[clang-tidy] Add a close-on-exec check on accept4() in Android module.

[yawanng]

Summary

accept4() is better to set SOCK_CLOEXEC flag to avoid file descriptor leakage.

[alexfh]

See the comment on D35372.

[alexfh]

LG

clang-tidy/android/AndroidTidyModule.cpp

 #include "../ClangTidy.h"
 #include "../ClangTidyModule.h"
 #include "../ClangTidyModuleRegistry.h"
+#include "CloexecAccept4Check.h"
 #include "CloexecCreatCheck.h"
 #include "CloexecDupCheck.h"
 #include "CloexecFopenCheck.h"

 class AndroidModule : public ClangTidyModule {
 public:
   void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
+    CheckFactories.registerCheck<CloexecAccept4Check>("android-cloexec-accept4");
     CheckFactories.registerCheck<CloexecCreatCheck>("android-cloexec-creat");
     CheckFactories.registerCheck<CloexecDupCheck>("android-cloexec-dup");
     CheckFactories.registerCheck<CloexecFopenCheck>("android-cloexec-fopen");

clang-tidy/android/CMakeLists.txt

 
 add_clang_library(clangTidyAndroidModule
   AndroidTidyModule.cpp
+  CloexecAccept4Check.cpp
   CloexecCheck.cpp
   CloexecCreatCheck.cpp
   CloexecDupCheck.cpp

clang-tidy/android/CloexecAccept4Check.h

+//===--- CloexecAccept4Check.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_ACCEPT4_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_ANDROID_CLOEXEC_ACCEPT4_H
+
+#include "CloexecCheck.h"
+
+namespace clang {
+namespace tidy {
+namespace android {
+
+/// Finds code that uses accept4() without using the SOCK_CLOEXEC flag.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/android-cloexec-accept4.html
+class CloexecAccept4Check : public CloexecCheck {
+public:
+  CloexecAccept4Check(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_ACCEPT4_H

clang-tidy/android/CloexecAccept4Check.cpp

+//===--- CloexecAccept4Check.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 "CloexecAccept4Check.h"
+#include "../utils/ASTUtils.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace android {
+
+void CloexecAccept4Check::registerMatchers(MatchFinder *Finder) {
+  auto SockAddrPointerType =
+      hasType(pointsTo(recordDecl(isStruct(), hasName("sockaddr"))));
+  auto SockLenPointerType = hasType(pointsTo(namedDecl(hasName("socklen_t"))));
+
+  registerMatchersImpl(Finder,
+                       functionDecl(returns(isInteger()), hasName("accept4"),
+                                    hasParameter(0, hasType(isInteger())),
+                                    hasParameter(1, SockAddrPointerType),
+                                    hasParameter(2, SockLenPointerType),
+                                    hasParameter(3, hasType(isInteger()))));
+}
+
+void CloexecAccept4Check::check(const MatchFinder::MatchResult &Result) {
+  insertMacroFlag(Result, "SOCK_CLOEXEC", /*ArgPos=*/3);
+}
+
+} // namespace android
+} // namespace tidy
+} // namespace clang

docs/ReleaseNotes.rst

       ``AllowConditionalIntegerCasts`` -> ``AllowIntegerConditions``,
       ``AllowConditionalPointerCasts`` -> ``AllowPointerConditions``.
 
+- New `android-cloexec-accept4
+  <http://clang.llvm.org/extra/clang-tidy/checks/android-cloexec-accept4.html>`_ check
+
+  Checks if the required file flag ``SOCK_CLOEXEC`` is present in the argument of
+  ``accept4()``.
+
 - New `android-cloexec-dup
   <http://clang.llvm.org/extra/clang-tidy/checks/android-cloexec-dup.html>`_ check
 

docs/clang-tidy/checks/android-cloexec-accept4.rst

+.. title:: clang-tidy - android-cloexec-accept4
+
+android-cloexec-accept4
+=======================
+
+``accept4()`` should include ``SOCK_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++
+
+  accept4(sockfd, addr, addrlen, SOCK_NONBLOCK);
+
+  // becomes
+
+  accept4(sockfd, addr, addrlen, SOCK_NONBLOCK | SOCK_CLOEXEC);

docs/clang-tidy/checks/list.rst

 =================
 
 .. toctree::
+   android-cloexec-accept4
    android-cloexec-creat
    android-cloexec-dup
    android-cloexec-fopen

test/clang-tidy/android-cloexec-accept4.cpp

+// RUN: %check_clang_tidy %s android-cloexec-accept4 %t
+
+typedef int socklen_t;
+struct sockaddr {};
+
+#define SOCK_NONBLOCK 1
+#define __O_CLOEXEC 3
+#define SOCK_CLOEXEC __O_CLOEXEC
+#define TEMP_FAILURE_RETRY(exp) \
+  ({                            \
+    int _rc;                    \
+    do {                        \
+      _rc = (exp);              \
+    } while (_rc == -1);        \
+  })
+#define NULL 0
+
+extern "C" int accept4(int sockfd, struct sockaddr *addr, socklen_t *addrlen, int flags);
+
+void a() {
+  accept4(0, NULL, NULL, SOCK_NONBLOCK);
+  // CHECK-MESSAGES: :[[@LINE-1]]:39: warning: 'accept4' should use SOCK_CLOEXEC where possible [android-cloexec-accept4]
+  // CHECK-FIXES: accept4(0, NULL, NULL, SOCK_NONBLOCK | SOCK_CLOEXEC);
+  TEMP_FAILURE_RETRY(accept4(0, NULL, NULL, SOCK_NONBLOCK));
+  // CHECK-MESSAGES: :[[@LINE-1]]:58: warning: 'accept4'
+  // CHECK-FIXES: TEMP_FAILURE_RETRY(accept4(0, NULL, NULL, SOCK_NONBLOCK | SOCK_CLOEXEC))
+}
+
+void f() {
+  accept4(0, NULL, NULL, 3);
+  // CHECK-MESSAGES: :[[@LINE-1]]:27: warning: 'accept4'
+  // CHECK-FIXES: accept4(0, NULL, NULL, 3 | SOCK_CLOEXEC)
+  TEMP_FAILURE_RETRY(accept4(0, NULL, NULL, 3));
+  // CHECK-MESSAGES: :[[@LINE-1]]:46: warning: 'accept4'
+  // CHECK-FIXES: TEMP_FAILURE_RETRY(accept4(0, NULL, NULL, 3 | SOCK_CLOEXEC))
+
+  int flag = SOCK_NONBLOCK;
+  accept4(0, NULL, NULL, flag);
+  TEMP_FAILURE_RETRY(accept4(0, NULL, NULL, flag));
+}
+
+namespace i {
+int accept4(int sockfd, struct sockaddr *addr, socklen_t *addrlen, int flags);
+
+void d() {
+  accept4(0, NULL, NULL, SOCK_NONBLOCK);
+  TEMP_FAILURE_RETRY(accept4(0, NULL, NULL, SOCK_NONBLOCK));
+}
+
+} // namespace i
+
+void e() {
+  accept4(0, NULL, NULL, SOCK_CLOEXEC);
+  TEMP_FAILURE_RETRY(accept4(0, NULL, NULL, SOCK_CLOEXEC));
+  accept4(0, NULL, NULL, SOCK_NONBLOCK | SOCK_CLOEXEC);
+  TEMP_FAILURE_RETRY(accept4(0, NULL, NULL, SOCK_NONBLOCK | SOCK_CLOEXEC));
+}
+
+class G {
+public:
+  int accept4(int sockfd, struct sockaddr *addr, socklen_t *addrlen, int flags);
+  void d() {
+    accept4(0, NULL, NULL, SOCK_NONBLOCK);
+    TEMP_FAILURE_RETRY(accept4(0, NULL, NULL, SOCK_NONBLOCK));
+  }
+};