[clang-tidy] Add a close-on-exec check on dup() in Android module.

Summary:
dup() is better to be replaced by fcntl() to avoid file descriptor leakage.

Differential Revision: https://reviews.llvm.org/D35364

llvm-svn: 310858

clang-tools-extra/clang-tidy/android/AndroidTidyModule.cpp

@@ -11,6 +11,7 @@
 #include "../ClangTidyModule.h"
 #include "../ClangTidyModuleRegistry.h"
 #include "CloexecCreatCheck.h"
+#include "CloexecDupCheck.h"
 #include "CloexecFopenCheck.h"
 #include "CloexecMemfdCreateCheck.h"
 #include "CloexecOpenCheck.h"
@@ -27,6 +28,7 @@ class AndroidModule : public ClangTidyModule {
 public:
   void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
     CheckFactories.registerCheck<CloexecCreatCheck>("android-cloexec-creat");
+    CheckFactories.registerCheck<CloexecDupCheck>("android-cloexec-dup");
     CheckFactories.registerCheck<CloexecFopenCheck>("android-cloexec-fopen");
     CheckFactories.registerCheck<CloexecMemfdCreateCheck>(
         "android-cloexec-memfd-create");

clang-tools-extra/clang-tidy/android/CMakeLists.txt

@@ -4,6 +4,7 @@ add_clang_library(clangTidyAndroidModule
   AndroidTidyModule.cpp
   CloexecCheck.cpp
   CloexecCreatCheck.cpp
+  CloexecDupCheck.cpp
   CloexecFopenCheck.cpp
   CloexecMemfdCreateCheck.cpp
   CloexecOpenCheck.cpp

clang-tools-extra/clang-tidy/android/CloexecCheck.cpp

@@ -100,6 +100,15 @@ void CloexecCheck::insertStringFlag(
                                       ReplacementText);
 }
 
+StringRef CloexecCheck::getSpellingArg(const MatchFinder::MatchResult &Result,
+                                       int N) const {
+  const auto *MatchedCall = Result.Nodes.getNodeAs<CallExpr>(FuncBindingStr);
+  const SourceManager &SM = *Result.SourceManager;
+  return Lexer::getSourceText(
+      CharSourceRange::getTokenRange(MatchedCall->getArg(N)->getSourceRange()),
+      SM, Result.Context->getLangOpts());
+}
+
 } // namespace android
 } // namespace tidy
 } // namespace clang

clang-tools-extra/clang-tidy/android/CloexecCheck.h

@@ -86,6 +86,10 @@ protected:
   /// \param ArgPos The 0-based position of the flag argument.
   void insertStringFlag(const ast_matchers::MatchFinder::MatchResult &Result,
                         const char Mode, const int ArgPos);
+
+  /// Helper function to get the spelling of a particular argument.
+  StringRef getSpellingArg(const ast_matchers::MatchFinder::MatchResult &Result,
+                           int N) const;
 };
 
 } // namespace android

clang-tools-extra/clang-tidy/android/CloexecDupCheck.cpp

@@ -0,0 +1,38 @@
+//===--- CloexecDupCheck.cpp - clang-tidy----------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "CloexecDupCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace android {
+
+void CloexecDupCheck::registerMatchers(MatchFinder *Finder) {
+  registerMatchersImpl(Finder,
+                       functionDecl(returns(isInteger()), hasName("dup"),
+                                    hasParameter(0, hasType(isInteger()))));
+}
+
+void CloexecDupCheck::check(const MatchFinder::MatchResult &Result) {
+  const std::string &ReplacementText =
+      (Twine("fcntl(") + getSpellingArg(Result, 0) + ", F_DUPFD_CLOEXEC)")
+          .str();
+
+  replaceFunc(Result,
+              "prefer fcntl() to dup() because fcntl() allows F_DUPFD_CLOEXEC",
+              ReplacementText);
+}
+
+} // namespace android
+} // namespace tidy
+} // namespace clang

clang-tools-extra/clang-tidy/android/CloexecDupCheck.h

@@ -0,0 +1,36 @@
+//===--- CloexecDupCheck.h - clang-tidy-------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_ANDROID_CLOEXEC_DUP_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_ANDROID_CLOEXEC_DUP_H
+
+#include "CloexecCheck.h"
+
+namespace clang {
+namespace tidy {
+namespace android {
+
+/// dup() is better to be replaced by fcntl(), which has close-on-exec flag.
+/// Find the usage of dup() and redirect user to use fcntl().
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/android-cloexec-dup.html
+class CloexecDupCheck : public CloexecCheck {
+public:
+  CloexecDupCheck(StringRef Name, ClangTidyContext *Context)
+      : CloexecCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace android
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_ANDROID_CLOEXEC_DUP_H

clang-tools-extra/docs/ReleaseNotes.rst

@@ -70,6 +70,11 @@ Improvements to clang-tidy
       ``AllowConditionalIntegerCasts`` -> ``AllowIntegerConditions``,
       ``AllowConditionalPointerCasts`` -> ``AllowPointerConditions``.
 
+- New `android-cloexec-dup
+  <http://clang.llvm.org/extra/clang-tidy/checks/android-cloexec-dup.html>`_ check
+
+  Detects usage of ``dup()``.
+
 - New `android-cloexec-memfd_create
   <http://clang.llvm.org/extra/clang-tidy/checks/android-cloexec-memfd_create.html>`_ check
 

clang-tools-extra/docs/clang-tidy/checks/android-cloexec-dup.rst

@@ -0,0 +1,18 @@
+.. title:: clang-tidy - android-cloexec-dup
+
+android-cloexec-dup
+===================
+
+The usage of ``dup()`` is not recommended, it's better to use ``fcntl()``,
+which can set the close-on-exec flag. Otherwise, an opened sensitive file would
+remain open across a fork+exec to a lower-privileged SELinux domain.
+
+Examples:
+
+.. code-block:: c++
+
+  int fd = dup(oldfd);
+
+  // becomes
+
+  int fd = fcntl(oldfd, F_DUPFD_CLOEXEC);

clang-tools-extra/docs/clang-tidy/checks/list.rst

@@ -5,6 +5,7 @@ Clang-Tidy Checks
 
 .. toctree::
    android-cloexec-creat
+   android-cloexec-dup
    android-cloexec-fopen
    android-cloexec-memfd-create
    android-cloexec-open

clang-tools-extra/test/clang-tidy/android-cloexec-dup.cpp

@@ -0,0 +1,31 @@
+// RUN: %check_clang_tidy %s android-cloexec-dup %t
+
+extern "C" int dup(int oldfd);
+void f() {
+  dup(1);
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: prefer fcntl() to dup() because fcntl() allows F_DUPFD_CLOEXEC [android-cloexec-dup]
+  // CHECK-FIXES: fcntl(1, F_DUPFD_CLOEXEC);
+  int oldfd = 0;
+  dup(oldfd);
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: prefer
+  // CHECK-FIXES: fcntl(oldfd, F_DUPFD_CLOEXEC);
+}
+
+namespace i {
+int dup(int oldfd);
+void g() {
+  dup(0);
+  int oldfd = 1;
+  dup(oldfd);
+}
+} // namespace i
+
+class C {
+public:
+  int dup(int oldfd);
+  void h() {
+    dup(0);
+    int oldfd = 1;
+    dup(oldfd);
+  }
+};