1 files changed, 218 insertions, 0 deletions
diff --git a/contrib/llvm/tools/clang/lib/StaticAnalyzer/Checkers/VforkChecker.cpp b/contrib/llvm/tools/clang/lib/StaticAnalyzer/Checkers/VforkChecker.cpp
new file mode 100644
index 0000000..26ffee8
--- /dev/null
+++ b/contrib/llvm/tools/clang/lib/StaticAnalyzer/Checkers/VforkChecker.cpp
@@ -0,0 +1,218 @@
+//===- VforkChecker.cpp -------- Vfork usage checks --------------*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines vfork checker which checks for dangerous uses of vfork.
+//  Vforked process shares memory (including stack) with parent so it's
+//  range of actions is significantly limited: can't write variables,
+//  can't call functions not in whitelist, etc. For more details, see
+//  http://man7.org/linux/man-pages/man2/vfork.2.html
+//
+//  This checker checks for prohibited constructs in vforked process.
+//  The state transition diagram:
+//  PARENT ---(vfork() == 0)--> CHILD
+//                                   |
+//                                   --(*p = ...)--> bug
+//                                   |
+//                                   --foo()--> bug
+//                                   |
+//                                   --return--> bug
+//
+//===----------------------------------------------------------------------===//
+
+#include "ClangSACheckers.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerHelpers.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/SymbolManager.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
+#include "clang/StaticAnalyzer/Core/Checker.h"
+#include "clang/StaticAnalyzer/Core/CheckerManager.h"
+#include "clang/AST/ParentMap.h"
+
+using namespace clang;
+using namespace ento;
+
+namespace {
+
+class VforkChecker : public Checker<check::PreCall, check::PostCall,
+                                    check::Bind, check::PreStmt<ReturnStmt>> {
+  mutable std::unique_ptr<BuiltinBug> BT;
+  mutable llvm::SmallSet<const IdentifierInfo *, 10> VforkWhitelist;
+  mutable const IdentifierInfo *II_vfork;
+
+  static bool isChildProcess(const ProgramStateRef State);
+
+  bool isVforkCall(const Decl *D, CheckerContext &C) const;
+  bool isCallWhitelisted(const IdentifierInfo *II, CheckerContext &C) const;
+
+  void reportBug(const char *What, CheckerContext &C,
+                 const char *Details = 0) const;
+
+public:
+  VforkChecker() : II_vfork(0) {}
+
+  void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
+  void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
+  void checkBind(SVal L, SVal V, const Stmt *S, CheckerContext &C) const;
+  void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
+};
+
+} // end anonymous namespace
+
+// This trait holds region of variable that is assigned with vfork's
+// return value (this is the only region child is allowed to write).
+// VFORK_RESULT_INVALID means that we are in parent process.
+// VFORK_RESULT_NONE means that vfork's return value hasn't been assigned.
+// Other values point to valid regions.
+REGISTER_TRAIT_WITH_PROGRAMSTATE(VforkResultRegion, const void *)
+#define VFORK_RESULT_INVALID 0
+#define VFORK_RESULT_NONE ((void *)(uintptr_t)1)
+
+bool VforkChecker::isChildProcess(const ProgramStateRef State) {
+  return State->get<VforkResultRegion>() != VFORK_RESULT_INVALID;
+}
+
+bool VforkChecker::isVforkCall(const Decl *D, CheckerContext &C) const {
+  auto FD = dyn_cast_or_null<FunctionDecl>(D);
+  if (!FD || !C.isCLibraryFunction(FD))
+    return false;
+
+  if (!II_vfork) {
+    ASTContext &AC = C.getASTContext();
+    II_vfork = &AC.Idents.get("vfork");
+  }
+
+  return FD->getIdentifier() == II_vfork;
+}
+
+// Returns true iff ok to call function after successful vfork.
+bool VforkChecker::isCallWhitelisted(const IdentifierInfo *II,
+                                 CheckerContext &C) const {
+  if (VforkWhitelist.empty()) {
+    // According to manpage.
+    const char *ids[] = {
+      "_exit",
+      "_Exit",
+      "execl",
+      "execlp",
+      "execle",
+      "execv",
+      "execvp",
+      "execvpe",
+      0,
+    };
+
+    ASTContext &AC = C.getASTContext();
+    for (const char **id = ids; *id; ++id)
+      VforkWhitelist.insert(&AC.Idents.get(*id));
+  }
+
+  return VforkWhitelist.count(II);
+}
+
+void VforkChecker::reportBug(const char *What, CheckerContext &C,
+                             const char *Details) const {
+  if (ExplodedNode *N = C.generateErrorNode(C.getState())) {
+    if (!BT)
+      BT.reset(new BuiltinBug(this,
+                              "Dangerous construct in a vforked process"));
+
+    SmallString<256> buf;
+    llvm::raw_svector_ostream os(buf);
+
+    os << What << " is prohibited after a successful vfork";
+
+    if (Details)
+      os << "; " << Details;
+
+    auto Report = llvm::make_unique<BugReport>(*BT, os.str(), N);
+    // TODO: mark vfork call in BugReportVisitor
+    C.emitReport(std::move(Report));
+  }
+}
+
+// Detect calls to vfork and split execution appropriately.
+void VforkChecker::checkPostCall(const CallEvent &Call,
+                                 CheckerContext &C) const {
+  // We can't call vfork in child so don't bother
+  // (corresponding warning has already been emitted in checkPreCall).
+  ProgramStateRef State = C.getState();
+  if (isChildProcess(State))
+    return;
+
+  if (!isVforkCall(Call.getDecl(), C))
+    return;
+
+  // Get return value of vfork.
+  SVal VforkRetVal = Call.getReturnValue();
+  Optional<DefinedOrUnknownSVal> DVal =
+    VforkRetVal.getAs<DefinedOrUnknownSVal>();
+  if (!DVal)
+    return;
+
+  // Get assigned variable.
+  const ParentMap &PM = C.getLocationContext()->getParentMap();
+  const Stmt *P = PM.getParentIgnoreParenCasts(Call.getOriginExpr());
+  const VarDecl *LhsDecl;
+  std::tie(LhsDecl, std::ignore) = parseAssignment(P);
+
+  // Get assigned memory region.
+  MemRegionManager &M = C.getStoreManager().getRegionManager();
+  const MemRegion *LhsDeclReg =
+    LhsDecl
+      ? M.getVarRegion(LhsDecl, C.getLocationContext())
+      : (const MemRegion *)VFORK_RESULT_NONE;
+
+  // Parent branch gets nonzero return value (according to manpage).
+  ProgramStateRef ParentState, ChildState;
+  std::tie(ParentState, ChildState) = C.getState()->assume(*DVal);
+  C.addTransition(ParentState);
+  ChildState = ChildState->set<VforkResultRegion>(LhsDeclReg);
+  C.addTransition(ChildState);
+}
+
+// Prohibit calls to non-whitelist functions in child process.
+void VforkChecker::checkPreCall(const CallEvent &Call,
+                                CheckerContext &C) const {
+  ProgramStateRef State = C.getState();
+  if (isChildProcess(State)
+      && !isCallWhitelisted(Call.getCalleeIdentifier(), C))
+    reportBug("This function call", C);
+}
+
+// Prohibit writes in child process (except for vfork's lhs).
+void VforkChecker::checkBind(SVal L, SVal V, const Stmt *S,
+                             CheckerContext &C) const {
+  ProgramStateRef State = C.getState();
+  if (!isChildProcess(State))
+    return;
+
+  const MemRegion *VforkLhs =
+    static_cast<const MemRegion *>(State->get<VforkResultRegion>());
+  const MemRegion *MR = L.getAsRegion();
+
+  // Child is allowed to modify only vfork's lhs.
+  if (!MR || MR == VforkLhs)
+    return;
+
+  reportBug("This assignment", C);
+}
+
+// Prohibit return from function in child process.
+void VforkChecker::checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const {
+  ProgramStateRef State = C.getState();
+  if (isChildProcess(State))
+    reportBug("Return", C, "call _exit() instead");
+}
+
+void ento::registerVforkChecker(CheckerManager &mgr) {
+  mgr.registerChecker<VforkChecker>();
+}