[analyzer] Modernize, improve and promote chroot checker

This change modernizes, improves and promotes the chroot checker from
alpha to the Unix family of checkers. This checker covers the POS05
recommendations for use of chroot.

The improvements included modeling of a success or failure from chroot
and not falsely reporting a warning along an error path. This was made
possible through modernizing the checker to be flow sensitive.

Author: einvbri

clang/docs/ReleaseNotes.rst

@@ -985,6 +985,9 @@ Moved checkers
   original checkers were implemented only using AST matching and make more
   sense as a single clang-tidy check.
 
+- The checker ``alpha.unix.Chroot`` was modernized, improved and moved from
+  alpha to a main Unix family checker.
+
 .. _release-notes-sanitizers:
 
 Sanitizers

clang/docs/analyzer/checkers.rst

@@ -1750,6 +1750,21 @@ Critical section handling functions modeled by this checker:
    }
  }
 
+.. _unix-Chroot:
+
+unix.Chroot (C)
+"""""""""""""""""""""
+Check improper use of chroot.
+
+.. code-block:: c
+
+ void f();
+
+ void test() {
+   chroot("/usr/local");
+   f(); // warn: no call of chdir("/") immediately after chroot
+ }
+
 .. _unix-Errno:
 
 unix.Errno (C)
@@ -3275,21 +3290,6 @@ SEI CERT checkers which tries to find errors based on their `C coding rules <htt
 alpha.unix
 ^^^^^^^^^^
 
-.. _alpha-unix-Chroot:
-
-alpha.unix.Chroot (C)
-"""""""""""""""""""""
-Check improper use of chroot.
-
-.. code-block:: c
-
- void f();
-
- void test() {
-   chroot("/usr/local");
-   f(); // warn: no call of chdir("/") immediately after chroot
- }
-
 .. _alpha-unix-PthreadLock:
 
 alpha.unix.PthreadLock (C)

clang/include/clang/StaticAnalyzer/Checkers/Checkers.td

@@ -598,14 +598,14 @@ def VforkChecker : Checker<"Vfork">,
   HelpText<"Check for proper usage of vfork">,
   Documentation<HasDocumentation>;
 
-} // end "unix"
-
-let ParentPackage = UnixAlpha in {
-
 def ChrootChecker : Checker<"Chroot">,
   HelpText<"Check improper use of chroot">,
   Documentation<HasDocumentation>;
 
+} // end "unix"
+
+let ParentPackage = UnixAlpha in {
+
 def PthreadLockChecker : Checker<"PthreadLock">,
   HelpText<"Simple lock -> unlock checker">,
   Dependencies<[PthreadLockBase]>,

clang/lib/StaticAnalyzer/Checkers/ChrootChecker.cpp

@@ -10,6 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "clang/AST/ASTContext.h"
+#include "clang/Basic/TargetInfo.h"
 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
 #include "clang/StaticAnalyzer/Core/Checker.h"
@@ -24,21 +26,30 @@
 using namespace clang;
 using namespace ento;
 
-namespace {
-
 // enum value that represent the jail state
-enum Kind { NO_CHROOT, ROOT_CHANGED, JAIL_ENTERED };
+enum ChrootKind { NO_CHROOT, ROOT_CHANGED, ROOT_CHANGE_FAILED, JAIL_ENTERED };
 
-bool isRootChanged(intptr_t k) { return k == ROOT_CHANGED; }
-//bool isJailEntered(intptr_t k) { return k == JAIL_ENTERED; }
+// Track chroot state changes for success, failure, state change
+// and "jail"
+REGISTER_TRAIT_WITH_PROGRAMSTATE(ChrootState, ChrootKind)
+
+// Track the call expression to chroot for accurate
+// warning messages
+REGISTER_TRAIT_WITH_PROGRAMSTATE(ChrootCall, const Expr *)
+
+namespace {
 
 // This checker checks improper use of chroot.
-// The state transition:
+// The state transitions
+//
+//                          -> ROOT_CHANGE_FAILED
+//                          |
 // 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.
   const BugType BT_BreakJail{this, "Break out of jail"};
@@ -49,20 +60,17 @@ class ChrootChecker : public Checker<eval::Call, check::PreCall> {
 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
+  /// Searches for the ExplodedNode where chroot was called.
+  static const ExplodedNode *getAcquisitionSite(const ExplodedNode *N,
+                                                CheckerContext &C);
+};
 
 bool ChrootChecker::evalCall(const CallEvent &Call, CheckerContext &C) const {
   if (Chroot.matches(Call)) {
@@ -80,19 +88,53 @@ bool ChrootChecker::evalCall(const CallEvent &Call, CheckerContext &C) const {
 void ChrootChecker::evalChroot(const CallEvent &Call, CheckerContext &C) const {
   ProgramStateRef state = C.getState();
   ProgramStateManager &Mgr = state->getStateManager();
+  const TargetInfo &TI = C.getASTContext().getTargetInfo();
+  SValBuilder &SVB = C.getSValBuilder();
+  BasicValueFactory &BVF = SVB.getBasicValueFactory();
+  ConstraintManager &CM = Mgr.getConstraintManager();
 
-  // 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);
+  const QualType sIntTy = C.getASTContext().getIntTypeForBitwidth(
+      /*DestWidth=*/TI.getIntWidth(), /*Signed=*/true);
+
+  const Expr *ChrootCE = Call.getOriginExpr();
+  if (!ChrootCE)
+    return;
+  const auto *CE = cast<CallExpr>(Call.getOriginExpr());
+
+  const LocationContext *LCtx = C.getLocationContext();
+  NonLoc RetVal =
+      C.getSValBuilder()
+          .conjureSymbolVal(nullptr, ChrootCE, LCtx, sIntTy, C.blockCount())
+          .castAs<NonLoc>();
+
+  ProgramStateRef StateChrootFailed, StateChrootSuccess;
+  std::tie(StateChrootFailed, StateChrootSuccess) = state->assume(RetVal);
+
+  const llvm::APSInt &Zero = BVF.getValue(0, sIntTy);
+  const llvm::APSInt &Minus1 = BVF.getValue(-1, sIntTy);
+
+  if (StateChrootFailed) {
+    StateChrootFailed = CM.assumeInclusiveRange(StateChrootFailed, RetVal,
+                                                Minus1, Minus1, true);
+    StateChrootFailed = StateChrootFailed->set<ChrootState>(ROOT_CHANGE_FAILED);
+    StateChrootFailed = StateChrootFailed->set<ChrootCall>(ChrootCE);
+    C.addTransition(StateChrootFailed->BindExpr(CE, LCtx, RetVal));
+  }
+
+  if (StateChrootSuccess) {
+    StateChrootSuccess =
+        CM.assumeInclusiveRange(StateChrootSuccess, RetVal, Zero, Zero, true);
+    StateChrootSuccess = StateChrootSuccess->set<ChrootState>(ROOT_CHANGED);
+    StateChrootSuccess = StateChrootSuccess->set<ChrootCall>(ChrootCE);
+    C.addTransition(StateChrootSuccess->BindExpr(CE, LCtx, RetVal));
+  }
 }
 
 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 there are no jail state, just return.
+  const ChrootKind k = C.getState()->get<ChrootState>();
   if (!k)
     return;
 
@@ -104,15 +146,35 @@ void ChrootChecker::evalChdir(const CallEvent &Call, CheckerContext &C) const {
     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);
+      if (Str->getString() == "/") {
+        state = state->set<ChrootState>(JAIL_ENTERED);
+      }
     }
   }
 
   C.addTransition(state);
 }
 
+const ExplodedNode *ChrootChecker::getAcquisitionSite(const ExplodedNode *N,
+                                                      CheckerContext &C) {
+  ProgramStateRef State = N->getState();
+  // When bug type is resource leak, exploded node N may not have state info
+  // for leaked file descriptor, but predecessor should have it.
+  if (!State->get<ChrootCall>())
+    N = N->getFirstPred();
+
+  const ExplodedNode *Pred = N;
+  while (N) {
+    State = N->getState();
+    if (!State->get<ChrootCall>())
+      return Pred;
+    Pred = N;
+    N = N->getFirstPred();
+  }
+
+  return nullptr;
+}
+
 // Check the jail state before any function call except chroot and chdir().
 void ChrootChecker::checkPreCall(const CallEvent &Call,
                                  CheckerContext &C) const {
@@ -121,17 +183,40 @@ void ChrootChecker::checkPreCall(const CallEvent &Call,
     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()) {
-        constexpr llvm::StringLiteral Msg =
-            "No call of chdir(\"/\") immediately after chroot";
-        C.emitReport(
-            std::make_unique<PathSensitiveBugReport>(BT_BreakJail, Msg, N));
-      }
+  const ChrootKind k = C.getState()->get<ChrootState>();
+  if (k == ROOT_CHANGED) {
+    ExplodedNode *Err =
+        C.generateNonFatalErrorNode(C.getState(), C.getPredecessor());
+    if (!Err)
+      return;
+    const Expr *ChrootExpr = C.getState()->get<ChrootCall>();
+
+    const ExplodedNode *ChrootCallNode = getAcquisitionSite(Err, C);
+    assert(ChrootCallNode && "Could not find place of stream opening.");
+
+    PathDiagnosticLocation LocUsedForUniqueing;
+    if (const Stmt *ChrootStmt = ChrootCallNode->getStmtForDiagnostics())
+      LocUsedForUniqueing = PathDiagnosticLocation::createBegin(
+          ChrootStmt, C.getSourceManager(),
+          ChrootCallNode->getLocationContext());
+
+    std::unique_ptr<PathSensitiveBugReport> R =
+        std::make_unique<PathSensitiveBugReport>(
+            BT_BreakJail, "No call of chdir(\"/\") immediately after chroot",
+            Err, LocUsedForUniqueing,
+            ChrootCallNode->getLocationContext()->getDecl());
+
+    R->addNote("chroot called here",
+               PathDiagnosticLocation::create(ChrootCallNode->getLocation(),
+                                              C.getSourceManager()),
+               {ChrootExpr->getSourceRange()});
+
+    C.emitReport(std::move(R));
+  }
 }
 
+} // namespace
+
 void ento::registerChrootChecker(CheckerManager &mgr) {
   mgr.registerChecker<ChrootChecker>();
 }

clang/test/Analysis/chroot.c

@@ -1,4 +1,4 @@
-// RUN: %clang_analyze_cc1 -analyzer-checker=alpha.unix.Chroot -verify %s
+// RUN: %clang_analyze_cc1 -analyzer-checker=unix.Chroot -verify %s
 
 extern int chroot(const char* path);
 extern int chdir(const char* path);
@@ -7,7 +7,7 @@ void foo(void) {
 }
 
 void f1(void) {
-  chroot("/usr/local"); // root changed.
+  chroot("/usr/local"); // expected-note {{chroot called here}}
   foo(); // expected-warning {{No call of chdir("/") immediately after chroot}}
 }
 
@@ -18,7 +18,37 @@ void f2(void) {
 }
 
 void f3(void) {
-  chroot("/usr/local"); // root changed.
+  chroot("/usr/local"); // expected-note {{chroot called here}}
   chdir("../"); // change working directory, still out of jail.
   foo(); // expected-warning {{No call of chdir("/") immediately after chroot}}
 }
+
+void f4(void) {
+  if (chroot("/usr/local") == 0) {
+      chdir("../"); // change working directory, still out of jail.
+  }
+}
+
+void f5(void) {
+  int v = chroot("/usr/local");
+  if (v == -1) {
+      foo();        // no warning, chroot failed
+      chdir("../"); // change working directory, still out of jail.
+  }
+}
+
+void f6(void) {
+  if (chroot("/usr/local") == -1) {
+      chdir("../"); // change working directory, still out of jail.
+  }
+}
+
+void f7(void) {
+  int v = chroot("/usr/local"); // expected-note {{chroot called here}}
+  if (v == -1) {
+      foo();        // no warning, chroot failed
+      chdir("../"); // change working directory, still out of jail.
+  } else {
+      foo();        // expected-warning {{No call of chdir("/") immediately after chroot}}
+  }
+}