Block signals while forking so they aren't run in the child process.

base/process/launch_posix.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/process/launch.h"
 
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <signal.h>
@@ skipping 59 matching lines @@
 // Set the process's "environment" (i.e. the thing that setenv/getenv
 // work with).
 void SetEnvironment(char** env) {
 #if defined(OS_MACOSX)
   *_NSGetEnviron() = env;
 #else
   environ = env;
 #endif
 }
 
+// Set the calling thread's signal mask to new_sigmask and return
+// the previous signal mask.
+sigset_t SetSignalMask(const sigset_t& new_sigmask) {
+  sigset_t old_sigmask;
+#if defined(OS_ANDROID)
+  // POSIX says pthread_sigmask() must be used in multi-threaded processes,
+  // but Android's pthread_sigmask() was broken until 4.1:
+  // https://code.google.com/p/android/issues/detail?id=15337
+  // http://stackoverflow.com/questions/13777109/pthread-sigmask-on-android-not-working
+  RAW_CHECK(sigprocmask(SIG_SETMASK, &new_sigmask, &old_sigmask) == 0);
+#else
+  RAW_CHECK(pthread_sigmask(SIG_SETMASK, &new_sigmask, &old_sigmask) == 0);
+#endif
+  return old_sigmask;
+}
+
 #if !defined(OS_LINUX) || \
     (!defined(__i386__) && !defined(__x86_64__) && !defined(__arm__))
 void ResetChildSignalHandlersToDefaults() {
   // The previous signal handlers are likely to be meaningless in the child's
   // context so we reset them to the defaults for now. http://crbug.com/44953
   // These signal handlers are set up at least in browser_main_posix.cc:
   // BrowserMainPartsPosix::PreEarlyInitialization and stack_trace_posix.cc:
   // EnableInProcessStackDumping.
   signal(SIGHUP, SIG_DFL);
   signal(SIGINT, SIG_DFL);
@@ skipping 297 matching lines @@
   InjectiveMultimap fd_shuffle1;
   InjectiveMultimap fd_shuffle2;
   fd_shuffle1.reserve(fd_shuffle_size);
   fd_shuffle2.reserve(fd_shuffle_size);
 
   scoped_ptr<char*[]> argv_cstr(new char*[argv.size() + 1]);
   scoped_ptr<char*[]> new_environ;
   if (options.environ)
     new_environ.reset(AlterEnvironment(*options.environ, GetEnvironment()));
 
+  sigset_t full_sigset;
+  sigfillset(&full_sigset);
+  const sigset_t orig_sigmask = SetSignalMask(full_sigset);
+
   pid_t pid;
 #if defined(OS_LINUX)
   if (options.clone_flags) {
+    RAW_CHECK(!(options.clone_flags & (CLONE_THREAD | CLONE_VM)));

[jln (very slow on Chromium), 2013/08/05 21:55:40]

Maybe add CLONE_SIGHAND as well here ?

Add a comment along the lines of "Signal handling in this function assumes the
creation of a new process, check that a thread is not being created by mistake
and that signal handling follows the process-creation rules".

[mdempsky_google, 2013/08/05 22:05:19]

Done.

     pid = syscall(__NR_clone, options.clone_flags, 0, 0, 0);
   } else
 #endif
   {
     pid = fork();
   }
 
+  // Always restore the original signal mask in the parent.
+  if (pid != 0) {
+    SetSignalMask(orig_sigmask);
+  }
+
   if (pid < 0) {
     DPLOG(ERROR) << "fork";
     return false;
   } else if (pid == 0) {
     // Child process
 
     // DANGER: fork() rule: in the child, if you don't end up doing exec*(),
     // you call _exit() instead of exit(). This is because _exit() does not
     // call any previously-registered (in the parent) exit handlers, which
     // might do things like block waiting for threads that don't even exist
@@ skipping 45 matching lines @@
           }
         }
       }
     }
 
 #if defined(OS_MACOSX)
     RestoreDefaultExceptionHandler();
 #endif  // defined(OS_MACOSX)
 
     ResetChildSignalHandlersToDefaults();
+    SetSignalMask(orig_sigmask);
 
 #if 0
     // When debugging it can be helpful to check that we really aren't making
     // any hidden calls to malloc.
     void *malloc_thunk =
         reinterpret_cast<void*>(reinterpret_cast<intptr_t>(malloc) & ~4095);
     mprotect(malloc_thunk, 4096, PROT_READ | PROT_WRITE | PROT_EXEC);
     memset(reinterpret_cast<void*>(malloc), 0xff, 8);
 #endif  // 0
 
@@ skipping 238 matching lines @@
                               std::string* output,
                               int* exit_code) {
   // Run |execve()| with the current environment and store "unlimited" data.
   GetAppOutputInternalResult result = GetAppOutputInternal(
       cl.argv(), NULL, output, std::numeric_limits<std::size_t>::max(), true,
       exit_code);
   return result == EXECUTE_SUCCESS;
 }
 
 }  // namespace base