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llvm-project/clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp

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//= CStringChecker.cpp - 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 "ClangSACheckers.h"
#include "InterCheckerAPI.h"
#include "clang/Basic/CharInfo.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/CheckerManager.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Support/raw_ostream.h"
using namespace clang;
using namespace ento;
namespace {
class CStringChecker : public Checker< eval::Call,
check::PreStmt<DeclStmt>,
check::LiveSymbols,
check::DeadSymbols,
check::RegionChanges
> {
mutable std::unique_ptr<BugType> 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;
CheckName CheckNameCStringNullArg;
CheckName CheckNameCStringOutOfBounds;
CheckName CheckNameCStringBufferOverlap;
CheckName CheckNameCStringNotNullTerm;
};
CStringChecksFilter Filter;
static void *getTag() { static int tag; return &tag; }
bool evalCall(const CallExpr *CE, 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;
bool wantsRegionChangeUpdate(ProgramStateRef state) const;
ProgramStateRef
checkRegionChanges(ProgramStateRef state,
const InvalidatedSymbols *,
ArrayRef<const MemRegion *> ExplicitRegions,
ArrayRef<const MemRegion *> Regions,
const CallEvent *Call) const;
typedef void (CStringChecker::*FnCheck)(CheckerContext &,
const CallExpr *) 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,
const Expr *Size,
const Expr *Source,
const Expr *Dest,
bool Restricted = false,
bool IsMempcpy = false) 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 evalStrcpyCommon(CheckerContext &C,
const CallExpr *CE,
bool returnEnd,
bool isBounded,
bool isAppending) const;
void evalStrcat(CheckerContext &C, const CallExpr *CE) const;
void evalStrncat(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;
// Utility methods
std::pair<ProgramStateRef , ProgramStateRef >
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);
static bool SummarizeRegion(raw_ostream &os, ASTContext &Ctx,
const MemRegion *MR);
// Re-usable checks
ProgramStateRef checkNonNull(CheckerContext &C,
ProgramStateRef state,
const Expr *S,
SVal l) const;
ProgramStateRef CheckLocation(CheckerContext &C,
ProgramStateRef state,
const Expr *S,
SVal l,
const char *message = nullptr) const;
ProgramStateRef CheckBufferAccess(CheckerContext &C,
ProgramStateRef state,
const Expr *Size,
const Expr *FirstBuf,
const Expr *SecondBuf,
const char *firstMessage = nullptr,
const char *secondMessage = nullptr,
bool WarnAboutSize = false) const;
ProgramStateRef CheckBufferAccess(CheckerContext &C,
ProgramStateRef state,
const Expr *Size,
const Expr *Buf,
const char *message = nullptr,
bool WarnAboutSize = false) const {
// This is a convenience override.
return CheckBufferAccess(C, state, Size, Buf, nullptr, message, nullptr,
WarnAboutSize);
}
ProgramStateRef CheckOverlap(CheckerContext &C,
ProgramStateRef state,
const Expr *Size,
const Expr *First,
const Expr *Second) const;
void emitOverlapBug(CheckerContext &C,
ProgramStateRef state,
const Stmt *First,
const Stmt *Second) const;
ProgramStateRef checkAdditionOverflow(CheckerContext &C,
ProgramStateRef state,
NonLoc left,
NonLoc right) const;
};
} //end anonymous namespace
REGISTER_MAP_WITH_PROGRAMSTATE(CStringLength, const MemRegion *, SVal)
//===----------------------------------------------------------------------===//
// Individual checks and utility methods.
//===----------------------------------------------------------------------===//
std::pair<ProgramStateRef , ProgramStateRef >
CStringChecker::assumeZero(CheckerContext &C, ProgramStateRef state, SVal V,
QualType Ty) {
Optional<DefinedSVal> val = V.getAs<DefinedSVal>();
if (!val)
return std::pair<ProgramStateRef , ProgramStateRef >(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,
const Expr *S, 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, S->getType());
if (stateNull && !stateNonNull) {
if (!Filter.CheckCStringNullArg)
return nullptr;
ExplodedNode *N = C.generateSink(stateNull);
if (!N)
return nullptr;
if (!BT_Null)
BT_Null.reset(new BuiltinBug(
Filter.CheckNameCStringNullArg, categories::UnixAPI,
"Null pointer argument in call to byte string function"));
SmallString<80> buf;
llvm::raw_svector_ostream os(buf);
assert(CurrentFunctionDescription);
os << "Null pointer argument in call to " << CurrentFunctionDescription;
// Generate a report for this bug.
BuiltinBug *BT = static_cast<BuiltinBug*>(BT_Null.get());
BugReport *report = new BugReport(*BT, os.str(), N);
report->addRange(S->getSourceRange());
bugreporter::trackNullOrUndefValue(N, S, *report);
C.emitReport(report);
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,
const Expr *S, SVal l,
const char *warningMsg) 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 = l.getAsRegion();
if (!R)
return state;
const ElementRegion *ER = dyn_cast<ElementRegion>(R);
if (!ER)
return state;
assert(ER->getValueType() == C.getASTContext().CharTy &&
"CheckLocation should only be called with char* ElementRegions");
// Get the size of the array.
const SubRegion *superReg = cast<SubRegion>(ER->getSuperRegion());
SValBuilder &svalBuilder = C.getSValBuilder();
SVal Extent =
svalBuilder.convertToArrayIndex(superReg->getExtent(svalBuilder));
DefinedOrUnknownSVal Size = Extent.castAs<DefinedOrUnknownSVal>();
// Get the index of the accessed element.
DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();
ProgramStateRef StInBound = state->assumeInBound(Idx, Size, true);
ProgramStateRef StOutBound = state->assumeInBound(Idx, Size, false);
if (StOutBound && !StInBound) {
ExplodedNode *N = C.generateSink(StOutBound);
if (!N)
return nullptr;
if (!BT_Bounds) {
BT_Bounds.reset(new BuiltinBug(
Filter.CheckNameCStringOutOfBounds, "Out-of-bound array access",
"Byte string function accesses out-of-bound array element"));
}
BuiltinBug *BT = static_cast<BuiltinBug*>(BT_Bounds.get());
// Generate a report for this bug.
BugReport *report;
if (warningMsg) {
report = new BugReport(*BT, warningMsg, N);
} else {
assert(CurrentFunctionDescription);
assert(CurrentFunctionDescription[0] != '\0');
SmallString<80> buf;
llvm::raw_svector_ostream os(buf);
os << toUppercase(CurrentFunctionDescription[0])
<< &CurrentFunctionDescription[1]
<< " accesses out-of-bound array element";
report = new BugReport(*BT, os.str(), N);
}
// 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.
report->addRange(S->getSourceRange());
C.emitReport(report);
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,
const Expr *Size,
const Expr *FirstBuf,
const Expr *SecondBuf,
const char *firstMessage,
const char *secondMessage,
bool WarnAboutSize) const {
// If a previous check has failed, propagate the failure.
if (!state)
return nullptr;
SValBuilder &svalBuilder = C.getSValBuilder();
ASTContext &Ctx = svalBuilder.getContext();
const LocationContext *LCtx = C.getLocationContext();
QualType sizeTy = Size->getType();
QualType PtrTy = Ctx.getPointerType(Ctx.CharTy);
// Check that the first buffer is non-null.
SVal BufVal = state->getSVal(FirstBuf, LCtx);
state = checkNonNull(C, state, FirstBuf, 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 = state->getSVal(Size, LCtx);
Optional<NonLoc> Length = LengthVal.getAs<NonLoc>();
if (!Length)
return state;
// Compute the offset of the last element to be accessed: size-1.
NonLoc One = svalBuilder.makeIntVal(1, sizeTy).castAs<NonLoc>();
NonLoc LastOffset = svalBuilder
.evalBinOpNN(state, BO_Sub, *Length, One, sizeTy).castAs<NonLoc>();
// Check that the first buffer is sufficiently long.
SVal BufStart = svalBuilder.evalCast(BufVal, PtrTy, FirstBuf->getType());
if (Optional<Loc> BufLoc = BufStart.getAs<Loc>()) {
const Expr *warningExpr = (WarnAboutSize ? Size : FirstBuf);
SVal BufEnd = svalBuilder.evalBinOpLN(state, BO_Add, *BufLoc,
LastOffset, PtrTy);
state = CheckLocation(C, state, warningExpr, BufEnd, firstMessage);
// If the buffer isn't large enough, abort.
if (!state)
return nullptr;
}
// If there's a second buffer, check it as well.
if (SecondBuf) {
BufVal = state->getSVal(SecondBuf, LCtx);
state = checkNonNull(C, state, SecondBuf, BufVal);
if (!state)
return nullptr;
BufStart = svalBuilder.evalCast(BufVal, PtrTy, SecondBuf->getType());
if (Optional<Loc> BufLoc = BufStart.getAs<Loc>()) {
const Expr *warningExpr = (WarnAboutSize ? Size : SecondBuf);
SVal BufEnd = svalBuilder.evalBinOpLN(state, BO_Add, *BufLoc,
LastOffset, PtrTy);
state = CheckLocation(C, state, warningExpr, BufEnd, secondMessage);
}
}
// Large enough or not, return this state!
return state;
}
ProgramStateRef CStringChecker::CheckOverlap(CheckerContext &C,
ProgramStateRef state,
const Expr *Size,
const Expr *First,
const Expr *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, LCtx);
SVal secondVal = state->getSVal(Second, LCtx);
Optional<Loc> firstLoc = firstVal.getAs<Loc>();
if (!firstLoc)
return state;
Optional<Loc> secondLoc = secondVal.getAs<Loc>();
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, Second);
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<DefinedOrUnknownSVal> reverseTest =
reverse.getAs<DefinedOrUnknownSVal>();
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, LCtx);
Optional<NonLoc> Length = LengthVal.getAs<NonLoc>();
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->getType());
Optional<Loc> FirstStartLoc = FirstStart.getAs<Loc>();
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<Loc> FirstEndLoc = FirstEnd.getAs<Loc>();
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<DefinedOrUnknownSVal> OverlapTest =
Overlap.getAs<DefinedOrUnknownSVal>();
if (!OverlapTest)
return state;
std::tie(stateTrue, stateFalse) = state->assume(*OverlapTest);
if (stateTrue && !stateFalse) {
// Overlap!
emitOverlapBug(C, stateTrue, First, Second);
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.generateSink(state);
if (!N)
return;
if (!BT_Overlap)
BT_Overlap.reset(new BugType(Filter.CheckNameCStringBufferOverlap,
categories::UnixAPI, "Improper arguments"));
// Generate a report for this bug.
BugReport *report =
new BugReport(*BT_Overlap,
"Arguments must not be overlapping buffers", N);
report->addRange(First->getSourceRange());
report->addRange(Second->getSourceRange());
C.emitReport(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<nonloc::ConcreteInt>()) {
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<NonLoc> maxMinusRightNL = maxMinusRight.getAs<NonLoc>()) {
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<DefinedOrUnknownSVal>());
if (stateOverflow && !stateOkay) {
// We have an overflow. Emit a bug report.
ExplodedNode *N = C.generateSink(stateOverflow);
if (!N)
return nullptr;
if (!BT_AdditionOverflow)
BT_AdditionOverflow.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 *warning =
"This expression will create a string whose length is too big to "
"be represented as a size_t";
// Generate a report for this bug.
BugReport *report = new BugReport(*BT_AdditionOverflow, warning, N);
C.emitReport(report);
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::VarRegionKind:
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<CStringLength>(MR);
return state->set<CStringLength>(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<CStringLength>(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.blockCount());
if (!hypothetical) {
if (Optional<NonLoc> strLn = strLength.getAs<NonLoc>()) {
// 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<DefinedOrUnknownSVal>(), true);
}
state = state->set<CStringLength>(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<loc::GotoLabel> Label = Buf.getAs<loc::GotoLabel>()) {
if (!Filter.CheckCStringNotNullTerm)
return UndefinedVal();
if (ExplodedNode *N = C.addTransition(state)) {
if (!BT_NotCString)
BT_NotCString.reset(new BuiltinBug(
Filter.CheckNameCStringNotNullTerm, categories::UnixAPI,
"Argument is not a null-terminated string."));
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";
// Generate a report for this bug.
BugReport *report = new BugReport(*BT_NotCString, os.str(), N);
report->addRange(Ex->getSourceRange());
C.emitReport(report);
}
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<StringRegion>(MR)->getStringLiteral();
return svalBuilder.makeIntVal(strLit->getByteLength(), sizeTy);
}
case MemRegion::SymbolicRegionKind:
case MemRegion::AllocaRegionKind:
case MemRegion::VarRegionKind:
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)
return UndefinedVal();
if (ExplodedNode *N = C.addTransition(state)) {
if (!BT_NotCString)
BT_NotCString.reset(new BuiltinBug(
Filter.CheckNameCStringNotNullTerm, categories::UnixAPI,
"Argument is not a null-terminated string."));
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";
// Generate a report for this bug.
BugReport *report = new BugReport(*BT_NotCString,
os.str(), N);
report->addRange(Ex->getSourceRange());
C.emitReport(report);
}
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<StringRegion>(bufRegion);
if (!strRegion)
return nullptr;
// Return the actual string in the string region.
return strRegion->getStringLiteral();
}
ProgramStateRef CStringChecker::InvalidateBuffer(CheckerContext &C,
ProgramStateRef state,
const Expr *E, SVal V,
bool IsSourceBuffer) {
Optional<Loc> L = V.getAs<Loc>();
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<loc::MemRegionVal> MR = L->getAs<loc::MemRegionVal>()) {
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<ElementRegion>(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,
RegionAndSymbolInvalidationTraits::TK_PreserveContents);
ITraits.setTrait(R, RegionAndSymbolInvalidationTraits::TK_SuppressEscape);
CausesPointerEscape = true;
}
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) {
const TypedValueRegion *TVR = dyn_cast<TypedValueRegion>(MR);
switch (MR->getKind()) {
case MemRegion::FunctionTextRegionKind: {
const NamedDecl *FD = cast<FunctionTextRegion>(MR)->getDecl();
if (FD)
os << "the address of the function '" << *FD << '\'';
else
os << "the address of a function";
return true;
}
case MemRegion::BlockTextRegionKind:
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 " << TVR->getValueType().getAsString();
return true;
case MemRegion::VarRegionKind:
os << "a variable of type" << TVR->getValueType().getAsString();
return true;
case MemRegion::FieldRegionKind:
os << "a field of type " << TVR->getValueType().getAsString();
return true;
case MemRegion::ObjCIvarRegionKind:
os << "an instance variable of type " << TVR->getValueType().getAsString();
return true;
default:
return false;
}
}
//===----------------------------------------------------------------------===//
// evaluation of individual function calls.
//===----------------------------------------------------------------------===//
void CStringChecker::evalCopyCommon(CheckerContext &C,
const CallExpr *CE,
ProgramStateRef state,
const Expr *Size, const Expr *Dest,
const Expr *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, LCtx);
QualType sizeTy = Size->getType();
ProgramStateRef stateZeroSize, stateNonZeroSize;
std::tie(stateZeroSize, stateNonZeroSize) =
assumeZero(C, state, sizeVal, sizeTy);
// Get the value of the Dest.
SVal destVal = state->getSVal(Dest, 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, 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.
const char * const writeWarning =
"Memory copy function overflows destination buffer";
state = CheckBufferAccess(C, state, Size, Dest, Source,
writeWarning, /* sourceWarning = */ nullptr);
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) {
loc::MemRegionVal destRegVal = destVal.castAs<loc::MemRegionVal>();
// Get the length to copy.
if (Optional<NonLoc> lenValNonLoc = sizeVal.getAs<NonLoc>()) {
// Get the byte after the last byte copied.
SVal lastElement = C.getSValBuilder().evalBinOpLN(state, BO_Add,
destRegVal,
*lenValNonLoc,
Dest->getType());
// The byte after the last byte copied is the return value.
state = state->BindExpr(CE, LCtx, lastElement);
} else {
// If we don't know how much we copied, we can at least
// conjure a return value for later.
SVal result = C.getSValBuilder().conjureSymbolVal(nullptr, CE, LCtx,
C.blockCount());
state = state->BindExpr(CE, LCtx, result);
}
} 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, C.getSVal(Dest),
/*IsSourceBuffer*/false);
// Invalidate the source (const-invalidation without const-pointer-escaping
// the address of the top-level region).
state = InvalidateBuffer(C, state, Source, C.getSVal(Source),
/*IsSourceBuffer*/true);
C.addTransition(state);
}
}
void CStringChecker::evalMemcpy(CheckerContext &C, const CallExpr *CE) const {
if (CE->getNumArgs() < 3)
return;
// 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);
ProgramStateRef state = C.getState();
evalCopyCommon(C, CE, state, CE->getArg(2), Dest, CE->getArg(1), true);
}
void CStringChecker::evalMempcpy(CheckerContext &C, const CallExpr *CE) const {
if (CE->getNumArgs() < 3)
return;
// 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.
const Expr *Dest = CE->getArg(0);
ProgramStateRef state = C.getState();
evalCopyCommon(C, CE, state, CE->getArg(2), Dest, CE->getArg(1), true, true);
}
void CStringChecker::evalMemmove(CheckerContext &C, const CallExpr *CE) const {
if (CE->getNumArgs() < 3)
return;
// 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);
ProgramStateRef state = C.getState();
evalCopyCommon(C, CE, state, CE->getArg(2), Dest, CE->getArg(1));
}
void CStringChecker::evalBcopy(CheckerContext &C, const CallExpr *CE) const {
if (CE->getNumArgs() < 3)
return;
// void bcopy(const void *src, void *dst, size_t n);
evalCopyCommon(C, CE, C.getState(),
CE->getArg(2), CE->getArg(1), CE->getArg(0));
}
void CStringChecker::evalMemcmp(CheckerContext &C, const CallExpr *CE) const {
if (CE->getNumArgs() < 3)
return;
// int memcmp(const void *s1, const void *s2, size_t n);
CurrentFunctionDescription = "memory comparison function";
const Expr *Left = CE->getArg(0);
const Expr *Right = CE->getArg(1);
const Expr *Size = CE->getArg(2);
ProgramStateRef state = C.getState();
SValBuilder &svalBuilder = C.getSValBuilder();
// See if the size argument is zero.
const LocationContext *LCtx = C.getLocationContext();
SVal sizeVal = state->getSVal(Size, LCtx);
QualType sizeTy = Size->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,
svalBuilder.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, LCtx).castAs<DefinedOrUnknownSVal>();
DefinedOrUnknownSVal RV =
state->getSVal(Right, LCtx).castAs<DefinedOrUnknownSVal>();
// See if they are the same.
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) {
state = StSameBuf;
state = CheckBufferAccess(C, state, Size, Left);
if (state) {
state = StSameBuf->BindExpr(CE, LCtx,
svalBuilder.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.
SVal CmpV = svalBuilder.conjureSymbolVal(nullptr, CE, LCtx,
C.blockCount());
state = state->BindExpr(CE, LCtx, CmpV);
C.addTransition(state);
}
}
}
}
void CStringChecker::evalstrLength(CheckerContext &C,
const CallExpr *CE) const {
if (CE->getNumArgs() < 1)
return;
// size_t strlen(const char *s);
evalstrLengthCommon(C, CE, /* IsStrnlen = */ false);
}
void CStringChecker::evalstrnLength(CheckerContext &C,
const CallExpr *CE) const {
if (CE->getNumArgs() < 2)
return;
// 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.
const Expr *Arg = CE->getArg(0);
SVal ArgVal = state->getSVal(Arg, LCtx);
state = checkNonNull(C, state, Arg, ArgVal);
if (!state)
return;
SVal strLength = getCStringLength(C, state, Arg, 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<NonLoc> strLengthNL = strLength.getAs<NonLoc>();
Optional<NonLoc> maxlenValNL = maxlenVal.getAs<NonLoc>();
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<DefinedOrUnknownSVal>());
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<NonLoc>();
if (strLengthNL) {
state = state->assume(C.getSValBuilder().evalBinOpNN(
state, BO_LE, resultNL, *strLengthNL, cmpTy)
.castAs<DefinedOrUnknownSVal>(), true);
}
if (maxlenValNL) {
state = state->assume(C.getSValBuilder().evalBinOpNN(
state, BO_LE, resultNL, *maxlenValNL, cmpTy)
.castAs<DefinedOrUnknownSVal>(), true);
}
}
} else {
// This is a plain strlen(), not strnlen().
result = strLength.castAs<DefinedOrUnknownSVal>();
// 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 {
if (CE->getNumArgs() < 2)
return;
// char *strcpy(char *restrict dst, const char *restrict src);
evalStrcpyCommon(C, CE,
/* returnEnd = */ false,
/* isBounded = */ false,
/* isAppending = */ false);
}
void CStringChecker::evalStrncpy(CheckerContext &C, const CallExpr *CE) const {
if (CE->getNumArgs() < 3)
return;
// char *strncpy(char *restrict dst, const char *restrict src, size_t n);
evalStrcpyCommon(C, CE,
/* returnEnd = */ false,
/* isBounded = */ true,
/* isAppending = */ false);
}
void CStringChecker::evalStpcpy(CheckerContext &C, const CallExpr *CE) const {
if (CE->getNumArgs() < 2)
return;
// char *stpcpy(char *restrict dst, const char *restrict src);
evalStrcpyCommon(C, CE,
/* returnEnd = */ true,
/* isBounded = */ false,
/* isAppending = */ false);
}
void CStringChecker::evalStrcat(CheckerContext &C, const CallExpr *CE) const {
if (CE->getNumArgs() < 2)
return;
//char *strcat(char *restrict s1, const char *restrict s2);
evalStrcpyCommon(C, CE,
/* returnEnd = */ false,
/* isBounded = */ false,
/* isAppending = */ true);
}
void CStringChecker::evalStrncat(CheckerContext &C, const CallExpr *CE) const {
if (CE->getNumArgs() < 3)
return;
//char *strncat(char *restrict s1, const char *restrict s2, size_t n);
evalStrcpyCommon(C, CE,
/* returnEnd = */ false,
/* isBounded = */ true,
/* isAppending = */ true);
}
void CStringChecker::evalStrcpyCommon(CheckerContext &C, const CallExpr *CE,
bool returnEnd, bool isBounded,
bool isAppending) const {
CurrentFunctionDescription = "string copy function";
ProgramStateRef state = C.getState();
const LocationContext *LCtx = C.getLocationContext();
// Check that the destination is non-null.
const Expr *Dst = CE->getArg(0);
SVal DstVal = state->getSVal(Dst, LCtx);
state = checkNonNull(C, state, Dst, DstVal);
if (!state)
return;
// Check that the source is non-null.
const Expr *srcExpr = CE->getArg(1);
SVal srcVal = state->getSVal(srcExpr, LCtx);
state = checkNonNull(C, state, srcExpr, srcVal);
if (!state)
return;
// Get the string length of the source.
SVal strLength = getCStringLength(C, state, srcExpr, srcVal);
// 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;
// If the function is strncpy, strncat, etc... it is bounded.
if (isBounded) {
// Get the max number of characters to copy.
const Expr *lenExpr = CE->getArg(2);
SVal lenVal = state->getSVal(lenExpr, LCtx);
// Protect against misdeclared strncpy().
lenVal = svalBuilder.evalCast(lenVal, sizeTy, lenExpr->getType());
Optional<NonLoc> strLengthNL = strLength.getAs<NonLoc>();
Optional<NonLoc> lenValNL = lenVal.getAs<NonLoc>();
// If we know both values, we might be able to figure out how much
// we're copying.
if (strLengthNL && lenValNL) {
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<DefinedOrUnknownSVal>());
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;
}
}
// We still want to know if the bound is known to be too large.
if (lenValNL) {
if (isAppending) {
// 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.
SVal dstStrLength = getCStringLength(C, state, Dst, DstVal);
if (dstStrLength.isUndef())
return;
if (Optional<NonLoc> dstStrLengthNL = dstStrLength.getAs<NonLoc>()) {
maxLastElementIndex = svalBuilder.evalBinOpNN(state, BO_Add,
*lenValNL,
*dstStrLengthNL,
sizeTy);
boundWarning = "Size argument is greater than the free space in the "
"destination buffer";
}
} else {
// For strncpy, 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) {
StateZeroSize = StateZeroSize->BindExpr(CE, LCtx, DstVal);
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<NonLoc>();
maxLastElementIndex = svalBuilder.evalBinOpNN(state, BO_Sub, *lenValNL,
one, sizeTy);
boundWarning = "Size argument is greater than the length of the "
"destination buffer";
}
}
// If we couldn't pin down the copy length, at least bound it.
// FIXME: We should actually run this code path for append as well, but
// right now it creates problems with constraints (since we can end up
// trying to pass constraints from symbol to symbol).
if (amountCopied.isUnknown() && !isAppending) {
// 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.
amountCopied = getCStringLength(C, state, lenExpr, srcVal, true);
assert(!amountCopied.isUndef());
if (Optional<NonLoc> amountCopiedNL = amountCopied.getAs<NonLoc>()) {
if (lenValNL) {
// amountCopied <= lenVal
SVal copiedLessThanBound = svalBuilder.evalBinOpNN(state, BO_LE,
*amountCopiedNL,
*lenValNL,
cmpTy);
state = state->assume(
copiedLessThanBound.castAs<DefinedOrUnknownSVal>(), true);
if (!state)
return;
}
if (strLengthNL) {
// amountCopied <= strlen(source)
SVal copiedLessThanSrc = svalBuilder.evalBinOpNN(state, BO_LE,
*amountCopiedNL,
*strLengthNL,
cmpTy);
state = state->assume(
copiedLessThanSrc.castAs<DefinedOrUnknownSVal>(), true);
if (!state)
return;
}
}
}
} 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();
// 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 (isAppending) {
// 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.
SVal dstStrLength = getCStringLength(C, state, Dst, DstVal);
if (dstStrLength.isUndef())
return;
Optional<NonLoc> srcStrLengthNL = amountCopied.getAs<NonLoc>();
Optional<NonLoc> dstStrLengthNL = dstStrLength.getAs<NonLoc>();
// If we know both string lengths, we might know the final string length.
if (srcStrLengthNL && dstStrLengthNL) {
// Make sure the two lengths together don't overflow a size_t.
state = checkAdditionOverflow(C, state, *srcStrLengthNL, *dstStrLengthNL);
if (!state)
return;
finalStrLength = svalBuilder.evalBinOpNN(state, BO_Add, *srcStrLengthNL,
*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<NonLoc> finalStrLengthNL = finalStrLength.getAs<NonLoc>()) {
if (srcStrLengthNL) {
// finalStrLength >= srcStrLength
SVal sourceInResult = svalBuilder.evalBinOpNN(state, BO_GE,
*finalStrLengthNL,
*srcStrLengthNL,
cmpTy);
state = state->assume(sourceInResult.castAs<DefinedOrUnknownSVal>(),
true);
if (!state)
return;
}
if (dstStrLengthNL) {
// finalStrLength >= dstStrLength
SVal destInResult = svalBuilder.evalBinOpNN(state, BO_GE,
*finalStrLengthNL,
*dstStrLengthNL,
cmpTy);
state =
state->assume(destInResult.castAs<DefinedOrUnknownSVal>(), 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;
}
// 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.
SVal Result = (returnEnd ? UnknownVal() : DstVal);
assert(state);
// If the destination is a MemRegion, try to check for a buffer overflow and
// record the new string length.
if (Optional<loc::MemRegionVal> dstRegVal =
DstVal.getAs<loc::MemRegionVal>()) {
QualType ptrTy = Dst->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 (boundWarning) {
if (Optional<NonLoc> maxLastNL = maxLastElementIndex.getAs<NonLoc>()) {
SVal maxLastElement = svalBuilder.evalBinOpLN(state, BO_Add, *dstRegVal,
*maxLastNL, ptrTy);
state = CheckLocation(C, state, CE->getArg(2), maxLastElement,
boundWarning);
if (!state)
return;
}
}
// Then, if the final length is known...
if (Optional<NonLoc> knownStrLength = finalStrLength.getAs<NonLoc>()) {
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) {
const char * const warningMsg =
"String copy function overflows destination buffer";
state = CheckLocation(C, state, Dst, lastElement, warningMsg);
if (!state)
return;
}
// If this is a stpcpy-style copy, the last element is the return value.
if (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, *dstRegVal,
/*IsSourceBuffer*/false);
// Invalidate the source (const-invalidation without const-pointer-escaping
// the address of the top-level region).
state = InvalidateBuffer(C, state, srcExpr, srcVal, /*IsSourceBuffer*/true);
// Set the C string length of the destination, if we know it.
if (isBounded && !isAppending) {
// 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 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 {
if (CE->getNumArgs() < 2)
return;
//int strcmp(const char *s1, const char *s2);
evalStrcmpCommon(C, CE, /* isBounded = */ false, /* ignoreCase = */ false);
}
void CStringChecker::evalStrncmp(CheckerContext &C, const CallExpr *CE) const {
if (CE->getNumArgs() < 3)
return;
//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 {
if (CE->getNumArgs() < 2)
return;
//int strcasecmp(const char *s1, const char *s2);
evalStrcmpCommon(C, CE, /* isBounded = */ false, /* ignoreCase = */ true);
}
void CStringChecker::evalStrncasecmp(CheckerContext &C,
const CallExpr *CE) const {
if (CE->getNumArgs() < 3)
return;
//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
const Expr *s1 = CE->getArg(0);
SVal s1Val = state->getSVal(s1, LCtx);
state = checkNonNull(C, state, s1, s1Val);
if (!state)
return;
// Check that the second string is non-null.
const Expr *s2 = CE->getArg(1);
SVal s2Val = state->getSVal(s2, LCtx);
state = checkNonNull(C, state, s2, s2Val);
if (!state)
return;
// Get the string length of the first string or give up.
SVal s1Length = getCStringLength(C, state, s1, s1Val);
if (s1Length.isUndef())
return;
// Get the string length of the second string or give up.
SVal s2Length = getCStringLength(C, state, s2, s2Val);
if (s2Length.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 = s1Val.castAs<DefinedOrUnknownSVal>();
DefinedOrUnknownSVal RV = s2Val.castAs<DefinedOrUnknownSVal>();
// 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 *s1StrLiteral = getCStringLiteral(C, state, s1, s1Val);
const StringLiteral *s2StrLiteral = getCStringLiteral(C, state, s2, s2Val);
bool canComputeResult = false;
if (s1StrLiteral && s2StrLiteral) {
StringRef s1StrRef = s1StrLiteral->getString();
StringRef s2StrRef = s2StrLiteral->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.
s1StrRef = s1StrRef.substr(0, (size_t)len->getZExtValue());
s2StrRef = s2StrRef.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 = s1StrRef.find('\0');
if (s1Term != StringRef::npos)
s1StrRef = s1StrRef.substr(0, s1Term);
size_t s2Term = s2StrRef.find('\0');
if (s2Term != StringRef::npos)
s2StrRef = s2StrRef.substr(0, s2Term);
// Use StringRef's comparison methods to compute the actual result.
int result;
if (ignoreCase) {
// Compare string 1 to string 2 the same way strcasecmp() does.
result = s1StrRef.compare_lower(s2StrRef);
} else {
// Compare string 1 to string 2 the same way strcmp() does.
result = s1StrRef.compare(s2StrRef);
}
// Build the SVal of the comparison and bind the return value.
SVal resultVal = svalBuilder.makeIntVal(result, CE->getType());
state = state->BindExpr(CE, LCtx, resultVal);
}
}
if (!canComputeResult) {
// Conjure a symbolic value. It's the best we can do.
SVal resultVal = svalBuilder.conjureSymbolVal(nullptr, CE, LCtx,
C.blockCount());
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);
if (CE->getNumArgs() < 2)
return;
// Sanity: does the search string parameter match the return type?
const Expr *SearchStrPtr = CE->getArg(0);
QualType CharPtrTy = SearchStrPtr->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, LCtx);
State = checkNonNull(C, State, SearchStrPtr, SearchStrVal);
if (!State)
return;
// Check that the delimiter string is non-null.
const Expr *DelimStr = CE->getArg(1);
SVal DelimStrVal = State->getSVal(DelimStr, LCtx);
State = checkNonNull(C, State, DelimStr, DelimStrVal);
if (!State)
return;
SValBuilder &SVB = C.getSValBuilder();
SVal Result;
if (Optional<Loc> SearchStrLoc = SearchStrVal.getAs<Loc>()) {
// 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, Result,
/*IsSourceBuffer*/false);
// 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()));
} 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);
}
//===----------------------------------------------------------------------===//
// The driver method, and other Checker callbacks.
//===----------------------------------------------------------------------===//
bool CStringChecker::evalCall(const CallExpr *CE, CheckerContext &C) const {
const FunctionDecl *FDecl = C.getCalleeDecl(CE);
if (!FDecl)
return false;
// FIXME: Poorly-factored string switches are slow.
FnCheck evalFunction = nullptr;
if (C.isCLibraryFunction(FDecl, "memcpy"))
evalFunction = &CStringChecker::evalMemcpy;
else if (C.isCLibraryFunction(FDecl, "mempcpy"))
evalFunction = &CStringChecker::evalMempcpy;
else if (C.isCLibraryFunction(FDecl, "memcmp"))
evalFunction = &CStringChecker::evalMemcmp;
else if (C.isCLibraryFunction(FDecl, "memmove"))
evalFunction = &CStringChecker::evalMemmove;
else if (C.isCLibraryFunction(FDecl, "strcpy"))
evalFunction = &CStringChecker::evalStrcpy;
else if (C.isCLibraryFunction(FDecl, "strncpy"))
evalFunction = &CStringChecker::evalStrncpy;
else if (C.isCLibraryFunction(FDecl, "stpcpy"))
evalFunction = &CStringChecker::evalStpcpy;
else if (C.isCLibraryFunction(FDecl, "strcat"))
evalFunction = &CStringChecker::evalStrcat;
else if (C.isCLibraryFunction(FDecl, "strncat"))
evalFunction = &CStringChecker::evalStrncat;
else if (C.isCLibraryFunction(FDecl, "strlen"))
evalFunction = &CStringChecker::evalstrLength;
else if (C.isCLibraryFunction(FDecl, "strnlen"))
evalFunction = &CStringChecker::evalstrnLength;
else if (C.isCLibraryFunction(FDecl, "strcmp"))
evalFunction = &CStringChecker::evalStrcmp;
else if (C.isCLibraryFunction(FDecl, "strncmp"))
evalFunction = &CStringChecker::evalStrncmp;
else if (C.isCLibraryFunction(FDecl, "strcasecmp"))
evalFunction = &CStringChecker::evalStrcasecmp;
else if (C.isCLibraryFunction(FDecl, "strncasecmp"))
evalFunction = &CStringChecker::evalStrncasecmp;
else if (C.isCLibraryFunction(FDecl, "strsep"))
evalFunction = &CStringChecker::evalStrsep;
else if (C.isCLibraryFunction(FDecl, "bcopy"))
evalFunction = &CStringChecker::evalBcopy;
else if (C.isCLibraryFunction(FDecl, "bcmp"))
evalFunction = &CStringChecker::evalMemcmp;
// If the callee isn't a string function, let another checker handle it.
if (!evalFunction)
return false;
// Make sure each function sets its own description.
// (But don't bother in a release build.)
assert(!(CurrentFunctionDescription = nullptr));
// Check and evaluate the call.
(this->*evalFunction)(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.
if (!C.isDifferent())
return false;
return true;
}
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<VarDecl>(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<StringLiteral>(Init))
continue;
Loc VarLoc = state->getLValue(D, C.getLocationContext());
const MemRegion *MR = VarLoc.getAsRegion();
if (!MR)
continue;
SVal StrVal = state->getSVal(Init, C.getLocationContext());
assert(StrVal.isValid() && "Initializer string is unknown or undefined");
DefinedOrUnknownSVal strLength =
getCStringLength(C, state, Init, StrVal).castAs<DefinedOrUnknownSVal>();
state = state->set<CStringLength>(MR, strLength);
}
C.addTransition(state);
}
bool CStringChecker::wantsRegionChangeUpdate(ProgramStateRef state) const {
CStringLengthTy Entries = state->get<CStringLength>();
return !Entries.isEmpty();
}
ProgramStateRef
CStringChecker::checkRegionChanges(ProgramStateRef state,
const InvalidatedSymbols *,
ArrayRef<const MemRegion *> ExplicitRegions,
ArrayRef<const MemRegion *> Regions,
const CallEvent *Call) const {
CStringLengthTy Entries = state->get<CStringLength>();
if (Entries.isEmpty())
return state;
llvm::SmallPtrSet<const MemRegion *, 8> Invalidated;
llvm::SmallPtrSet<const MemRegion *, 32> SuperRegions;
// First build sets for the changed regions and their super-regions.
for (ArrayRef<const MemRegion *>::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<SubRegion>(MR)) {
MR = SR->getSuperRegion();
SuperRegions.insert(MR);
}
}
CStringLengthTy::Factory &F = state->get_context<CStringLength>();
// 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<SubRegion>(Super)) {
Super = SR->getSuperRegion();
if (Invalidated.count(Super)) {
Entries = F.remove(Entries, MR);
break;
}
}
}
return state->set<CStringLength>(Entries);
}
void CStringChecker::checkLiveSymbols(ProgramStateRef state,
SymbolReaper &SR) const {
// Mark all symbols in our string length map as valid.
CStringLengthTy Entries = state->get<CStringLength>();
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 {
if (!SR.hasDeadSymbols())
return;
ProgramStateRef state = C.getState();
CStringLengthTy Entries = state->get<CStringLength>();
if (Entries.isEmpty())
return;
CStringLengthTy::Factory &F = state->get_context<CStringLength>();
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<CStringLength>(Entries);
C.addTransition(state);
}
#define REGISTER_CHECKER(name) \
void ento::register##name(CheckerManager &mgr) { \
CStringChecker *checker = mgr.registerChecker<CStringChecker>(); \
checker->Filter.Check##name = true; \
checker->Filter.CheckName##name = mgr.getCurrentCheckName(); \
}
REGISTER_CHECKER(CStringNullArg)
REGISTER_CHECKER(CStringOutOfBounds)
REGISTER_CHECKER(CStringBufferOverlap)
REGISTER_CHECKER(CStringNotNullTerm)
void ento::registerCStringCheckerBasic(CheckerManager &Mgr) {
registerCStringNullArg(Mgr);
}
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