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//== ReturnPointerRangeChecker.cpp ------------------------------*- 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 file defines ReturnPointerRangeChecker, which is a path-sensitive check
// which looks for an out-of-bound pointer being returned to callers.
//
//===----------------------------------------------------------------------===//
#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugReporterVisitors.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/DynamicExtent.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
using namespace clang;
using namespace ento;
namespace {
class ReturnPointerRangeChecker :
public Checker< check::PreStmt<ReturnStmt> > {
// FIXME: This bug correspond to CWE-466. Eventually we should have bug
// types explicitly reference such exploit categories (when applicable).
const BugType BT{this, "Buffer overflow"};
public:
void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
};
}
void ReturnPointerRangeChecker::checkPreStmt(const ReturnStmt *RS,
CheckerContext &C) const {
ProgramStateRef state = C.getState();
const Expr *RetE = RS->getRetValue();
if (!RetE)
return;
// Skip "body farmed" functions.
if (RetE->getSourceRange().isInvalid())
return;
SVal V = C.getSVal(RetE);
const MemRegion *R = V.getAsRegion();
const ElementRegion *ER = dyn_cast_or_null<ElementRegion>(R);
if (!ER)
return;
DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();
// Zero index is always in bound, this also passes ElementRegions created for
// pointer casts.
if (Idx.isZeroConstant())
return;
// FIXME: All of this out-of-bounds checking should eventually be refactored
// into a common place.
DefinedOrUnknownSVal ElementCount = getDynamicElementCount(
state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType());
// We assume that the location after the last element in the array is used as
// end() iterator. Reporting on these would return too many false positives.
if (Idx == ElementCount)
return;
ProgramStateRef StInBound, StOutBound;
std::tie(StInBound, StOutBound) = state->assumeInBoundDual(Idx, ElementCount);
if (StOutBound && !StInBound) {
ExplodedNode *N = C.generateErrorNode(StOutBound);
if (!N)
return;
constexpr llvm::StringLiteral Msg =
"Returned pointer value points outside the original object "
"(potential buffer overflow)";
// Generate a report for this bug.
auto Report = std::make_unique<PathSensitiveBugReport>(BT, Msg, N);
Report->addRange(RetE->getSourceRange());
const auto ConcreteElementCount = ElementCount.getAs<nonloc::ConcreteInt>();
const auto ConcreteIdx = Idx.getAs<nonloc::ConcreteInt>();
const auto *DeclR = ER->getSuperRegion()->getAs<DeclRegion>();
if (DeclR)
Report->addNote("Original object declared here",
{DeclR->getDecl(), C.getSourceManager()});
if (ConcreteElementCount) {
SmallString<128> SBuf;
llvm::raw_svector_ostream OS(SBuf);
OS << "Original object ";
if (DeclR) {
OS << "'";
DeclR->getDecl()->printName(OS);
OS << "' ";
}
OS << "is an array of " << ConcreteElementCount->getValue() << " '";
ER->getValueType().print(OS,
PrintingPolicy(C.getASTContext().getLangOpts()));
OS << "' objects";
if (ConcreteIdx) {
OS << ", returned pointer points at index " << ConcreteIdx->getValue();
}
Report->addNote(SBuf,
{RetE, C.getSourceManager(), C.getLocationContext()});
}
bugreporter::trackExpressionValue(N, RetE, *Report);
C.emitReport(std::move(Report));
}
}
void ento::registerReturnPointerRangeChecker(CheckerManager &mgr) {
mgr.registerChecker<ReturnPointerRangeChecker>();
}
bool ento::shouldRegisterReturnPointerRangeChecker(const CheckerManager &mgr) {
return true;
}
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