[clang-tidy] Refactor the code and add a close-on-exec check on memfd_create() in Android module.

Summary:
1. Refactor the structure of the code by adding a base class for all close-on-exec checks, which implements most of the needed functions.
2. memfd_create() is better to set MFD_CLOEXEC flag to avoid file descriptor leakage.

Reviewers: alexfh, aaron.ballman, hokein

Reviewed By: alexfh, hokein

Subscribers: Eugene.Zelenko, chh, cfe-commits, srhines, mgorny, JDevlieghere, xazax.hun

Tags: #clang-tools-extra

Differential Revision: https://reviews.llvm.org/D35372

llvm-svn: 310630

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

@@ -12,6 +12,7 @@
 #include "../ClangTidyModuleRegistry.h"
 #include "CloexecCreatCheck.h"
 #include "CloexecFopenCheck.h"
+#include "CloexecMemfdCreateCheck.h"
 #include "CloexecOpenCheck.h"
 #include "CloexecSocketCheck.h"
 
@@ -27,6 +28,8 @@ public:
   void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
     CheckFactories.registerCheck<CloexecCreatCheck>("android-cloexec-creat");
     CheckFactories.registerCheck<CloexecFopenCheck>("android-cloexec-fopen");
+    CheckFactories.registerCheck<CloexecMemfdCreateCheck>(
+        "android-cloexec-memfd-create");
     CheckFactories.registerCheck<CloexecOpenCheck>("android-cloexec-open");
     CheckFactories.registerCheck<CloexecSocketCheck>("android-cloexec-socket");
   }

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

@@ -2,8 +2,10 @@ set(LLVM_LINK_COMPONENTS support)
 
 add_clang_library(clangTidyAndroidModule
   AndroidTidyModule.cpp
+  CloexecCheck.cpp
   CloexecCreatCheck.cpp
   CloexecFopenCheck.cpp
+  CloexecMemfdCreateCheck.cpp
   CloexecOpenCheck.cpp
   CloexecSocketCheck.cpp
 

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

@@ -0,0 +1,105 @@
+//===--- CloexecCheck.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 "CloexecCheck.h"
+#include "../utils/ASTUtils.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Lexer.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace android {
+
+namespace {
+
+const char *const FuncDeclBindingStr = "funcDecl";
+const char *const FuncBindingStr = "func";
+
+// Helper function to form the correct string mode for Type3.
+// Build the replace text. If it's string constant, add <Mode> directly in the
+// end of the string. Else, add <Mode>.
+std::string buildFixMsgForStringFlag(const Expr *Arg, const SourceManager &SM,
+                                     const LangOptions &LangOpts, char Mode) {
+  if (Arg->getLocStart().isMacroID())
+    return (Lexer::getSourceText(
+                CharSourceRange::getTokenRange(Arg->getSourceRange()), SM,
+                LangOpts) +
+            " \"" + Twine(Mode) + "\"")
+        .str();
+
+  StringRef SR = cast<StringLiteral>(Arg->IgnoreParenCasts())->getString();
+  return ("\"" + SR + Twine(Mode) + "\"").str();
+}
+} // namespace
+
+void CloexecCheck::registerMatchersImpl(
+    MatchFinder *Finder, internal::Matcher<FunctionDecl> Function) {
+  // We assume all the checked APIs are C functions.
+  Finder->addMatcher(
+      callExpr(
+          callee(functionDecl(isExternC(), Function).bind(FuncDeclBindingStr)))
+          .bind(FuncBindingStr),
+      this);
+}
+
+void CloexecCheck::insertMacroFlag(const MatchFinder::MatchResult &Result,
+                                   StringRef MacroFlag, int ArgPos) {
+  const auto *MatchedCall = Result.Nodes.getNodeAs<CallExpr>(FuncBindingStr);
+  const auto *FlagArg = MatchedCall->getArg(ArgPos);
+  const auto *FD = Result.Nodes.getNodeAs<FunctionDecl>(FuncDeclBindingStr);
+  SourceManager &SM = *Result.SourceManager;
+
+  if (utils::exprHasBitFlagWithSpelling(FlagArg->IgnoreParenCasts(), SM,
+                                        Result.Context->getLangOpts(),
+                                        MacroFlag))
+    return;
+
+  SourceLocation EndLoc =
+      Lexer::getLocForEndOfToken(SM.getFileLoc(FlagArg->getLocEnd()), 0, SM,
+                                 Result.Context->getLangOpts());
+
+  diag(EndLoc, "%0 should use %1 where possible")
+      << FD << MacroFlag
+      << FixItHint::CreateInsertion(EndLoc, (Twine(" | ") + MacroFlag).str());
+}
+
+void CloexecCheck::replaceFunc(const MatchFinder::MatchResult &Result,
+                               StringRef WarningMsg, StringRef FixMsg) {
+  const auto *MatchedCall = Result.Nodes.getNodeAs<CallExpr>(FuncBindingStr);
+  diag(MatchedCall->getLocStart(), WarningMsg)
+      << FixItHint::CreateReplacement(MatchedCall->getSourceRange(), FixMsg);
+}
+
+void CloexecCheck::insertStringFlag(
+    const ast_matchers::MatchFinder::MatchResult &Result, const char Mode,
+    const int ArgPos) {
+  const auto *MatchedCall = Result.Nodes.getNodeAs<CallExpr>(FuncBindingStr);
+  const auto *FD = Result.Nodes.getNodeAs<FunctionDecl>(FuncDeclBindingStr);
+  const auto *ModeArg = MatchedCall->getArg(ArgPos);
+
+  // Check if the <Mode> may be in the mode string.
+  const auto *ModeStr = dyn_cast<StringLiteral>(ModeArg->IgnoreParenCasts());
+  if (!ModeStr || (ModeStr->getString().find(Mode) != StringRef::npos))
+    return;
+
+  const std::string &ReplacementText = buildFixMsgForStringFlag(
+      ModeArg, *Result.SourceManager, Result.Context->getLangOpts(), Mode);
+
+  diag(ModeArg->getLocStart(), "use %0 mode '%1' to set O_CLOEXEC")
+      << FD << Mode
+      << FixItHint::CreateReplacement(ModeArg->getSourceRange(),
+                                      ReplacementText);
+}
+
+} // namespace android
+} // namespace tidy
+} // namespace clang

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

@@ -0,0 +1,95 @@
+//===--- CloexecCheck.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.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file contains the declaration of the CloexecCheck class, which is the
+/// base class for all of the close-on-exec checks in Android module.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_ANDROID_CLOEXEC_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_ANDROID_CLOEXEC_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace android {
+
+/// \brief The base class for all close-on-exec checks in Android module.
+/// To be specific, there are some functions that need the close-on-exec flag to
+/// prevent the file descriptor leakage on fork+exec and this class provides
+/// utilities to identify and fix these C functions.
+class CloexecCheck : public ClangTidyCheck {
+public:
+  CloexecCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+
+protected:
+  void
+  registerMatchersImpl(ast_matchers::MatchFinder *Finder,
+                       ast_matchers::internal::Matcher<FunctionDecl> Function);
+
+  /// Currently, we have three types of fixes.
+  ///
+  /// Type1 is to insert the necessary macro flag in the flag argument. For
+  /// example, 'O_CLOEXEC' is required in function 'open()', so
+  /// \code
+  ///   open(file, O_RDONLY);
+  /// \endcode
+  /// should be
+  /// \code
+  ///   open(file, O_RDONLY | O_CLOEXE);
+  /// \endcode
+  ///
+  /// \param [out] Result MatchResult from AST matcher.
+  /// \param MacroFlag The macro name of the flag.
+  /// \param ArgPos The 0-based position of the flag argument.
+  void insertMacroFlag(const ast_matchers::MatchFinder::MatchResult &Result,
+                       StringRef MarcoFlag, int ArgPos);
+
+  /// Type2 is to replace the API to another function that has required the
+  /// ability. For example:
+  /// \code
+  ///   creat(path, mode);
+  /// \endcode
+  /// should be
+  /// \code
+  ///   open(path, O_CREAT | O_WRONLY | O_TRUNC | O_CLOEXEC, mode)
+  /// \endcode
+  ///
+  /// \param [out] Result MatchResult from AST matcher.
+  /// \param WarningMsg The warning message.
+  /// \param FixMsg The fix message.
+  void replaceFunc(const ast_matchers::MatchFinder::MatchResult &Result,
+                   StringRef WarningMsg, StringRef FixMsg);
+
+  /// Type3 is also to add a flag to the corresponding argument, but this time,
+  /// the flag is some string and each char represents a mode rather than a
+  /// macro. For example, 'fopen' needs char 'e' in its mode argument string, so
+  /// \code
+  ///   fopen(in_file, "r");
+  /// \endcode
+  /// should be
+  /// \code
+  ///   fopen(in_file, "re");
+  /// \endcode
+  ///
+  /// \param [out] Result MatchResult from AST matcher.
+  /// \param Mode The required mode char.
+  /// \param ArgPos The 0-based position of the flag argument.
+  void insertStringFlag(const ast_matchers::MatchFinder::MatchResult &Result,
+                        char Mode, const int ArgPos);
+};
+
+} // namespace android
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_ANDROID_CLOEXEC_H

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

@@ -0,0 +1,32 @@
+//===--- CloexecMemfdCreateCheck.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 "CloexecMemfdCreateCheck.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace android {
+
+void CloexecMemfdCreateCheck::registerMatchers(MatchFinder *Finder) {
+  auto CharPointerType = hasType(pointerType(pointee(isAnyCharacter())));
+  registerMatchersImpl(
+      Finder, functionDecl(returns(isInteger()), hasName("memfd_create"),
+                           hasParameter(0, CharPointerType),
+                           hasParameter(1, hasType(isInteger()))));
+}
+
+void CloexecMemfdCreateCheck::check(const MatchFinder::MatchResult &Result) {
+  insertMacroFlag(Result, "MFD_CLOEXEC", /*ArgPos=*/1);
+}
+
+} // namespace android
+} // namespace tidy
+} // namespace clang

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

@@ -0,0 +1,35 @@
+//===--- CloexecMemfdCreateCheck.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_MEMFD_CREATE_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_ANDROID_CLOEXEC_MEMFD_CREATE_H
+
+#include "CloexecCheck.h"
+
+namespace clang {
+namespace tidy {
+namespace android {
+
+/// Finds code that uses memfd_create() without using the MFD_CLOEXEC flag.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/android-cloexec-memfd-create.html
+class CloexecMemfdCreateCheck : public CloexecCheck {
+public:
+  CloexecMemfdCreateCheck(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_MEMFD_CREATE_H

clang-tools-extra/docs/ReleaseNotes.rst

@@ -70,6 +70,12 @@ Improvements to clang-tidy
       ``AllowConditionalIntegerCasts`` -> ``AllowIntegerConditions``,
       ``AllowConditionalPointerCasts`` -> ``AllowPointerConditions``.
 
+- New `android-cloexec-memfd_create
+    <http://clang.llvm.org/extra/clang-tidy/checks/android-cloexec-memfd_create.html>`_ check
+
+    Checks if the required file flag ``MFD_CLOEXEC`` is present in the argument of
+      ``memfd_create()``.
+
 - New `bugprone-integer-division
   <http://clang.llvm.org/extra/clang-tidy/checks/bugprone-integer-division.html>`_ check
 

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

@@ -0,0 +1,18 @@
+.. title:: clang-tidy - android-cloexec-memfd-create
+
+android-cloexec-memfd-create
+============================
+
+``memfd_create()`` should include ``MFD_CLOEXEC`` in its type argument to avoid
+the file descriptor leakage. Without this flag, an opened sensitive file would
+remain open across a fork+exec to a lower-privileged SELinux domain.
+
+Examples:
+
+.. code-block:: c++
+
+  memfd_create(name, MFD_ALLOW_SEALING);
+
+  // becomes
+
+  memfd_create(name, MFD_ALLOW_SEALING | MFD_CLOEXEC);

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

@@ -6,6 +6,7 @@ Clang-Tidy Checks
 .. toctree::
    android-cloexec-creat
    android-cloexec-fopen
+   android-cloexec-memfd-create
    android-cloexec-open
    android-cloexec-socket
    boost-use-to-string

clang-tools-extra/test/clang-tidy/android-cloexec-memfd-create.cpp

@@ -0,0 +1,63 @@
+// RUN: %check_clang_tidy %s android-cloexec-memfd-create %t
+
+#define MFD_ALLOW_SEALING 1
+#define __O_CLOEXEC 3
+#define MFD_CLOEXEC __O_CLOEXEC
+#define TEMP_FAILURE_RETRY(exp) \
+  ({                            \
+    int _rc;                    \
+    do {                        \
+      _rc = (exp);              \
+    } while (_rc == -1);        \
+  })
+#define NULL 0
+
+extern "C" int memfd_create(const char *name, unsigned int flags);
+
+void a() {
+  memfd_create(NULL, MFD_ALLOW_SEALING);
+  // CHECK-MESSAGES: :[[@LINE-1]]:39: warning: 'memfd_create' should use MFD_CLOEXEC where possible [android-cloexec-memfd-create]
+  // CHECK-FIXES: memfd_create(NULL, MFD_ALLOW_SEALING | MFD_CLOEXEC)
+  TEMP_FAILURE_RETRY(memfd_create(NULL, MFD_ALLOW_SEALING));
+  // CHECK-MESSAGES: :[[@LINE-1]]:58: warning: 'memfd_create'
+  // CHECK-FIXES: TEMP_FAILURE_RETRY(memfd_create(NULL, MFD_ALLOW_SEALING | MFD_CLOEXEC))
+}
+
+void f() {
+  memfd_create(NULL, 3);
+  // CHECK-MESSAGES: :[[@LINE-1]]:23: warning: 'memfd_create'
+  // CHECK-FIXES: memfd_create(NULL, 3 | MFD_CLOEXEC)
+  TEMP_FAILURE_RETRY(memfd_create(NULL, 3));
+  // CHECK-MESSAGES: :[[@LINE-1]]:42: warning: 'memfd_create'
+  // CHECK-FIXES: TEMP_FAILURE_RETRY(memfd_create(NULL, 3 | MFD_CLOEXEC))
+
+  int flag = 3;
+  memfd_create(NULL, flag);
+  TEMP_FAILURE_RETRY(memfd_create(NULL, flag));
+}
+
+namespace i {
+int memfd_create(const char *name, unsigned int flags);
+
+void d() {
+  memfd_create(NULL, MFD_ALLOW_SEALING);
+  TEMP_FAILURE_RETRY(memfd_create(NULL, MFD_ALLOW_SEALING));
+}
+
+} // namespace i
+
+void e() {
+  memfd_create(NULL, MFD_CLOEXEC);
+  TEMP_FAILURE_RETRY(memfd_create(NULL, MFD_CLOEXEC));
+  memfd_create(NULL, MFD_ALLOW_SEALING | MFD_CLOEXEC);
+  TEMP_FAILURE_RETRY(memfd_create(NULL, MFD_ALLOW_SEALING | MFD_CLOEXEC));
+}
+
+class G {
+public:
+  int memfd_create(const char *name, unsigned int flags);
+  void d() {
+    memfd_create(NULL, MFD_ALLOW_SEALING);
+    TEMP_FAILURE_RETRY(memfd_create(NULL, MFD_ALLOW_SEALING));
+  }
+};