Add CloseStdinAndStdout().

There will be no reason to leave the handler process connected to its
invoker’s stdin or stdout.

On the other hand, I’m currently leaving it connected to the original
and stderr, as these may be useful for diagnostics.

R=rsesek@chromium.org

Review URL: https://codereview.chromium.org/818573002

util/posix/close_stdio.cc

@@ -0,0 +1,52 @@
+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "util/posix/close_stdio.h"
+
+#include <fcntl.h>
+#include <paths.h>
+#include <unistd.h>
+
+#include "base/basictypes.h"
+#include "base/files/scoped_file.h"
+#include "base/logging.h"
+#include "base/posix/eintr_wrapper.h"
+
+namespace crashpad {
+
+namespace {
+
+void CloseStdioStream(int desired_fd, int oflag) {
+  base::ScopedFD fd(HANDLE_EINTR(open(_PATH_DEVNULL, oflag)));
+  if (fd == desired_fd) {
+    // Weird, but play along.
+    ignore_result(fd.release());
+  } else {
+    PCHECK(fd.get() >= 0) << "open";
+    PCHECK(HANDLE_EINTR(dup2(fd.get(), desired_fd)) != -1) << "dup2";
+    fd.reset();
+  }
+}
+
+}  // namespace
+
+void CloseStdinAndStdout() {
+  // Open /dev/null for stdin and stdout separately, so that it can be opened
+  // with the correct mode each time. This ensures that attempts to write to
+  // stdin or read from stdout fail with EBADF.
+  CloseStdioStream(STDIN_FILENO, O_RDONLY);
+  CloseStdioStream(STDOUT_FILENO, O_WRONLY);
+}
+
+}  // namespace crashpad

util/posix/close_stdio.h

@@ -0,0 +1,42 @@
+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef CRASHPAD_UTIL_POSIX_CLOSE_STDIO_H_
+#define CRASHPAD_UTIL_POSIX_CLOSE_STDIO_H_
+
+namespace crashpad {
+
+//! \brief Closes `stdin` and `stdout` by opening `/dev/null` over them.
+//!
+//! It is normally inadvisable to `close()` the three standard input/output
+//! streams, because they occupy special file descriptors. Closing them outright
+//! could result in their file descriptors being reused. This causes problems
+//! for library code (including the standard library) that expects these file
+//! descriptors to have special meaning.
+//!
+//! This function discards the standard input and standard output streams by
+//! opening `/dev/null` and assigning it to their file descriptors, closing
+//! whatever had been at those file descriptors previously.
+//!
+//! `stderr`, the standard error stream, is not closed. It is often useful to
+//! retain the ability to send diagnostic messages to the standard error stream.
+//!
+//! \note This function can only maintain its guarantees in a single-threaded
+//!     process, or in situations where the caller has control of all threads in
+//!     the process.
+void CloseStdinAndStdout();
+
+}  // namespace crashpad
+
+#endif  // CRASHPAD_UTIL_POSIX_CLOSE_STDIO_H_

util/util.gyp

@@ -99,6 +99,8 @@
         'numeric/in_range_cast.h',
         'numeric/int128.h',
         'numeric/safe_assignment.h',
+        'posix/close_stdio.cc',
+        'posix/close_stdio.h',
         'posix/drop_privileges.cc',
         'posix/drop_privileges.h',
         'posix/process_info.h',