Namespace sandbox: add important security checks

content/common/sandbox_linux/sandbox_debug_handling_linux.cc

+// Copyright 2015 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 "content/common/sandbox_linux/sandbox_debug_handling_linux.h"
+
+#include <errno.h>
+#include <signal.h>
+#include <sys/prctl.h>
+#include <unistd.h>
+
+#include "base/command_line.h"
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/strings/safe_sprintf.h"
+#include "content/public/common/content_switches.h"
+
+namespace content {
+
+namespace {
+
+void DoChrootSignalHandler(int) {
+  const int old_errno = errno;
+  const char kFirstMessage[] = "Chroot signal handler called.\n";
+  ignore_result(write(STDERR_FILENO, kFirstMessage, sizeof(kFirstMessage) - 1));
+
+  const int chroot_ret = chroot("/");
+
+  char kSecondMessage[100];
+  const ssize_t printed = base::strings::SafeSPrintf(
+      kSecondMessage, "chroot() returned %d. Errno is %d.\n", chroot_ret,
+      errno);
+  if (printed > 0 && printed < static_cast<ssize_t>(sizeof(kSecondMessage))) {
+    ignore_result(write(STDERR_FILENO, kSecondMessage, printed));
+  }
+  errno = old_errno;
+}
+
+// This is a quick hack to allow testing sandbox crash reports in production
+// binaries.
+// This installs a signal handler for SIGUSR2 that performs a chroot().
+// In most of our BPF policies, it is a "watched" system call which will
+// trigger a SIGSYS signal whose handler will crash.
+// This has been added during the investigation of https://crbug.com/415842.
+void InstallCrashTestHandler() {
+  struct sigaction act = {};
+  act.sa_handler = DoChrootSignalHandler;
+  CHECK_EQ(0, sigemptyset(&act.sa_mask));
+  act.sa_flags = 0;
+
+  PCHECK(0 == sigaction(SIGUSR2, &act, NULL));
+}
+
+bool IsSandboxDebuggingEnabled() {
+  const base::CommandLine& command_line =
+      *base::CommandLine::ForCurrentProcess();
+  return command_line.HasSwitch(switches::kAllowSandboxDebugging);
+}
+
+}  // namespace
+
+// static
+bool SandboxDebugHandling::SetDumpableStatusAndHandlers() {
+  if (IsSandboxDebuggingEnabled()) {
+    // If sandbox debugging is allowed, install a handler for sandbox-related
+    // crash testing.
+    InstallCrashTestHandler();
+    return true;
+  }
+
+  if (prctl(PR_SET_DUMPABLE, 0) != 0) {
+    PLOG(ERROR) << "Failed to set non-dumpable flag";
+    return false;
+  }
+
+  return prctl(PR_GET_DUMPABLE) == 0;
+}
+
+}  // namespace content