[clang] [clang][analyzer] Add checker 'security.SetgidSetuidOrder'. (PR #91445)

[Balazs Benics via cfe-commits]

=?utf-8?q?Balázs_Kéri?= <balazs.keri at ericsson.com>,
=?utf-8?q?Balázs_Kéri?= <balazs.keri at ericsson.com>,
=?utf-8?q?Balázs_Kéri?= <balazs.keri at ericsson.com>,
=?utf-8?q?Balázs_Kéri?= <balazs.keri at ericsson.com>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/91445 at github.com>


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@@ -0,0 +1,196 @@
+//===-- SetgidSetuidOrderChecker.cpp - check privilege revocation calls ---===//
+//
+// 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 a checker to detect possible reversed order of privilege
+//  revocations when 'setgid' and 'setuid' is used.
+//
+//===----------------------------------------------------------------------===//
+
+#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/ProgramState.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
+
+using namespace clang;
+using namespace ento;
+
+namespace {
+
+enum SetPrivilegeFunctionKind { Irrelevant, Setuid, Setgid };
+
+class SetgidSetuidOrderChecker
+    : public Checker<check::PostCall, check::DeadSymbols, eval::Assume> {
+  const BugType BT_WrongRevocationOrder{
+      this, "Possible wrong order of privilege revocation"};
+
+  const CallDescription SetuidDesc{CDM::CLibrary, {"setuid"}, 1};
+  const CallDescription SetgidDesc{CDM::CLibrary, {"setgid"}, 1};
+
+  const CallDescription GetuidDesc{CDM::CLibrary, {"getuid"}, 0};
+  const CallDescription GetgidDesc{CDM::CLibrary, {"getgid"}, 0};
+
+  CallDescriptionSet OtherSetPrivilegeDesc{
+      {CDM::CLibrary, {"seteuid"}, 1},   {CDM::CLibrary, {"setegid"}, 1},
+      {CDM::CLibrary, {"setreuid"}, 2},  {CDM::CLibrary, {"setregid"}, 2},
+      {CDM::CLibrary, {"setresuid"}, 3}, {CDM::CLibrary, {"setresgid"}, 3}};
+
+public:
+  SetgidSetuidOrderChecker() {}
+
+  void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
+  void checkDeadSymbols(SymbolReaper &SymReaper, CheckerContext &C) const;
+  ProgramStateRef evalAssume(ProgramStateRef State, SVal Cond,
+                             bool Assumption) const;
+
+private:
+  ProgramStateRef processSetuid(ProgramStateRef State, const CallEvent &Call,
+                                CheckerContext &C) const;
+  ProgramStateRef processSetgid(ProgramStateRef State, const CallEvent &Call,
+                                CheckerContext &C) const;
+  ProgramStateRef processOther(ProgramStateRef State, const CallEvent &Call,
+                               CheckerContext &C) const;
+  /// Check if a function like \c getuid or \c getgid is called directly from
+  /// the first argument of function called from \a Call.
+  bool isFunctionCalledInArg(const CallDescription &Desc,
+                             const CallEvent &Call) const;
+  void emitReport(ProgramStateRef State, CheckerContext &C) const;
+};
+
+} // end anonymous namespace
+
+/// Store if there was a call to 'setuid(getuid())' or 'setgid(getgid())' not
+/// followed by other different privilege-change functions.
+/// If the value \c Setuid is stored and a 'setgid(getgid())' call is found we
+/// have found the bug to be reported. Value \c Setgid is used too to prevent
+/// warnings at a setgid-setuid-setgid sequence.
+REGISTER_TRAIT_WITH_PROGRAMSTATE(LastSetPrivilegeCall, SetPrivilegeFunctionKind)
+/// Store the symbol value of the last 'setuid(getuid())' call. This is used to
+/// detect if the result is compared to -1 and avoid warnings on that branch
+/// (which is the failure branch of the call).
+REGISTER_TRAIT_WITH_PROGRAMSTATE(LastSetuidCallSVal, SymbolRef)
+
+void SetgidSetuidOrderChecker::checkPostCall(const CallEvent &Call,
+                                             CheckerContext &C) const {
+  ProgramStateRef State = C.getState();
+  if (SetuidDesc.matches(Call)) {
+    State = processSetuid(State, Call, C);
+  } else if (SetgidDesc.matches(Call)) {
+    State = processSetgid(State, Call, C);
+  } else if (OtherSetPrivilegeDesc.contains(Call)) {
+    State = processOther(State, Call, C);
+  }
+  if (State)
+    C.addTransition(State);
+}
+
+void SetgidSetuidOrderChecker::checkDeadSymbols(SymbolReaper &SymReaper,
+                                                CheckerContext &C) const {
+  ProgramStateRef State = C.getState();
+
+  SymbolRef LastSetuidSym = State->get<LastSetuidCallSVal>();
+  if (!LastSetuidSym)
+    return;
+
+  if (!SymReaper.isDead(LastSetuidSym))
+    return;
+
+  State = State->set<LastSetuidCallSVal>(SymbolRef{});
+  C.addTransition(State, C.getPredecessor());
+}
+
+ProgramStateRef SetgidSetuidOrderChecker::evalAssume(ProgramStateRef State,
+                                                     SVal Cond,
+                                                     bool Assumption) const {
+  SValBuilder &SVB = State->getStateManager().getSValBuilder();
+  SymbolRef LastSetuidSym = State->get<LastSetuidCallSVal>();
+  if (!LastSetuidSym)
+    return State;
+
+  // Check if the most recent call to 'setuid(getuid())' is assumed to be -1.
+  auto FailVal =
+      SVB.evalBinOpNN(State, BO_EQ, nonloc::SymbolVal(LastSetuidSym),
+                      SVB.makeIntVal(-1, false), SVB.getConditionType())
+          .getAs<DefinedOrUnknownSVal>();
+  if (!FailVal)
+    return State;
+  auto IsFailBranch = State->assume(*FailVal);
+  if (IsFailBranch.first && !IsFailBranch.second) {
+    // This is the 'setuid(getuid())' == -1 case.
+    // On this branch we do not want to emit warning.
+    State = State->set<LastSetuidCallSVal>(SymbolRef{});
+    State = State->set<LastSetPrivilegeCall>(Irrelevant);
+  }
+  return State;
+}
+
+ProgramStateRef SetgidSetuidOrderChecker::processSetuid(
+    ProgramStateRef State, const CallEvent &Call, CheckerContext &C) const {
+  bool IsSetuidWithGetuid = isFunctionCalledInArg(GetuidDesc, Call);
+  if (State->get<LastSetPrivilegeCall>() != Setgid && IsSetuidWithGetuid) {
+    State = State->set<LastSetuidCallSVal>(Call.getReturnValue().getAsSymbol());
+    return State->set<LastSetPrivilegeCall>(Setuid);
+  }
+  State = State->set<LastSetuidCallSVal>(SymbolRef{});
+  return State->set<LastSetPrivilegeCall>(Irrelevant);
+}
+
+ProgramStateRef SetgidSetuidOrderChecker::processSetgid(
+    ProgramStateRef State, const CallEvent &Call, CheckerContext &C) const {
+  bool IsSetgidWithGetgid = isFunctionCalledInArg(GetgidDesc, Call);
+  State = State->set<LastSetuidCallSVal>(SymbolRef{});
+  if (State->get<LastSetPrivilegeCall>() == Setuid) {
+    if (IsSetgidWithGetgid) {
+      State = State->set<LastSetPrivilegeCall>(Irrelevant);
+      emitReport(State, C);
+      // return nullptr to prevent adding transition with the returned state
+      return nullptr;
+    }
+    return State->set<LastSetPrivilegeCall>(Irrelevant);
+  } else
+    return State->set<LastSetPrivilegeCall>(IsSetgidWithGetgid ? Setgid
+                                                               : Irrelevant);
+}
+
+ProgramStateRef SetgidSetuidOrderChecker::processOther(
+    ProgramStateRef State, const CallEvent &Call, CheckerContext &C) const {
+  State = State->set<LastSetuidCallSVal>(SymbolRef{});
+  return State->set<LastSetPrivilegeCall>(Irrelevant);
+}
+
+bool SetgidSetuidOrderChecker::isFunctionCalledInArg(
+    const CallDescription &Desc, const CallEvent &Call) const {
+  if (const auto *CE =
+          dyn_cast<CallExpr>(Call.getArgExpr(0)->IgnoreParenImpCasts()))
+    return Desc.matchesAsWritten(*CE);
+  return false;
+}
+
+void SetgidSetuidOrderChecker::emitReport(ProgramStateRef State,
+                                          CheckerContext &C) const {
+  if (ExplodedNode *N = C.generateNonFatalErrorNode(State)) {
+    llvm::StringLiteral Msg =
+        "A 'setgid(getgid())' call following a 'setuid(getuid())' "
+        "call is likely to fail; probably the order of these "
+        "statements is wrong";
+    C.emitReport(std::make_unique<PathSensitiveBugReport>(
+        BT_WrongRevocationOrder, Msg, N));
----------------
steakhal wrote:

I was expecting a visitor highlighting the previous `setuid` call.
Without a visitor, or note tag, the call wouldn't be mentioned in the report.

https://github.com/llvm/llvm-project/pull/91445