Mac: Other approach for IPCing child task_ts.

base/process_util_posix.cc

Index: base/process_util_posix.cc
diff --git a/base/process_util_posix.cc b/base/process_util_posix.cc
index 21626732b8c23eac4a1d59bfea816dca70c35fc8..a771fa25293cc810026157c129b03a04931cfd80 100644
--- a/base/process_util_posix.cc
+++ b/base/process_util_posix.cc
@@ -21,11 +21,16 @@
 #include "base/logging.h"
 #include "base/platform_thread.h"
 #include "base/process_util.h"
+#include "base/rand_util.h"
 #include "base/scoped_ptr.h"
 #include "base/sys_info.h"
 #include "base/time.h"
 #include "base/waitable_event.h"
 
+#if defined(OS_MACOSX)
+#include "base/mach_ipc_mac.h"
+#endif
+
 const int kMicrosecondsPerSecond = 1000000;
 
 namespace base {
@@ -280,11 +285,148 @@ void SetAllFDsToCloseOnExec() {
   }
 }
 
+#if defined(OS_MACOSX)
+static std::string MachErrorCode(kern_return_t err) {
+  return StringPrintf("0x%x %s", err, mach_error_string(err));
+}
+
+// Forks the current process and returns the child's |task_t| in the parent
+// process.
+static pid_t fork_and_get_task(task_t* child_task) {
+  const int kTimeoutMs = 100;
+  kern_return_t err;
+
+  // Put a random number into the channel name, so that a compromised renderer
+  // can't pretend being the child that's forked off.
+  std::string mach_connection_name = StringPrintf(
+      "com.google.Chrome.samplingfork.%p.%d",
+      child_task, base::RandInt(0, std::numeric_limits<int>::max()));
+  ReceivePort parent_recv_port(mach_connection_name.c_str());
+
+  // Error handling philosophy: If Mach IPC fails, don't touch |child_task| but
+  // return a valid pid. If IPC fails in the child, the parent will have to wait
+  // until kTimeoutMs is over. This is not optimal, but I've never seen it
+  // happen, and stuff should still mostly work.
+  pid_t pid = fork();
+  switch (pid) {
+    case -1:
+      return pid;
+    case 0: {  // child
+      ReceivePort child_recv_port;
+
+      MachSendMessage child_message(/* id= */0);
+      if (!child_message.AddDescriptor(mach_task_self())) {
+        LOG(ERROR) << "child AddDescriptor(mach_task_self()) failed.";
+        return pid;
+      }
+      mach_port_t raw_child_recv_port = child_recv_port.GetPort();
+      if (!child_message.AddDescriptor(raw_child_recv_port)) {
+        LOG(ERROR) << "child AddDescriptor(" << raw_child_recv_port
+                   << ") failed.";
+        return pid;
+      }
+
+      MachPortSender child_sender(mach_connection_name.c_str());
+      err = child_sender.SendMessage(child_message, kTimeoutMs);
+      if (err != KERN_SUCCESS) {
+        LOG(ERROR) << "child SendMessage() failed: " << MachErrorCode(err);
+        return pid;
+      }
+
+      MachReceiveMessage parent_message;
+      err = child_recv_port.WaitForMessage(&parent_message, kTimeoutMs);
+      if (err != KERN_SUCCESS) {
+        LOG(ERROR) << "child WaitForMessage() failed: " << MachErrorCode(err);
+        return pid;
+      }
+
+      if (parent_message.GetTranslatedPort(0) == MACH_PORT_NULL) {
+        LOG(ERROR) << "child GetTranslatedPort(0) failed.";
+        return pid;
+      }
+      err = task_set_bootstrap_port(mach_task_self(),
+                                    parent_message.GetTranslatedPort(0));
+      if (err != KERN_SUCCESS) {
+        LOG(ERROR) << "child task_set_bootstrap_port() failed: "
+                   << MachErrorCode(err);
+        return pid;
+      }
+      break;
+    }
+    default: {  // parent
+      MachReceiveMessage child_message;
+      err = parent_recv_port.WaitForMessage(&child_message, kTimeoutMs);
+      if (err != KERN_SUCCESS) {
+        LOG(ERROR) << "parent WaitForMessage() failed: " << MachErrorCode(err);
+        return pid;
+      }
+
+      if (child_message.GetTranslatedPort(0) == MACH_PORT_NULL) {
+        LOG(ERROR) << "parent GetTranslatedPort(0) failed.";
+        return pid;
+      }
+      *child_task = child_message.GetTranslatedPort(0);
+
+      if (child_message.GetTranslatedPort(1) == MACH_PORT_NULL) {
+        LOG(ERROR) << "parent GetTranslatedPort(1) failed.";
+        return pid;
+      }
+      MachPortSender parent_sender(child_message.GetTranslatedPort(1));
+
+      MachSendMessage parent_message(/* id= */0);
+      if (!parent_message.AddDescriptor(bootstrap_port)) {
+        LOG(ERROR) << "parent AddDescriptor(" << bootstrap_port << ") failed.";
+        return pid;
+      }
+
+      err = parent_sender.SendMessage(parent_message, kTimeoutMs);
+      if (err != KERN_SUCCESS) {
+        LOG(ERROR) << "parent SendMessage() failed: " << MachErrorCode(err);
+        return pid;
+      }
+      break;
+    }
+  }
+  return pid;
+}
+
 bool LaunchApp(const std::vector<std::string>& argv,
                const environment_vector& environ,
                const file_handle_mapping_vector& fds_to_remap,
                bool wait, ProcessHandle* process_handle) {
-  pid_t pid = fork();
+  return LaunchAppAndGetTask(
+      argv, environ, fds_to_remap, wait, NULL, process_handle);
+}
+#endif  // defined(OS_MACOSX)
+
+#if defined(OS_MACOSX)
+bool LaunchAppAndGetTask(
+#else
+bool LaunchApp(
+#endif
+    const std::vector<std::string>& argv,
+    const environment_vector& environ,
+    const file_handle_mapping_vector& fds_to_remap,
+    bool wait,
+#if defined(OS_MACOSX)
+    task_t* task_handle,
+#endif
+    ProcessHandle* process_handle) {
+  pid_t pid;
+#if defined(OS_MACOSX)
+  if (task_handle == NULL) {
+    pid = fork();
+  } else {
+    // On OS X, the task_t for a process is needed for several reasons. Sadly,
+    // the function task_for_pid() requires privileges a normal user doesn't
+    // have. Instead, a short-lived Mach IPC connection is opened between parent
+    // and child, and the child sends its task_t to the parent at fork time.
+    *task_handle = MACH_PORT_NULL;
+    pid = fork_and_get_task(task_handle);
+  }
+#else
+  pid = fork();
+#endif
   if (pid < 0)
     return false;