal>(Extent); |
| |
| // Get the index of the accessed element. |
| DefinedOrUnknownSVal &Idx = cast<DefinedOrUnknownSVal>(ER->getIndex()); |
| |
| const GRState *StInBound = state->AssumeInBound(Idx, Size, true); |
| const GRState *StOutBound = state->AssumeInBound(Idx, Size, false); |
| if (StOutBound && !StInBound) { |
| ExplodedNode *N = C.GenerateSink(StOutBound); |
| if (!N) |
| return NULL; |
| |
| if (!BT_Bounds) |
| BT_Bounds = new BuiltinBug("Out-of-bound array access", |
| "Byte string function accesses out-of-bound array element " |
| "(buffer overflow)"); |
| |
| // 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. |
| |
| // Generate a report for this bug. |
| BuiltinBug *BT = static_cast<BuiltinBug*>(BT_Bounds); |
| RangedBugReport *report = new RangedBugReport(*BT, BT->getDescription(), N); |
| |
| report->addRange(S->getSourceRange()); |
| C.EmitReport(report); |
| return NULL; |
| } |
| |
| // Array bound check succeeded. From this point forward the array bound |
| // should always succeed. |
| return StInBound; |
| } |
| |
| const GRState *CStringChecker::CheckBufferAccess(CheckerContext &C, |
| const GRState *state, |
| const Expr *Size, |
| const Expr *FirstBuf, |
| const Expr *SecondBuf) { |
| // If a previous check has failed, propagate the failure. |
| if (!state) |
| return NULL; |
| |
| ValueManager &VM = C.getValueManager(); |
| SValuator &SV = VM.getSValuator(); |
| ASTContext &Ctx = C.getASTContext(); |
| |
| QualType SizeTy = Ctx.getSizeType(); |
| QualType PtrTy = Ctx.getPointerType(Ctx.CharTy); |
| |
| // Check that the first buffer is non-null. |
| SVal BufVal = state->getSVal(FirstBuf); |
| state = CheckNonNull(C, state, FirstBuf, BufVal); |
| if (!state) |
| return NULL; |
| |
| // Get the access length and make sure it is known. |
| SVal LengthVal = state->getSVal(Size); |
| NonLoc *Length = dyn_cast<NonLoc>(&LengthVal); |
| if (!Length) |
| return state; |
| |
| // Compute the offset of the last element to be accessed: size-1. |
| NonLoc One = cast<NonLoc>(VM.makeIntVal(1, SizeTy)); |
| NonLoc LastOffset = cast<NonLoc>(SV.EvalBinOpNN(state, BinaryOperator::Sub, |
| *Length, One, SizeTy)); |
| |
| // Check that the first buffer is sufficently long. |
| Loc BufStart = cast<Loc>(SV.EvalCast(BufVal, PtrTy, FirstBuf->getType())); |
| SVal BufEnd |
| = SV.EvalBinOpLN(state, BinaryOperator::Add, BufStart, LastOffset, PtrTy); |
| state = CheckLocation(C, state, FirstBuf, BufEnd); |
| |
| // If the buffer isn't large enough, abort. |
| if (!state) |
| return NULL; |
| |
| // If there's a second buffer, check it as well. |
| if (SecondBuf) { |
| BufVal = state->getSVal(SecondBuf); |
| state = CheckNonNull(C, state, SecondBuf, BufVal); |
| if (!state) |
| return NULL; |
| |
| BufStart = cast<Loc>(SV.EvalCast(BufVal, PtrTy, SecondBuf->getType())); |
| BufEnd |
| = SV.EvalBinOpLN(state, BinaryOperator::Add, BufStart, LastOffset, PtrTy); |
| state = CheckLocation(C, state, SecondBuf, BufEnd); |
| } |
| |
| // Large enough or not, return this state! |
| return state; |
| } |
| |
| const GRState *CStringChecker::CheckOverlap(CheckerContext &C, |
| const GRState *state, |
| const Expr *Size, |
| const Expr *First, |
| const Expr *Second) { |
| // 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 NULL; |
| |
| ValueManager &VM = state->getStateManager().getValueManager(); |
| SValuator &SV = VM.getSValuator(); |
| ASTContext &Ctx = VM.getContext(); |
| const GRState *stateTrue, *stateFalse; |
| |
| // Get the buffer values and make sure they're known locations. |
| SVal FirstVal = state->getSVal(First); |
| SVal SecondVal = state->getSVal(Second); |
| |
| Loc *FirstLoc = dyn_cast<Loc>(&FirstVal); |
| if (!FirstLoc) |
| return state; |
| |
| Loc *SecondLoc = dyn_cast<Loc>(&SecondVal); |
| if (!SecondLoc) |
| return state; |
| |
| // Are the two values the same? |
| DefinedOrUnknownSVal EqualTest = SV.EvalEQ(state, *FirstLoc, *SecondLoc); |
| llvm::tie(stateTrue, stateFalse) = state->Assume(EqualTest); |
| |
| if (stateTrue && !stateFalse) { |
| // If the values are known to be equal, that's automatically an overlap. |
| EmitOverlapBug(C, stateTrue, First, Second); |
| return NULL; |
| } |
| |
| // Assume the two expressions are not equal. |
| assert(stateFalse); |
| state = stateFalse; |
| |
| // Which value comes first? |
| QualType CmpTy = Ctx.IntTy; |
| SVal Reverse = SV.EvalBinOpLL(state, BinaryOperator::GT, |
| *FirstLoc, *SecondLoc, CmpTy); |
| DefinedOrUnknownSVal *ReverseTest = dyn_cast<DefinedOrUnknownSVal>(&Reverse); |
| if (!ReverseTest) |
| return state; |
| |
| llvm::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. |
| Loc *tmpLoc = FirstLoc; |
| FirstLoc = SecondLoc; |
| SecondLoc = tmpLoc; |
| |
| // Switch the Exprs as well, so that they still correspond. |
| const Expr *tmpExpr = First; |
| First = Second; |
| Second = tmpExpr; |
| } |
| } |
| |
| // Get the length, and make sure it too is known. |
| SVal LengthVal = state->getSVal(Size); |
| NonLoc *Length = dyn_cast<NonLoc>(&LengthVal); |
| if (!Length) |
| return state; |
| |
| // Convert the first buffer's start address to char*. |
| // Bail out if the cast fails. |
| QualType CharPtrTy = Ctx.getPointerType(Ctx.CharTy); |
| SVal FirstStart = SV.EvalCast(*FirstLoc, CharPtrTy, First->getType()); |
| Loc *FirstStartLoc = dyn_cast<Loc>(&FirstStart); |
| if (!FirstStartLoc) |
| return state; |
| |
| // Compute the end of the first buffer. Bail out if THAT fails. |
| SVal FirstEnd = SV.EvalBinOpLN(state, BinaryOperator::Add, |
| *FirstStartLoc, *Length, CharPtrTy); |
| Loc *FirstEndLoc = dyn_cast<Loc>(&FirstEnd); |
| if (!FirstEndLoc) |
| return state; |
| |
| // Is the end of the first buffer past the start of the second buffer? |
| SVal Overlap = SV.EvalBinOpLL(state, BinaryOperator::GT, |
| *FirstEndLoc, *SecondLoc, CmpTy); |
| DefinedOrUnknownSVal *OverlapTest = dyn_cast<DefinedOrUnknownSVal>(&Overlap); |
| if (!OverlapTest) |
| return state; |
| |
| llvm::tie(stateTrue, stateFalse) = state->Assume(*OverlapTest); |
| |
| if (stateTrue && !stateFalse) { |
| // Overlap! |
| EmitOverlapBug(C, stateTrue, First, Second); |
| return NULL; |
| } |
| |
| // Assume the two expressions don't overlap. |
| assert(stateFalse); |
| return stateFalse; |
| } |
| |
| void CStringChecker::EmitOverlapBug(CheckerContext &C, const GRState *state, |
| const Stmt *First, const Stmt *Second) { |
| ExplodedNode *N = C.GenerateSink(state); |
| if (!N) |
| return; |
| |
| if (!BT_Overlap) |
| BT_Overlap = new BugType("Unix API", "Improper arguments"); |
| |
| // Generate a report for this bug. |
| RangedBugReport *report = |
| new RangedBugReport(*BT_Overlap, |
| "Arguments must not be overlapping buffers", N); |
| report->addRange(First->getSourceRange()); |
| report->addRange(Second->getSourceRange()); |
| |
| C.EmitReport(report); |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // Evaluation of individual function calls. |
| //===----------------------------------------------------------------------===// |
| |
| void CStringChecker::EvalCopyCommon(CheckerContext &C, const GRState *state, |
| const Expr *Size, const Expr *Dest, |
| const Expr *Source, bool Restricted) { |
| // See if the size argument is zero. |
| SVal SizeVal = state->getSVal(Size); |
| QualType SizeTy = Size->getType(); |
| |
| const GRState *StZeroSize, *StNonZeroSize; |
| llvm::tie(StZeroSize, StNonZeroSize) = AssumeZero(C, state, SizeVal, SizeTy); |
| |
| // If the size is zero, there won't be any actual memory access. |
| if (StZeroSize) |
| C.addTransition(StZeroSize); |
| |
| // If the size can be nonzero, we have to check the other arguments. |
| if (StNonZeroSize) { |
| state = StNonZeroSize; |
| state = CheckBufferAccess(C, state, Size, Dest, Source); |
| if (Restricted) |
| state = CheckOverlap(C, state, Size, Dest, Source); |
| if (state) |
| C.addTransition(state); |
| } |
| } |
| |
| |
| void CStringChecker::EvalMemcpy(CheckerContext &C, const CallExpr *CE) { |
| // void *memcpy(void *restrict dst, const void *restrict src, size_t n); |
| // The return value is the address of the destination buffer. |
| const Expr *Dest = CE->getArg(0); |
| const GRState *state = C.getState(); |
| state = state->BindExpr(CE, state->getSVal(Dest)); |
| EvalCopyCommon(C, state, CE->getArg(2), Dest, CE->getArg(1), true); |
| } |
| |
| void CStringChecker::EvalMemmove(CheckerContext &C, const CallExpr *CE) { |
| // void *memmove(void *dst, const void *src, size_t n); |
| // The return value is the address of the destination buffer. |
| const Expr *Dest = CE->getArg(0); |
| const GRState *state = C.getState(); |
| state = state->BindExpr(CE, state->getSVal(Dest)); |
| EvalCopyCommon(C, state, CE->getArg(2), Dest, CE->getArg(1)); |
| } |
| |
| void CStringChecker::EvalBcopy(CheckerContext &C, const CallExpr *CE) { |
| // void bcopy(const void *src, void *dst, size_t n); |
| EvalCopyCommon(C, C.getState(), CE->getArg(2), CE->getArg(1), CE->getArg(0)); |
| } |
| |
| void CStringChecker::EvalMemcmp(CheckerContext &C, const CallExpr *CE) { |
| // int memcmp(const void *s1, const void *s2, size_t n); |
| const Expr *Left = CE->getArg(0); |
| const Expr *Right = CE->getArg(1); |
| const Expr *Size = CE->getArg(2); |
| |
| const GRState *state = C.getState(); |
| ValueManager &ValMgr = C.getValueManager(); |
| SValuator &SV = ValMgr.getSValuator(); |
| |
| // See if the size argument is zero. |
| SVal SizeVal = state->getSVal(Size); |
| QualType SizeTy = Size->getType(); |
| |
| const GRState *StZeroSize, *StNonZeroSize; |
| llvm::tie(StZeroSize, StNonZeroSize) = 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 (StZeroSize) { |
| state = StZeroSize; |
| state = state->BindExpr(CE, ValMgr.makeZeroVal(CE->getType())); |
| C.addTransition(state); |
| } |
| |
| // If the size can be nonzero, we have to check the other arguments. |
| if (StNonZeroSize) { |
| state = StNonZeroSize; |
| |
| // 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 = cast<DefinedOrUnknownSVal>(state->getSVal(Left)); |
| DefinedOrUnknownSVal RV = cast<DefinedOrUnknownSVal>(state->getSVal(Right)); |
| |
| // See if they are the same. |
| DefinedOrUnknownSVal SameBuf = SV.EvalEQ(state, LV, RV); |
| const GRState *StSameBuf, *StNotSameBuf; |
| llvm::tie(StSameBuf, StNotSameBuf) = state->Assume(SameBuf); |
| |
| // If the two arguments might be the same buffer, we know the result is zero, |
| // and we only need to check one size. |
| if (StSameBuf) { |
| state = StSameBuf; |
| state = CheckBufferAccess(C, state, Size, Left); |
| if (state) { |
| state = StSameBuf->BindExpr(CE, ValMgr.makeZeroVal(CE->getType())); |
| C.addTransition(state); |
| } |
| } |
| |
| // If the two arguments might be different buffers, we have to check the |
| // size of both of them. |
| if (StNotSameBuf) { |
| state = StNotSameBuf; |
| state = CheckBufferAccess(C, state, Size, Left, Right); |
| if (state) { |
| // The return value is the comparison result, which we don't know. |
| unsigned Count = C.getNodeBuilder().getCurrentBlockCount(); |
| SVal CmpV = ValMgr.getConjuredSymbolVal(NULL, CE, CE->getType(), Count); |
| state = state->BindExpr(CE, CmpV); |
| C.addTransition(state); |
| } |
| } |
| } |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // The driver method. |
| //===----------------------------------------------------------------------===// |
| |
| bool CStringChecker::EvalCallExpr(CheckerContext &C, const CallExpr *CE) { |
| // Get the callee. All the functions we care about are C functions |
| // with simple identifiers. |
| const GRState *state = C.getState(); |
| const Expr *Callee = CE->getCallee(); |
| const FunctionDecl *FD = state->getSVal(Callee).getAsFunctionDecl(); |
| |
| if (!FD) |
| return false; |
| |
| // Get the name of the callee. If it's a builtin, strip off the prefix. |
| llvm::StringRef Name = FD->getName(); |
| if (Name.startswith("__builtin_")) |
| Name = Name.substr(10); |
| |
| FnCheck EvalFunction = llvm::StringSwitch<FnCheck>(Name) |
| .Cases("memcpy", "__memcpy_chk", &CStringChecker::EvalMemcpy) |
| .Cases("memcmp", "bcmp", &CStringChecker::EvalMemcmp) |
| .Cases("memmove", "__memmove_chk", &CStringChecker::EvalMemmove) |
| .Case("bcopy", &CStringChecker::EvalBcopy) |
| .Default(NULL); |
| |
| // If the callee isn't a string function, let another checker handle it. |
| if (!EvalFunction) |
| return false; |
| |
| // Check and evaluate the call. |
| (this->*EvalFunction)(C, CE); |
| return true; |
| } |