ChrootChecker.cpp
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//===-- ChrootChecker.cpp - chroot usage checks ---------------------------===//
//
// 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 chroot checker, which checks improper use of chroot.
//
//===----------------------------------------------------------------------===//
#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/CallEvent.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/SymbolManager.h"
using namespace clang;
using namespace ento;
namespace {
// enum value that represent the jail state
enum Kind { NO_CHROOT, ROOT_CHANGED, JAIL_ENTERED };
bool isRootChanged(intptr_t k) { return k == ROOT_CHANGED; }
//bool isJailEntered(intptr_t k) { return k == JAIL_ENTERED; }
// This checker checks improper use of chroot.
// The state transition:
// NO_CHROOT ---chroot(path)--> ROOT_CHANGED ---chdir(/) --> JAIL_ENTERED
// | |
// ROOT_CHANGED<--chdir(..)-- JAIL_ENTERED<--chdir(..)--
// | |
// bug<--foo()-- JAIL_ENTERED<--foo()--
class ChrootChecker : public Checker<eval::Call, check::PreCall> {
// This bug refers to possibly break out of a chroot() jail.
mutable std::unique_ptr<BuiltinBug> BT_BreakJail;
const CallDescription Chroot{"chroot", 1}, Chdir{"chdir", 1};
public:
ChrootChecker() {}
static void *getTag() {
static int x;
return &x;
}
bool evalCall(const CallEvent &Call, CheckerContext &C) const;
void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
private:
void evalChroot(const CallEvent &Call, CheckerContext &C) const;
void evalChdir(const CallEvent &Call, CheckerContext &C) const;
};
} // end anonymous namespace
bool ChrootChecker::evalCall(const CallEvent &Call, CheckerContext &C) const {
if (Call.isCalled(Chroot)) {
evalChroot(Call, C);
return true;
}
if (Call.isCalled(Chdir)) {
evalChdir(Call, C);
return true;
}
return false;
}
void ChrootChecker::evalChroot(const CallEvent &Call, CheckerContext &C) const {
ProgramStateRef state = C.getState();
ProgramStateManager &Mgr = state->getStateManager();
// Once encouter a chroot(), set the enum value ROOT_CHANGED directly in
// the GDM.
state = Mgr.addGDM(state, ChrootChecker::getTag(), (void*) ROOT_CHANGED);
C.addTransition(state);
}
void ChrootChecker::evalChdir(const CallEvent &Call, CheckerContext &C) const {
ProgramStateRef state = C.getState();
ProgramStateManager &Mgr = state->getStateManager();
// If there are no jail state in the GDM, just return.
const void *k = state->FindGDM(ChrootChecker::getTag());
if (!k)
return;
// After chdir("/"), enter the jail, set the enum value JAIL_ENTERED.
const Expr *ArgExpr = Call.getArgExpr(0);
SVal ArgVal = C.getSVal(ArgExpr);
if (const MemRegion *R = ArgVal.getAsRegion()) {
R = R->StripCasts();
if (const StringRegion* StrRegion= dyn_cast<StringRegion>(R)) {
const StringLiteral* Str = StrRegion->getStringLiteral();
if (Str->getString() == "/")
state = Mgr.addGDM(state, ChrootChecker::getTag(),
(void*) JAIL_ENTERED);
}
}
C.addTransition(state);
}
// Check the jail state before any function call except chroot and chdir().
void ChrootChecker::checkPreCall(const CallEvent &Call,
CheckerContext &C) const {
// Ignore chroot and chdir.
if (Call.isCalled(Chroot) || Call.isCalled(Chdir))
return;
// If jail state is ROOT_CHANGED, generate BugReport.
void *const* k = C.getState()->FindGDM(ChrootChecker::getTag());
if (k)
if (isRootChanged((intptr_t) *k))
if (ExplodedNode *N = C.generateNonFatalErrorNode()) {
if (!BT_BreakJail)
BT_BreakJail.reset(new BuiltinBug(
this, "Break out of jail", "No call of chdir(\"/\") immediately "
"after chroot"));
C.emitReport(std::make_unique<PathSensitiveBugReport>(
*BT_BreakJail, BT_BreakJail->getDescription(), N));
}
}
void ento::registerChrootChecker(CheckerManager &mgr) {
mgr.registerChecker<ChrootChecker>();
}
bool ento::shouldRegisterChrootChecker(const CheckerManager &mgr) {
return true;
}