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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++ -*-//
//
// 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 <string.h>.
//
//===----------------------------------------------------------------------===//
#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<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;
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<const MemRegion *> ExplicitRegions,
ArrayRef<const MemRegion *> Regions,
const LocationContext *LCtx,
const CallEvent *Call) const;
typedef void (CStringChecker::*FnCheck)(CheckerContext &,
const CallExpr *) const;
CallDescriptionMap<FnCheck> 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<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,
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<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,
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<ElementRegion>(R);
if (!ER)
return state;
if (ER->getValueType() != C.getASTContext().CharTy)
return state;
// Get the size of the array.
const auto *superReg = cast<SubRegion>(ER->getSuperRegion());
DefinedOrUnknownSVal Size =
getDynamicExtent(state, superReg, C.getSValBuilder());
// 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) {
// 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<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>();
SVal Offset = svalBuilder.evalBinOpNN(State, BO_Sub, *Length, One, SizeTy);
if (Offset.isUnknown())
return nullptr;
NonLoc LastOffset = Offset.castAs<NonLoc>();
// Check that the first buffer is sufficiently long.
SVal BufStart =
svalBuilder.evalCast(BufVal, PtrTy, Buffer.Expression->getType());
if (Optional<Loc> BufLoc = BufStart.getAs<Loc>()) {
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<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.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<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.Expression, 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.Expression->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.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<PathSensitiveBugReport>(
*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<BuiltinBug *>(BT_Null.get());
auto Report = std::make_unique<PathSensitiveBugReport>(*BT, WarningMsg, N);
Report->addRange(S->getSourceRange());
if (const auto *Ex = dyn_cast<Expr>(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<BuiltinBug *>(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<PathSensitiveBugReport>(*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<PathSensitiveBugReport>(*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<PathSensitiveBugReport>(*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<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.
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<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.getLocationContext(),
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) {
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<StringRegion>(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<StringRegion>(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<NonLoc> Length = LengthVal.getAs<NonLoc>();
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<NonLoc>();
SVal Offset = svalBuilder.evalBinOpNN(state, BO_Sub, *Length, One, sizeTy);
if (Offset.isUnknown())
return true; // cf top comment
NonLoc LastOffset = Offset.castAs<NonLoc>();
// Check that the first buffer is sufficiently long.
SVal BufStart = svalBuilder.evalCast(BufVal, PtrTy, FirstBuf->getType());
Optional<Loc> BufLoc = BufStart.getAs<Loc>();
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<ElementRegion>(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<SubRegion>(ER->getSuperRegion());
DefinedOrUnknownSVal SizeDV = getDynamicExtent(state, superReg, svalBuilder);
// Get the index of the accessed element.
DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();
ProgramStateRef StInBound = state->assumeInBound(Idx, SizeDV, true);
return static_cast<bool>(StInBound);
}
ProgramStateRef CStringChecker::InvalidateBuffer(CheckerContext &C,
ProgramStateRef state,
const Expr *E, SVal V,
bool IsSourceBuffer,
const Expr *Size) {
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->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<FunctionCodeRegion>(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<TypedValueRegion>(MR)->getValueType().getAsString();
return true;
case MemRegion::NonParamVarRegionKind:
os << "a variable of type"
<< cast<TypedValueRegion>(MR)->getValueType().getAsString();
return true;
case MemRegion::ParamVarRegionKind:
os << "a parameter of type"
<< cast<TypedValueRegion>(MR)->getValueType().getAsString();
return true;
case MemRegion::FieldRegionKind:
os << "a field of type "
<< cast<TypedValueRegion>(MR)->getValueType().getAsString();
return true;
case MemRegion::ObjCIvarRegionKind:
os << "an instance variable of type "
<< cast<TypedValueRegion>(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<NonLoc> SizeNL = SizeVal.getAs<NonLoc>();
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<DefinedOrUnknownSVal>(), 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>();
DefinedOrUnknownSVal RV =
State->getSVal(Right.Expression, LCtx).castAs<DefinedOrUnknownSVal>();
// 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<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 {
// 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<NonLoc> strLengthNL = strLength.getAs<NonLoc>();
// Get the string length of the destination buffer.
SVal dstStrLength = getCStringLength(C, state, Dst.Expression, DstVal);
Optional<NonLoc> dstStrLengthNL = dstStrLength.getAs<NonLoc>();
// 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<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) {
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<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;
}
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<NonLoc>())
return;
freeSpace =
svalBuilder.evalBinOp(state, BO_Sub, freeSpace,
svalBuilder.makeIntVal(1, sizeTy), sizeTy);
Optional<NonLoc> freeSpaceNL = freeSpace.getAs<NonLoc>();
// 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<DefinedOrUnknownSVal>());
// 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<NonLoc>();
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<NonLoc> amountCopiedNL = amountCopied.getAs<NonLoc>();
// 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<NonLoc> finalStrLengthNL = finalStrLength.getAs<NonLoc>()) {
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<DefinedOrUnknownSVal>(),
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<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;
}
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<loc::MemRegionVal> dstRegVal =
DstVal.getAs<loc::MemRegionVal>()) {
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<NonLoc> maxLastNL = maxLastElementIndex.getAs<NonLoc>()) {
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<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) {
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>();
DefinedOrUnknownSVal RV = RightVal.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 *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<DefinedSVal>();
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);
// Sanity: does the search string parameter match 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<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.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 <class _InputIterator, class _OutputIterator>
// _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<CallExpr>(Call.getOriginExpr());
if (!CE)
return nullptr;
const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(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<CallExpr>(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<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 = C.getSVal(Init);
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);
}
ProgramStateRef
CStringChecker::checkRegionChanges(ProgramStateRef state,
const InvalidatedSymbols *,
ArrayRef<const MemRegion *> ExplicitRegions,
ArrayRef<const MemRegion *> Regions,
const LocationContext *LCtx,
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 {
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);
}
void ento::registerCStringModeling(CheckerManager &Mgr) {
Mgr.registerChecker<CStringChecker>();
}
bool ento::shouldRegisterCStringModeling(const CheckerManager &mgr) {
return true;
}
#define REGISTER_CHECKER(name) \
void ento::register##name(CheckerManager &mgr) { \
CStringChecker *checker = mgr.getChecker<CStringChecker>(); \
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)
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